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Title: Viscoelastic Behaviour, Thermal Properties and Morphology for New Composites from Recycled HDPE, EPDM, Ground Tyre Rubber (GTR) and Bitumen Authors: Olga Grigoryeva Emilio Lievana Alexander Tolstov Olga Starostenko Alexander Fainleib Joseph Karger-Kocsis PAPER DEADLINE: **10 Dec 2003** PAPER LENGTH: **6 PAGES MAXIMUM (excluding this cover paper)** SEND PAPER TO: Professor Lin YE

Chair of ACCM-4 Centre for Advanced Materials Technology School of Aerospace, Mechanical & Mechatronic Engineering Building No. J07 University of Sydney NSW 2006, Australia

Tel: ++61-2-9351-4798 Fax: ++61-2-9351-3760 E-mail: ye@aeromech.usyd.edu.au

Viscoelastic Behaviour, Thermal Properties and Morphology for New Composites from Recycled HDPE,

EPDM, Ground Tyre Rubber (GTR) and Bitumen

Olga Grigoryeva*, Alexander Tolstov, Olga Starostenko, Alexander Fainleib Institute of Macromolecular Chemistry of the National Academy of Sciences of

Ukraine, Kharkivske shose 48, 02160 Kyiv, Ukraine

Emilio Lievana, J. Karger-Kocsis Institut für Verbundwerkstoffe GmbH (Institute for Composite Materials), University

of Kaiserslautern, POBox 3049, D-67653 Kaiserslautern, Germany,

ABSTRACT

Structure-property relationships for new composites prepared from recycled HDPE,

EPDM, ground tyre rubber (GTR) and bitumen have been studied by a combination of DMTA, DSC and SEM techniques and tensile tests. The better mechanical performance determined for a composition containing a preheated and rolled mixture of GTR and bitumen have been explained by a better mixing of the components and formation of the essential interface layer due to the reclaiming (for GTR) and compatibilizing (for composite) role of the bitumen.

INTRODUCTION Thermoplastic elastomers (TPEs), especially blends of elastomer and thermoplastic

obtained by dynamic vulcanization of rubber in thermoplastic and having characteristics of elastomers while maintaining the thermoplasticity [1] attract a great interest of scientists and producers. High value composites can be produced by a replacement of virgin components of TPEs (fully or partly) by recycled polymers. Obtaining materials of beneficial properties is not easy task due to very poor compatibility of the components. To be reactively compatibilized (it seems to be most effective method) the components (at least their surface) of high value composites including GTR should be activated by thermal, thermal-mechanical, thermal-chemical and other methods [2,3] and additional compatibilizers should be used [3-5].

In our previous works we have compared [6] behaviour of virgin and recycled polyethylenes (low and high density polyethylenes, LDPER and HDPER, respectively) in basic and compatibilized [7] composite formulations and combined [8-11] the methods of GTR devulcanization and the following reactive compatibilization of a reclaimed GTR with other components.

* Correspondence Author, Institute of Macromolecular Chemistry of the National Academy of Sciences of Ukraine, Kharkivske shose 48, 02160 Kyiv, Ukraine, fax:(380)445524064, e-mail: fainleib@i.kiev.ua

In this study the reactively compatibilized high value composites based on recycled HDPE (HDPER), EPDM and partially devulcanized GTR were prepared. A new modifier, bitumen, contributing to GTR devulcanization and further compatibilization of all the composite components have been utilized. The structure-property relationships were investigated using DSC, DMTA and SEM techniques.

EXPERIMENTAL

Recycled high-density polyethylene (HDPER) from post-consumer bottle transportation crates collected in Kyiv (Ukraine) was used, the HDPER melt flow index (MFI) was: MFI190/2.16 = 2.13 g/10 min. GTR fraction with a particle size of 0.4 to 0.7 mm was kindly provided by Scanrub AS (Viborg, Danmark). Ethylene/propylene/diene monomer (EPDM) containing rubber (Buna® EP G 6470 of Bayer) was used. The EPDM rubber with 71 wt % of ethylene and 4.5 wt % of ethylidene norbornen contents, respectively, had a Mooney viscosity, ML(1+4) 125oC, 59. Bitumen used was a BN-4 grade according to the State Standard SS 6617-76.

HDPER and EPDM were used as received. GTR was used as received and in some TPE formulations it was mixed with bitumen (1/1 by weight) and the mixture was preheated at 170oC for 4 hours and further rolled for 40 min prior to introducing to TPE recipes. In all cases, the mastication of composition by Brabender Plasticorder was carried out at 160oC and 80 rpm for 15 min.

The viscoelastic behaviour of the resulting TPEs was investigated using a DMTA device (Eplexor 150N of Gabo Qualimeter, Ahlden, Germany). Rectangular sheets having a dimension of 6×1×0.25 cm3 were subjected to oscillating tensile loading. The testing temperature ranged from -105°C to 150°C selecting a heating rate of 3°C/min.

Differential scanning calorimetric studies were carried out using a DuPont thermal analyzer model 910. The scans were taken in the temperature range from -100°C to 200°C with a programmed heating rate of 20°C/min. Melting temperature (Tm) corresponding to the maximum in fusion endotherm, was noted.

Tensile tests were performed on dumbbell specimens at ambient temperature at a crosshead speed of 100 mm/min using Instron-1122 type universal testing machine. The average data for 6-7 specimens were taken for consideration. The parameters such as tensile strength at break (TS) and elongation at break (EB) were determined.

The fracture surface of the specimens was inspected by using a scanning electron microscope JSM-5400 of Jeol (Tokyo, Japan). RESULTS AND DISCUSSION Dynamic Mechanical Thermal Analysis (DMTA)

It was found that the damping behaviour (i.e., the character of E'=f (T) dependencies) of all of the blends studied is quite similar to HDPER and it is typical for thermoplastic compositions. We infer that in all the blends HDPER forms continuous thermoplastic phase (matrix) while crosslinked rubber components (EPDM, reclaimed GTR) form a dispersed phase.

The Tg values of the TPEs and the individual components as well as the corresponding E" values at Tg are listed in Table I. HDPER/EPDM blend produced by the mastication in Brabender plasticorder exhibits the transition at –31oC (Tg2) as a result of overlapping Tg’s of amorphous phases of EPDM (Tg2) and HDPER (Tg3), while a second transition at 68oC (Tg4) is characteristic for HDPER. Shifting the first

lower Tg2 on 5oC towards higher temperature compared to (Tg2) of individual EPDM evidences of mixing amorphous phases of EPDM and HDPER.

The damping behaviour of HDPER/EPDM/GTR TPE is characterized by appearance of new relaxation transition at -50oC (Tg1) characteristic for introduced GTR and by shifting other Tg's peaks towards lower temperatures. This, along with the lower values of storage moduli (E') and higher values of E" at Tg evidences of significant growth of chain flexibility of the components, especially in rubber rich phases. It can be caused mainly by disordering the matrix due to dispersion of GTR crosslinked particles. The latter is confirmed by a significant growth of E" values (from ~ 20 up to 90 MPa) in the temperature region below Tg1.

Table I DMTA data for individual components and TPEs

Tg [oC] for Phases Rich in:

GTR EPDM HDPER

E" Value at Tgi [MPa] Sample code

Composition [wt%]

Tg1 Tg2 Tg3 Tg4 h1 h2 h3 h4- HDPER

- - -15 60 - - 65 100

- EPDM

- -36 - - - 102 - -

B1 HDPER / EPDM = 61.5 / 38.5*

- -31 - 68 - 134 - 30

B2 HDPER / EPDM / GTR** = 40 / 25 / 35 -50 -42 - 54 160 150 - 21

B3 HDPER / EPDM / (GTR/ bitumen)** = 40 / 25 / 17.5 / 17.5

-49 -35 - 42 121 158 - 35

B4 HDPER / EPDM / (GTR/ bitumen)*** =40 / 25 / 17.5 / 17.5

-48 -33 - 53 63 110 - 41

* ratio of HDPER / EPDM=61.5/38.5 wt % is equal to 40/25 wt % in the ternary blends; ** the TPE was obtained by mastication in Brabender Plasticorder; *** the TPE was obtained by preheating of GTR/bitumen blend followed by its rolling and then by mastication in Brabender Plasticorder.

As for the damping behaviour of HDPER/EPDM/ (GTR/bitumen) TPEs one can see a shift of Tg1 and Tg2 towards higher temperatures compared to the recipes without bitumen. This, along with decreasing E" values in the temperature region below Tg1, as well as increasing E' values in the region above Tg1 transition, evidences of increasing crosslinking degree of the blends. It can be explained by the dynamic vulcanization of dispersed rubbers inside plastic HDPER matrix, confirming the role of bitumen as a curing agent for the rubbers. In addition, it was found that the B4 TPE is characterized by significant decrease of segmental motion onset (onset of Tg1) from –65oC to –75oC that means improving GTR chain flexibility, obviously due to bitumen induced degradation of GTR followed by (re)covulcanization of devulcanized GTR, EPDM and bitumen. Differential Scanning Calorimetry (DSC)

DSC curves for individual polymers and TPEs produced are shown in Figure 1. First off all, both EPDM and HDPER show a melting of their crystallites in the blends, i.e. have both amorphous and crystalline phases. Second, some depression of the melting temperature (Tm) values for both EPDM and HDPER in the blends is observed in comparison to the individual polymers depending on the composition and processing conditions used (cf. Table II). The maximal reduction of Tm reaches ~5oC for EPDM and

~6oC for HDPER for HDPER/EPDM/GTR/bitumen TPEs. It may be caused by formation of crystallites having a smaller size or by increasing unsoundness of crystallites formed. For HDPER matrix of the TPEs a significant shift of onset of melting temperature, Tmonset, towards higher temperature and narrowing a temperature interval of crystallites melting, ∆Tm, is observed in comparison to individual HDPER. We suppose that the growth of Tmonset from 37oC (for individual HDPER) up to 70-75oC (for HDPER as a component in blend) observed can be caused by a disappearance of smaller less perfect crystallites involved into the amorphous phase. The narrowing the melting interval, ∆Tm, for HDPER crystallites from 123oC (for individual polymer) up to 85oC (in HDPER/EPDM blends), and further to 71-76oC (for GTR-containing TPEs) testifies of decrease of dispersion of dimensions of HDPER crystallites in the blends.

- 1 0 0 - 5 0 0 5 0 1 0 0 1 5 0 2 0 0

END

O

END

O

HDP E R

E P DMbitume n

a )

- 1 0 0 - 5 0 0 5 0 1 0 0 1 5 0 2 0 0

B 4

B 2

B 3

B 1

T em pera ture , oC

b )

FIGURE 1. DSC traces for: (a) individual EPDM, HDPER and bitumen (indicated in the plot); (b) TPEs produced (the codes of the curves correspond to the compositions in the Table I).

Table II DSC data and tensile properties of TPEs

Tm [oC]

∆Tm = Tmend - Tmonset [oC]

Sample code

Composition

EPDM HDPER EPDM HDPER

TS [MPa]

EB[%]

- HDPER - 136 - 123 17.7 10 - EPDM 47 - 37 - 11.2 820

B1 HDPER / EPDM 45 135 43 85 11.6 750B2 HDPER / EPDM / GTR 45 132 21 76 3.9 40 B3 HDPER / EPDM / (GTR/bitumen) 42 130 35 72 4.0 65 B4 HDPER / EPDM / (GTR/bitumen) 45 133 26 71 6.3 300

Scanning Electronic Microscopy (SEM)

Figure 2 depicts SEM photomicrographs taken from the cut surface of the sheets of GTR-based TPEs listed in Tables I and II. One can clearly see that GTR particles directly dispersed in HDPER/EPDM blend (sample B2) are very poorly bonded to the matrix and a lot of large and small strip breakages are observed. The GTR particles debond from the matrix indicating for lacking interaction between them and, as a result, the sample exhibits low tensile properties (cf. Table II).

B4B3B2

FIGURE 2. SEM photomicrographs of surfaces for the TPE samples produced (the codes of the curves correspond to the compositions in the Tables I and II).

A better bonding between GTR particles and matrix is observed for the formulations produced by using bitumen (sample B3) and especially for TPE produced with GTR/bitumen preheating, rolling and further mastication by Brabender plasticorder (sample B4). It can be seen that surface of the last sample of TPE looks very homogeneous and there are no visible strip breakages that is a result of better bonding between GTR particles and thermoplastic matrix via formation of an improved interface layer. Understandably, the TPE sample (sample B4) exhibits high tensile properties (cf. Table II). CONCLUSIONS

Thermoplastic elastomers containing recycled HDPER and GTR have been prepared by using technology of dynamic vulcanization and reactive compatibilization. Structure-property relationships for TPEs produced have been investigated and the effectiveness of producing methods used has been compared. A significant improvement of both TS and EB values has been achieved for HDPER/EPDM/GTR/bitumen TPEs produced with preheating and rolling of GTR/bitumen before mastication of the formulation by

Brabender plasticorder. The comparative analysis of DMTA, DSC and SEM experimental results has shown that significant improvement of tensile properties achieved in comparison to TPEs containing unmodified GTR is a result of the effect of bitumen as a suitable reclaiming agent for GTR, and further as a compatibilizer for GTR/bitumen containing TPEs.

ACKNOWLEDGEMENT

The work was fulfilled under the financial support of EU (INCO-Copernicus contract No.: ICA2-CT-2001-10003 and STCU Agreement No.: 3009). REFERENCES

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