i

Contamination in Recycling Thermoplastics used for manufacturing of

Consumer Durable Products

by

Elli Lazzaro

A thesis submitted to the school of Engineering and Industrial

Sciences, Swinburne University of Technology, in fulfilment of the

requirements to the degree of Master of Engineering by Research.

Hawthorn, Melbourne, Australia

November 2009

ii

DECLARATION

I, Elli Lazzaro, declare that this thesis is my own work. Where other sources of

knowledge have been used, they have been acknowledged with references made in the

text of this thesis.

Signature: …………………………………………………….

Date: ………………………………………………………….

iii

ACKNOWLEDGEMENTS

This project was funded by the Australian Government through AusIndustry and MRI

Australia.

I would like to acknowledge the continued assistance and support of my supervisors,

Igor Sbarski and John Bishop. Igor Sbarski is a research leader in the field of polymer

science at the Industrial Research Institute, Swinburne. His contribution to this research,

with his extensive knowledge and years of experience, has been invaluable.

I would also like to acknowledge my parents, Marc and Dilys Lazzaro, for their continued

support and my partner, Stu Hutchison, for his encouragement and motivation.

iv

Contamination in Recycling Thermoplastics used for manufacturing of Consumer Durable Products ABSTRACT

Diminishing land fill capacity and increased volume of waste consumer durable

products are the main drivers for the recycling of engineering thermoplastics.

Consumer durables focused on in this study include long term products, specifically

waste electrical and electronic equipment (WEEE). WEEE can be recycled in bulk or as

separated components of a disassembled machine. Bulk recycling with limited sorting is

the economically preferred option however, blending incompatible plastics, without

modification, often limits the end use of the recycled plastics. The decision to apply

expensive sorting techniques at the end of a products life should be based on

processability and mechanical properties of the engineering thermoplastics

contaminated by other polymeric materials.

This project investigates the thermal, rheological and mechanical properties of a

range of binary blends of recycled thermoplastics. An amorphous polymer, Acrylonitrile-

Butadiene-Styrene (ABS), and a semi-crystalline polymer, Polypropylene (PP), have

been blended with contaminant amounts (0-30%) of other amorphous and crystalline

polymers. Models were developed for the prediction of the properties as a function of

contamination level.

The results show that generally, these thermoplastics should be separated prior

to processing to optimize the properties of the recycled plastics. However, the

properties for some of the blends with a certain level of contamination are sufficient,

such that they can be used for various applications where the use of sorting techniques

is not economically viable.

v

Contamination in Recycling Thermoplastics used for manufacturing of Consumer Durable Products

TABLE OF CONTENTS DECLARATION .................................................................................................... II

ACKNOWLEDGEMENTS ................................................................................... III

ABSTRACT ........................................................................................................ IV

TABLE OF CONTENTS ...................................................................................... V

LIST OF TABLES ............................................................................................... IX

LIST OF FIGURES ............................................................................................. XI

NOMENCLATURE ........................................................................................... XIV

ABREVIATIONS .............................................................................................. XVII

1 INTRODUCTION ......................................................................................... 1-1

1.1 Introduction ...................................................................................................................... 1-1

1.2 Plastic Recycling ............................................................................................................. 1-1

1.2.1. Plastic Recovery ............................................................................................................ 1-2

1.3 Polymer Selection ............................................................................................................ 1-5

1.4 Polymer Recyclate Applications .................................................................................... 1-7

1.4.1. Recycled materials and homologous polymer blends ................................................... 1-7

1.4.1.1. Acrylonitrile Butadiene Styrene, ABS .................................................................... 1-7

1.4.1.2. High Impact Polystyrene, HIPS ............................................................................. 1-7

1.4.1.3. Polypropylene, PP ................................................................................................. 1-8

1.4.1.4. Nylon ..................................................................................................................... 1-8

vi

1.5 Project Aims ..................................................................................................................... 1-9

1.6 Contribution to new knowledge ..................................................................................... 1-9

1.7 Thesis Structure ............................................................................................................ 1-10

1.7.1. Chapter 1 : Introduction .............................................................................................. 1-10

1.7.2. Chapter 2 : Literature Review ..................................................................................... 1-10

1.7.3. Chapter 3 : Methodology ............................................................................................. 1-10

1.7.4. Chapter 4 : Thermal Properties of contaminated plastics ........................................... 1-10

1.7.5. Chapter 5 : Processability of contaminated plastics ................................................... 1-10

1.7.6. Chapter 6 : Mechanical Properties of contaminated plastics ...................................... 1-11

1.7.7. Chapter 7 : Conclusions.............................................................................................. 1-11

2 LITERATURE REVIEW ............................................................................... 2-1

2.1 Introduction ...................................................................................................................... 2-1

2.2 Blends ............................................................................................................................... 2-1

2.3 Miscibility.......................................................................................................................... 2-2

2.4 Blend Properties .............................................................................................................. 2-3

2.5 Recycled materials and homologous polymer blends ................................................ 2-4

2.5.1. Acrylonitrile Butadiene Styrene (ABS) ......................................................................... 2-4

2.5.2. Polypropylene (PP) ...................................................................................................... 2-4

2.5.3. High Impact Polystyrene (HIPS) .................................................................................. 2-5

2.5.4. Polyamide (PA, Nylon) ................................................................................................. 2-6 2.6 Non-homologous polymer blends ................................................................................. 2-7

2.6.1. VIRGIN BLENDS ......................................................................................................... 2-7

2.6.1.1. ABS contaminated with HIPS ................................................................................ 2-7

2.6.1.2. ABS contaminated with PA ................................................................................... 2-8

2.6.1.3. PP contaminated with ABS ................................................................................. 2-10

2.6.2. RECYLCED BLENDS ................................................................................................ 2-12

2.6.2.1. ABS contaminated with HIPS .............................................................................. 2-12

2.6.2.2. ABS contaminated with PA ................................................................................. 2-13

2.6.1.3. PP contaminated with HIPS ................................................................................ 2-14

2.7 Application of Recycled Blends ................................................................................... 2-15

2.7.1. Blends ........................................................................................................................ 2-15 2.8 Summary......................................................................................................................... 2-17

vii

3 METHODOLOGY ........................................................................................ 3-1

3.1 Introduction ...................................................................................................................... 3-1

3.2 Materials ........................................................................................................................... 3-1

3.3 Processing........................................................................................................................ 3-2

3.3.1. Extrusion ...................................................................................................................... 3-2

3.3.2. Injection Moulding ........................................................................................................ 3-5

3.4 Thermal Properties .......................................................................................................... 3-7

3.4.1. Glass Transition ........................................................................................................... 3-7

3.4.2. Degradation Region ..................................................................................................... 3-8 3.5 Rheological Properties .................................................................................................... 3-9

3.5.1. Parallel Plate Rheology.............................................................................................. 3-11

3.5.1.1. Flow ................................................................................................................... 3-12

3.5.1.2. Linear viscoelasticity ......................................................................................... 3-13

3.5.1.3. Dynamic Loading ............................................................................................... 3-13

3.5.2. Melt Flow Rate ........................................................................................................... 3-14

3.6 Mechanical Properties ................................................................................................... 3-16

3.6.1. Tensile and Flexural Testing ...................................................................................... 3-16

3.6.2. Impact Testing ........................................................................................................... 3-20

3.6.3. Dynamic Mechanical Analysis ................................................................................... 3-21

3.6.3.1. Time Temperature Superposition ...................................................................... 3-21

3.7 Statistical Analysis of Property Data ........................................................................... 3-23

3.7.1. Characterisation of the Sample Population ............................................................... 3-23

3.7.2. Statistical Analysis ..................................................................................................... 3-26

4 THERMAL PROPERTIES OF CONTAMINATED PLASTICS ..................... 4-1 4.1 Glass Transition ............................................................................................................... 4-1

4.2 Degradation Region ......................................................................................................... 4-5

5 PROCESSABILITY OF CONTAMINATED PLASTICS ............................... 5-1

5.1 Processability .................................................................................................................. 5-1

5.2 Melt Flow Rate .................................................................................................................. 5-1

5.3 Rheology........................................................................................................................... 5-8

5.3.1. Flow analysis of ABS/PP blends .................................................................................. 5-8

5.3.2. Linear Viscoelasticity of ABS/PP blends .................................................................... 5-11

5.3.3. Flow curve modelling ................................................................................................. 5-12

viii

6 MECHANICAL ANALYSIS OF CONTAMINATED PLASTICS ................... 6-1

6.1 Recycling .......................................................................................................................... 6-1

6.2 Contaminated Plastics .................................................................................................... 6-3

6.2.1. Contaminated ABS blends ........................................................................................... 6-3

6.2.2. Contaminated PP blends ........................................................................................... 6-10 6.3 Verification of Modulus through DMA measurements .............................................. 6-18

6.4 Dynamic Mechanical Analysis...................................................................................... 6-26

6.4.1. ABS contaminated with PP ........................................................................................ 6-26

6.4.2. ABS contaminated with HIPS .................................................................................... 6-31

6.4.3. ABS contaminated with nylon .................................................................................... 6-33

7 CONCLUSIONS .......................................................................................... 7-1

7.1 Statistical analysis of Mechanical Properties ............................................................... 7-1

7.2 Thermal Properties .......................................................................................................... 7-2

7.3 Processability .................................................................................................................. 7-2

7.4 Mechanical Properties ..................................................................................................... 7-4

8 REFERENCES ............................................................................................ 8-1

9 APPENDIX I................................................................................................. 9-1

9.1 Rheology........................................................................................................................... 9-1

9.1.1. Flow curves .................................................................................................................. 9-1

9.1.2. Linear viscoelasticity .................................................................................................... 9-4

9.1.3. Cox-Merz transforms ................................................................................................... 9-5

9.2 Mechanical Properties ..................................................................................................... 9-9

9.2.1. Flexural strength of ABS/PP blends ............................................................................ 9-9

9.2.2. Impact strength of contaminated ABS blends............................................................ 9-10

9.2.3. Williams-Landel-Ferry (WLF), shift factors ................................................................ 9-11

ix

LIST OF TABLES Table 1.1: Dismantling Times of WEEE (Banfield, 2000) ............................................................ 1-3

Table 1.2: Average Polymer Composition of plastic product covers (Rios, 2003) ...................... 1-5

Table 1.3: Polymer Composition of fridge shredder residue, (Pascoe, 2005) ............................ 1-6

Table 2.1: Mechanical properties of virgin and recycled ABS plastics, (Liu & Bertilsson, 1999) 2-4

Table 2.2: Mechanical properties of virgin and recycled PP plastics, (Santana et al, 2003) ...... 2-5

Table 2.3: Mechanical properties of virgin and recycled HIPS plastics, (Santana et al, 2003) ... 2-6

Table 2.4: Mechanical properties of compatibilised and impact modified blends, (Liu et al, 2002a

& 2002b) ....................................................................................................................................... 2-9

Table 2.5: Properties of Engineering Thermoplastics, (Fried, 2003) ......................................... 2-15

Table 2.6: Physical and Thermal Properties of Consumer Durable Thermoplastics, (Fried, 2003)

.................................................................................................................................................... 2-16

Table 3.1: BASF material properties ........................................................................................... 3-1

Table 3.2: Contaminant level in ABS blends ............................................................................... 3-3

Table 3.3: Contaminant level in PP blends ................................................................................. 3-3

Table 3.4: Processing temperature variables, extruder zones (T1, T2, T3, Td, respectively) and

injection molding ........................................................................................................................... 3-5

Table 3.5: Conditions for MFR measurements .......................................................................... 3-14

Table 3.6: Statistical Analysis of virgin PP and ABS ................................................................. 3-27

Table 3.7: Sample size for the mechanical properties of ABS and PP based blends ............... 3-27

Table 4.1: Glass transition temperatures of virgin amorphous materials (0C) ............................. 4-1

Table 4.2a: Glass transition temperatures of thermally recycled ABS dominant blends (0C) ..... 4-2

Table 4.2b: Glass transition temperatures of thermally recycled PP dominant blends (0C) ....... 4-2

Table 4.3: Glass transition temperatures of ABS contaminated with PP blends (0C) ................. 4-2

Table 5.1a: Standard deviation in Melt Flow Rate of recycled ABS contaminated with PP ........ 5-4

Table 5.1b: Standard deviation in Melt Flow Rate of recycled PP contaminated with ABS ........ 5-4

Table 5.2a: Model constants for ABS contaminated with PP ...................................................... 5-5

Table 5.2b: Model constants for PP contaminated with ABS ...................................................... 5-6

Table 5.3a: Power Law constants for thermally recycled ABS contaminated with PP .............. 5-18

Table 5.3b: Power Law constants for thermally recycled PP contaminated with ABS .............. 5-18

Table 5.4a: Power Law constants for post consumer recycled ABS contaminated with PP .... 5-18

Table 5.4b: Power Law constants for post consumer recycled PP contaminated with ABS .... 5-18

Table 6.1a: Tensile strength (Fmax), MPa ................................................................................ 6-2

Table 6.1b: Flexural strength (Fmax), MPa ............................................................................... 6-2

Table 6.1c: Impact strength, kJm-2 .............................................................................................. 6-2

Table 6.2: Mechanical Properties of ABS contaminated with HIPS ............................................ 6-6

x

Table 6.3a: Mechanical Properties of thermally recycled ABS contaminated with PP ............... 6-6

Table 6.3b: Mechanical properties of post consumer recycled ABS contaminated with PP ....... 6-6

Table 6.4: Mechanical Properties of ABS contaminated with Nylon ........................................... 6-8

Table 6.5a Predictive model constants for Tensile and Flexural Strength of contaminated ABS

blends ........................................................................................................................................... 6-9

Table 6.5b Predictive model constants for Impact strength of contaminated ABS blends...... 6-10

Table 6.6: Mechanical Properties of PP contaminated with HIPS ............................................ 6-13

Table 6.7a: Mechanical Properties of thermally recycled PP contaminated with ABS ............. 6-14

Table 6.7b: Mechanical Properties of post consumer recycled PP contaminated with ABS .... 6-15

Table 6.8: Mechanical Properties of PP contaminated with Nylon ............................................ 6-16

Table 6.9a Predictive model constants for Tensile and Flexural strength of contaminated PP

blends ......................................................................................................................................... 6-17

Table 6.9b Predictive model constants for Impact strength of contaminated PP blends ........ 6-17

Table 6.10: Modulus for uncontaminated thermally recycled polymers, MPa ........................... 6-18

Table 6.11a: Modulus of thermally recycled ABS contaminated with PP, MPa ........................ 6-20

Table 6.11b: Modulus of thermally recycled PP contaminated with ABS, MPa ........................ 6-20

Table 6.12: Model constants for Modulus of contaminated ABS blends ................................... 6-23

Table 6.13: Model constants for Modulus of contaminated PP blends ..................................... 6-25

Table 6.14: WLF constants for ABS contaminated with PP ...................................................... 6-29

Table 6.15: WLF constants for PP contaminated with ABS ...................................................... 6-30

Table 6.16: WLF constants for ABS contaminated with HIPS .................................................. 6-32

Table 6.17: WLF constants for ABS contaminated with Nylon .................................................. 6-34

Table I.1: Shift Factors, tA , for ABS contaminated with PP ..................................................... 9-11

Table I.2: Shift Factors, tA , for PP contaminated with ABS ..................................................... 9-11

Table I.3: Shift Factors, tA , for ABS contaminated with HIPS ................................................. 9-11

Table I.4: Shift Factors, tA , for ABS contaminated with Nylon ................................................ 9-11

xi

LIST OF FIGURES

Figure 2.1 Behaviour of blended materials ................................................................................ 2-3

Figure 3.1 The barrel of a single screw extruder, (Chokshi, R., and Zia, H., 2004) .................. 3-3

Figure 3.2 Axon single screw extruder ...................................................................................... 3-4

Figure 3.3 Control panel and die formation of the extruder ....................................................... 3-4

Figure 3.4 Battenfeld Injection Moulder (Model BA 350 / 75 PLUS) ......................................... 3-6

Figure 3.5 Die cavity of the Battenfeld Injection Moulder for mechanical testing specimens ... 3-6

Figure 3.6 TA instruments SDT 2960 ........................................................................................ 3-8

Figure 3.7 Parallel plate configurations (Semancik, 1997) ...................................................... 3-11

Figure 3.8 TA instruments AR 2000 parallel plate rheometer ................................................. 3-12

Figure 3.9 CEAST Modular Melt Flow instrument ................................................................... 3-15

Figure 3.10 Typical stress-strain curve ................................................................................... 3-17

Figure 3.11 Zwick Z010 universal tester and grips for tensile testing ..................................... 3-18

Figure 3.12 Flexural testing apparatus for the Zwick Z010 universal tester ........................... 3-19

Figure 3.13 CEAST Resil impact tester and sample jaw ........................................................ 3-20

Figure 3.14 TA instruments DMA 2980, cantilever configuration ............................................ 3-22

Figure 3.15 Tensile strength histogram for thermally recycled PP .......................................... 3-23

Figure 3.16 Tensile strength histogram for thermally recycled ABS ....................................... 3-24

Figure 3.17 Impact strength histogram for thermally recycled PP .......................................... 3-24

Figure 3.18 Impact strength histogram for thermally recycled ABS ........................................ 3-25

Figure 4.1 Glass transition temperature of ABS contaminated with PP .................................... 4-3

Figure 4.2 Glass transition temperature of PP contaminated with ABS .................................... 4-3

Figure 4.3 Tan Delta curves of post consumer recycled ABS/PP blends ................................. 4-4

Figure 4.4 TGA plots for thermally recycled PP contaminated with ABS .................................. 4-6

Figure 4.5 TGA plots for thermally recycled PP contaminated with HIPS ................................ 4-6

Figure 4.6 TGA plots for thermally and post consumer recycled materials............................... 4-7

Figure 4.7 TGA plots for post consumer recycled ABS contaminated with PP ......................... 4-7

Figure 4.8 TGA plots for post consumer recycled PP contaminated with ABS ......................... 4-8

Figure 5.1a Melt Flow Rate of recycled ABS contaminated with PP blends ............................. 5-3

Figure 5.1b Melt Flow Rate of recycled PP contaminated with ABS blends ............................. 5-3

Figure 5.2a Melt density of recycled ABS contaminated with PP blends .................................. 5-4

Figure 5.2b Melt density of recycled PP contaminated with ABS blends .................................. 5-5

Figure 5.3 Melt Flow Rate of thermally recycled ABS contaminated with HIPS ....................... 5-6

Figure 5.4 Melt Flow Rate of thermally recycled PP contaminated with HIPS .......................... 5-7

Figure 5.5 Flow curves of uncontaminated recycled ABS and PP, 2400C ................................ 5-9

xii

Figure 5.6 Flow curves of thermally recycled PP contaminated with ABS, 2400C .................. 5-10

Figure 5.7 Linear Viscoelasticity of thermally recycled blends, 2400C .................................... 5-11

Figure 5.8a Dynamic curves for ABS contaminated with PP, 2400C ...................................... 5-12

Figure 5.8b Dynamic curves for PP contaminated with ABS, 2400C ...................................... 5-13

Figure 5.9 Comparison of Flow curves and Cox-Merz transformation of thermally recycled

polymers, 2400C .................................................................................................................. 5-14

Figure 5.10 Cox-Merz transformation of thermally recycled ABS contaminated with PP, 2400C

............................................................................................................................................ .5-16

Figure 5.11 Power-law fits for Cox-Merz transformation of thermally recycled ABS contaminated

with PP, 2400C .................................................................................................................... 5-16

Figure 5.12 Cox-Merz transformation of thermally recycled PP contaminated with ABS, 2400C.

............................................................................................................................................. 5-17

Figure 5.13 Power-law fits for Cox-Merz transformation of thermally recycled PP contaminated

with ABS, 2400C .................................................................................................................. 5-17

Figure 6.1 Typical stress strain curve ........................................................................................ 6-2

Figure 6.2 Tensile and Flexural strength of recycled ABS contaminated with HIPS ................ 6-5

Figure 6.3 Impact strength of recycled ABS contaminated with HIPS ...................................... 6-5

Figure 6.4 Tensile strength of recycled ABS contaminated with PP ......................................... 6-7

Figure 6.5 Impact strength of recycled ABS contaminated with PP .......................................... 6-7

Figure 6.6 Tensile and Flexural strength of recycled ABS contaminated with Nylon ................ 6-8

Figure 6.7 Impact strength of recycled ABS contaminated with Nylon ..................................... 6-9

Figure 6.8 Tensile and Flexural strength of recycled PP contaminated with HIPS ................. 6-12

Figure 6.9 Impact strength of recycled PP contaminated with HIPS ....................................... 6-12

Figure 6.10 Tensile strength of recycled PP contaminated with ABS ..................................... 6-13

Figure 6.11 Impact strength of recycled PP contaminated with ABS ...................................... 6-14

Figure 6.12 Tensile and Flexural strength of recycled PP contaminated with Nylon .............. 6-15

Figure 6.13 Impact strength of recycled PP contaminated with Nylon .................................... 6-16

Figure 6.14 Storage Modulus of ABS contaminated with PP .................................................. 6-19

Figure 6.15 Storage Modulus of PP contaminated with ABS .................................................. 6-19

Figure 6.16 Modulus of thermally recycled ABS contaminated with PP ................................. 6-20

Figure 6.17 Modulus of post consumer recycled ABS contaminated with PP ........................ 6-21

Figure 6.18 Modulus of thermally recycled ABS contaminated with HIPS .............................. 6-22

Figure 6.19 Modulus of thermally recycled ABS contaminated with Nylon ............................. 6-22

Figure 6.20 Modulus of thermally recycled PP contaminated with ABS ................................. 6-23

Figure 6.21 Modulus of post consumer recycled PP contaminated with ABS ........................ 6-24

Figure 6.22 Modulus of thermally recycled PP contaminated with HIPS ................................ 6-24

Figure 6.23 Modulus of thermally recycled PP contaminated with Nylon ............................... 6-25

xiii

Figure 6.24 Measured data and the master curve for ABS contaminated with 10 % PP........ 6-27

Figure 6.25 Master curves for ABS contaminated with PP at 1050C ...................................... 6-28

Figure 6.26 Shift Factors for ABS contaminated with PP ........................................................ 6-28

Figure 6.27 Master curves for PP contaminated with ABS at 1050C ...................................... 6-29

Figure 6.28 Shift Factors for PP contaminated with ABS ........................................................ 6-30

Figure 6.29 Master curves for ABS contaminated with HIPS at 1050C ................................... 6-31

Figure 6.30 Shift Factors for ABS contaminated with HIPS .................................................... 6-32

Figure 6.31 Master curves for ABS contaminated with Nylon at 1050C .................................. 6-33

Figure 6.32 Shift Factors for ABS contaminated with Nylon ................................................... 6-34

Figure I.1 Flow curves of recycled polymers ............................................................................. 9-1

Figure I.2 Flow curves of thermally recycled contaminated ABS blends .................................. 9-1

Figure I.3 Flow curves of thermally recycled contaminated PP blends ...................................... 9-2

Figure I.4 Flow curves of post consumer contaminated ABS blends ........................................ 9-2

Figure I.5 Flow curves of post consumer contaminated PP blends .......................................... 9-3

Figure I.6 Flow curves of post consumer contaminated PP blends .......................................... 9-3

Figure I.7 Linear viscoelasticity of thermally recycled blends ................................................... 9-4

Figure I.8 Linear viscoelasticity of post consumer recycled blends .......................................... 9-4

Figure I.9 Flow curves and Cox-Merz transformation of thermally recycled polymers ............. 9-5

Figure I.10 Cox-Merz transformation of thermally recycled ABS contaminated with PP .......... 9-5

Figure I.11 Power-law fits for Cox-Merz transformation of thermally recycled ABS contaminated

with PP .................................................................................................................................. 9-6

Figure I.12 Cox-Merz transformation of recycled PP contaminated with ABS .......................... 9-6

Figure I.13 Power-law fits for Cox-Merz transformation of thermally recycled PP contaminated

with ABS ................................................................................................................................ 9-7

Figure I.14 Cox-Merz transformation of post consumer ABS contaminated with PP ................ 9-7

Figure I.15 Cox-Merz transformation of post consumer PP contaminated with ABS ................ 9-8

Figure I.16 Flexural strength of recycled ABS contaminated with PP ....................................... 9-9

Figure I.17 Flexural strength of recycled PP contaminated with ABS ....................................... 9-9

Figure I.18 Impact strength of contaminated ABS blends ....................................................... 9-10

xiv

NOMENCLATURE G∆ Gibbs free energy J

H∆ Enthalpy J

S∆ Entropy J K-1

T measurement temperature K

T1 zone 1 in extruder 0C

T2 zone 2 in extruder 0C

T3 zone 3 in extruder 0C

Td die temperature 0C

Tg glass transition temperature 0C

E’ storage modulus MPa

E” loss modulus MPa

δtan tangent of the phase angle, [G’/G”]

TiO2 titanium dioxide

'G storage (dynamic) modulus MPa

"G loss modulus MPa

*G complex modulus MPa

iφ volume fraction of polymer

µ , 'η dynamic viscosity (Newtonian) Pa.s

η apparent viscosity Pa.s

*η complex viscosity Pa.s

k consistency index

n power law index

•

shear rate s-1

ω oscillation frequency s-1

τ shear stress Pa

l0 initial gauge length mm

W0 initial gauge width mm

t0 initial gauge thickness mm

F applied tensile force N

A0 gauge cross sectional area m2

xv

σ Stress Pa

ε Strain

l Elongation mm

le elongation gauge length mm

lb break gauge length mm

E tensile modulus (Young’s modulus) Pa

R rate of cross head motion mm s-1

D midspan deflection at test termination mm

Y Deflection mm

L length of specimen mm

B width of specimen mm

0T reference temperature K

T measurement temperature K

tA shift factor

21 ,CC WLF constants

N sample size

x Mean

sd standard deviation

%RSD relative standard deviation

se standard error

Z 96.1=Z abscissa of the normal curve for 95% confidence

interval

%E assumed error

MFR melt flow rate g/10min

0MFR melt flow rate at 0% contamination g/10min

MFRK linear MFR constant

21 , MFRMFR KK quadratic MFR constants

ϕ fraction of contaminant, (0 ϕ 0.30)

ρ Density kg m-3

0ρ density at 0% contamination kg m-3

ρK linear density constant

xvi

maxσK linear tensile/flexural strength constant

maxσ tensile/flexural strength/maximum stress MPa

0maxσ strength of uncontaminated polymer MPa

maxFK exponential impact strength constant

maxF impact strength kJ m-2

0maxF impact strength of uncontaminated polymer kJ m-2

EK linear modulus constant

xvii

ABREVIATIONS

ABS Acrylonitrile-butadiene-styrene

ACT Australian Composite Technology

ASTM Australian Standard

CESA Consumer Electronics Suppliers Association

Cm Cox-Merz transformation

DMA dynamic mechanical analysis

DMTA dynamic mechanical thermal analysis

DSC differential scanning calorimetry

HIPS High Impact Polystyrene

HP Hewlett Packard

IRIS Industrial Research Institute, Swinburne

ISO International Standard

MA maleic anhydride

MFR Melt flow rate

MMA methyl methacrylates

PA Polyamides, including nylon 6

PACIA Plastics and Chemicals Industries Association

Pc post consumer

PC Polycarbonate

PE Polyethylene

PMMA Poly(methyl methacrylate)

POE-g-MA maleic anhydride grafted polyethylene-octene elastomer

PP Polypropylene

PVC Polyvinyl chloride

SAN Poly(styrene-co-acrylonitrile)

SEBS Styrene-b-ethylene-co-butylene-b-styrene copolymer

SEM scanning electron microscope

SMA styrene maleic anhydride

SMA25 styrene maleic anhydride with 25% maleic anhydride

TA Thermal Advantage

TGA Thermal Gravimetric Analysis

xviii

TTS Temperature Time Superposition

TV Television

WEEE Waste Electrical and Electronic Equipment

WLF Williams-Landel-Ferry

1-1

1 INTRODUCTION

1.1 Introduction

This project focuses on the recycling of polymers in waste electrical and

electronic equipment. Blends of recycled polymers were investigated to determine if

contamination will significantly affect the materials properties in considering further

applications of the recycled material. The project was conducted in collaboration with

the Industrial Research Institute Swinburne (IRIS) and MRI. MRI aims to divert the main

portion of e-waste from landfill, with a degree of recycling already in place. However, to

transform e-waste into e-commerce, recycling of plastics requires investigation.

1.2 Plastic Recycling

Diminishing land fill capacity is one of the main drivers for plastic recycling,

particularly in countries of high population density such as Japan, Germany, etc. Other

factors include the environmental benefits, the rising price of non renewable raw

materials and consumers’ perception of product stewardship. For instance, over the last

10 years recycling of plastics in Australia increased 280% from 93,547 tonnes in 1997 to

261,109 tonnes in 2007 (PACIA, 2008). Close to 50% of the plastic was recycled in

Victoria. The consumption of plastic in 1997 was 1,336,386 tonnes, compared to 1,

710,085 tonnes in 2007, which corresponds to recycle rates of 7 and 15.3%,

respectively. A large portion (~85%) of the plastic recycled was packaging material.

The recycling rate of packaging material continues to improve, while the rate of plastics

from consumer durable products has remained constant over the last 10 years. “The

rate of recycling consumer durables is influence by the time is remains in use and the

growth in its consumption”, (PACIA, 2008).

Consumer durables are non-packaging products that have varying life-spans

including toothbrushes and pens (short-term) and computer casings and whitegoods

inserts (long-term). Properties of recycled consumer durable engineering plastics can

be higher than virgin commodity. The mechanical properties are retained, even after

medium to long term use (~10years). In some cases, engineering plastics are recycled

into high value consumer durables, in which the market value exceeds recovery costs.

Major recycling of engineering plastics includes computer and electronic housing,

automotive plastics and CD’s. The use of recyclate in vehicles has increased, but

1-2

stigma in using recyclate in engineering applications has hindered widespread use,

(Scheirs, 1998).

The consumer durable engineering plastics focused on in this study were derived

from waste electrical and electronic equipment (WEEE), which includes the casings of

computers, televisions and other electronic equipment. Generally, the life time of these

consumer durables is 5-10years, inducing a disposal lag, (Scheirs, 1998). However,

rapid advances in technology continually reduce the product life span of WEEE, to less

than 2 years in some cases, (Brennan, 2002), “representing a significant loss of non-

renewable resources” (Katos & Hoye, 2005). It was estimated that about 500,000

computers become obsolete each year in Victoria, with the vast majority not being

recycled and adding to the State's waste, (John Thwaites, 2005).

The growth of the amount of WEEE has prompted the Australian government to

work on establishing a product stewardship scheme to collect and recycle WEEE (Katos

& Hoye, 2005). Byte back is a computer take back program sponsored by Sustainability

Victoria, the City of Boroondara, Hewlett Packard (HP), Sims E Recycling and K&S

Environmental. Old, unused computers are collected for reuse or recycling. Computers

that are not directly reused are taken to a recovery centre for disassembly and sorting of

the materials (i.e. metals, plastics, etc). The materials are then transported to the

respective recycling stream (Doran, 2006).

1.2.1. Plastic Recovery There are three types of recycled material sources, pre consumer, post

consumer (industrial) and post consumer (domestic), (Scheirs, 1998), with each source

of material arising from a different stage in the product life cycle. Obsolete electrical and

electronic equipment of interest in this study is a domestic post consumer source.

The first stage in recycling plastics is to identify and separate the plastic by either

disassembly or bulk recycling. Debate continues over the method, taking into

consideration economic factors verses effectiveness of separation.

Disassembly is preferred if the equipment is without complexity and easily

disassembled. Typically, a piece of equipment can take 5-20 minutes to disassemble,

see Table 1.1.

1-3

Table 1.1: Dismantling Times of WEEE (Banfield, 2000)

Table not available – see printed version

Identification of the plastic can be achieved manually, using a trained eye.

However, as the complexity of materials increases with the manipulation of blends, more

precise techniques are preferred. An example is spectroscopy: Raman scattering, in

which an unknown plastic sample is scanned (manually) reflecting Raman scattered

radiation as a distinctive vibrational signature of a specific plastic. The polymer or blend

of polymers is identified through comparison to a library of standards, (Rios, 2003),

which can then be separated into its respective stream.

Bulk recycling is preferred if the piece of equipment requires extensive

disassembly and is composed of a wide variety of materials, includes items such as key

boards. Firstly, the piece of equipment is shredded. Metallic components are removed

first: ferrous materials by magnetic separation, non ferrous materials by an Eddy-current

separator.

The technique used to separate the individual polymers is largely dependent on

the difference in the property that is the basis for the separation.

Density based separating was the first technology used to separate polymers of differing

density by manipulating the properties of a solution. However, this is limited to polymers

of different densities, so that the specific densities of the polymers requiring separation

do not overlap. Density based separation is also of limited use for ‘modified’ polymers.

Density methods include: float-sink (wet, dry, hydrophobic, preferential solvent

absorption) and hydro cyclone, (Scheirs, 1998). Electrostatic sorting involves the

transfer of charge between two different polymers, the surface of one polymer adopting

a positive charge, and the other a negative charge, (Scheirs, 1998).

1-4

Disassembly is time consuming and labour intensive, consequently limiting the

throughput volume. On the other hand, large volumes can be processed with bulk

recycling, but with a high capital and compromised purity of the separated material

depending on the method of sorting.

Contamination and modification of the plastics used in the manufacture of

electronic products impact on the recyclability of the plastics. For instance, brominated

flame retardants are hazardous and reprocessing the contaminated plastics is

undesirable. Brennan et al conducted a survey on computer casing plastics and flame

retardation. It revealed that 68 of the 100 samples were flame retarded, of these, half

contained bromine (Brennan, 2002). Modified plastics include a base polymer filled with

another material to enhance a specific property important to the end use application.

Identification and separation of these materials are difficult and reprocessing can be

detrimental to the properties of the combined material. Ultimately, the properties of the

recycled material are highly dependent on the composition on the original material and

the separation of the materials.

1-5

1.3 Polymer Selection

There are two types of plastics, thermoplastics and thermosetting plastics. They

both consist of long chain-like molecules, but differ in their intermolecular forces.

Thermoplastics have weak Van der Waals attraction holding the chains together,

which is easily weakened upon heating leading to the softening of the plastic. For this

reason waste thermoplastics can be recovered and reprocessed.

The polymers that are most significant in Waste Electrical and Electronic Equipment

include:

• ABS - Acrylonitrile butadiene styrene

• SAN - Poly(styrene-co-acrylonitrile)

• HIPS - High-impact polystyrene

• PC - Polycarbonate

• PP, PE - Polyolefins

• PA - Polyamides, including nylon 6

• PVC - Polyvinyl chloride

The approximate proportions of these plastics in some common WEEE are represented

in Table 1.2 and 1.3.

Thermoplastics can be subdivided into two categories, crystalline (ordered) and

amorphous (random). Polyamides and polyolefins are generally crystalline/semi-

crystalline, and the other above mentioned plastics are amorphous. Crystallinity varies

depending on process condition and the thermal history of the material, which

consequently impacts on the mechanical properties (Utraki, 2002).

Table 1.2: Average Polymer Composition of plastic product covers (Rios, 2003)

Table not available – see printed version

1-6

Table 1.3: Polymer Composition of fridge shredder residue, (Pascoe, 2005)

Table not available – see printed version

Ragosta et al (2001) investigated blends of ABS with PVC. Mechanical testing of

ABS/PVC blends showed that the addition of recycled PVC to ABS significantly reduced

the mechanical properties. Thermosetting plastics, such as PVC, have strong covalent

bonding between the chains, which deteriorate with excessive heat and prevents the

softening of these types of plastics. In thermo mechanical reprocessing the thermal

degradation of the PVC is enhanced by the main parameters for blending: increasing

temperature, mixing time and mechanical stresses. Furthermore, degraded PVC may

induce thermo oxidation of the butadiene phase in the ABS. In conclusion, the

properties of PVC and PVC blends would be dramatically depressed by thermal

reprocessing hence PVC will not be used in this study.

1-7

1.4 Polymer Recyclate Applications

Once the material has been sorted, there are two methods of recycling

engineering plastics. If a recycled material retains properties similar to its original

application, it can be reused in the same or similar application. This is referred to as

closed loop recycling. However, if the material significantly loses these properties

through recycling it may be reused in a different application, known as cascade

recycling, (Scheirs, 1998). The main aim of recycling is to optimise the materials

properties thereby, maximising its value upon reuse. This is limited by the level of

contamination and related to the extent of sorting.

1.4.1. Recycled materials and homologous polymer blends

1.4.1.1. Acrylonitrile Butadiene Styrene, ABS

The high impact strength of ABS make it applicable for use in outer casings, including

computer housing, telephones, fax machines, vacuums, refrigerator liners and washing

machines inserts and various automotive applications.

ABS has been used in closed loop applications in the production of new housing for

WEEE and in automotive parts. Homologous blends are preferred, containing up to

25wt% recycled material and the balance virgin ABS. This controls the colour and

enhances the mechanical properties (Scheirs, 1998).

1.4.1.2. High Impact Polystyrene, HIPS

HIPS has similar physical properties to ABS, such that separating these two polymers is

difficult due to their relatively similar densities. Both polymers have high impact

resistance attributed to the dispersion of small rubber particles within the brittle matrix

(Fried, 2003). Therefore, HIPS is used for similar applications including electronic

housing and fridge inserts.

1-8

1.4.1.3. Polypropylene, PP

Polypropylene is a low density thermoplastic, used for its toughness, and fatigue and

chemical resistance (Crawford, 1998). These properties make polypropylene attractive

in the automotive industry, including fascias, bumpers and battery casing. Recycled PP

is also largely used in the automotive industry (Scheirs, 1998).

1.4.1.4. Nylon

Nylon has a relatively higher tensile strength and melting temperature, but low impact

strength. It is not suited to applications with of high surface area to volume ratio

subjected to high speed impacts, but is commonly used for fittings in WEEE.

1-9

1.5 Project Aims

The main objective of this research is to develop models to predict the properties

of recycled thermoplastics as a function of contaminant level. These models can be

used as a tool to determine the properties of materials with a known level of

contamination based on the extent to sorting. The research will include a

comprehensive study of the recycled blends properties including thermal, rheological

and mechanical analysis. Models will be formulated by measuring the properties of a

range of polymeric blends of recycled materials used for the manufacturing of consumer

durable products.

1.6 Contribution to new knowledge

Research in the field of recycled consumer durable plastics is relatively new.

There have been a number of articles written that have identified the drawbacks of the

different recycling methods, including the reduction in properties of contaminated

recycled materials related sorting ((Rios, 2003), (Xu et al., 2006), (Pascoe, 2004 &

2005)). Properties of blends of virgin materials have been investigated that indicate the

effect of contamination ((Gupta et al., 1990), (Liu et al., 2002a)). In addition, properties

of blends of recycled materials have been investigated ((Lindsey et al., 1982), (Liu et al.,

2002b), (Santana, 2003)). However, only a small variety of blends have been analysed

and the measured properties lack detail.

This research was dedicated to relating the properties of a contaminated,

recycled material to the level of contamination. Different blends of recycled material that

simulate a level of contamination were analyzed for an extensive range of material

properties that provide information on the processing of the material and the

performance of the material in its end use application. This included thermal, rheological

and mechanical. Relationships between the properties and the level of contamination

have been modeled to predict a property for any level of contamination. The predictive

models are a simple tool that can be used to estimate the properties of contaminated

materials if an approximate level of contamination in a binary mixture is known. In

addition, dynamic mechanical analysis is a novel method for determining thermal-

mechanical properties of a recycled consumer durable material. It was used to provide

an indication of the mechanical properties over long term use of the material and to

identify phase transitions.

1-10

1.7 Thesis Structure 1.7.1. Chapter 1 : Introduction The introduction outlines the drivers behind researching the recycling of consumer

durable plastics, including methods of sorting and the potential of contamination during

the recycling process. It lists the major plastics found in WEEE and introduces the

concept of intentionally contaminating plastics to model the properties of a material with

different levels of contamination.

1.7.2. Chapter 2 : Literature Review The literature review outlines experimental work performed by other researches in the

field of recycling consumer durable plastics. Researchers have investigated the impact

on the materials properties due to recycling the individual thermoplastics. The review

focuses on miscibility of binary polymer blends and the effect of contamination on a

materials property.

1.7.3. Chapter 3 : Methodology Experimental methodology for material processing and property analysis is described in

this section. The methodology is based on the relevant Australian standards.

1.7.4. Chapter 4 : Thermal Properties of contaminated plastics Thermal properties are evaluated in this chapter to indicate a material behaviour during

processing conditions and to determine thermal processing limits.

1.7.5. Chapter 5 : Processability of contaminated plastics Processability further reflects limits on processing conditions caused by contamination.

The melt flow rate and rheology reflect the flowability of the contaminated material during

processing.

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1.7.6. Chapter 6 : Mechanical Properties of contaminated plastics Mechanical properties indicate the behaviour of a contaminated material during use and

are used in identifying a suitable application for a material. The mechanical analysis of

the materials includes standard tests of tensile, flexural and impact strength, as well as,

dynamic mechanical analysis which models long term behaviour via time-temperature

superposition. Predictive models have been developed to assist in estimating a property

of a material based on the level of contamination.

1.7.7. Chapter 7 : Conclusions

The effect of contamination on a materials property is important when considering a

material for an end use application and consequently, the extent of sorting required

during the recycling process. Conclusions are drawn on property deterioration that limits

the level of contamination. In addition, models of property change with the level of

contamination provide an indication of the interaction between the blended polymers.

2-1

2 LITERATURE REVIEW

2.1 Introduction

Homologous and non-homologous contamination of virgin materials has been

investigated previously. However, blending of recycled materials, particularly consumer

durable plastics, is a relatively novel field. This study investigates blended recycled

materials that represent a know level of contamination. Typically, recycled plastics

exhibit lowered properties, including reduced molecular weight, decreased viscosity and

decreased mechanical properties. This is a result of factors associated with

reprocessing, including degradation and contamination (Case & Korzen, 2000).

2.2 Blends

A polymer blends is a mixture of at least two polymers. Homologous polymer

blends are a mixture of compatible homologous polymers. Typically, it is narrow

molecular weight distribution fractions of the same polymer. An example of homologous

polymer blends is the mixing of a portion of recycled material with virgin material of the

same polymer. On the other hand, non-homologous polymer blends is a blend of two or

more different polymers; it could be recycled polymers, virgin polymers or a combination

of both (Utracki, 1989). In this research, the contaminant is the component in the blend

present at less than 30%.

2-2

2.3 Miscibility

Miscibility is the mutual solubility of polymers within a blend. A blend is miscible,

if it is homogeneous down to the molecular level. It is governed by a negative value of

the Gibbs free energy of mixing.

STHG ∆−∆=∆ (2.1)

The miscibility of a polymer blend depends on the processing conditions and

other variables including temperature, pressure, molecular weight and chain structure.

A blend is immiscible if the Gibbs free energy is positive for the entire composition range

of the mixture of polymers: this means that the polymers coexist at equilibrium as two

distinct phases. Apart from immiscible, a mixture of polymers can be partially miscible or

totally miscible. For total miscibility, over the entire composition range

• the Gibbs free energy must be negative

• the second derivative of G with respect to volume fraction of one of the

components of the polymer mixture, iφ , must be positive

0 0,

2

2

>

∂∆∂<∆

Tpi

GGφ

and

The second derivative may not be satisfied over the entire composition range. At these

compositions the mixture will phase separate at equilibrium into two phases containing

different compositions of polymers, which is referred to as a phase rich in one of the

component polymers. This is partial miscibility (Fried, 2003), (Utracki, 1989).

Compatibilisation is the modification to the interfacial properties of an immiscible

polymer blend. This forms a polymer alloy (Utracki, 1989). Polymer alloys will not be

developed in this research as the aim of the research is to look at contamination as an

undesirable outcome of recycling and to develop models to predict the effect of recycling

on a material’s property. In addition, compatibilisation requires additional material that is

not within the scope of the project.

2-3

2.4 Blend Properties

Polymer blends are designed to retain the desirable properties of each

constituent. Properties of miscible blends are intermediate between those of the

individual components in the blend, referred to as additive behaviour. The additive

behaviour is often referred to as the “rule of mixtures”. Deviations from the rule reflect

the effects of blending. Ideally, blending two constituents enhance a material’s property

beyond simple additivity; thereby exhibiting synergistic behaviour, see Figure 2.1, (Fried,

2003).

Synergistic behaviour

Property additive

Blend composition

Figure 2.1 Behaviour of blended materials

2-4

2.5 Recycled materials and homologous polymer blends

2.5.1. Acrylonitrile Butadiene Styrene (ABS)

ABS is one of the cheapest and hence, most abundant engineering

thermoplastics. The most significant problem in recycling ABS is the oxidative

degradation of the rubber, butadiene. Liu & Bertilsson, (1999) recycled plastic material

obtained from dismantled cars. The material was identified as ABS based on solubility

and the results from differential scanning calorimetry (DSC). Mechanical test samples

were prepared using a co rotating twin screw extruder and injection moulding. Identical

specimens were prepared with virgin materials as a source of comparison for

mechanical testing. The research showed a reduction in impact strength and toughness

through recycling; resulting from the degradation of the rubber matrix in the recycled

material, see Table 2.1.

Table 2.1: Mechanical properties of virgin and recycled ABS plastics, (Liu & Bertilsson, 1999)

Table not available – see printed version

2.5.2. Polypropylene (PP)

PP is a low density consumer durable. In research by Santana et al (2003), the

mechanical properties of polypropylene recycled from mineral water bottles were used to

evaluate the effects of recycling. Virgin material was purchased as a comparison.

Recycled PP exhibited better elongation at break, while all other thermo mechanical

properties indicated that the effect of recycling PP is negligible, see Table 2.2. The

variation between virgin and recycled PP can be attributed to the different grade of the

polymers: the virgin material is a single grade obtained from a single supplier whereas

the recycled material is a mixture of grades from various polymer suppliers. In addition,

it is likely that the recycled material had additives used to enhance the properties for the

purpose of its original application.

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Table 2.2: Mechanical properties of virgin and recycled PP plastics, (Santana et al, 2003)

Table not available – see printed version

2.5.3. High Impact Polystyrene (HIPS)

HIPS is an abundant engineering plastic in computers and other electronic

equipment. HIPS dominant post consumer equipment is generally fitted with

incompatible polymers that would require expensive disassembly and is highly

contaminated through the use of additives, such as flame retardants.

Xu et al (2000) studied blends of post consumer HIPS with virgin polymer,

analysing the impact of recycling on various mechanical properties. Post consumer

material was obtained from printer and monitor housing. The original manufacturer of

the material was unknown; hence the virgin polymer was selected based on matching

the rheological properties with the recycled material. Blends of 0, 25, 50, 75, 85,

100wt% virgin material were prepared. The blends were pseudo plastic (shear thinning -

viscosity decreases with increasing shear rate), as predicted by Utracki (1989)

“polymeric melts dominantly display pseudo plasticity”. Furthermore, the viscosity

measurements were similar for all blend types since the grade of the virgin material was

selected by matching the rheological properties of the recycled material. In terms of

mechanical properties, the tensile measurements and impact strength for the blends

increased with increasing content of post consumer resin (Xu et al, 2000).

Similar research was carried out by Santana et al (2003). Works by Santana et

al investigated HIPS recycled from disposable cups. Reprocessed and virgin materials

were thermo mechanically tested to evaluate the effects of recycling. Following works

by Xu et al., the tensile strength of the recycled material was superior. However, the

elongation at break and the impact strength of the recycled material was significantly

reduced (Santana et al, 2003).

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Table 2.3: Mechanical properties of virgin and recycled HIPS plastics, (Santana et al, 2003)

Table not available – see printed version

Considering that a degree of degradation would have occurred over the product

life cycle, the superior mechanical properties of the post consumer material imply that

the original plastic of the product was of higher mechanical quality than the virgin

polymer selected for comparison. In addition, it is possible that modifiers have been

added to enhance some of the properties depending on the requirements for its original

application. These factors can account for the difference in the results between

researchers.

2.5.4. Polyamide (PA, Nylon)

Polyamide is semicrystalline with a low glass transition. It is often glass or fibre

filled to improve the stiffness at elevated temperature. Liu et al (2002b) investigated

recycling two different grades of polyamide obtained from a dismantled car, one glass

filled and one mineral filled. The glass filled grade has greater tensile properties, but

lower elongation at break and impact strength. Liu et al (2002b) suggested that the

glass fibres present in the polymer matrix lower the impact strength by acting as sites for

stress concentrations and initiation points for cracks to develop during impact (Liu et al,

2002b).

Styrene-b-ethylene-co-butylene-b-styrene copolymer, SEBS-MA was added to

the PA as a toughing agent and impact modifier. This addition significantly increased

the elongation at break and the impact strength, while depressing the tensile properties

(Liu et al, 2002b).

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2.6 Non-homologous polymer blends

2.6.1. VIRGIN BLENDS

Blends of virgin materials have been investigated by a number of researchers,

((Gupta et al, 1990), (Markin & Williams, 1980), (Balakrishnan & Neelakantan, 1998),

(Lindsey et al, 1981), (Liu et al, 2002a), (Chiu et al, 2004)). The results have been used

to evaluate the effects of contamination.

2.6.1.1. ABS contaminated with HIPS

Fridge door liners are typically laminated sheets of ABS and HIPS. An ABS skin

is coextruded over the less expensive HIPS because ABS has superior chemical

resistance. Once a refrigerator becomes waste, the polymers in the plastic scrap cannot

easily be separated. Lindsey and colleagues blended ABS and HIPS to investigate the

effect of not separating these plastics. A number of blends using virgin materials were

prepared over an extensive composition range.

Mechanical tests were carried out to evaluate the effect of contamination and to

determine the potential reuse of the blends from the processed scrap. Measurements of

modulus, yield strength and % elongation over the entire composition range lie close to

the rule of mixture. This behaviour is characteristic for miscible blends.

Microscopic observations contrasted the mechanical testing, indicating

incompatibility of the two polymers. This was observed by phase segregation that had

occurred during the processing of the blends, whereby the less ductile ABS formed a

skin around the specimen. However, this may not have been detrimental for the end use

of the reprocessed scrap since these two polymers are coextruded to attain the same

affect when producing refrigerator door lining (Lindsey et al, 1981).

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2.6.1.2. ABS contaminated with PA

ABS is an amorphous styrene-acrylonitrile with a dispersed butadiene phase that

improves strength. On the other hand, PA is a semicrystalline engineering plastic, with

good chemical and abrasion resistance. Liu et al (2002a) attempts to combine the

feature of each thermoplastic by producing an ABS dominant blend, simulating ABS

contaminated with PP.

Compatibility of ABS/Nylon 6 blends has been extensively investigated, and

ultimately compatibilisation is essential to produce materials with usable properties. A

number of compatibiliser/modifiers have been trialled, including methyl methacrylate

(MMA), acrylonitrile, styrene maleic anhydride (SMA) and maleic anhydride (MA). The

compatibiliser used by Liu et al (2002a), styrene-maleic anhydride with 25% maleic

anhydride (SMA25), binds with the amine group of PA forming a block copolymer with

SMA and PA blocks, thus reducing the interfacial tension between PA and SAN. SEM

micrographs revealed that compatibilisation increased as the amount of SMA25 in the

blend increased. This was seen as the reduction in PA particle size dispersed within the

polymer matrix. The compatibilised blend showed improved tensile modulus, yield

strength and elongation at break compared to uncontaminated ABS. However,

compatibilisation did not improve the impact strength of the ABS blend, which was

halved with PA contamination. This led to the addition of a core shell impact modifier,

EXL3300, which doubled the impact strength of the compatibilised blend, similar in value

to the impact strength of uncontaminated ABS.

In a concurrent study, Liu et al (2002b) investigated the use of another impact

modifier that is commonly blended with recycled PA. SEBS-MA, does not improve

impact properties of ABS/PA blends because SEBS-MA is incompatible with ABS.

Micrographs confirmed the poor affinity between ABS and SEBS-MA.

2-9

Table 2.4: Mechanical properties of compatibilised and impact modified blends, (Liu et al, 2002a & 2002b)

Table not available – see printed version

Commercial blends of immiscible polymers generally contain compatibiliser that

can be used to compatibilise an unmodified blend of recycled materials, thereby

eliminating an external compatibiliser. A small amount of a commercial blend (Triax

1120, ABS/PA) was blended with an unmodified ABS/PA blend. The mixture exhibited

superior ductility and similar impact strength, compared to uncontaminated ABS.

Another commercial blend (Cadon G2320, ABS/SMA with glass fibres) was mixed with

an impact modified ABS/PA blend for the purpose of compatibilisation. Ductility was 4

fold greater than uncontaminated ABS, but impact strength was lowered (see Table 2.4).

The glass fibres, present in the Cadon G2320 blend, are relatively well bonded yet they

act as stress concentrators, which lead to lowered impact strength (Liu et al, 2002b).

The compatibilising effect of the addition of both commercial blends was observed in

SEM micrographs by the small domain size of PA within the blend matrix.

Chiu et al (2004) researched the effect of ABS/PA compatibilisation with maleic

anhydride grafted polyethylene-octene elastomer (POE-g-MA). The optimum blend

ratio, 80wt% Nylon6 : 20wt% ABS, was determined, based on notched impact strength.

Holes in the morphology were the result of the dissolution of ABS dispersed in the nylon

6 phase, where the smallest particles coincide with the 80:20 blend.

2-10

Impact strength improved as a result of increasing POE-g-MA addition (0, 3.6, 5,

10phr); with approximately a 4 fold increase by the addition of 10phr compatibiliser. The

impact strength was enhanced by increasing the amount of compatibiliser, which

reduced the size of the dispersed ABS particles. Compatibility of the polymer system

was emphasized in the rheological properties of the blend. The shear viscosity of the

blend was lower than either polymer. However, the addition of POE-g-MA increased the

shear viscosity, as the compatibiliser effectively increased the interfacial interaction

between nylon 6 and ABS (Chiu et al, 2004).

2.6.1.3. PP contaminated with ABS

Gupta et al. (1990a, 1990b) investigated mechanical and melt rheological

properties of virgin blends of PP contaminated with ABS, PP as the major component

and a varying content of ABS (0, 5, 10, 20, 30%).

The results show that the addition of a small amount of ABS improved the impact

strength to a maximum value at 10% ABS. While increasing the ABS content beyond

10% only increased the shear induced fracture with ductility. “Ductile fracture results in

plastic flow due to recovery of stresses immediately after fracture”. Markin and Williams

(1980) refer to a type of skin-core morphology, which is phase segregation caused

during injection molding of the test specimens. The formation of an ABS-rich skin leaves

a major portion of the fracture surface (the PP-rich core) poorer in ABS content, thus

reducing the impact strength of PP/ABS blends. This was observed in the electron

micrographs of the impact fractured surfaces. Similarly, elongation and the point of

break were significantly reduced because of the brittle nature of ABS. In contrast, ABS

addition had only a minimal effect on the tensile yield strength.

Melt properties of the blends were analysed with a capillary rheometer. The

results clearly showed that viscosity at a given shear rate increased with increased ABS

content in the blends. In addition, the decrease in melt viscosity with increased shear

rate was approximately linear, and consistent with the following power law relationship:

indexlaw power

===

•

nnbB b

1- η

(2.2)

The power law exponent,n decreased with increased ABS content in the blends, which

corresponds to increased pseudo-plasticity with increased ABS content.

2-11

In conclusion, small amounts of ABS did improve the mechanical properties of

the material, while increasing pseudo-plasticity. However, high levels of ABS in PP

(10%) reduced the mechanical properties of the material, which was assumed to be the

result of phase segregation and ABS skin formation during processing.

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2.6.2. RECYLCED BLENDS

2.6.2.1. ABS contaminated with HIPS

Brennan et al (2002) surveyed a number of pieces of computer casing to

determine the two most widely used plastics for these applications: ABS at 45wt% and

HIPS at 21wt%. The thermo mechanical properties of the recycled plastics were

compared to the virgin plastics. Additionally, various ABS contaminated with HIPS

blends (10, 50, 90% HIPS) of the recycled plastics were analysed as an indication of the

impact of contamination and the miscibility of the blended polymers. The glass transition

temperature, Tg, for the materials was determined using dynamic mechanical thermal

analysis (DMTA). Assuming that the virgin materials were the same grade as the

recycled plastics, recycling lowered the Tg for the uncontaminated polymers, ABS and

HIPS, 102 to 960C and 104 to 1020C, respectively. The blends exhibited a single Tg

peak and the glass transition of the ABS contaminated with HIPS increased

proportionally with increasing HIPS content, according to the “rule of mixtures”. These

characteristics indicate that these ABS contaminated with HIPS blends are

homogeneous and miscible. While an incompatible blend would exhibit two glass

transition temperatures, one for each component, and they would not vary over the

composition range.

HIPS is often referred to as ductile and ABS as semi-brittle. Recycling the

uncontaminated polymers, ABS and HIPS, led to an increase in tensile modulus and

decrease of % elongation, indicating a reduction in ductility and an increase in stiffness.

This was more prominent for HIPS. The increased stiffness of the recycled plastics was

reiterated by the substantial deterioration of impact strength. This may be the result of

degradation and the presence of impurities (i.e. the pigment TiO2) within the polymer

matrix, causing inhomogeneity. The effect of blending varied between the mechanical

properties. Tensile strength decreased with HIPS content according to the rule of

mixtures. Modulus did not change with HIPS contamination because ABS and HIPS

have the same modulus. However, it can be assumed that the blends follow the rule of

mixtures for modulus. While the elongation properties of the blends reflected synergistic

behaviour attributed to favourable interactions between the polymers. In fact, blending

“improved the elongation properties that were otherwise lost due to the recycling

process”. Contrarily, impact strength was further decreased by HIPS contamination and

negatively deviated from the rule of mixtures over the composition range. This was the

only indication that the polymers are not compatible (Brennan et al, 2002).

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In conclusion, HIPS contamination improved some of the properties that were

adversely affected by recycling ABS. The authors suggest that the addition of impact

modifiers would enhance the recyclate blend, superior to either one of the recycled

polymers.

2.6.2.2. ABS contaminated with PA

Liu et al (2002b) investigated compatibilisation of ABS contaminated with PA

using recycled ABS and two grades of PA (glass filled PA and mineral filled PA) from

dismantled cars. The presence of 20% PA reduced the elongation at break and impact

strength, particularly contamination with the glass filled PA. SEM micrographs show that

the glass fibres were poorly bonded to the polymer matrix, rationalising the inferior

mechanical properties.

Additional recycled plastics were introduced to simulate the mixture of plastics

from a dismantled car, with the aim of producing useful materials without sorting. The

blending was based on the polymer ratio of the plastic proportion of a specific type of

car, ABS/(ABS/PC)/PMMA/glass reinforced PA, in respective proportions 40/40/10/10.

Since, ABS, PC and PMMA are either miscible or compatible, compatibilisation was only

required for the PA phase. SMA25 was used to compatibilise PA as it is miscible or

compatible with the other three components of the blend. In addition, EXL3300 was

added as an impact modifier. The mechanical properties for this mixed plastic blend

were greater than the ABS/PA blend. This was attributed to the lowered content of the

PA and the presence of the inherently tough PC (Liu, 2002b).

2-14

2.6.1.3. PP contaminated with HIPS

Santana et al (2003) studied compatibilizing post consumer PP contaminated

with HIPS, referencing against virgin blends (14, 25, 33 wt% HIPS). PP and HIPS were

recycled from mineral water bottles and disposable cups, respectively.

In all instances, the recycled blends exhibited higher mechanical properties

compared to the virgin blends, indicating that the recycled material was higher grade.

Impact strength and elongation at break decreased with increasing HIPS content. This

was illustrated in phase morphology by weak adherence of the dispersed HIPS phase in

the PP matrix. The decline in impact strength for recycled blends was greater, which

indicates that the effect of recycling was more significant on recycled HIPS. Therefore,

as the content of HIPS increased in the recycled blends, the depression of properties

was enhanced, (Santana et al, 2003).

The PP contaminated with HIPS blends were compatibilised with varying

amounts of SEBS (5-7%). The tensile stress at maximum load and hence, interfacial

adhesion increased with lower SEBS content (5%). Furthermore, SEM micrographs

analysing the phase morphology showed that the size of the dispersed HIPS phase was

smaller for 5% SEBS, which resulted in a higher overall HIPS interfacial area. Thus, 5%

SEBS was the optimal compatibiliser content (Santana et al, 2003).

2-15

2.7 Application of Recycled Blends

Appropriate applications for the recycled polymers can be determined by

comparing the properties of the material with virgin materials, see Table 2.5 for the

properties of individual engineering thermoplastics.

Table 2.5: Properties of Engineering Thermoplastics, (Fried, 2003)

Table not available – see printed version

2.7.1. Blends

There are a number of considerations that should be considered when designing

a polymer blend which may reduce time spent on trial and error.

Step 1: Identify properties desired by the blend and select polymers that could achieve a

number of the properties

Step 2: Match the polymers to assure the most suitable complementarily of properties

Step 3: Miscibility and compatibility of the blended polymers

Step 4: Economic evaluation, including cost of processing, additives and final value of

blended material

2-16

Physical properties are significant in the thermo mechanical reprocessing stage

of preparing a blend. Ideally, the melt temperature of the individual polymers should be

close to improve processability in terms of viscosity and mechanical mixing. It is also

convenient to blend polymers with relatively close densities to eliminate expensive

separation processes (i.e. mixture of ABS and HIPS, (Pascoe, 2004)), see Table 2.6 for

the above mentioned physical and thermal properties of various consumer durable

thermoplastics.

During the recycling process the materials are not blended out of choice, but for

reasons associated with separation of the individual polymers. For instance, time to fully

disassemble a piece of WEEE or the physical similarities which prevent complete

separation of the shredded materials.

Table 2.6: Physical and Thermal Properties of Consumer Durable Thermoplastics, (Fried, 2003)

Table not available – see printed version

2-17

2.8 Summary

This chapter highlights the limited research that has been carried out to

investigate blending of recycled consumer durable thermoplastics, especially materials

from WEEE. Blends of virgin materials, such as ABS contaminated with HIPS and ABS

contaminated with PA, were analysed and these results can be used to indicate the

effect that contamination has in the recycling of these thermoplastics. ABS

contaminated with HIPS proved to be a compatible blend. This was an important

outcome for Lindsey et al (1981), as their investigation was based on the future recycling

of refrigerator door liners that consist of ABS laminated HIPS sheets. Whereas, PA had

significant adverse effects on the properties of ABS, which Liu et al (2002a) took into

account and used compatibilisers. However, blends of virgin materials cannot be

directly compared to recycled materials because modifiers that have been used to

enhance the functionality of the material for its original use can play an important role in

blends.

Brennan et al (2002) used ABS and HIPS based computer casings and analysed

a small range of blends. Based on the analysis of glass transition temperature and

simple mechanical properties, the ABS and HIPS appear compatible and miscible when

blended. Liu et al (2002b) investigated improving a blend of ABS contaminated with PA,

attempting to improve the material’s properties using additives to compatibilise and

modifiers to improve impact strength. An ABS dominant blend, consisting of typical

materials obtained from a dismantled car including PA, was compared to the initial

blends of ABS contaminated with PA. The multi-plastic blend containing other materials,

including PC and PMMA, had superior mechanical properties. Blends of recycled PP

contaminated with HIPS were compatibilised by Santana et al, (2003), to enhance the

mechanical properties. Compatibiliser level was varied to determine the optimal level

based on SEMS micrographs used to observe the size and distribution of the dispersed

phase, which is an indicator of interfacial adhesion and thus, improved mechanical

properties.

3-1

3 METHODOLOGY 3.1 Introduction

This chapter includes a list of the materials and the methodology applied

throughout the research, including a description of the processing and the material

testing.

Polymers were blended using a single screw extruder with different portions of

the contaminated polymer to represent known levels of contamination. The pelletised

extrudate was processed into test specimens for the purpose of thermal, rheological and

mechanical testing.

3.2 Materials

Granulated injection molding grade virgin materials manufactured by BASF were

purchased from Marplex Australia Ltd, Terluran®GP-22 natural (ABS), Moplen EP203N

(PP), Polystyrol 476L (HIPS) and Ultramid®B3S (Nylon 6), see Table 3.1. The virgin

material was reprocessed in a 12mm Axon Pacific laboratory single screw extruder to

simulate recycling and to ensure a direct uncontaminated comparison with actual

recycled material. Crushed recycled material was donated by Australian Composite

Technologies (ACT), including recycled car bumpers (PP) and recycled outer casings of

computers (ABS).

Table 3.1: BASF material properties

Material Density

(g/cm3)

Impact

Strength

(kJ/m2)

Tensile Stress

at Yield

(MPa)

Melt Flow Rate

(g/10 min)

ABS Terluran®GP-22 1.04 26 45 21

HIPS Polystyrol 476L 1.05 11 26 5.8

PP Moplen EP203N 0.896 10 20 11

PA 6 Ultramid®B3S 1.13 4.0 90 198

3-2

3.3 Processing

3.3.1. Extrusion

A polymer was mixed with a measured volume of another polymer and blended

in an Axon single screw extruder, see Figure 3.1 and 3.2 (see Table 3.2 and 3.3 for

blend composition). The amount of minor polymer in these binary blends represents a

level of contamination, which indicates a degree of sorting. Granular polymer was fed

into the barrel of the extruder via a storage hopper. The barrel of the extruder is divided

into three sections, the feed, compression and metering section.

Feed zone: The purpose of this zone is to preheat and supply the plastic. A single

screw with constant flight depth must be designed to convey sufficient material further

down the barrel. Electrical heaters along the length of the barrel ensure the plastic has

melted prior to entering the metering zone.

Compression/Transition zone: The flight of the screw decreases in the compression

zone, enhancing mixing. Reducing the flight depth increases the shear rate thereby

decreasing the viscosity of the polymer mixture. In addition to mixing, the changing

screw depth removes any trapped air from proceeding further and improves heat

transfer by reducing the thickness of the plastic in contact with the heated barrel.

Metering zone: In the metering zone the flight depth remains constant, but significantly

shallower than at the feed. The shearing action of the screw further mixes the polymers

and forces the plastic melt out of the barrel through the die (Fried, 2003), (Crawford,

1998).

The die shapes the extrudate, forming strands of plastic which were solidified in a water

bath. Finally, the long lengths of solid plastic are pelletised.

3-3

Image not available – see printed version

Figure 3.1 The barrel of a single screw extruder, (Chokshi, R., and Zia, H., 2004)

Table 3.2: Contaminant level in ABS blends

Contaminant Contaminant level, vol %

PP 10, 20, 30

HIPS 10, 20, 30

Nylon 6 5, 10, 20

Table 3.3: Contaminant level in PP blends

Contaminant Contaminant level, vol %

ABS 10, 20, 30

HIPS 10, 20, 30

Nylon 6 5, 10, 20

3-4

Figure 3.2 Axon single screw extruder

Feed Hopper

Die

Barrel Section

Figure 3.3 Control panel and die formation of the extruder

3-5

3.3.2. Injection Moulding

Injection moulding produces a wide array of articles, ranging from electronic

housing to automotive parts to food containers. Granular or powdered polymer/plastic

stock stored in a hopper is fed into the barrel where it is softened by heating. The

softened plastic is forced through a nozzle into a chilled water cooled mould, which is

clamped closed. Time is allowed for the plastic to solidify before the item is ejected from

the mould. Solidification time is dependent on the material, in this instance, 5 seconds

was sufficient.

Prior to molding, the feed material was dried under vacuum, for at least 18 hours,

at 900C to eliminate air bubbles forming in the injection molding process. Mechanical

test specimens were formed in a Battenfeld Injection Moulder (Model BA 350 / 75

PLUS), see Figure 3.3 and 3.4, (see Table 3.4 for processing conditions).

Table 3.4: Processing temperature variables, extruder zones (T1, T2, T3, Td, respectively) and injection molding

Material Processing

Temperature Range1 Extruder Zones IM Temperature

Terluran®GP-22 natural (ABS) 220-2600C 210, 220, 230, 235 25, 190, 220, 240

Polystyrol 476L (HIPS) 180-2600C 200, 210, 220, 225 25, 190, 220, 240

Moplen EP203N (PP) 210-2500C 200, 210, 220, 225 25, 190, 220, 240

Ultramid®B3S (Nylon 6) 250-2700C 220, 230, 240, 245 25, 190, 220, 240

1 Product data sheet supplied by BASF plastics

3-6

Figure 3.4 Battenfeld Injection Moulder (Model BA 350 / 75 PLUS)

Figure 3.5 Die cavity of the Battenfeld Injection Moulder for mechanical testing

specimens

Die Cavity

3-7

3.4 Thermal Properties

3.4.1. Glass Transition

The glass transition temperature, Tg, was measured with the help of differential

scanning calorimetry on DSC 2920 (TA instruments) and dynamic mechanical analysis

on DMA 2980 (TA Instruments). TA Universal Analysis software was used to view and

analyse the data.

Differential scanning calorimetry compares the heat input rate required to

maintain the specimen and a reference at the same rate of temperature rise. The

differential heat flow is recorded as a function of temperature, plotted as a thermo gram.

Dynamic mechanical analysis, DMA, is a relatively new method imported from

the field of rheology. Similar to a traditional mechanical tensile tester, DMA measures a

sample’s response to an applied force and the relationship between stress and strain,

the modulus, is calculated. Modulus is a measure of the material’s stiffness, varying with

temperature and applied stress. DMA supplies an oscillating force causing a sine wave

stress resulting in a sine wave strain. The amplitude of the sine waves and the phase

lag between the applied stress and the strain response are important parameters used in

the calculation of modulus. This includes the storage modulus, G’, and loss modulus,

G”, which are measures of a material’s ability to store and lose energy, respectively.

The tangent of the phase angle (tan) is the ratio of the storage and loss modulus, also

called damping. Damping is an indicator of how efficiently a material loses energy to

molecular rearrangement and internal frictions (Menard & Raton, 1999).

Dynamic Mechanical Analysis is widely used to identify transitions in a polymer

that may be difficult to detect in less sensitive instruments, such as DSC. The glass

transition temperature can be determined a number of ways, this includes the

temperature at the onset of G’ drop, the peak of G” or the peak of tan (Menard & Raton,

1999). It is important to adopt a consistent approach for the comparison of the various

blends. The temperature at the peak of tan is the most commonly used for polymers,

although none of the methods are favoured.

The glass transition temperature was captured by a temperature ramp, room

temperature to 1500C at 100C per minute on the DMA 2980 (TA Instruments) using

Thermal Advantage instrument control software.

3-8

3.4.2. Degradation Region

Determination of the onset of polymer degradation is observed by heating a

known sample weight at a constant rate. The sample begins to volatilise once it has

reached the onset of degradation, which is identified as a drop in weight.

TA instruments SDT 2960 was used to indicate the onset of degradation by

means of Thermal Gravimetric Analysis, TGA, using Thermal Advantage instrument

control software, see Figure 3.5. Pelletised samples of similar weight (10mg) and shape

were analysed to ensure uniform surface area to volume ratio between the samples and

hence, consistent heating.

Figure 3.6 TA instruments SDT 2960

3-9

3.5 Rheological Properties

“Rheology is the science of deformation and flow” (Utracki, 1989). Rheology is

important to assess the processability of a polymer.

Newton’s law of viscosity describes the viscous flow of a Newtonian fluid relating shear

stress,τ , to shear strain rate, •γ :

Newtonian)viscosity dynamic (

==

•

µµτ (3.1)

The viscosity of a Newtonian fluid is a function of temperature and pressure,

while independent of the shear strain rate. Simple non-Newtonian behaviour is a

function of temperature, pressure and shear rate, where complex behaviour incorporates

all three variables as well as time (Fried, 2003).

Non-Newtonian fluids are divided up into two systems, dilatant (or shear

thickening) and pseudo plastic (or shear thinning). The basis for the systems is the

relationship between apparent viscosity,η , and shear rate, •γ .

•=γ

τη (3.2)

Polymeric melts dominantly display pseudo plasticity. The viscosity of a pseudo plastic

decreases with increasing shear rate.

The power law is the most widely used model for pseudo plastic behaviour to

describe the change of viscosity as a function of shear (Utracki, 1989), (Utracki, 2002).

indexlaw power

indexy consistenc

===

•

nk

k n

τ

(3.3)

The power law index, n , can be used to describe the three basic types of flow,

n =1 Newtonian behaviour

n <1 Shear thinning (or Pseudo plastic)

n >1 Shear thickening

3-10

The power law can be rearranged and include the term of the apparent viscosity

using the shear rate and apparent viscosity at a reference state, 0 and ηγ•

0 respectively

(Crawford, 1998).

nn 1

00

−

•

•

=

γ

γηη

(3.4)

The power law provides a good approximation at the high strain rates experienced

during extrusion and injection moulding.

There are two types of instruments for determining the rheological properties of a

material: capillary and rotational.

Capillary rheometry forces a fluid through a tube, establishing a relation between

volumetric flow rate and pressure drop due to friction. This technique is superior for high

viscous media as higher shear rates can be attained.

Rotational rheometers involve the shearing of a sample fluid due to rotation,

including concentric cylinder, cone and plate and parallel plate rheometers. At higher

shear rates, material failure is prevalent, especially for high viscous materials. Failure or

slippage can occur due to loss of adhesion between the sample and the plates, and

secondary flow resulting in a breakdown of laminar flow. However, empirical

relationships, based on oscillating shear flow experiments, can extend the shear rate

range. One such relationship is the Cox-Merz rule:

( )[ ] 21

22* /'' ωηη G+= (3.5)

( ) ( )

"'

'"1'

21

2*

ηηη

ηηωηωηγη

γω

γω

i−=

+==

∗

=

=

•

•

•

*η is the complex viscosity, 'η dynamic viscosity, 'G the dynamic rigidity modulus and

ω the oscillation frequency (Ferguson and Kemblowski, 1991).

3-11

3.5.1. Parallel Plate Rheology

Melt rheological properties were measured on an AR 2000 (TA instruments)

parallel plate rheometer with aluminium 25mm parallel plate geometry, see Figure 3.7.

TA Data Analysis software was used to view and model the data.

The main advantage of parallel plate rheometers over other rotation rheometers

is the easily adjustable gap, which is useful in measurements over a temperature range

as it accounts for expansion of the material.

There are two common approaches to rotational rheometry, controlled rate and

controlled stress, see Figure 3.6. Controlled rate: the lower plate is rotated and the

response of the upper plate is the measured torque (Semancik, 1997), (Ferguson and

Kemblowski, 1991). Controlled stress: the lower plate is kept stationary while a stress is

applied to the upper plate, and the rotation of that plate is measured (Semancik, 1997).

The AR 2000 is stress controlled.

Image not available – see printed version

Figure 3.7 Parallel plate configurations (Semancik, 1997)

Melt rheology measures the viscoelastic properties, which are typically steady

shear for a polymer melt. However, materials with a high viscosity tend to fail at

moderate shear rates using parallel plate configurations. In these cases, dynamic

loading (oscillation) within the materials linear viscoelastic region is appropriate, from

which extended steady shear information can be estimated using models.

3-12

Figure 3.8 TA instruments AR 2000 parallel plate rheometer

3.5.1.1. Flow

Steady shear experiments were carried out at low to moderate shear rates. In this

mode of operation, an increasing stress was applied to a sample and the strain response

and strain rate (shear rate) were measured (Whittingstall, 1997). The measured

viscosity over a range of shear rates provides an indication of the stability of the material

and the processability of the material.

Flow tests were carried out for each blend at the processing temperature used

throughout the investigation, 2400C, at a frequency of 1Hz.

3-13

3.5.1.2. Linear viscoelasticity

The linear viscoelastic region was evaluated to determine the conditions suitable

for dynamic loading experiments. In this case, a stress sweep was utilised for this

purpose, as stress is the controlled variable from which strain is calculated. The linear

region occurs where strain increases linearly with stress, constant modulus.

Stress sweep measurements were carried out at the same temperature and frequency

conditions as flow analysis with the stress controlled between 0.3 to 3500Pa.

3.5.1.3. Dynamic Loading Oscillation involves applying a sinusoidal stress wave and measuring the resultant

strain response (Whittingstall, 1997).

At the processing temperature, and the stress selected from within the linear viscoelastic

region, a frequency sweep was carried out for the range 0.1 to 100Hz. The data was

modelled to show the materials behaviour at higher shear rates.

3-14

3.5.2. Melt Flow Rate

Melt flow rate measures the rates of extrusion of a thermoplastic through an

orifice of specific length and diameter under prescribed conditions of temperature and

load. It is primarily a means of measuring the uniformity of the flow rate of a material

and can be used to distinguish between different grades of a material. It correlates to

the processability of a material, which can be compromised by the presence of additives.

Typically, a set volume of material is loaded into the preheated apparatus. A

volume of sample is pushed through the die of the instrument by the force of a standard

load. The MFR is determined by the volume extruded over a fixed time. An estimate of

density can be calculated from the measured weight of the extrudate. Reproducibility

can be achieved by ensuring the following factors are consistent throughout the

measurements, apparatus preheat time, volume of material loaded, packaging of loaded

material and moisture content of material.

Melt flow rate was measured on CEAST Modular Melt Flow, model 7024, ascribed for

ISO and ASTM standards, see Figure 3.8. Measurements were carried out according to

ASTM D1238 with conditions set based on test measurement A, see Table 3.5.

Table 3.5: Conditions for MFR measurements

ABS based blends PP based blends

Start Measurement Position Position

Type of step Time Time

End of Test Time Time

Work Temperature 200 0C 230 0C

Load 5 kg 2.16 kg

Die Length 8 mm 8 mm

Die Diameter 2.095 mm 2.095 mm

3-15

Figure 3.9 CEAST Modular Melt Flow instrument

3-16

3.6 Mechanical Properties 3.6.1. Tensile and Flexural Testing

A typical tensile test involves a dumbbell shaped sample clamped and held static

at one end and pulled at a constant rate of elongation at the other end (Fried, 2003).

Strain rate is typically between 0.5-500mm/min, depending on the standard selected for

testing (Utracki, 2002). The dimensions of the specimen include gage length, l0

=100mm, width, W0 = 10.3mm and thickness, t0 = 2.1mm.

A0

l0

W0

The applied tensile force, F, is measured up to the point of failure. Stress is

highest at the thinnest part, the gage length l, causing the specimen to snap close to the

centre. However, stress concentration at the clamped ends reduces the incidence of

premature failure. The tensile response is represented as a plot of stress () verses

strain () (Fried, 2003), see Figure 3.9.

0A

F = (3.6)

0ll

= (3.7)

length gage initiallength, gage elongation ==−= 0lel;0lell

3-17

Figure 3.10 Typical stress-strain curve

Tensile modulus (Young’s modulus, E), is the initial slope of the stress-strain curve.

Hooke’s Law relates stress and strain by the tensile modulus:

E = (3.8)

Tensile strength is the maximum stress value, beyond this stress decreases with

increasing strain. This is the point before the onset of gage narrowing, or ‘necking’.

Elongation at break is the extent of elongation of the plastic specimen prior to breaking.

100l

ll

0

0b ×−

(3.9)

ABS

PP

Strain %

break

break

Fmax

Fmax

E

Stress

3-18

Figure 3.11 Zwick Z010 universal tester and grips for tensile testing

Similarly, the flexural properties can be determined. Flexural testing was

performed on injection molded bars, 63 × 12.5 × 3mm. According to ASTM D 790, the

span to depth ratio was 16, such that the support span was 48mm. The rate of cross

head motion, R, and the midspan deflection at test termination, D, were determined

based on the standard.

3FL

bt 22

= (3.10)

2L

t6Υ=

(3.11)

specimen the of width b ,deflection theY ==

3-19

Figure 3.12 Flexural testing apparatus for the Zwick Z010 universal tester

Tensile and flexural properties were measured on a conventional mechanical

tester, Zwick model Z010, according to ASTM D 638 and 790, respectively. See Figure

3.10 for Zwick instrument and grips set up for tensile tests, and Figure 3.11 for the

flexural test apparatus. TestXpert 8.1 was used to run the tester and to evaluate the

results.

3-20

3.6.2. Impact Testing

One of the most significant properties for engineering plastics is impact strength,

representing the toughness of a material.

Methods for testing impact strength include Izod and Charpy tests. In these tests

a hammer like weight of known energy strikes the flat plane of a specimen. The energy

absorbed by the polymer is the difference in potential energy of the hammer before and

after impact (Utracki, 2002). Notches are machined into the specimen to standardise the

impact results against stress concentrators within the plastic and to assess the

sensitivity to weakening (Fried, 2003).

Notched samples were analysed for Izod impact strength conducted on a CEAST

Resil impact tester according to ASTM D 256-00, see Figure 3.12.

Figure 3.13 CEAST Resil impact tester and sample jaw

3-21

3.6.3. Dynamic Mechanical Analysis

DMA take multiple measurements across a temperature or frequency range, i.e.

1Hz is equivalent to 1 cycle per second. Hence, DMA is significantly more efficient in

obtaining dynamic mechanical data, as traditional mechanical analysis can only run a

single experiment on a sample at a fixed temperature and a fixed strain rate (Menard &

Raton, 1999). The value of storage modulus calculated by DMA is approximately

equivalent to Young’s modulus and can be used to compare the analysis methods.

Dynamic modulus was measured on TA instruments Dynamic Mechanical

Analyser 2980 using Thermal Advantage instrument control software. Injection molded

bars were prepared, 63 × 12.5 × 3mm. Testing was performed on a dual cantilever

configuration, shown in Figure 3.13.

Dynamic modulus was measured by the temperature ramp: room temperature to

1500C at 100C per minute. The dynamic (storage) modulus at room temperature was

comparable to the Young’s modulus derived from simple tensile tests.

3.6.3.1. Time Temperature Superposition

The modulus of polymeric materials during deformation and flow is dependent on

temperature and time (frequency). Under load, the chains of a polymeric material

realign to minimize localized stresses, changing the modulus over time. Time

Temperature Superposition (TTS) is used to treat limited laboratory data obtained from

short term experiments to predict properties over a broad time scale.

There are two assumptions that are the basis for the transform:

• Molecular rearrangement occurs at an accelerated rate at higher temperatures

• Temperature is directly related to time.

To obtain long term data for a desired (reference) temperature, 0T , short term

experiments need to be conducted at elevated temperatures. Shift factors; tA , predict

the horizontal shift for the short term curves at the elevated temperature relative to the

reference temperature.

3-22

The Williams-Landel-Ferry (WLF) equation is used to describe time-temperature

behaviour near the glass transition region, based on the assumption that above glass

transition temperature, Tg, the fractional free volume increases linearly with temperature:

( )( )02

01logTTCTTC

At −+−−

= (3.12)

where 1C and 2C are constants and T , is the measurement temperature.

Isothermal frequency sweeps were conducted over a temperature range. Short

term analysis covered the range 0.1-100Hz, at 5 points per decade. Low temperature

frequency sweeps can model properties over an extensive time period, relating the

change in dynamic properties during a typical period of use. The higher temperature

frequency sweeps includes the glass transition temperature range. Time temperature

superposition data and the William-Landel-Ferry model can be used to predict various

properties over time near the glass transition temperature.

The analysis was only applicable to ABS dominant blends, as ABS is an

amorphous material that has a glass transition at practical working temperatures.

TA Data Analysis software was utilized to perform the Time-Temperature

Superposition transformation, with the ability to model WLF for the calculated shift

factors.

Figure 3.14 TA instruments DMA 2980, cantilever configuration

3-23

3.7 Statistical Analysis of Property Data

3.7.1. Characterisation of the Sample Population

Characterisation of the sample population is necessary for continuous application

of statistical analysis of the property data. A large, randomly selected population was

measured for two different properties that are typical of the range of properties relevant

to this study, tensile and impact strength. In addition, the two uncontaminated base

polymers were analysed to ensure that the characteristic population assumed for the

range of blends was valid. Histograms in Figure 3.14-3.17 show the typical bell shaped

curve of a normally distributed population with a 95% confidence interval. Tensile

strength data appears to have the least variance, indicating that fewer samples are

required to achieve a 95% confidence interval.

Figure 3.15 Tensile strength histogram for thermally recycled PP

3-24

Figure 3.16 Tensile strength histogram for thermally recycled ABS

Figure 3.17 Impact strength histogram for thermally recycled PP

3-25

Figure 3.18 Impact strength histogram for thermally recycled ABS

3-26

3.7.2. Statistical Analysis

Various statistical parameter can be determined for a given sample size, N , based on a

normally distributed population, including

mean, x :

Nxx i

= (3.13)

standard deviation, sd :

( )

1

2

−−

=N

xxsd i (3.14)

relative standard deviation, %RSD :

100% ×=xsdRSD (3.15)

standard error, se :

Nsdse = (3.16)

The required sample size to achieve a 95% confidence interval for the data can be

calculated:

2

%%

×=ERSDZN (3.17)

where 96.1=Z for a 95% confidence interval with an assumed error of 10%.

The highest RSD% representing the worst case scenario was selected to standardize

the minimum number of samples required.

Table 3.6 is a statistical analysis of the tensile and impact properties of the PP and ABS

sampled for population characterization.

3-27

Table 3.6: Statistical Analysis of virgin PP and ABS

Tensile Strength Impact Strength MPa kJ/m2 PP ABS PP ABS X 19.6 42.5 12.5 17.8 1.0 1.9 1.1 0.93 RSD% 5.2 4.5 9 5 Se 0.089 0.16 0.13 0.13 N 130 130 72 124 N required 1 1 3 1

For mechanical analysis of all materials/blends, a minimum of 5 samples were

tested for tensile and flexural properties and 8 samples for impact strength. The

number of samples were confirmed in the statistical analysis of each blends based on

the largest measured standard deviation, or worst case, see Table 3.7. Tensile and

Flexural properties were easily within the confidence interval for the number of samples

tested. Likewise, the sample size for impact tests was adequate, with the exception of

one blend in the ABS/Nylon blends. This is 1 out of 28 blends where the measurement

of more than 8 samples was required.

Table 3.7: Sample size for the mechanical properties of ABS and PP based blends

ABS/PP pcABS/PP ABS/HIPS ABS/Nylon PP/HIPS PP/Nylon Tensile Strength

RSD% 3.2 5.9 0.42 0.95 1.2 2.0 N 1 2 1 1 1 1

Flexural Strength RSD% 4.5 4.0 1.1 1.8 0.93 7.1 N 1 1 1 1 1 2

Impact Strength RSD% 6.4 11 3.0 23 7.3 11 N 2 5 1 20 3 6

pc denotes post consumer (ACT) recycled blends

4-1

4 THERMAL PROPERTIES OF CONTAMINATED PLASTICS

4.1 Glass Transition

Glass transition temperature, Tg, is applicable to amorphous polymers, including

ABS and HIPS, and semi-crystalline polymers, such as PP. PP has a sub zero glass

transition temperature (-150C, Fried, 2003), which won’t be measured in this

investigation due to practical limitations. At Tg the amorphous phase is converted from a

hard glass like state to a rubbery phase, which is important to the mechanical properties

of the polymer. The glass transition temperature can be determined a number of ways,

in this case it is the peak of tan from DMA (see Figure 4.3).

The glass transition temperature of ABS and HIPS is approximately 1120C and

1080C, respectively. Thermal recycling does not appear to affect the glass transition

temperature of these two polymers (see Table 4.1 and 4.2a, b). Post consumer (ACT)

recycled ABS had a slightly lower glass transition temperature of 1100C (see Table 4.3).

Contamination of ABS causes minimal shift in the position of Tg, regardless of whether

the contaminant polymer is amorphous (HIPS) or semi-crystalline (Nylon or PP), (see

Table 4.2a and Figure 4.1). However the effect is greater for post consumer recycled

blends, such that the presence of PP in ABS elevates Tg, (see Table 4.3 and Figure 4.3).

This can be attributed to the presence of additives and possible contamination of the

post consumer recycled PP. It is likely that the Tg of the fillers used to increase the

impact strength of PP bumpers is outside the range measured. Contaminated PP

blends adopts the Tg of the amorphous polymers, regardless of the level of

contamination (see Table 4.2b and Figure 4.2).

Table 4.1: Glass transition temperatures of virgin amorphous materials (0C)

Material Tg Virgin ABS 112 Virgin HIPS 108

4-2

Table 4.2a: Glass transition temperatures of thermally recycled ABS dominant blends (0C)

Contaminant level, v/v% 0 5 10 20 30 100 PP 112 - 112 111 - -15* HIPS 112 - 112 112 112 108 Nylon 112 111 111 110 - Na

* Glass transition temperature from text, (Fried, 2003)

Table 4.2b: Glass transition temperatures of thermally recycled PP dominant blends (0C)

Contaminant level, v/v% 0 10 20 30 100 ABS -15* 112 111 111 112 HIPS -15* 108 107 107 108

*(Fried, 2003)

Table 4.3: Glass transition temperatures of ABS contaminated with PP blends (0C)

Contaminant level, v/v% 0 10 20 30 Thermal 112 112 111 112 Post Consumer 110 109 111 112

4-3

Figure 4.1 Glass transition temperature of ABS contaminated with PP

Figure 4.2 Glass transition temperature of PP contaminated with ABS

4-4

1 11

1

1

1

1

1

1

1

1

1

1

1

1

11 1

2 22

2

2

2

2

2

2

2

2

2

22

2 2

3 33

3

3

3

3

3

3

3

33

3 3

4 4 44

4

4

44

4

4

44 4

5 5 5 55

55 5

55 5 5 5

6 6 6 6 66

6 66

6 6 6 67 7 7 7 7 7 7 7 7 7 7 7 78 8 8 8 8 8 8 8 8 8 8 8 8

0.5

1.0

1.5

Tan

Del

ta

80 100 120 140

Temperature (°C) Universal V4.3A TA Instruments

Figure 4.3 Tan Delta curves of post consumer recycled ABS/PP blends

1

2

3

1 rABS

2 rABSPP_90:10

3 rABSPP_80:20

4 rABSPP_70:30

5 rPPABS_70:30

6 rPPABS_80:20

7 rPPABS_90:10

8 rPP

4

5 6

7 8

4-5

4.2 Degradation Region

Degradation temperature is the temperature where a material begins to

decompose, in the case of polymers by chain scission and vaporisation. Thermal

degradation varied between investigated polymers. TGA of thermally recycled material

clearly shows that ABS degrades at a higher temperature to PP, 4000C and 3000C,

respectively (see Figure 4.4). The extent of the shift in degradation temperature due to

recycling was greatest for polypropylene. Increasing the amount of contaminant added

to polypropylene elevated the degradation temperature region (see Figure 4.5, 4.6). For

instance, the degradation temperature of PP contaminated with ABS increased as the

proportion of contaminant increased, approaching the degradation region of

uncontaminated ABS.

Post consumer recycled material appears to have multiple onsets of degradation

at different temperatures (see Figure 4.7). Blends of these materials also have these

multiple degradation stages. This indicates the intentional addition of additives, which

was used to optimize specific material properties required for the original application,

rather than random contamination in the recycling process. This could include impact

modifiers or additives for aesthetic purposes.

Post consumer recycled PP contaminated with ABS blends behaved similarly to

thermally recycled blends, such that increased levels of ABS elevated the degradation

temperature (see Figure 4.8). On the other hand, increasing the level of contaminant PP

in ABS corresponded to an elevation in degradation temperature (see Figure 4.7).

However, the shift in the degradation temperature of the ABS contaminated with PP

blends was minor and may be accounted to inconsistency within the supplied material

and fluctuation in the measurements.

4-6

0

20

40

60

80

100

Wei

ght (

%)

0 100 200 300 400 500

Temperature (°C)

ABSvirgin–– –– – ABSrecycle––––––– PPvirgin–– –– – PPrecycle––––––– vPPvABS (70:30)–– –– – rPPrABS (70:30)––––––– rPPrABS (80:20)––––––– rPPrABS (90:10)–––––––

Universal V4.3A TA Instruments

Figure 4.4 TGA plots for thermally recycled PP contaminated with ABS

0

20

40

60

80

100

Wei

ght (

%)

0 100 200 300 400 500

Temperature (°C)

HIPSvirgin.001–– –– – HIPSrecycle.001––––––– PPvirgin.001–– –– – PPrecycle––––––– vPPvHIPS_(7030).002–– –– – rPPrHIPS_(7030).001––––––– rPPrHIPS_(8020).001––––––– rPPrHIPS_(9010).001–––––––

Universal V4.3A TA Instruments

Figure 4.5 TGA plots for thermally recycled PP contaminated with HIPS

4-7

Thermal rPP

Thermal rABS

ACT rPP

ACT rABS

20

40

60

80

100W

eigh

t (%

)

150 250 350 450

Temperature (°C) Universal V4.3A TA Instruments

Figure 4.6 TGA plots for thermally and post consumer recycled materials

1 1 1 11

1

1

1

1

1

1

1

2 2 2 2 2 2 2 22

2

2

2

2

2

2

2

2

3 3 3 3 3 3 3 33

3

3

3

3

3

3

3

4 4 4 4 4 4 4 4

4

4

4

4

4

4

4

4

1234

20

40

60

80

100

Wei

ght (

%)

0 100 200 300 400

Temperature (°C)

1 rABS_ACT.001–––––––2 rABSPP9010_ACT.001–––––––3 rABSPP8020_ACT.001–––––––4 rABSPP7030_ACT.001–––––––

Universal V4.3A TA Instruments

Figure 4.7 TGA plots for post consumer recycled ABS contaminated with PP

4-8

1 1 1 1 11

1

1

1

1

1

1

2 2 2 2 2 2 2 22

2

2

2

2

2

2

2

2

2

3 3 3 3 3 3 33

3

3

3

3

3

3

3

3

3

3

4 4 4 4 4 4 44

4

4

4

4

4

4

4

4

4

4

1

23420

40

60

80

100W

eigh

t (%

)

0 100 200 300 400

Temperature (°C)

1 rPPABS7030_ACT–––––––2 rPPABS8020_ACT–––––––3 rPPABS9010_ACT–––––––4 rPP_ACT–––––––

Universal V4.3A TA Instruments

Figure 4.8 TGA plots for post consumer recycled PP contaminated with ABS

5-1

5 PROCESSABILITY OF CONTAMINATED PLASTICS 5.1 Processability

Recycling the individual polymers did not alter the processability of the material,

but it did change the appearance through yellowing. Contamination did affect the

processability, such that the extrusion of nylon contaminated materials was interrupted

by the breaking of the brittle extrudate strands. Poor processability was also observed in

injection molding where mechanical specimens of Nylon contaminated materials and PP

contaminated ABS frequently broke in the mold cavity. The processability of post

consumer recycled ABS/PP blends appeared greater than thermal recycled blends,

improving as the level of the ‘contaminant’ increased. This may be a result of the

complex interactions between the post consumer plastics and the additives present in

the post consumer materials. Metal and resin contamination was evident in the post

consumer recycled material, which caused blockages in the screens that filtered the feed

through the extruder. Melt flow rate was measured as a preliminary investigation of

processability, while rheological properties were performed at processing conditions.

5.2 Melt Flow Rate

Melt flow rate, MFR, measurements were carried out for all blends, with the

exception of nylon contaminated materials due to the obvious signs of incompatibility

during sample preparation.

Initially, the processability of the individual plastics was investigated. The MFR

for thermally recycled PP and ABS were 12.7 and 1.40g/10min, respectively.

Comparatively, the MFR for post consumer ACT recycled PP and ABS was 13.9 and 8.8

g/10min, respectively. The MFR of post consumer recycled plastics was significantly

higher, especially the ABS. A high MFR implies low resistance to flow, a result of low

molecular weight and low interaction between polymer chains. The processing and

recycling conditions would change the length and alignment of the polymer chains,

typically improving flowability through degrading the molecular structure. However, this

is commonly offset by the negative impacts that recycling has on other properties,

including thermal and mechanical.

5-2

The effect of PP contamination in ABS appears additive, such that the MFR

increased linearly with an increasing level of contaminant (PP), see Figure 5.1a and

Table 5.2a. Whereas, the ABS contaminated PP follows a quadratic relationship with a

minimum at 25 and 15% for thermally and post consumer recycled blends, respectively,

which indicates a negative deviation from the rule of mixtures, see Figure 5.1b and Table

5.2b. However, the accuracy of these models are compromised by the significant

variation at high level of contamination (30% PP in ABS and 30% ABS in PP), which is

evident in the standard deviation; see Figures 5.1a & 5.1b and Tables 5.1a and 5.1b.

Variation in measurements within the same blend indicates poor uniformity of the flow

rate and non-homogenous blending, particularly noticeable at these high contamination

levels. This can be expected as a homogenous mixture is impossible to achieve on a

laboratory scale, single screw extruder especially with immiscible materials. Melt flow

results were confirmed by rheology, which shows that ABS was more viscous at the

processing temperature and PP contamination decreased the viscosity, see section 5.3.

Density was measured along with MFR. The densities for ABS and PP for

thermally recycled materials were 0.940 and 0.738, respectively, and for post consumer

recycled 1.05 g/mL, and 0.818g/mL, respectively. The density of the blended materials

decreased in proportion to the amount of PP added, as the density of PP is lower than

ABS, see Figure 5.2a. This is clearly shown in the models that relate density to

contaminant level, see Table 5.2a. The model constants for PP contaminated ABS

show that the change of density with contaminant level was approximately 3 times

greater for post consumer blends. Figure 5.2a shows the divergence in the density of

post consumer materials from thermally recycled material see Figure 5.2a and Table

5.2b, where, the post consumer PP contaminated ABS maintains a higher density over

the investigated range of blends. In contrast, the density of ABS contaminated PP

increased with increasing level of ABS, see Figure 5.2b. At these contamination levels,

the change in density with level is the same, regardless of the source of the recycled

material, as shown by the constant, K, see Table 5.2b.

5-3

Figure 5.1a Melt Flow Rate of recycled ABS contaminated with PP blends

Figure 5.1b Melt Flow Rate of recycled PP contaminated with ABS blends

5-4

Table 5.1a: Standard deviation in Melt Flow Rate of recycled ABS contaminated with PP

Contaminant level, v/v% 0 10 30

Thermally Recycled MFR 1.4 2.1 5.3 standard deviation 0.062 0.070 0.71

Post Consumer Recycled MFR 8.8 9.0 10.7 standard deviation 0.17 0.32 1.2

Table 5.1b: Standard deviation in Melt Flow Rate of recycled PP contaminated with ABS

Contaminant level, v/v% 0 10 30

Thermally Recycled MFR 12.7 10.7 9.7 standard deviation 0.27 0.20 0.78

Post Consumer Recycled MFR 13.9 12.2 14.0 standard deviation 0.49 0.40 1.5

Figure 5.2a Melt density of recycled ABS contaminated with PP blends

5-5

Figure 5.2b Melt density of recycled PP contaminated with ABS blends

0MFRKMFR MFR += ϕModel MRF Linear

(5.1)

022

1 MFRKKMFR MFRMFR ++= ϕϕModel MFRQuadratic

(5.2)

0ρϕρ ρ += KModeldensity Linear

(5.3)

polymer ateduncontamin ofdensity polymer ateduncontamin of RateFlow Melt

30)0(0 tcontaminan of fraction

constants

==

≤≤=

=

0

0

21

.,,,

ρ

ϕϕρ

MFR

KKKK MFRMFRMFR

Table 5.2a: Model constants for ABS contaminated with PP

KMFR MFR0 K 0 Thermal 13 1.15 -0.1 0.942 Post Consumer 6.6 8.62 -0.27 1.05

5-6

Table 5.2b: Model constants for PP contaminated with ABS

KMFR1 KMFR2 MFR0 K 0 Thermal 51 -25 12.7 0.11 0.738 Post Consumer 88 -26 13.9 0.11 0.818

The trend of MFR for the HIPS contaminated blends varied depending on the

material that it was contaminating. The MFR for uncontaminated HIPS is 5.35g/10min, a

flowability in between ABS (1.40g/10min) and PP (12.7g/10min). HIPS contaminated

ABS blends appears to follow the rule of mixtures, where increasing the amount of HIPS

increases the MFR of the blend, see Figure 5.3. This is consistent with compatible

materials. On the other hand, the addition of HIPS to PP does not appear to alter the

flowability of the material, see Figure 5.4.

Figure 5.3 Melt Flow Rate of thermally recycled ABS contaminated with HIPS

5-7

Figure 5.4 Melt Flow Rate of thermally recycled PP contaminated with HIPS

5-8

5.3 Rheology

Melt rheology testing was performed on thermal and post consumer recycled

ABS/PP blends.

The samples for rheology analysis were prepared via two different methods, a

result of the material processability. Small scale, manual injection molding was practical

for easy to process blends. Whereas, materials with a relatively high viscosity at the

processing temperature were suited to machine driven injection molding (according to

section 3.3.2.), whereby samples were cut to size from a larger sheet. Different flow

patterns arise from different sample preparation methods, which compromise the

repeatability of the results and comparison of results between samples prepared from

the two methods. However, the variability was minimal as shown in Figure 5.5, where

rPP is small scale injection molding and rPP_[IM] had been cut from a larger sheet. The

comparison between the rheological results was demonstrated repeatedly.

5.3.1. Flow analysis of ABS/PP blends

Flow rheology analysis was carried out at the processing temperature, 2400C, at

a frequency of 1Hz. The viscosity was measured at low to moderate shear rates, which

simulate a range of processes. Low shear rates include compression molding and

calendaring, at moderate shear rates, extrusion.

PP has a relatively stable viscosity over a range of low shear rates, see Figure

5.5. The viscous stability of PP, which characterises Newtonian flow, is shown in section

5.3.3. The exception is the specimen of thermally recycled PP that was produced by

cutting larger injected molded sheets, rPP240_[IM]. The injection molding of the sheet

results in parallel linear molecular alignment compared to rotational flow of the

specimens produced on the small scale injection molder. The linear alignment opposes

the rotation of the rheometer, which causes the specimen’s anomaly at low shear rates.

The viscosity of the post consumer (ACT) recycled PP was slightly higher than

the thermally recycled materials. Whereas, the post consumer (ACT) recycled ABS had

a lower viscosity, see Figure 5.5. The variation between the thermal recycled and post

consumer sources of recycled material can be attributed to a number of factors

including, the grade of the original material, additives used to enhance the properties of

the material depending on the original application, previous processing conditions and

exposure factors during product use.

5-9

0.1000 1.000 10.00 100.0shear rate (1/s)

10.00

100.0

1000

10000

1.000E5

visc

osity

(Pa.

s)

rPPrPP240_[IM]rPP_ACT_2rPP_ACTrABSrABS_2rABS_ACT

Figure 5.5 Flow curves of uncontaminated recycled ABS and PP, 2400C

() thermally recycled PP, () thermally recycled PP _ samples cut from a larger

injection molded sheet, () post consumer recycled PP _ samples 2, () post consumer

recycled PP _ samples 1, () thermally recycled ABS _ sample 1, () thermally recycled

ABS _ sample 2, (∇ ) post consumer recycled ABS

Increasing the amount of ABS contamination in PP blends, increased the

viscosity, Figure 5.6 shows this trend for thermally recycled blends. Conversely,

increasing the level of PP contamination in ABS lowered the viscosity. Flow curves for

all ABS contaminated PP and the PP contaminated ABS blends studied can be found in

Appendix I – section 9.1.1.

High shear (as per injection molding) rheological data was difficult to obtain on a

rotational rheometer, as the material failed (Shah, V., 1998). The flow curves show

signs of sample failure at moderate shear rates ( 10s-1); where the viscosity values

deviate from a smooth flow curve, see Figure 5.5. In the following sections, dynamic

loading measurements have been used to model flow curves over an extended shear

range with Cox-Merz transformation.

5-10

0.1000 1.000 10.00 100.0shear rate (1/s)

1.000

10.00

100.0

1000

10000

1.000E5

visc

osity

(Pa.

s)

rPPrPPABS9010rPPABS8020rPPABS7030rABS

Figure 5.6 Flow curves of thermally recycled PP contaminated with ABS, 2400C

() uncontaminated PP, () 10% ABS, () 20% ABS, () 30% ABS, () uncontaminated

ABS

5-11

5.3.2. Linear Viscoelasticity of ABS/PP blends

Modelling the flow properties of a polymer requires dynamic loading experiments

within the materials linear viscoelastic region. Stress sweeps provided a viscoelastic

profile that was used to identify the linear region based on a constant storage and loss

modulus. The profiles were similar for all ABS contaminated PP and PP contaminated

ABS blends, below is a graph showing the profiles of a few select blends that represent

the extent of variation within the blends, see Figure 5.7. The linear region is in the stress

range of 1-1000Pa. For the purpose of dynamic loading experiments, 50Pa is clearly

within the region for all blends and an appropriate value to set as the controlled

parameter. Profiles of all the ABS/PP blends studies can be found in Appendix I –

section 9.1.2.

1.000 10.00 100.0 1000 10000osc. stress (Pa)

1000

10000

1.000E5

G' (

Pa)

rPPrPPABS9010rPPABS7030rABSPP7030rABSPP9010

Figure 5.7 Linear Viscoelasticity of thermally recycled blends, 2400C

() uncontaminated PP, () 10% ABS, () 30% ABS, () 30% PP, () 10% PP

5-12

5.3.3. Flow curve modelling

Flow curves were generated for all the ABS/PP blends from Cox-Merz

transformations of constant stress frequency sweeps, measured at 2400C. Figure 5.8a

has the dynamic curves of ABS contaminated with PP blends, and Figure 5.8b the

dynamic curves of PP contaminated with ABS blends.

1.000 10.00 100.0 1000ang. frequency (rad/s)

1000

10000

1.000E5

1.000E6

G' (

Pa)

rABSPP9010rABSPP8020rABSPP7030

Figure 5.8a Dynamic curves for ABS contaminated with PP, 2400C

() 10% PP, () 20% PP, () 30% PP

5-13

1.000 10.00 100.0 1000ang. frequency (rad/s)

100.0

1000

10000

1.000E5

G' (

Pa)

rPPABS7030rPPABS8020rPPABS9010rPP

Figure 5.8b Dynamic curves for PP contaminated with ABS, 2400C

() uncontaminated PP, () 10% ABS, () 20% ABS, () 30% ABS

At low to moderate shear rates, the measured flow curves, and hence viscosity,

match the modelled curve from the Cox Merz transformation, see Figure 5.9. However,

the sample begins to fail at moderate shear rates, shown as a deviation of the data from

the Cox-Merz relation.

5-14

0.1000 1.000 10.00 100.0 1000shear rate (1/s)

10.00

100.0

1000

10000

1.000E5

visc

osity

(Pa.

s)

rPP cmrPPrABS cmrABS

(cm denotes Cox-Merz transformation)

Figure 5.9 Comparison of Flow curves and Cox-Merz transformation of thermally

recycled polymers, 2400C

() uncontaminated PP, () uncontaminated ABS, Cox-Merz transform,

() uncontaminated PP, () uncontaminated ABS

5-15

At 2400C, the log viscosity of the ABS and blends of ABS contaminated with PP

decreased linearly with increasing log shear rates, see Figure 5.9 and 5.10. This trend

is shear thinning or pseudo plasticity. Whereas the viscosity of PP and blends of PP

contaminated with ABS approaches Newtonian flow at low shear rates and shear

thinning at high shear rates, see Figure 5.9 and 5.12. The rate index, n, of the power

law is an indication of the flow type, see Table 5.3a, b and 5.4a, b. •

= nkτ (5.4)

index

indexy consistenc

rate ==nk

The rate index, n, is used to describe the three basic types of flow,

n=1 Newtonian behaviour

n<1 shear thinning (or Pseudoplastic)

n>1 shear thickening

The power law constants vary within and between blends, where the addition of

ABS contamination to PP increased the viscosity and increased pseudo-plasticity. The

increase in pseudo-plasticity was most evident at low shears, which was shown by the

increased slope of the flow curve; see Figure 5.12 and the decreased rate index, see

Table 5.3b and 5.4b. At higher shear rates, the variation in the value of the rate index

between the blends becomes negligible. This was also observed from the power law fit,

in which the gradient of the slopes appear the same, see Figure 5.13.

On the other hand, PP contamination of ABS does not simply reduce the

viscosity and pseudo-plasticity, with increased level of contamination. The viscosity of

these blends appears to peak at low contaminant levels (10% PP), see Table 5.3a. This

indicates a strong interaction between the blended materials at this level, linked to the

size and size distribution of the PP in the ABS matrix. This is similar to the phenomena

described by Gupta et al (1990), which suggests that at low concentrations the size of

the dispersed phase is small, which is less deformable, hence producing a high melt

viscosity.

5-16

1.000 10.00 100.0 1000shear rate (1/s)

100.0

1000

10000

1.000E5

visc

osity

(Pa.

s)

rPP cmrPP_2 cmrABSPP7030 cmrABSPP7030_2 cmrABSPP8020 cmrABSPP8020_2 cmrABSPP9010 cmrABSPP9010_2 cm

Figure 5.10 Cox-Merz transformation of thermally recycled ABS contaminated with

PP, 2400C

() uncontaminated PP _ sample 1, () uncontaminated PP _ sample 2, (∇ ) 30% PP _

sample 1, () 30% PP _ sample 2, () 20% PP _ sample 1, () 20% PP _ sample 2,

() 10% PP _ sample 1, () 10% PP _ sample 2

1.000 10.00 100.0 1000shear rate (1/s)

100.0

1000

10000

1.000E5

1.000E6

shea

r stre

ss (P

a)

rPP cmrPP_2 cmrABSPP7030 cmrABSPP7030_2 cmrABSPP8020 cmrABSPP8020_2 cmrABSPP9010 cmrABSPP9010_2 cm

Figure 5.11 Power-law fits for Cox-Merz transformation of thermally recycled ABS

contaminated with PP, 2400C

5-17

1.000 10.00 100.0 1000shear rate (1/s)

100.0

1000

10000

visc

osity

(Pa.

s)

rPP cmrPP_2 cmrPPABS9010 cmrPPABS9010_2 cmrPPABS8020 cmrPPABS8020_2 cmrPPABS7030 cmrPPABS7030_2 cm

Figure 5.12 Cox-Merz transformation of thermally recycled PP contaminated with ABS,

2400C

() uncontaminated PP _ sample 1, () uncontaminated PP _ sample 2, () 10% ABS _

sample 1, () 10% ABS _ sample 2, () 20% ABS _ sample 1, () 20% ABS _ sample 2,

( ∇ ) 30% ABS _ sample 1, () 30% ABS _ sample 2

1.000 10.00 100.0 1000shear rate (1/s)

100.0

1000

10000

1.000E5

1.000E6

shea

r st

ress

(P

a)

rPP cmrPP_2 cmrPPABS9010 cmrPPABS9010_2 cmrPPABS8020 cmrPPABS8020_2 cmrPPABS7030 cmrPPABS7030_2 cm

Figure 5.13 Power-law fits for Cox-Merz transformation of thermally recycled PP

contaminated with ABS, 2400C

5-18

Table 5.3a: Power Law constants for thermally recycled ABS contaminated with PP

low shears high shears Contaminant level, v/v% Viscosity Rate Index Viscosity Rate Index

0 6660 0.469 6710 0.537 10 11300 0.504 11700 0.503 20 8460 0.520 8870 0.515 30 5850 0.556 6340 0.534

Table 5.3b: Power Law constants for thermally recycled PP contaminated with ABS

low shears high shears Contaminant level, v/v% Viscosity Rate Index Viscosity Rate Index

0 1290 0.847 2430 0.624 10 1760 0.808 2840 0.640 20 2280 0.765 3390 0.636 30 3000 0.688 3690 0.627

Table 5.4a: Power Law constants for post consumer recycled ABS contaminated with PP

low shears high shears Contaminant level, v/v% Viscosity Rate Index Viscosity Rate Index

0 6280 0.513 6260 0.547 10 3360 0.547 3200 0.583 20 3720 0.585 4190 0.565 30 3440 0.584 3760 0.578

Table 5.4b: Power Law constants for post consumer recycled PP contaminated with ABS

low shears high shears Contaminant level, v/v% Viscosity Rate Index Viscosity Rate Index

0 3200 0.760 4200 0.652 10 3970 0.689 5010 0.621 20 4790 0.606 5190 0.580 30 3780 0.616 4450 0.575

5-19

The Cox-Merz flow curves for the post consumer recycled materials follow that of

the thermally recycled material. Over the range of blends, the addition of PP decreased

the viscosity and increased the viscous stability, approaching Newtonian flow at low

shear rates see Tables 5.3b and 5.4b. Contamination increased the variability in the

results within the post consumer blends, moreover it cannot be definitively stated that a

blend with 10% PP is more or less viscous than 30% PP, see Table 5.4b. This is

because the unblended post consumer material was not initially homogeneous for two

factors (1) the additives used in the original application of the material and (2) the

different grades that made up the recycled material. In addition, the analysis

temperature may be a contributing factor to the variation between the different recycling

methods, due to variation within the unblended materials.

Flow curves and Cox-Merz transformations of all the ABS/PP blends studied can be

found in Appendix I – section 9.1.3.

6-1

6 MECHANICAL ANALYSIS OF CONTAMINATED PLASTICS

Acrylonitrile-butadiene-styrene, high impact polystyrene, polypropylene and

Nylon are widely used thermoplastics. ABS and HIPS are amorphous, whereas, PP and

Nylon are semi-crystalline polymers. ABS and PP were selected as the base materials

for blending with the other polymers. The minor component in the blends (0-30%)

represents a known level of contamination, corresponding to the extent of sorting during

the recycling process. Mechanical properties were measured as an indication of the

materials characteristic during use, which links the material to a suitable application.

6.1 Recycling Typical stress-strain curves of the individual polymers highlights the difference in

mechanical properties. The initial linear increase of stress with strain is the modulus.

After the linear section the curve peaks at the maximum stress, which is a quantitative

expression of the tensile strength of the material. Beyond the peak the properties of the

original material are no longer retained. The following information can be obtained from

Figure 6.1, comparing the curve of ABS and PP:

• ABS has a steeper linear slope, hence greater modulus

• ABS has a higher maximum stress, indicating greater strength

• ABS has a narrower peak, where the area under the peak is the ‘work to

maximum stress’

• ABS breaks soon after the peak of maximum stress, whereas PP breaks after

significant elongation, indicating that ABS is brittle in comparison

The effect of thermal and post consumer (ACT) recycling on the tensile and

flexural properties of the individual thermoplastics appeared to be negligible. Thermal

recycling only had a minor effect on the impact strength of the individual polymers. At

most, recycling ABS resulted in a 6% reduction in impact strength; see Table 6.1a, b, c.

The extent of the effect that recycling has on the post consumer materials was

impossible to assess because the properties of the original material are unknown.

However, post consumer PP had considerably higher impact strength than the thermally

recycled material, which indicates the presence of impact modifiers.

6-2

During impact testing, a number of samples of recycled PP broke differently to the

other materials tested, complete break as opposed to partial break. Different break

types made it difficult to compare the methods of recycling and the effect of

contamination on the impact strength, as stated by the standard ASTM D 256-00.

Figure 6.1 Typical stress strain curve

Table 6.1a: Tensile strength (Fmax), MPa

Virgin Thermal Recycling

Post Consumer Recycling

PP 19.3 19.4 17.3 ABS 43.8 42.5 41.1

Table 6.1b: Flexural strength (Fmax), MPa

Virgin Thermal Recycling

Post Consumer Recycling

PP 28.8 30.7 27.1 ABS 74.9 75.7 63.7

Table 6.1c: Impact strength, kJm-2

Virgin Thermal Recycling

Post Consumer Recycling

PP 13.3 13.5 24.6 ABS 22.2 20.9 26.8

ABS

PP

Strain %

break

break

Fmax

Fmax

E

Stress

6-3

6.2 Contaminated Plastics

6.2.1. Contaminated ABS blends

The effect of contamination on the mechanical properties varied depending on

the interaction between the contaminant and ABS. Tensile and flexural properties of the

ABS were reduced by contamination with HIPS and PP. For example, an addition of

30% volume of HIPS reduced both the tensile and flexural strength by 20%, see Table

6.2. Likewise, 30% PP contamination reduced the tensile and flexural strength by

almost 40%, see Table 6.3a.

The properties of the HIPS contaminated blends were intermediate between

those of the individual components, such that they would lie on a line that connected the

properties of the pure components. In this case, a 10% incremental increase in the

amount of HIPS corresponds to a 10% reduction of the tensile and flexural strength

relative to the properties of the individual materials. Therefore, this mixture follows

closely to the rules of mixtures, which indicates that the HIPS and ABS are somewhat

compatible. A linear line of best fit relates the properties with the level of contamination

for the measured range, see Figure 6.2. This can be used to predict the tensile and

flexural properties of a material based on the contaminant level, see Table 6.5a for the

predictive model constants of the lines of best fit for all contaminated ABS blends.

In contrast, the properties of the PP contaminated ABS blends were lower than

expected based on the level of contaminant and the properties of the individual

components. In this case, the majority of points measured for the various blends would

lie below a linear line that connected the two unblended materials, such that

contamination causes a negative deviation from the rule of mixtures. This indicates that

these ABS and PP are incompatible. The tensile strength of the 30% contaminated

blend is equivalent to 60% or double the actual contamination by following the rule of

mixtures, see Table 6.3a. The reduction in mechanical properties with contaminant level

was less pronounced for post consumer PP contaminated ABS. This was obvious in the

constants for predictive modelling, where the rate of change of the mechanical

properties for post consumer blends was close to half that of the thermally recycled

blends, see Figure 6.4 and Table 6.5a. In fact, the reduction in mechanical properties of

post consumer blends follows closely to the rule of mixtures, suggesting favourable

interactions within the polymer blend. This can be accounted for by the presence of

6-4

additives, which enhance the properties of the individual polymers, as well as the

immiscible polymer blend.

Different break types in impact testing made it difficult to compare the impact

strength of the different recycling methods. The thermally recycled PP contaminated

ABS blends partially broke and the post consumer recycled material broke completely.

However, the fact that the majority of post consumer recycled blends broke completely

indicates qualitatively that this material was somewhat more brittle. Gupta et al. (1990b)

investigated the morphology of an ABS/PP blend and stated that phase separation

occurs. Phase segregation tends to occur in the molding process causing weakening of

the internal structure (Lindsey et al., 1981). Markin and Williams, Gupta et al. (1989b)

and Lindsey et al. (1981) suggest that the less ductile material, predominantly ABS,

formed a skin around the bar. The PP rich core has various sized ABS droplets

dispersed throughout, the number, shape and size distribution varying with ABS content,

(Gupta et al., 1989a). The core is a large part of the fracture surface and the absence of

ABS will significantly reduce the impact strength. Contamination significantly reduced

the impact strength of the material, regardless of the whether the material was

amorphous (HIPS), see Figure 6.3, or semi-crystalline (PP), see Figure 6.5.

Nylon has a greater tensile strength than ABS; however, the contamination of

ABS for all levels of nylon contamination only increased the tensile strength by 3%,

which is equivalent to only 10% contamination see Figure 6.6 and Table 6.4. On the

other hand, the flexural strength of nylon is less than ABS. Although, the flexural

strength was reduced by only 6% for all levels of nylon contamination, the reduction of

flexural strength is equivalent to pure Nylon. Whether the ABS was contaminated by 5%

or 20% nylon, the change in the tensile and flexural properties of the blends relative to

ABS was the same. In both cases, the negative deviation from the rule of mixtures

indicated that ABS and nylon are not compatible even though nylon contamination

improves tensile strength. Incompatibility of nylon in ABS was further highlighted in the

impact strength. The addition of only 5% Nylon halved the impact strength of the

material, see Figure 6.7.

6-5

Figure 6.2 Tensile and Flexural strength of recycled ABS contaminated with HIPS

Figure 6.3 Impact strength of recycled ABS contaminated with HIPS

6-6

Table 6.2: Mechanical Properties of ABS contaminated with HIPS

Contaminant level, v/v% 0 10 20 30 100 Tensile strength, MPa 42.5 38.7 36.4 34.0 22.6 % change -9 -14 -20 -47 Rule of Mixtures equivalent contamination 0 19 31 43 100 Flexural strength, MPa 75.7 69.0 66.6 63.4 45.5 % change -9 -12 -16 -40 Rule of Mixtures equivalent contamination 0 22 30 41 100 Impact strength, kJ/m2 20.9 10.4 7.40 6.07 8.98 % change -50 -65 -71 -57

Table 6.3a: Mechanical Properties of thermally recycled ABS contaminated with PP

Contaminant level, v/v% 0 10 20 30 100 Tensile strength, MPa 42.5 38.6 31.7 28.3 19.4 % change -9 -25 -33 -54 Rule of Mixtures equivalent contamination 0 17 47 62 100 Flexural strength, MPa 75.7 64.8 54.7 47.5 30.7 % change -14 -28 -37 -59 Rule of Mixtures equivalent contamination 0 24 47 63 100 Impact strength, kJ/m2 20.9 11.4 5.65 3.52 n/a % change -45 -73 -83

Table 6.3b: Mechanical properties of post consumer recycled ABS contaminated with PP

Contaminant level, v/v% 0 10 20 30 100 Tensile strength, MPa 42.0 41.9 36.2 32.7 17.3 % change 0 -14 -22 -59 Rule of Mixtures equivalent contamination 0 0 24 38 100 Flexural strength, MPa 67.4 63.8 57.5 51.5 25.7 % change -5 -15 -24 -62 Rule of Mixtures equivalent contamination 0 9 24 38 100 Impact strength*, kJ/m2 2.08 2.04 0.91 0.87 n/a % change -2 -56 -58

*Complete Break

See figures in Appendix I – section 9.2.1. for flexural strength curves of ABS

contaminated with PP.

6-7

Figure 6.4 Tensile strength of recycled ABS contaminated with PP

Figure 6.5 Impact strength of recycled ABS contaminated with PP

6-8

Table 6.4: Mechanical Properties of ABS contaminated with Nylon

Contaminant level, v/v% 0 5 10 20 100 Tensile strength, MPa 42.5 43.8 43.8 43.7 52.4 % change 3.0 3.1 2.9 23 Flexural strength, MPa 75.7 71.0 70.5 69.9 71.7 % change -6.2 -6.9 -7.7 -5.3 Impact strength, kJ/m2 20.9 8.06 2.12 1.07 n/a % change -61 -90 -95

Figure 6.6 Tensile and Flexural strength of recycled ABS contaminated with Nylon

6-9

Figure 6.7 Impact strength of recycled ABS contaminated with Nylon

polymer ateduncontamin of strength30)0(0 tcontaminan of fraction

constant strength

strength Flexural and Tensile for Model Linear

=≤≤=

=+=

0max

max

0maxmaxmax

.σ

ϕϕ

σϕσ

σ

σ

KK

Table 6.5a Predictive model constants for Tensile and Flexural Strength of contaminated ABS blends

Tensile strength, MPa Flexural strength, MPa

Contaminant Recycle Type Kmax max0 Kmax max0 HIPS Thermal -28 42 -39 75 PP Thermal -50 43 -95 75 PP Post Consumer -34 43 -54 68

6-10

polymer ateduncontamin of strength30)0(0 tcontaminan of fraction

constant strength

strength Impact for Model lExponentia

=≤≤=

==

0max

max

0maxmax

.

max

F

KeFF

F

KF

ϕϕ

ϕ

Table 6.5b Predictive model constants for Impact strength of contaminated ABS blends

Contaminant Recycle Type KFmax Fmax0 HIPS Thermal -4.55 20.5 PP Thermal -6.04 20.5 PP Post Consumer -3.41 2.26 Nylon Thermal -16.5 20.5

6.2.2. Contaminated PP blends

Contamination by the amorphous polymers, ABS and HIPS, enhanced the tensile

and flexural properties of PP, as both contaminants have superior mechanical

properties. For instance, 20% contamination of either polymer increases the tensile

strength by approximately 10%, see Table 6.6 and 6.7a. The relationship between the

proportion of ABS and the mechanical properties was linear, see Table 6.9a for the

predictive model constants. However, these blends did not obey the rule of mixtures,

such that although the incremental increase in strength was constant, it was less than

what would be expected for a specific level of contamination, see Table 6.7a. For

example, the change in tensile strength resulting from 20% ABS contamination was

equivalent to 10% contamination for additive behaviour. Unlike ABS, there was no

relationship between tensile or flexural strength and HIPS contaminant level, see Figure

6.8. Regardless of the contamination level, PP/HIPS blends had a tensile strength close

to the measured value of uncontaminated HIPS, approximately 15% higher than the

tensile strength for uncontaminated PP, see Table 6.6. Conversely, HIPS contamination

had a negligible effect on the flexural properties, yet the flexural strength of

uncontaminated HIPS was 50% greater, see Table 6.6.

6-11

Blending with an incompatible polymer weakens the internal structure, which is

prone to impact testing. In this instance, the impact strength of the blends was lower

than the PP, even when the contaminant (ABS) had greater impact strength, see Table

6.7a. 20% contamination of ABS and HIPS resulted in 75% and 85% reduction in

impact strength, respectively. The predictive model constants imply that HIPS

contamination had a greater effect on impact strength, whereby the exponential constant

of the HIPS model was 7.4s-1 compared to ABS, 5.7s-1. ABS and HIPS contaminated

blends partially broke, which was mainly associated with phase segregation and the

tough outer layer.

The different recycling methods were quantitatively assessed for the PP

contaminated with ABS blends. Contamination of the post consumer material caused a

greater reduction in the impact strength, where the exponential time constant of post

consumer blends was 10.1s-1, compared to the thermally recycled blends 5.7s-1. For

instance, the addition of 20% ABS reduced the impact strength of post consumer (ACT)

and thermally recycled material by 90 and 75%, respectively, see Table 6.3a, b and

Figure 6.5.

The addition of Nylon had a negligible effect on the tensile and flexural strength

of PP, see Figure 6.12. The effect of contamination on impact strength was difficult to

compare to PP based materials contaminated with the amorphous polymers. This was

attributed to the different break types between the blends. However, contamination did

reduce the impact strength as contaminant level increased, see Figure 6.13. Nylon

blends broke completely on impact; halving the impact strength with only 10%

contamination, see Table 6.8. See Table 6.9b for the predictive model constants of the

lines of best fit for all contaminated PP blends.

6-12

Figure 6.8 Tensile and Flexural strength of recycled PP contaminated with HIPS

Figure 6.9 Impact strength of recycled PP contaminated with HIPS

6-13

Table 6.6: Mechanical Properties of PP contaminated with HIPS

Contaminant level, v/v% 0 10 20 30 100 Tensile strength, MPa 19.4 21.1 21.2 21.4 22.6 % change 9 9 10 16 Rule of Mixtures equivalent contamination 0 54 58 62 100 Flexural strength, MPa 30.7 28.7 30.5 31.7 45.5 % change -6 -1 3 48 Rule of Mixtures equivalent contamination 0 -13 -1 7 100 Impact strength, kJ/m2 13.5 5.2 2.22 1.88 8.98 % change -61 -84 -86 -33

Figure 6.10 Tensile strength of recycled PP contaminated with ABS

6-14

Figure 6.11 Impact strength of recycled PP contaminated with ABS

Table 6.7a: Mechanical Properties of thermally recycled PP contaminated with ABS

Contaminant level, v/v% 0 10 20 30 100 Tensile strength, MPa 19.4 20.8 21.5 23.0 42.5 % change 7 11 19 119 Rule of Mixtures equivalent contamination 0 6 9 16 100 Flexural strength, MPa 30.7 33.6 35.2 37.7 75.7 % change 10 15 23 147 Rule of Mixtures equivalent contamination 0 7 10 16 100 Impact strength, kJ/m2 13.5 5.98 3.36 3.04 20.9 % change -56 -75 -77 55

6-15

Table 6.7b: Mechanical Properties of post consumer recycled PP contaminated with ABS

Contaminant level, v/v% 0 10 20 30 100 Tensile strength, MPa 17.3 17.6 18.7 21.1 42.0 % change 1 8 22 143 Rule of Mixtures equivalent contamination 0 1 6 15 100 Flexural strength, MPa 25.7 27.2 29.8 32.5 67.4 % change 6 16 27 162 Rule of Mixtures equivalent contamination 0 4 10 16 100 Impact strength, kJ/m2 24.6 8.77 2.22 1.57 n/a % change -64 -91 -94

See figures in Appendix I – section 9.2.1. for flexural strength curves and section 9.2.2.

for impact strength curve of PP contaminated with ABS.

Figure 6.12 Tensile and Flexural strength of recycled PP contaminated with Nylon

6-16

Figure 6.13 Impact strength of recycled PP contaminated with Nylon

Table 6.8: Mechanical Properties of PP contaminated with Nylon

Contaminant level, v/v% 0 5 10 20 100 Tensile strength, MPa 19.4 24.2 22.2 21.2 52.4 % change 25 15 9 170 Rule of Mixtures equivalent contamination 0 15 9 5 100 Flexural strength, MPa 30.7 28.0 29.3 29.4 71.7 % change -9 -4 -4 134 Rule of Mixtures equivalent contamination 0 -6 -3 -3 100 Impact strength, kJ/m2 13.5 11.4 7.60 5.71 5.45 % change -16 -44 -58 -60

6-17

Table 6.9a Predictive model constants for Tensile and Flexural strength of contaminated PP blends

Tensile strength, MPa Flexural strength, MPa

Contaminant Recycle Type Kmax max0 Kmax max0 ABS Thermal 11 19 23 31 ABS Post Consumer 12 17 23 25

Table 6.9b Predictive model constants for Impact strength of contaminated PP blends

Contaminant Recycle Type KFmax Fmax0 HIPS Thermal -7.42 13.3 ABS Thermal -5.70 13.3 ABS Post Consumer -10.1 24.6 Nylon Thermal -4.45 13.3

6-18

6.3 Verification of Modulus through DMA measurements Dynamic Mechanical Analysis is a simple method for calculating the components

of the complex modulus. The storage (dynamic) modulus, G’, is the real part of the

complex modulus, G*, which is represented as a complex function under sinusoidal

conditions.

iG" + G' = *G (6.1)

The storage modulus of the initial elastic region corresponds to Young’s

modulus, E. This was measured with increasing temperature.

The storage modulus of amorphous polymer, ABS, measured at room

temperature was 2000MPa. The modulus remained relatively constant until the onset of

glass transition at approximately 1000C, see Figure 6.14. On the other hand, the storage

modulus for PP decreased with increasing temperature from the initial value at room

temperature, 820MPa, see Figure 6.15.

For the majority of the polymers and polymer blends at approximately room

temperature, the storage modulus coincided well with Young’s modulus measured using

simple tensile measurements, with a maximum variance of approximately 10%, see

Table 6.10. Contamination reduced the modulus of ABS regardless of the contaminant.

The modulus for thermally recycled ABS contaminated with PP blends changes linearly

with the relative amount of contaminant polymer in the blend, following the rule of

mixtures. For instance, the addition of 10% PP in ABS, results in approximately 10%

decreases in the modulus, see Figure 6.16. At higher temperatures it appears that the

storage modulus between the blends of different contamination levels converge at the

glass transition, such that the addition of 10% PP in ABS, resulted in a less than 10%

decreases in the modulus, see Figure 6.14.

Table 6.10: Modulus for uncontaminated thermally recycled polymers, MPa

ABS PP HIPS Nylon Simple Tensile 2235 735 2060 1955 DMA 2000 820 1885 1500

6-19

11

11

11

1

1

1

1

1

1

1

1 1 1 1

22

22

22

2

2

2

2

2

2

2 2 2 2

33

3

3

33

3

3

3

3

3

3

3 3 3 30

500

1000

1500

2000

2500S

tora

ge M

odul

us (M

Pa)

30 50 70 90 110 130 150

Temperature (°C)

1 rABS–––––––2 rABS:rPP_90:10–––––––3 rABS:rPP_80:20–––––––

Universal V4.3A TA Instruments

Figure 6.14 Storage Modulus of ABS contaminated with PP

1

1

1

1

1

1

11

11

11

1 1

2

2

2

2

2

2

2

2

2

2

22

22

3

3

3

3

3

3

3

3

3

3

33

33

0

200

400

600

800

1000

1200

Sto

rage

Mod

ulus

(M

Pa)

30 50 70 90 110 130 150

Temperature (°C)

1 rPP–––––––2 rPP:rABS_90:10–––––––3 rPP:rABS_80:20–––––––

Universal V4.3A TA Instruments

Figure 6.15 Storage Modulus of PP contaminated with ABS

1 rABS

2 rABSPP_90/10

3 rABSPP_80/20

1

2

3

1

2

3

1 rPP

2 rPPABS_90/10

3 rPPABS_80/20

6-20

Table 6.11a: Modulus of thermally recycled ABS contaminated with PP, MPa

Contaminant level, v/v% 0 10 20 30 Simple Tensile 2236 1986 1791 1649 DMA 2000 1911 1841 na % difference -12 -4 3

Table 6.11b: Modulus of thermally recycled PP contaminated with ABS, MPa

Contaminant level, v/v% 0 10 20 30 Simple Tensile 736 904 1003 1174 DMA 818 976 1005 1115 % difference 10 7 0 -5

Figure 6.16 Modulus of thermally recycled ABS contaminated with PP

6-21

The modulus of post consumer recycled ABS contaminated with PP blends

followed closely to the rule of mixtures, with a similar trend for both methods of analysis.

However, the modulus measured by the simple tensile test was 10% greater than that

measured across the blends using DMA, see Figure 6.17. This was also observed for

thermally recycled HIPS and nylon contaminated ABS, such that the value of the

modulus varies between the methods of analysis while the change of modulus with

proportion of contamination follows the same trend, see Figure 6.18 and 6.19. For HIPS

contaminated ABS, the modulus of ABS was not effected with up to 30% HIPS.

Nylon contamination reduced the modulus of ABS to some extent, whereby the addition

of 20% nylon causes a reduction of less than 10%.

PP modulus was elevated by the presence of the contaminants, ABS, nylon and

HIPS. The modulus measured by DMA increased close to the rule of mixtures. A

contamination level of 20% of HIPS, ABS or nylon resulted in approximately 20%

increase in modulus; see Figure 6.20, 6.22 and 6.23. Similar to ABS contaminated with

PP, the modulus of post consumer PP contaminated with ABS blends measured by

simple tensile testing was 10% greater than that measured by DMA, see Figure 6.21.

Figure 6.17 Modulus of post consumer recycled ABS contaminated with PP

6-22

Figure 6.18 Modulus of thermally recycled ABS contaminated with HIPS

Figure 6.19 Modulus of thermally recycled ABS contaminated with Nylon

6-23

Table 6.12: Model constants for Modulus of contaminated ABS blends

DMA Simple Tensile

Contaminant Recycle Type KE E KE E PP Thermal -793 1997 -1960 2209 PP Post Consumer -829 2050 -785 2510 HIPS Thermal 0 2000 0 2236 Nylon Thermal -730 2007 -350 2296

Figure 6.20 Modulus of thermally recycled PP contaminated with ABS

6-24

Figure 6.21 Modulus of post consumer recycled PP contaminated with ABS

Figure 6.22 Modulus of thermally recycled PP contaminated with HIPS

6-25

Figure 6.23 Modulus of thermally recycled PP contaminated with Nylon

Table 6.13: Model constants for Modulus of contaminated PP blends

DMA Simple Tensile

Contaminant Recycle Type KE E KE E ABS Thermal 922 840 1410 742 ABS Post Consumer 1090 967 1730 1134 HIPS Thermal 1030 818 1570 813 Nylon Thermal 766 840 - -

6-26

6.4 Dynamic Mechanical Analysis

In this section, DMA was used to extend the frequency range and hence, time

range of the material under load, generating a master curve. Time temperature

superposition converts small range frequency sweeps to extended time scales. This is

achieved by correlating changes in the mechanical properties with temperature to

changes with time. The Williams-Landel-Ferry (WLF) equation was used to describe

time-temperature behaviour near the glass transition region. The master curve steps

through the glass transition, which is at the maximum slope of storage modulus, G’. At

the reference temperature, CT 00 105= , the amorphous polymers, ABS and HIPS, have

a step transition at 1 and 10rad/s, respectively, see Figure 6.29. Whereas, the semi-

crystalline materials do not have a transition under these conditions and the storage

modulus remains relatively constant over time, see Figure 6.27 and 6.31 (noting that PP

has a sub zero glass transition). Therefore, only contaminated thermally recycled ABS

blends were analysed using this method due to the practical limitations of measurements

in the glass transition region of PP.

6.4.1. ABS contaminated with PP

Figure 6.24 shows the short term measured data compared to the master curve

generated at 0T for a blend of ABS contaminated with 10% PP. Time is the inverse of

frequency, hence, the storage modulus decreased with increasing time. Similarly, the

storage modulus decreased with increasing temperature at the glass transition region.

6-27

1.000E-4 0.01000 1.000 100.0 10000 1.000E6 1.000E8ang. frequency (rad/s)

1.000E6

1.000E7

1.000E8

1.000E9

1.000E10

G' (

Pa)

rABSrPP9010, 85.0rABSrPP9010, 95.0rABSrPP9010, 105.0rABSrPP9010, 115.0rABSrPP9010, 125.0rABSrPP9010, 105 0 tts

Figure 6.24 Measured data and the master curve for ABS contaminated with 10 % PP

(tts denotes time temperature superposition of the master curve)

() 850C, () 950C, () 1050C, () 1150C, (∇ ) 1250C, (×) Master curve at 1050C

For ABS contaminated with PP blends, the slope of the transition step decreased

as the level of PP increased to a point where the transition step of the PP dominant

blends was not clearly defined, see Figure 6.25 and 6.27. Initially, PP contamination

caused a reduction in storage modulus. However, in the long term, PP contamination

suppressed the reduction of the modulus at the transition, shown by the divergence of

storage modulus between the blends with different contaminant level, see Figure 6.25.

For instance, at a time after the transition the modulus of ABS contaminated with 30%

PP was almost an order of magnitude greater than 10% contamination. In contrast, the

storage modulus of PP contaminated with ABS blends converged as time increased,

such that in the long term, modulus was not affected by the amount of contamination,

see Figure 6.27.

6-28

1.000E-4 0.01000 1.000 100.0 10000 1.000E6 1.000E8ang. frequency (rad/s)

1.000E6

1.000E7

1.000E8

1.000E9

1.000E10

G' (

Pa)

rABSrABSrPP9010rABSrPP8020rABSrPP7030

Figure 6.25 Master curves for ABS contaminated with PP at 1050C

() uncontaminated ABS, () 10% PP, () 20% PP, () 30% PP

Figure 6.26 Shift Factors for ABS contaminated with PP

6-29

Table 6.14: WLF constants for ABS contaminated with PP

Contaminant level, v/v% 0 10 20 30 C1 23 18 20 23 C2 108 89 102 118

The constants for the WLF equation, C1 and C2, are similar for all the blends of

ABS contaminated with PP, see Table 6.14, derived from WLF curve fits of Figure 6.26.

When the transition is clearly defined, as for ABS dominant blends, C2 is an indication of

the transition temperature. This is contrasted by PP, nylon and blends of PP

contaminated with ABS, where the transitions weren’t defined and the constants, C1, C2,

vary significantly with contamination level, see Table 6.15.

1.000E-4 0.01000 0.1000 1.000 10.00 100.0 1000 10000 1.000E5 1.000E7ang. f requency (rad/s)

1.000E7

1.000E8

1.000E9

G' (

Pa)

rPPrABS9010rPPrABS8020rPPrABS7030

Figure 6.27 Master curves for PP contaminated with ABS at 1050C

() 10% ABS, () 20% ABS, () 30% ABS

6-30

Figure 6.28 Shift Factors for PP contaminated with ABS

Table 6.15: WLF constants for PP contaminated with ABS

Contaminant level, v/v% 10 20 30 C1 7.2E+07 182 74 C2 5.7E+08 1071 411

6-31

6.4.2. ABS contaminated with HIPS

HIPS contamination of ABS did not appear to impact on the storage modulus

over the extended time range despite the fact that that the storage modulus of HIPS was

less that ABS, see Figure 6.29. Figure 6.30 shows that the WLF curve fits of the shift

factors for each blend lie on the same curve. Hence, the constants of the WLF equation,

C1 and C2, were the same for all three levels of contamination, 17 and 83K, respectively,

see Table 6.16. Uncontaminated ABS is the curve shown on Figure 6.30 close to the

trend for the blends, but only with data values up to 1150C. This curve is steeper than

the ABS contaminated with HIPS blends, thus higher value WLF constants. HIPS, on

the other hand, has a flatter curve, and consequently lower value constants.

1.000E-4 0.01000 1.000 100.0 10000 1.000E6 1.000E8ang. f requency (rad/s)

1.000E5

1.000E6

1.000E7

1.000E8

1.000E9

1.000E10

G' (

Pa)

rABSrABSrHIPS9010rABSrHIPS8020rABSrHIPS7030rHIPS

Figure 6.29 Master curves for ABS contaminated with HIPS at 1050C

() uncontaminated ABS, () 10% HIPS, () 20% HIPS, () 30% HIPS,

() uncontaminated HIPS

6-32

Figure 6.30 Shift Factors for ABS contaminated with HIPS

Table 6.16: WLF constants for ABS contaminated with HIPS

Contaminant level, v/v% 0 10 20 30 100 C1 23 17 16 17 12 C2 108 83 82 85 73

6-33

6.4.3. ABS contaminated with nylon

Nylon contamination of ABS had the same effect on the storage modulus as PP.

The magnitude of the transition decreased with increased level of contamination, so that

in the short term nylon reduced the modulus, while in the long term nylon contamination

improved it, see Figure 6.31. Nylon, a crystalline material, does not have a glass

transition at 1050C over the measured frequency range, see Figure 6.31. Analogous to

PP, the WLF constants for nylon were many orders of magnitude higher than ABS, while

the values of the ABS blends were similar regardless of the level of contamination, see

Table 6.17. This was shown in the WLF fit relating shift factor to temperature, where the

trend for nylon followed a different trend, see Figure 6.32.

1.000E-6 1.000E-4 0.01000 1.000 100.0 10000 1.000E6 1.000E8ang. frequency (rad/s)

1.000E6

1.000E7

1.000E8

1.000E9

1.000E10

G' (

Pa)

rABSrABSrNylon9505rABSrNylon9010rABSrNylon8020rNylon

Figure 6.31 Master curves for ABS contaminated with Nylon at 1050C

() uncontaminated ABS, () 5% Nylon, () 10% Nylon, () 20% Nylon,

() uncontaminated Nylon

6-34

Figure 6.32 Shift Factors for ABS contaminated with Nylon

Table 6.17: WLF constants for ABS contaminated with Nylon

Contaminant level, v/v% 0 5 10 20 100 C1 23 16 17 15 2.2E+07 C2 108 80 89 79 9.1E+07

See tables in Appendix I – section 9.2.3. for shift factors, tA , of each of the blends

analysed by DMA.

7-1

7 CONCLUSIONS

Binary blends of thermally recycled plastics were prepared to investigate the

effect of contamination on an amorphous polymer, ABS, and semi-crystalline polymer,

PP. The effect of contamination is partly dependent on the compatibility of the blended

materials and partly on the properties of the contaminant relative to the other material. A

contaminant that has lower properties will typically lower the property of that material

that it is added to. If the property of the material changes relative to the amount of

contaminant added, it follows the rules of mixtures and the mixture is considered

compatible.

Post consumer ABS/PP blends were prepared to compare against thermally

recycled blends. Minor variations and similar property trends between the recycling

methods are evidence of differences in the lifecycle and not attributed by contamination.

However, it is difficult to compare the two different recycling methods because the initial

virgin materials could have had substantially different properties resulting from different

manufacturing techniques and the use of additives to enhance the properties of the

material for its original use. Additionally, variation in exposure during a products lifecycle

will affect the extent of degradation of various properties.

7.1 Statistical analysis of Mechanical Properties

The mechanical properties of the recycled ABS and PP were normally

distributed, which was the basis for assuming that the population of these plastics

contaminated with small amounts (0-30%) of another plastic was normally distributed.

Statistical analysis indicated that to achieve a 95% confidence interval a minimum of 5

samples was required for tensile and flexural tests, and 8 for impact strength. The larger

sample size required for impact testing can be attributed to the significant variation of

impact strength in testing the material. There were a number of factors that may

account for this higher variance; predominantly the fact that the impact surface is

relatively small and any variation in the structure will affect the strength. Contamination

introduced a material into the structure, potentially an incompatible material which

results in an un-homogenous blend. This has the greatest, yet inconsistent, effect on

impact strength.

7-2

Statistical analysis of the various blends corroborated the initially stated sample

requirements determined from the ABS and PP.

7.2 Thermal Properties

The two amorphous polymers have a glass transition temperature in the

measureable range, while this transition is not a characteristic of crystalline material and

the semi crystalline PP has a sub zero Tg. Furthermore, the degradation temperature of

the amorphous polymers was greater than the crystalline polymers, which means that

higher temperatures can be applied to the amorphous materials. Recycling the

individual amorphous polymers, ABS and HIPS, did not significantly affected these

thermal properties. Whereas, the degradation temperature of the crystalline polymers,

particularly PP, was lowered, this limits the process temperature.

Contamination of ABS with semi-crystalline polymers lowered the degradation

temperature, while the degradation temperature of PP increased with the presence of

amorphous contaminants. This was expected due to the relative difference in

degradation temperature between the amorphous and semicrystalline/crystalline

polymers. The effect of contamination on the glass transition region for thermally

recycled material was negligible. In contrast, the glass transition temperature of post

consumer ABS increased with the addition of PP, possibly a result of the presence of

additives used for the purpose of the original material.

7.3 Processability

ABS contaminated with the semi-crystalline and crystalline polymers, PP and

Nylon respectively, was difficult to handle at room temperature during processing. This

was because the blending of the incompatible materials significantly lowered mechanical

properties at room temperature, and the material became brittle. In fact, solely based on

the difficulties during processing, both ABS and PP were incompatible with nylon.

Melt flow rate is a measure of the flowability of a material. Furthermore, the

rheological analysis highlights the effect of shear in relation to material flowability,

measured by viscosity as a function of shear rate. Shear induced on a material varies

between processes. For example, compression molding (low), extrusion (moderate) and

injection molding (high) operate at different shear rates.

7-3

Thermally recycled ABS was highly viscous and had a low flowability at the

processing temperature of 2400C. Qualitatively, by comparison of flow curves, PP was

less viscous and had a greater flowability and HIPS was half way between the two.

Contamination of PP with HIPS did not appear to affect the MFR, while the addition of

ABS reduced the flow of the material at the processing temperature. Flowability of post

consumer ABS was 3 times greater than the thermally recycled material. Hence, the

difference in the flowability of the individual post consumer materials was significantly

less, corresponding to a smaller change in flowability and viscosity relative to the level of

contaminant.

The contamination of ABS with PP or HIPS increased the flowability of the

material. This was further confirmed by the results from the rheological analysis of ABS

contaminated with PP. At low to moderate shear rates, ABS had a much higher

viscosity and pseudo plasticity at the processing temperature than PP. The addition of

PP appeared to systematically decrease pseudo plasticity of the ABS blend relative to

the amount of PP, approaching Newtonian behaviour as PP dominated the blend. The

reduction in viscosity with contamination means that the process temperature can be

lowered. This is advantageous for ABS because the butadiene in the polymer matrix is

sensitive to decomposition during processing.

Changes in thermal and rheological properties, due to contamination, should be

taken into account to identify operating parameters of processing techniques.

7-4

7.4 Mechanical Properties

Recycling did not substantially affect the mechanical properties of the individual

polymers, with the exception of impact strength.

HIPS contamination reduced the tensile and flexural properties of ABS, however,

these properties changed according to the proportion of HIPS in the blends, thus

following the rules of mixing. In addition, the amorphous contaminant, HIPS, did not

change the storage modulus over time, which further indicated that the HIPS and ABS

were somewhat compatible. A blend of HIPS and ABS containing less than 10% HIPS

will be suitable for a similar end use application if a reduction in impact strength can be

tolerated. This is advantageous because in a practical recycling operation it would be

difficult to completely separate these plastics due to their similar physical properties.

The tensile and flexural properties of ABS were reduced with the contaminant

level of semi-crystalline material, PP, while the crystalline material had no effect on

these properties. However, both materials caused a negative deviation from the rule of

mixtures as contaminant. This relationship indicates that ABS was incompatible with PP

and nylon, and that sorting and separation of these plastics is favourable.

Contamination of ABS with the semi-crystalline/crystalline materials changed the storage

modulus with time. In the short term, contamination reduced the modulus. However, the

shallower transition resulting from contamination suppressed the reduction in modulus,

which ultimately led to an improved modulus beyond the transition. The long term

benefit of contamination will depend on the scope of the products life cycle. Impact

strength of ABS was significantly impacted by contamination, such that 10% PP and 5%

nylon halved the impact strength. Since ABS can simply be separated from PP based

on density difference, simple sorting would produce higher value products that could

offset the costs of recycling. Although nylon contaminated ABS retains tensile and

flexural properties, the effect of nylon contamination on impact strength and

processability reduced the materials usefulness. In the case of nylon contamination,

separation is essential.

Contamination of PP with the amorphous polymers, ABS and HIPS, enhanced

the tensile and flexural properties, while nylon had no effect. However, the relation

between the tensile and flexural properties and the level of contaminant indicated that

the contaminants were incompatible with PP. This was further emphasized by the

significant effect that contamination had on the impact strength of the blended materials.

7-5

In conclusion, the thermal, rheological and mechanical properties of the

individual plastics were almost retained after thermal recycling. If impact strength is an

essential property, ABS with contaminant levels less than 10% HIPS and PP, and less

than 5% nylon, would be practical. Modifiers could be used to improve the interaction

between polymers within an incompatible blend, thereby improving the materials

properties. Otherwise, any mixture of polymers can be produced economically, without

sophisticated sorting, to produce low value products. Incomplete separation of the

materials investigated in this project will ultimately lead to plastics of inferior properties

that may not be useful in applications that the material was originally used for. Bollards

and railway beams are currently manufactured in Australia from post-consumer recycled

thermoplastics.

There are a number of areas in recycled consumer durable plastics that require

further investigation in the future. This includes:

• Test materials for chemical resistance, which may be an important property

for some of the applications of the recycled material.

• Extend the range of contaminants to include the wide range of minor

components found in WEEE.

• Increase the number of contaminants in a blend. This is because a product

may consist of more than two polymeric materials.

• Addition of modifiers to improve the interaction between the polymers in a

blend. Typically, this will improve some, if not all, of the properties of the

material.

• Accelerated aging of the virgin plastics by using UV radiation. This may

involve different lengths of exposure to simulate the variation in the lifecycle

of a product.

• Multiple thermal recycling, including aging the material with UV radiation in

between recycling.

8-1

8 REFERENCES Balakrishnan, S., and Neelakantan, N., (1998), “Mechanical Properties of Blends of Polycarbonates with Unmodified and Maleic Anhydride Grafted ABS”, Polymer International, Vol.45, UK Balart, R. Lopez, J., Garcia, D., and Salvador, M., (2005), “Recycling of ABS and PC from electrical and electronic waste. Effect of miscibility and previous degradation on final performance of industrial blends”, European Polymer Journal, Vol.41, Spain Banfield, Mark, (2000), Appliance Recycling Project - Pilot disassembly plant for whitegoods http://www.ecorecycle.sustainability.vic.gov.au/resources/documents/Appliance_Recycling_Project_Pilot_disassembly_plant_for_whi.pdf Brennan, L., Isaac, D., and Arnold, J., (2002), “Recycling of Acrylonitrile-Butadiene-Styrene and High-Impact Polystyrene from Waste Computer Equipment”, Journal of Applied Polymer Science, Vol.86, Wiley Periodicals, Inc., UK Case, R., and Korzen, A., (2000), “The effects of regrind loading levels and heat history on the properties of selected engineering polymers”, SPE ANTEC Proceedings, Vol. III, pp. 3124–3133 Chiu, H., and Hsiao, Y., (2004), “Studies on Impact-Modified Nylon 6/ABS Blends”, Polymer Engineering and Science, Vol.44 (No.12), Society of Plastics Engineers, Taiwan Chokshi, R., and Zia, H., (2004), “Hot-Melt Extrusion Technique: A Review”, Iranian Journal of Pharmaceutical Research, Iran http://www.ijpr-online.com/Docs/20041/IJPR206_files/image005.jpg&imgrefurl

Crawford, R.J., (1998), “Plastics Engineering”, 3rd edition, Butterworth-Heinemann, UK Consumer Electronics Suppliers Association [CESA], (2003), Beyond the Dead TV: Managing End-of-Life Consumer Electronics in Victoria - Full Report (1.17MB) http://www.ecorecycle.sustainability.vic.gov.au/www/html/834-tv--disassembly-trials.asp Doran, C., (2006), Byteback, http://www.ecorecycle.sustainability.vic.gov.au/www/html/1107-byteback.asp?intSiteID=1, Sustainability Victoria EcoRecycle Victoria, (2004). “Annual Survey of Victorian recycling industries”, http://www.ecorecycle.sustainability.vic.gov.au/resources/documents/Annual_Survey_of_Victorian_Recycling_Industries_2003-04.pdf Fried, J.R., (2003), “Polymer Science and Technology”, 2nd edition, Pearson Education Inc./Prentice Hall Professional Technical Reference, USA

8-2

Ferguson, J., and Kemblowski, Z., (1991), “Applied Fluid Rheology”, Elsevier Science P/L, UK Gupta, A., Jain, A., and Maiti, S., (1990), ‘Studies on Binary and Ternary Blends of Polypropylene with ABS and LDPE. II. Impact and Tensile Properties’, Journal of Applied Polymer Science, Vol. 39, pp. 515-530. Hylton, D.C., (2004), “Understanding Plastic Testing”, Carl Hanser Verlag, Munich Katos, G., and Hoye, J., (2005), “Household Electrical and Electronic Waste Benchmark Survey 2005”, Ipsos, Australia Lindsey C., Barlow, J., and Paul, D., (1981), “Blends from Reprocessed Coextruded Products”, Journal of Applied Polymer Science, Vol.26, John Wiley and Sons, Inc., USA Liu, X., and Bertilsson, H., (1999), “Recycling of ABS and ABS/PC”, Journal of Applied Polymer Science, Vol.74, John Wiley and Sons, Inc, Sweden Liu, X., Boldizar, A., Rigdahl, M., and Bertilsson, H., (2002a), “Mechanical Properties and Fracture Behavior of Blends of Acrylonitrile-Butadiene-Styrene Copolymer and Crystalline Engineering Plastics”, Journal of Applied Polymer Science, Vol.86, John Wiley and Sons, Inc, Sweden Liu, X., Boldizar, A., Rigdahl, M., and Bertilsson, H., (2002b), “Recycling of Blends of Acrylonitrile-Butadiene-Styrene (ABS) and Polyamide”, Journal of Applied Polymer Science, Vol.86, Wiley Periodicals, Inc., Sweden Markin and Williams, (1980), Journal of Applied Polymer Science, Vol. 25, Wiley Periodicals, Inc., p2451. Menard, K.P., and Raton, B., (1999), “Dynamic Mechanical Analysis, a practical introduction”, CRC Press, Fla. Mikulec, M., and Brooks, T., (2000), “Blend of Post Industrial ABS and PMMA Improves Thermal and Impact Properties”, SPE ANTEC Proceedings, Vol. III, p. 2667 Ohishi, H., Ikehara, T., and Nishi, T., (2001), “Phase Morphologies and Mechanical Properties of High Impact Polystyrene (HIPS) and Polycarbonate Blends Compatibilized with Polystyrene and Polyarylate Block Copolymer”, Journal of Applied Polymer Science, Vol.80, John Wiley and Sons, Inc., Japan Pascoe, R.D., (2004), “The use of selective depressants for the separation of ABS and HIPS by froth flotation”, Minerals Engineering, Vol.18, Elsevier Ltd., UK Pascoe, R.D., (2005), “Investigation of hydrocyclones for the separation of shredder fridge plastics”, Elsevier

8-3

Paul, S., and Kale, D., (2001), “Blends of Acrylonitrile-Butadiene-Styrene/Waste Poly(ethylene terephthalate) Compatibilized by Styrene Maleic Anhydride”, Journal of Applied Polymer Science, Vol.80, John Wiley and Sons, Inc, India Plastics and Chemicals Industries Association [PACIA], (2005), 2005 National Plastics Recycling Survey, Victoria, Australia Plastics and Chemicals Industries Association [PACIA], (2008), 2008 National Plastics Recycling Survey, Victoria, Australia, http://www.pacia.org.au/_uploaditems/docs/Recycling%20Survey%202008%20Report.pdf Ragosta, G., Musto, P., Martuscelli, E., and Russo, P., (2001), “Recycling of a plastic car component having a multilayer structure: Morphological and mechanical analysis”, Journal of Materials Science, Vol.36, Kluwer Academic Publishers, Italy Rios, P., Stuart, J., and Grant, E., (2003), “Plastics Disassembly versus Bulk Recycling: Engineering Design for End-of-Life Electronics Resource Recovery”, Environmental Science and Technology, vol.37(no.23), American Chemical Society Rubin, I., (1990), “Handbook of Plastic Materials and Technology”, Wiley Interscience, New York Santana, R.M., and Manrich, S., (2003), “Studies on Morphology and Mechanical Properties of PP/HIPS Blends from Postconsumer Plastic Waste”, Journal of Applied Polymer Science, Vol.87, Wiley Periodicals, Inc., Brazil Scheirs, J., (1998), “Polymer Recycling: Science, Technology and Applications”, John Wiley & Sons Ltd, England Shah, V., (1998), Handbook of Plastic Testing Technology, 2nd edition, SPE, John Wiley & Sons Ltd, USA Sepe, M.P., (1998), “Dynamic Mechanical Analysis for Plastic Engineering”, William Andrew Publishing. Semancik, J.R., (1997), “Yield stress measurements using controlled stress rheometry”, TA Techpublications, RH058 Utraki, L.A., (2002), “Polymer Blends Handbook”, Vol 1-2, Springer-Verlag Utraki, L.A., (1989), “Polymer Alloys and Blends: Thermodynamics and Rheology”, Hanser Publishers, Germany Whittingstall, P., (1997), “Paint evaluation using rheometry”, TA Techpublications, RH059

8-4

Xu, G.; Qiao, J.; Kuswanti, C.; Simenz, M.; Koelling, K.; Stuart, J.A.; Lilly, B, ., (2000),

“Insights into reuse of High Impact Polystyrene from post-consumer electronics

equipment housing”, Proceedings of the 2000 IEEE International Symposium on

Electronics and the Environment, Page(s):348 – 353, San Francisco, CA, USA

9-1

9 APPENDIX I

9.1 Rheology 9.1.1. Flow curves

0.1000 1.000 10.00shear rate (1/s)

10.00

100.0

1000

10000

1.000E5

visc

osity

(P

a.s)

rPPrPP240_[IM]rPP_ACTrPP_ACT_2rABSrABS_2rABS_ACT

Figure I.1 Flow curves of recycled polymers

0.1000 1.000 10.00 100.0shear rate (1/s)

1.000

10.00

100.0

1000

10000

1.000E5

visc

osity

(P

a.s)

rABSrABSPP9010rABSPP8020rABSPP7030rPP

Figure I.2 Flow curves of thermally recycled contaminated ABS blends

9-2

0.1000 1.000 10.00 100.0shear rate (1/s)

1.000

10.00

100.0

1000

10000

1.000E5

visc

osity

(P

a.s)

rPPrPPABS9010rPPABS8020rPPABS7030rABS

Figure I.3 Flow curves of thermally recycled contaminated PP blends

0.1000 1.000 10.00 100.0shear rate (1/s)

10.00

100.0

1000

10000

1.000E5

visc

osity

(P

a.s)

rABS_ACTrABSPP9010_ACTrABSPP8020_ACTrABSPP7030_ACTrPP_ACT

Figure I.4 Flow curves of post consumer contaminated ABS blends

9-3

0.1000 1.000 10.00 100.0shear rate (1/s)

1.000

10.00

100.0

1000

10000

visc

osity

(P

a.s)

rPP_ACTrPPABS9010_ACTrPPABS8020_ACTrPPABS7030_ACT

Figure I.5 Flow curves of post consumer contaminated PP blends

0.1000 1.000 10.00shear rate (1/s)

1.000

10.00

100.0

1000

10000

visc

osity

(P

a.s)

rPP_ACTrPPABS9010_ACTrPPABS8020_ACTrPPABS7030_ACT

Figure I.6 Flow curves of post consumer contaminated PP blends

9-4

9.1.2. Linear viscoelasticity

1.000 10.00 100.0 1000 10000osc. stress (Pa)

1000

10000

1.000E5

G' (

Pa)

rPPrPPABS9010rPPABS7030rABSPP7030rABSPP9010

Figure I.7 Linear viscoelasticity of thermally recycled blends

1.000 10.00 100.0 1000 10000osc. stress (Pa)

1000

10000

1.000E5

G' (

Pa)

rPP_ACTrPPABS8020_ACTrPPABS7030_ACTrABSPP7030_ACTrABSPP8020_ACT

Figure I.8 Linear viscoelasticity of post consumer recycled blends

9-5

9.1.3. Cox-Merz transforms

0.1000 1.000 10.00 100.0 1000shear rate (1/s)

10.00

100.0

1000

10000

1.000E5vi

scos

ity (

Pa.

s)

rPP cmrPPrABS cmrABS

Figure I.9 Flow curves and Cox-Merz transformation of thermally recycled polymers

1.000 10.00 100.0 1000shear rate (1/s)

100.0

1000

10000

1.000E5

visc

osity

(P

a.s)

rPP cmrPP_2 cmrABSPP7030 cmrABSPP7030_2 cmrABSPP8020 cmrABSPP8020_2 cmrABSPP9010 cmrABSPP9010_2 cm

Figure I.10 Cox-Merz transformation of thermally recycled ABS contaminated with PP

9-6

1.000 10.00 100.0 1000shear rate (1/s)

100.0

1000

10000

1.000E5

1.000E6

shea

r st

ress

(P

a)

rPP cmrPP_2 cmrABSPP7030 cmrABSPP7030_2 cmrABSPP8020 cmrABSPP8020_2 cmrABSPP9010 cmrABSPP9010_2 cm

Figure I.11 Power-law fits for Cox-Merz transformation of thermally recycled ABS

contaminated with PP

1.000 10.00 100.0 1000shear rate (1/s)

100.0

1000

10000

visc

osity

(P

a.s)

rPP cmrPP_2 cmrPPABS9010 cmrPPABS9010_2 cmrPPABS8020 cmrPPABS8020_2 cmrPPABS7030 cmrPPABS7030_2 cm

Figure I.12 Cox-Merz transformation of recycled PP contaminated with ABS

9-7

1.000 10.00 100.0 1000shear rate (1/s)

100.0

1000

10000

1.000E5

1.000E6

shea

r st

ress

(P

a)

rPP cmrPP_2 cmrPPABS9010 cmrPPABS9010_2 cmrPPABS8020 cmrPPABS8020_2 cmrPPABS7030 cmrPPABS7030_2 cm

Figure I.13 Power-law fits for Cox-Merz transformation of thermally recycled PP

contaminated with ABS

1.000 10.00 100.0 1000shear rate (1/s)

100.0

1000

10000

visc

osity

(P

a.s)

rABSPP7030_ACT cmrABSPP7030_ACT_2 cmrABSPP8020_ACT cmrABSPP9010_ACT cmrABSPP9010_ACT_2 cmrABS_ACT cmrABS_ACT_2 cm

Figure I.14 Cox-Merz transformation of post consumer ABS contaminated with PP

9-8

1.000 10.00 100.0 1000shear rate (1/s)

100.0

1000

10000

visc

osity

(P

a.s)

rPPABS7030_ACT cmrPPABS7030_ACT_2 cmrPPABS8020_ACT cmrPPABS9010_ACT_2 cmrPPABS9010_ACT cmrPP_ACT cmrPP_ACT_2 cm

Figure I.15 Cox-Merz transformation of post consumer PP contaminated with ABS

9-9

9.2 Mechanical Properties 9.2.1. Flexural strength of ABS/PP blends

Figure I.16 Flexural strength of recycled ABS contaminated with PP

Figure I.17 Flexural strength of recycled PP contaminated with ABS

9-10

9.2.2. Impact strength of contaminated ABS blends

Figure I.18 Impact strength of contaminated ABS blends

9-11

9.2.3. Williams-Landel-Ferry (WLF), shift factors

Table I.1: Shift Factors, tA , for ABS contaminated with PP

Contaminant level, v/v% Temperature, 0C 0 10 20 30

85 5.19 5.03 4.75 4.52 95 2.59 2.59 2.59 2.59 105 0 0 0 0 115 -1.86 -1.85 -1.86 -1.88 125 n/a -3.14 -3.15 -3.18

Table I.2: Shift Factors, tA , for PP contaminated with ABS

Contaminant level, v/v% Temperature, 0C 10 20 30

85 2.24 3.33 3.65 95 1.40 2.03 2.23 105 0.00 0.00 0.00 115 -1.30 -1.86 -1.89 125 -2.74 -3.25 -3.35

Table I.3: Shift Factors, tA , for ABS contaminated with HIPS

Contaminant level, v/v% Temperature, 0C 0 10 20 30 100

85 5.19 5.19 5.19 5.08 4.50 95 2.59 2.59 2.59 2.49 1.90 105 0 0 0 0 0 115 -1.86 -1.84 -1.82 -1.81 -1.30 125 n/a -3.13 -3.12 -3.11 -2.62

Table I.4: Shift Factors, tA , for ABS contaminated with Nylon

Contaminant level, v/v% Temperature, 0C 0 5 10 20 100

85 5.19 5.19 4.96 4.88 4.54 95 2.59 2.59 2.59 2.52 2.27 105 0 0 0 0 0 115 -1.86 -1.81 -1.80 -1.70 -2.43 125 n/a -3.05 -3.10 -2.86 -5.03