Materials and Design 30 (2009) 557–562

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Materials and Design

journal homepage: www.elsevier .com/locate /matdes

Thermal degradation of banana pseudo-stem filled unplasticized polyvinylchloride (UPVC) composites

E.S. Zainudin a,*, S.M. Sapuan a, K. Abdan a, M.T.M. Mohamad b

a Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysiab Faculty of Agriculture, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia

a r t i c l e i n f o

Article history:Received 25 February 2008Accepted 23 May 2008Available online 9 July 2008

Keywords:A. Natural materialsA. Composites:. . ..polymer matrixC. Moulding

0261-3069/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.matdes.2008.05.060

* Corresponding author. Tel.: +60 3 89466317; fax:E-mail address: edisyam@eng.upm.edu.my (E.S. Za

a b s t r a c t

The thermal behaviour of banana pseudo-stem (BPS) filled unplastisized polyvinyl chloride (UPVC) com-posites was studied by means of thermogravimetric analysis. The effects of fiber loading and resin mod-ification on the thermal stability of the composites were evaluated. Resin modifications were carried outby acrylic to improve the fiber–matrix adhesion. From the study, the thermal stability of the compositeswas found to be higher than that of BPS fiber and the UPVC matrix. It is shown that the incorporation ofBPS filler decreases the thermal stability of BPS/UPVC composites for the case of non acrylic. The thermalstability of BPS/UPVC composite with acrylic is found to be higher compared to BPS/UPVC compositewithout acrylic.

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

The increase concern of environments resulted from the use ofsynthetic fiber reinforced polymer composite has triggered re-search effort to develop new forms of composites such as naturalfiber composites. Besides possessing good specific physical proper-ties, natural fiber composite is also cost-effective and environmen-tally friendly. The use of natural fibers such as banana pseudo-stem,oil palm empty fruit bunch and rayon fiber in some polymers hasdemonstrated promising results in the past especially in the pres-ence of the interfacial bonding agents [1–3]. According to Pothanand Thomas [1], the storage modulus value was found to be higherfor the silane treated banana fiber/polyester composites as com-pared to pure PE resin. In the case of oil palm empty fruit bunch fi-ber, Rozman et al. [2] found that the composites with couplingagent showed higher flexural and impact strength than those withuntreated fiber. Another finding by Escamilla et al. [3] that graftedrayon had better thermal properties than ungrafted rayon due togood compatibility and homogeneous. These composites not onlyhave good mechanical and thermal characteristics but they alsodo not pose health hazard and their uses are cost-effective [4–7].

Polyvinyl chloride (PVC) is a thermally unstable material, espe-cially at high temperature in the presence of oxygen and humidity.The inclusion of natural filler in polymer that affects the thermalperformance of composites has been studied in the past [3,5–9].Since most polymers are processed at high temperature, thermal

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+60 3 86567122.inudin).

stability of natural fibers or fillers is one of the factors to be consid-ered in developing natural fiber composites [9,10].

In this paper, thermal decomposition behaviour of BPS/UPVCcomposites is presented based on thermogravimetric and deriva-tive thermogravimetric analyses. This study aimed at observingthe variation in thermal degradation by reinforcing the UPVC withBPS filler at different mass fractions.

2. Experimental

2.1. Materials

The matrix used in this study was UPVC (IR064) supplied byPolymer Resources Sdn. Bhd., Kelang, Selangor, Malaysia. ThisUPVC was a medium molecular weight resin designed for generalpurpose application. It was a rigid polymer with amorphous struc-ture. Some additives were inserted together into the pure PVC tomake it unplastisized, which were in the powder form. The BPS fil-ler used in this study was taken from banana tree trunk, which isknown as a ‘pseudo-stem’. Detail properties and the type of bananaused cannot be revealed by the supplier (Baala Bharat Agri Indus-tries, Andhra Pradesh, India) due to the confidential nature of theinformation and data. Tables 1, 2a and b show the important prop-erties of BPS filler and UPVC respectively.

2.2. Incorporation of BPS filler

Melt blending was carried out at 150 �C and 50 rpm rotor speedin a HAAKE Rheomixer having a mixing chamber attachment. The

Table 2aProperties of UPVC [1]

Specification Value Units

Specific gravity 1.4–1.43 g/cm3

Specific heat 0.25 kcal/kg/�CThermal conductivity 0.13 kcal cm H�CCoefficient of linear expansion 5.0 � 10�5 /�CTensile strength @20 �C 500 kg/cm2

Elongation (Min) 80 %Modulus of elasticity 1200-1500 MPaWater absorption <4 mg/cm2

Table 2bDetails of the additives used in the pure PVC (provided by supplier)

Ingredients Formulations (phr)

Poly(vinyl chloride) resin 100.0Tin stabilizer (heat stabilizer) 2.0Calcium stearate (internal lubricant) 0.5Stearic acid (external lubricant) 0.6Titanium oxide (pigment) 4.0

Table 3Blend of formulation of BPS/UPVC composite

Constituent Weight for each blending process (g)

UPVC C1 C2 C3 C4

UPVC 44.0 39.6 35.2 30.8 26.4BPS filler – 4.4 8.8 13.2 17.6

Table 4Blend of formulation of BPS/UPVC composite

Constituent Weight for each blending process (g)

UPVC CA1 CA2 CA3 CA4

UPVC 44.0 36.9 32.8 28.7 24.6BPS filler – 4.1 8.2 12.3 16.4Acrylic FM50 – 2.95 2.63 2.30 2.00

Table 1Properties of BPS filler [4]

Property Value

Density (g/cm3) 1.35Elongation at break (%) 5–6Cellulose content (%) 63–64Lignin content (%) 5Tensile strength (MPa) 550 ± 6.7Young’s modulus (GPa) 20Diameter (lm) 120 ± 5.8Microfibrillar angle (�) 11Lumen size (lm) 5

0

20

40

60

80

100

0 100 200 300 4

Temper

Wei

gh

t lo

ss(%

)

Fig. 1a. TG curves for

558 E.S. Zainudin et al. / Materials and Design 30 (2009) 557–562

blending process for the incorporation of BPS filler was calculatedbased on the maximum capacity of high speed mixer. The blendingwas done as the full capacity of this machine was 44 g for eachblending process. Table 3 shows the blend formulation of BPS/UPVC composite for the incorporation of BPS filler. BPS/UPVC com-posites were denoted by the symbols C1, C2, C3 and C4 (see Table3), while the addition of acrylic FM50 (also supplied by PolymerResources Sdn. Bhd., Selangor, Malaysia) were denoted by CA1,CA2, CA3 and CA4 (see Table 4). In these notations, C representsBPS filler and UPVC composite, CA represents BPS/UPVC compositewith the addition of acrylic FM50 and the digit denotes the weightpercentage of filler.

2.3. Incorporation of BPS filler with acrylic FM50

The acrylic FM50, which consists of poly (methyl methacry-lates) (PMMA) was also used to blend UPVC. Table 4 shows theblend of formulation with the addition of acrylic FM50.

2.4. Sample fabrication of BPS/UPVC composite for TGA

For measuring thermal degradation in the thermogravimetricanalysis, the BPS filler and UPVC composite samples did not requireany specific dimension. In most cases, the typical sample weightfor TG analysis was 2–50 mg. After the blending process, the com-posite was cut into smaller pieces for each type of compositeformulation.

2.5. Thermogravimetric analysis (TGA)

The weights of BPS/UPVC composite samples were in the rangeof 13–57 mg and they were scanned from 30 to 800 �C, at a heatingrate of 10 �C/min. In TGA, the crucible was called aluminum samplepan and it was used to place the sample for each formulation. The

00 500 600 700 800

ature (°C)

BPS filler

UPVC

acrylic

pure component.

-13

-11

-9

-7

-5

-3

-1

1

0 100 200 300 400 500 600 700 800

Der

ivat

ive

wei

gh

t (%

/min

)

BPS filler

UPVC

acrylic

Temperature °C

Fig. 1b. DTG curves for pure component.

Table 5Degradation temperature of pure individual component obtained from TG and DTGcurves

Pure component Temperature (�C)

T5% Peak 1 Peak 2 Peak 3

UPVC matrix 246.81 267.987 434.93 NoneBPS filler 55.97 58.34 266.65 462.39Acrylic FM50 265.96 372.55 None None

E.S. Zainudin et al. / Materials and Design 30 (2009) 557–562 559

purge gas used was nitrogen at a flow rate of 20 ml/min. Each sam-ple result was recorded after running the process for 3 h. The re-sults were obtained in a graphical form; TG and DTG curves. Forthe TG curve, the 5% onset of degradation was performed at a pointwhere the major weight loss was determined while for the DTGcurve, the maximum rate of weight loss of the sample was deter-mined. The TG and DTG curves were generated automatically afterthe heating commenced.

0

20

40

60

80

100

0 100 200 300 40

Wei

gh

t (%

)

Temperatu

Fig. 2a. TG curves of unmodifi

3. Results and discussion

3.1. Thermal analysis of composites

Thermogravimetric analysis (TGA) and derivative thermogravi-metric (DTG) analysis curves of UPVC are shown in Fig. 1a and band the data are simplified in Table 5. The characteristics of theTG curve for the first basic degradation step were obtained byapplying the Perkin–Elmer Standard Program: onset temperatureof a 5% weight loss deviation from the baseline (T5%). Peak temper-ature from DTG shows the maximum rate of weight loss.

For UPVC compound resin, the first stage degradation is asshown in Fig. 1b occurred in the temperature in the range of213–362 �C at a peak at 268 �C while the second stage occurredat the range of 361–536 �C at a peak at 435 �C. It has been sug-gested by Semsarzadeh et al. [9] that the first stage correspondedto the dehydrochlorination of the polymer with the succeeding for-mation of conjugated double bonds. This was considered to be themain reaction and hydrogen chloride (HCl) was assumed to be the

0 500 600 700 800

C1

C2

C3

C4

re °C

ed BPS/UPVC composites.

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

0 100 200 300 400 500 600 700 800

deriv

ativ

e we

ight

(%/m

in)

C1C2C3C4

TemperatureoC

Fig. 2b. DTG curves of unmodified BPS/UPVC composites.

Table 6Degradation temperatures of BPS/UPVC composites obtained from TG and DTG curves

Temperature (�C)

T5% Peak 1 Peak 2 Peak 3

UPVC 246.81 267.97 434.93 NoneC1 236.17 279.15 431.06 711.38C2 223.40 271.92 432.87 702.34C3 210.64 261.27 435.46 701.23C4 208.51 256.13 435.43 673.39

Table 7Degradation temperature of BPS–UPVC–Acrylic FM50 composites

Temperature (�C)

T5% Peak 1 Peak 2 Peak 3

UPVC 246.81 267.97 434.93 NoneAcrylic FM50 265.96 372.55 None NoneCA1 238.30 293.33 437.27 NoneCA2 229.79 285.60 436.34 NoneCA3 217.02 268.60 441.57 NoneCA4 208.51 265.04 439.79 None

0

20

40

60

80

100

0 200 40

Wei

gh

t (%

)

Tempe

Fig. 3a. TG curves of acrylic mod

560 E.S. Zainudin et al. / Materials and Design 30 (2009) 557–562

main volatile product of degradation. The second stage was re-ported to correspond to the separation of polyene structure se-quences formed during the first stage that contributed to themeasured weight loss of the UPVC resin. At the end of degradation,a black char (carbonaceous residue) was obtained.

In the current study, it was found that after the final thermaldegradation, black carbonaceous residues were present, and thesame observation was reported by Abu Bakar et al. [5]. Thermaldegradation of natural fiber mostly attributed from the decomposi-tion of hemicelluloses, lignin and cellulose [5]. Rowell [10] also re-ported that hemicellulose and cellulose degraded by heat muchbefore the lignin. In this study, the degradation of BPS filler curvesis shown in Fig. 1a and b where, at the onset temperature T5% of56 �C of BPS filler is the lowest compared to other components.Based on the DTG curve (Fig. 1b) of BPS filler, there was a minorpeak in temperature range between 35 and 116 �C. At this temper-ature, BPS filler was heated and thus the moisture content of theBPS fillers evaporated as vapours due to the heating process. Themore intense peak of DTG implied that the maximum rate of weightloss of BPS filler occurred at 267 �C (Fig. 1b). Meanwhile, for the TGcurve, the second step of weight loss related to the individual com-ponent was 45.5 wt% within the temperature range of 164–308 �C.

0 600 800

CA1

CA2CA3

CA4

rature °C

ified BPS/UPVC composites.

CA1

-8

-7

-6

-5

-4

-3

-2

-1

0

0 100 200 300 400 500 600 700 800

Wei

gh

t (%

/min

)CA1

CA2

CA3

CA4

Temperature °C

Fig. 3b. DTG curves of acrylic modified BPS/UPVC composites.

Fig. 4a. SEM photomicrograph of the impact fracture of acrylic modified BPS/UPVCcomposite [�100].

Fig. 4b. SEM photomicrograph of the impact fracture of unmodified BPS/UPVCcomposite [�100].

E.S. Zainudin et al. / Materials and Design 30 (2009) 557–562 561

The TG curve in Fig. 1a for pure acrylic FM50 which consists ofpolymethyl methacrylates (PMMA) revealed that the only onestage of degradation was observed in the temperature range of205–477 �C with a peak at 373 �C and weight loss of 96.8 wt%.However, Abu Bakar et al. [5] stated that the degradation temper-ature of PMMA was in the range of 250–380 �C with a peak of420 �C and weight loss of 97 wt%.

The TG and DTG curves of BPS/UPVC composites (C1–C4) in Fig.2a and b shows that the volatilization of moisture correlation dueto the loss of water in BPS filler still occurred in temperature rangeof 35–195 �C for all filler formulations even after the BPS filler wasincorporated into the UPVC matrix. However, due to the dryingprocess, which occurred before the degradation commenced, it af-fected the whole initial degradation process because the wholecomposites varied with the addition of filler. Table 6 shows thechange of thermal stability, and this phenomenon occurred be-cause BPS filler has weak thermal stability compared with UPVCmatrix. The addition of more filler in the onset temperature, T5%

caused the thermal stability of BPS/UPVC to decrease.Three stages of degradation process have been determined in

this study. The thermal stability of BPS/UPVC composite decreasedwith the increase of filler loading. It is because the thermal stabilityof BPS filler is much lower than the thermal stability of neat UPVCmatrix. The first two peaks (first and second) for all DTG curves(Fig. 2b) in the temperature range of 135–341 �C, with the peakrange of 256–279 �C and 343–530 �C with peak range of 431–436 �C correspond to the decomposition behaviour of the UPVCmatrix. It is also evident that the incorporation of BPS filler didnot affect the decomposition behaviour of the UPVC matrix. Thereason for the significant different of the decrease of the first andsecond peak ranging at the temperatures of 256–279 �C and 431–436 �C may be due to different cellulose constituents in types ofthe BPS filler as well as additives used in the fabrication of UPVC.

3.2. Thermal analysis of composites with acrylic FM50

Table 7 shows the values of degradation temperature for theBPS/UPVC composite with acrylic FM50 (see also Fig. 3a and b).From this study, it was found that with the addition of acrylicFM50, the thermal stability of BPS/UPVC composites is higher thanBPS/UPVC without acrylic (as compared to Table 6). The thermalstability of modified BPS/UPVC composites was found to be higherthan that of untreated fiber composite and can be explained based

562 E.S. Zainudin et al. / Materials and Design 30 (2009) 557–562

on the better thermal stability of treated fibers and improved fi-ber–matrix interactions in treated fiber composites. Fig. 4a and bshows the micrographs of acrylic modified and unmodified BPS/UPVC composite respectively where the modified composite showsbetter interfacial bonding between the fiber and matrix.

4. Conclusions

The thermal stability of modified and unmodified BPS/UPVCcomposites has been studied. The results showed that the BPS fillerdegraded before UPVC matrix and the BPS/UPVC composites aremore stable than both components. However as the amount ofBPS filler is increased, the decreases in the thermal stability ofBPS/UPVC composites took place. In the case of BPS filler thedecomposition starts from 58 �C. For neat UPVC, decomposition be-gins at 268 �C. In the case of 10% BPS/UPVC composite, the degra-dation begins at the temperature of 279 �C. As the amount of BPSfiller is increased up to 40%, the decomposition temperature de-creases down to 256 �C. The thermal stability of acrylic modifiedBPS/UPVC composites was found to be higher than that of unmod-ified BPS/UPVC composites.

Acknowledgement

The author wishes to thank Universiti Putra Malaysia for thefinancial support to conduct the research.

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