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Effect of Cobalt Stearate on Natural Weathering of LLDPE/Soya PowderBlendsS. T. Sama; H. Ismaila; Z. Ahmada School of Materials and Mineral Resources Engineering, Pulau Pinang, Malaysia

Online publication date: 09 June 2011

To cite this Article Sam, S. T. , Ismail, H. and Ahmad, Z.(2011) 'Effect of Cobalt Stearate on Natural Weathering ofLLDPE/Soya Powder Blends', Polymer-Plastics Technology and Engineering, 50: 9, 957 — 968To link to this Article: DOI: 10.1080/03602559.2011.553863URL: http://dx.doi.org/10.1080/03602559.2011.553863

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Effect of Cobalt Stearate on Natural Weatheringof LLDPE/Soya Powder Blends

S. T. Sam, H. Ismail, and Z. AhmadSchool of Materials and Mineral Resources Engineering, Pulau Pinang, Malaysia

A protein-based natural polymer, soya powder, was melt blendedwith linear-low density polyethylene (LLDPE). Cobalt stearate(CS) was used as a pro-oxidant. The blends were exposed to naturalweathering for 6 months. The susceptibility of the LLDPE/soyapowder, based on its tensile properties, morphology, thermal behav-iour and chemical and physical changes was measured every threemonths. The tensile strength and elongation at break (Eb) of theblends with CS were more susceptible compared to the blends with-out CS. During weathering, the crystallinity and weight lossincreased with the addition of CS in the blends, however molecularweight was reduced.

Keywords Cobalt stearate; LLDPE; Molecular weight; Naturalweathering; Soya powder

INTRODUCTION

Disposal of plastic waste is a serious environmentalproblem. Polyolefin, such as polyethylene (PE), polypro-pylene (PP), polyvinyl chloride (PVC), polystyrene (PS)contribute much to solid waste. Polyethylene contributesaround 40% to the plastics used in packaging applications.PE is highly resistant to chemical degradation, weather andbiodegradation. Therefore, this kind of plastic accumulatesin the environment easily. The desire to produce a moreenvironmental friendly polymer has directed scientists toinvestigate alternatives. Much research on biopolymers,including PLA[1–4], PCL[5–9], PHB[10–12] and PVA[13–17],has been conducted in recent years. The properties of thebiopolymers have been proven to meet mechanical, thermaland rheological requirements. However, the cost of thesepolymers is still expensive compared to existing polyolefin.

One alternative that accelerates the biodegradation ofpolyethylene is the incorporation of biodegradable fillerinto the polymer[18]. Starches that have been applied innon-degradable matrices are corn starch[19–21], ricestarch[22–24], tapioca starch[25–28] and banana starch[18,29–30].The biodegradability of the non-degradable=starch blendshas been proven in studies. Besides the starch-based

biodegradable natural polymer, soya protein-basedpolymer is a potential natural polymer that can be blendedwith petroleum based polymers to accelerate its degradati-on. The composition of soya powder is mainly derivedfrom proteins or peptides and less so from carbohydrates.Soya protein-based polymers and blends show good mech-anical, thermal and physical properties in previousresearch. Swain et al. studied the spectral, mechanicaland thermal properties of cross-linked soya protein con-centrate[31]. Several studies also investigated the blends ofsoya protein polymer with poly (vinyl alcohol)[32] andpoly(e-caprolactone)[33].

Apart from incorporating natural polymer into non-degradable polymer, another approach to induce biodegra-dation of polyethylene is adding pro-oxidant into thepolyolefin[34]. Pro-oxidants are complexes of metal ionsthat can accelerate the oxidative process, consequentlyreducing the molecular weight of the polymer on the levelthat biodegradation takes place[34–35]. This phenomenon,in which the natural degradation of polyolefin is sped upfrom hundred years to few years by metal salt, is widelyknown as oxo-biodegradation.

In this work, an attempt was made to obtain a degrad-able polymer by blending a soya protein based product,soya powder, with oxo-biodegradable LLDPE. Cobalt stea-rate (CS), as a pro-oxidant, was added into LLDPE to pro-duce oxo-degradable polymer. There is not much researchon the incorporation of a pro-oxidant into polyolefin=soyapowder blends. Degradation was estimated by a naturalweathering test. The effects of the addition of CS and soyapowder content on the degradation behaviour of LLDPEwere observed through measurement of the tensile proper-ties, surface morphology, weight loss, Fourier transforminfrared (FTIR) spectroscopy and Differential ScanningCalorimetry (DSC) of the blends. The degradation mech-anism of each component in the blends was proposed.

EXPERIMENTAL

Materials

LLDPE (ETILINAS LL0209SA) was supplied byPolyethylene Malaysia Sdn. Bhd. The melt flow index

Address correspondence to H. Ismail, School of Materials andMineral Resources Engineering, 14300 Nibong Tebal, PulauPinang, Malaysia. E-mail: hanafi@eng.usm.my

Polymer-Plastics Technology and Engineering, 50: 957–968, 2011

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ISSN: 0360-2559 print=1525-6111 online

DOI: 10.1080/03602559.2011.553863

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was 0.90 g=10min, and the density was 0.921 g=cm3. Thenumber average molecular weight (Mn) and weight averagemolecular weight (Mw) of LLDPE are 27.7� 103 Da and97� 103 Da, respectively. Soya powder, with a melt flowindex of 1.0 g (10min)�1, was purchased from HasratBestari (M) Sdn Bhd. The average granular size was12 mm, and the protein content was 56%. CS was purchasedfrom Aldrich Chemical Company, Inc (Milwaukee, WI).

Sample Preparation

Melt blending was carried out in a Haake Reodrive 5000internal mixer. LLDPE was physically premixed with CSbefore putting it in the chamber. The premix was first put

in the chamber, slowly adding the soya powder. The oper-ating temperature of the internal mixer was maintained ataround 150�C with a rotor speed of 50 rpm. The blendratios are shown in Table 1. LLDPE=soya powder blendswere compression moulded using a hot press. The hot presstemperature was maintained at 150�C. Moulded sampleswere cut into dumb-bell shapes according to ISO 527before being exposed to the environment.

Natural Weathering

An outdoor weathering test was performed by exposingdumbbell samples of LLDPE=soya powder blends to sun-light. The test was conducted in Universiti Sains Malaysia,(latitude 5�80N, longitude 100�290E) for a period of oneyear, from August 2009 to January 2010. The meteorologi-cal data such as average temperature, rainfall, and relativehumidity were obtained from the nearest meteorology sta-tion in Butterworth (latitude 5�280N, longitude 100�230E).Figure 1 shows the data obtained from the meteorologystation, and the average of the data for each month wasused. The test was carried out based on ISO 877.2. Thedumbbell samples were arranged on an exposure rackfacing the south at an inclination angle of 45�. After theexposure period the samples were washed with distilledwater, dried drying to constant weight in an air-dryingoven at 70�C and weighed before subjecting to furthertesting.

ANALYTICAL METHOD

Tensile Properties

Tensile specimens (ASTM D638) were cut from eachsheet. Tensile tests were performed using an InstronUniversal Testing Machine (Instron 3366). Five samples ofeach composition were strained at a rate of 50mm min�1

TABLE 1Formulation of LLDPE=soya powder blends

Materials Formulation (wt %)

LLDPE 100% LLDPELLDPE=5 soyapowder

95% LLDPE þ 5% soyapowder

LLDPE=10 soyapowder

90% LLDPE þ 10% soyapowder

LLDPE=15 soyapowder

85% LLDPE þ 15% soyapowder

LLDPE=20 soyapowder

80% LLDPE þ 20% soyapowder

LLDPE=30 soyapowder

70% LLDPE þ 30% soyapowder

LLDPE=40 soyapowder

60% LLDPE þ 40% soyapowder

�0.2wt% of cobalt stearate was added into CS-added blendsduring mixing

FIG. 1. Outdoor temperature and rainfall during the 6 months weathering test.

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at room temperature, and average values of Eb, tensilestrength and modulus were determined. The retention ofthese properties was calculated with the Equation 1:

�retention ð%Þ ¼ Value after Degradation

Value before Degradation� 100%

�ð1Þ

Morphological Study

Scanning electron microscopy (SEM) was used to exam-ine the surface changes of the samples after the naturalweathering test. The surface of the sample was sputteredwith gold to prevent the accumulation of static electriccharge during scanning. After gold coating, the sampleswere analysed under an electron microscope (VPFESEM)model SUPRA 35VP with a voltage of 10 kV.

Fourier Transform Infrared (FTIR) Analysis

After natural weathering, the molecular change of theblends was investigated using an FTIR spectrometer(Perkin-Elmer model Series 2). The equipment was oper-ated at a 4 cm�1 resolution level in the scanning range from4000–400 cm�1. Thin sample sheets with 1-mm thicknesseswere tested according to the attenuated reflection method.The Carbonyl index (CI) was used as a parameter toobserve the degree of degradation of the LLDPE=soyapowder blends. CI was calculated according to the baselinemethod, i.e., the ratio of absorption bands at 1710 and2844 cm�1.

Differential Scanning Calorimetry

A Perkin-Elmer DSC 7 thermal analyser was used todetermine the thermal behaviour of the samples after theweathering test. The preparation and parameters of theDSC tests were based on ASTM D3418-03 under nitrogenatmosphere. Samples (5–10mg) were encapsulated in alu-minium pans and subjected to thermal cycles. The firstheating process removed the effect of previous heat historyin the samples. The samples were cooled to room tempera-ture at a constant cooling rate of 10�C=min to favour crys-tallisation. Then, the second heating was run at 10�C=minin the temperature range of 30-175�C. The heat of fusionwas calculated by integrating the areas under the endo-thermic curves. The percentage of crystallinity of theLLDPE phase was calculated using Equation 2:

�% crystallinity ¼

DH�f

DHof

� 100%

�ð2Þ

where DHof is the heat of fusion for 100% crystalline poly-

ethylene and DH�f is the heat of fusion for semicrystalline

LLDPE.

Weight Loss

After exposure to the natural weathering test, the sam-ples were rinsed thoroughly using distilled water and driedto a constant weight in an oven. The weight loss percentagewas calculated with the Equation 3:

�% Weight Loss ¼ ðWi �Wf Þ

Wi� 100

�ð3Þ

Gas Permeation Chromatography (GPC)

GPC analysis was performed at 140�C using an Agilent1200 GPC system connected to a Shodex K-806 andK-.802 column. Chloroform was used as the solvent, witha flow rate of 0.80mL=min. The system was calibrated usinga polystyrene standard with an average molecular weightranging from 1,000 to 5,000,000. The blends were dissolvedin chloroform at a temperature of 40�C for 1 week. Addi-tionally, 50 ml samples were filtered through a 0.45 mm poly-tetrafluoroethylene (PTFE) filter to remove contaminantsand solid particles. The number average molecular weightMn, weight average molecular weight Mw, and polydisper-sity index (PDI) of the samples were determined from GPC.

RESULTS AND DISCUSSION

Tensile Properties

Figure 2 shows the tensile strength of the LLDPE=soyapowder blends with and without CS after 3 months and 6months of exposure to natural weathering. A general trendcan be seen in the Figure 2, which shows that the tensilestrength of all the samples decreased after weathering.Qureshi et al.[36] proved that a change in mechanicalproperties is a good indicator of polymer degradation.The retention of tensile strength after the weathering testdecreased with increasing soya powder content. Thisreduction might be due to leaching of soya powder onthe surface and the biodegradation of soya powder in theblends. A study also indicated that, after weathering, thebiodegradable filler leached out due to the presence ofmoisture in the environment[37].

The tensile properties of CS added blends are only avail-able for 3 months outdoor exposure. It is because the sam-ple could not be subjected to a tensile test after 6 months ofweathering due to the sample fragmentation. The tensilestrength trend of the blends with CS was the same withthe blends without CS. However, the tensile strength ofthe blends with 20wt% soya powder dropped drasticallyafter 3 months of natural weathering. For blends with30wt% and 40wt%, the tensile test could not be performedbecause the weathered samples were highly degraded andtotally lost their mechanical properties. CS produced freeradicals with the presence of UV and heat. The surfacedegradation of the blends occurred when the free radicals

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reacted with oxygen and produced peroxides and hydro-peroxides[35]. It is interesting that, for every blend ratio,the tensile strength of the blends with CS after 3 monthswas lower than blends without CS even after 6 months ofweathering. This is because the LLDPE phase in the blendswith CS underwent oxo-biodegradation and formedhydroxyl and carbonyl groups. The formation of thesegroups is important for furthering the degradationprocess[38]. The presence of carbonyl groups was indicatedby FTIR, as discussed in the section below.

Figure 3 shows the Eb of the LLDPE=soya blends with-out CS after exposure to natural weathering. Eb exhibited

a similar trend in tensile strength (Figure 2). The retentionof the Eb after weathering decreased with increasing soyapowder content in the blends. This might be due to theleaching effect on the surface of the blends and fungus col-onisation after the weathering test. Figure 4(a)–(d) showmicrographs of the weathered samples without CS after 6months of exposure to Malaysian weather. Figure 4(a)shows the micrographs of weathered samples of pureLLDPE. Some fungus colonised on the surface of theLLDPE. However, no cracks or pores can be observed inthe micrograph. The cracks might be due to UV and heatfrom the environment. Consequently, deterioration of the

FIG. 2. Comparison of tensile strength for the blends with and without CS after weathering.

FIG. 3. Comparison of Eb for the blends with and without CS after weathering.

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polymer chain resulted in the reduction of Eb. Pores andfungal colonisation can be observed on the surface of theblends (Figure 4(b)–(c)) with soya powder.

The presence of pores might be due to the leaching ofsoya powder from the blends. In Figure 4(d), the micro-graph shows that the surface of the blends was fully occu-pied and consumed by fungus. Therefore, the retention inEb of the blends with 40wt% soya powder was the lowest.Table 2 demonstrates the Eb and its retention in the blendswith the presence of CS after 3 months of exposure tonatural weathering. The results clearly indicate the abiotic

oxidation effect of CS in pure LLDPE and LLDPE=soyapowder blends. The addition of CS in LLDPE=soyapowder blends significantly reduced the Eb after the weath-ering test. The micrographs in Figure 5(a)–(d) show thevariation of soya powder content in the blends after 3months of natural weathering. The amount of fungus col-onisation in the blends with CS was higher compared tothe blends without CS. Moreover, the size of the poreswas bigger for the CS added blends. These results suggestthat the addition of CS to the blends increased theirdegradation.

FIG. 4. (a)–(d) Morphological surface (500�) of blends without CS but with soya powder content of a) 0wt%; b) 5wt%; c) 20wt%; d) 40wt% after 6

months of outdoor exposure.

TABLE 2Retention of tensile properties for LLDPE=soya powder blends after different periods of natural weathering

Tensile strength (%) Elongation at break (%) Young’s Modulus (%)

Sample 3 months 6 months 3 months 6 months 3 months 6 months

LLDPE 75.6 49.9 73.3 49.2 178.1 184.0LLDPE=5% soya powder 74.9 45.8 71.3 38.2 203.5 208.2LLDPE=20% soya powder 54.0 43.4 49.9 24.1 212.4 216.7LLDPE=40% soya powder 47.0 28.1 38.2 15.1 200.9 207.5LLDPE=CS 48.5 fragmented 26.1 fragmented 202.4 fragmentedLLDPE=5% soya powder=CS 45.9 fragmented 22.6 fragmented 220.3 fragmentedLLDPE=20% soya powder=CS fragmented fragmented fragmented fragmented fragmented fragmentedLLDPE=40% soya powder=CS fragmented fragmented fragmented fragmented fragmented fragmented

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Figure 6 depicts the effect of natural weatheringexposure on the Young’s Modulus (with and without CS)of different soya powder content blends. Generally, theYoung’s modulus increased over a specific weatheringexposure period. This might be due to the effect of

photo-oxidation inducing peroxide radical crosslinkingand polymer chain scission during the weathering test,consequently causing embrittlement. There are some simi-lar results of the effect of weathering on Young’s modulusof polyolefins[39–41]. The Young’s modulus of the blends

FIG. 5. (a)–(d) Morphological surface (500�) of blends with CS and soya powder contents of a) 0wt%; b) 5wt%; c) 20wt%; d) 40wt% after 6 months

of outdoor exposure.

FIG. 6. Young’s modulus of tensile strength for the blends with and without CS after weathering.

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with CS was higher than the blends without CS. Therefore,CS is expected to play an important role in inducing oxi-dation into the polymer matrix, as will be discussed inthe next section.

FTIR Studies

FTIR spectra were used to investigate the structuralchanges that occurred after environmental degradation.Figure 7 compares the FTIR spectra of samples with andwithout the addition of CS after outdoor exposure. FromIR absorption spectra, the most important changes werein the carbonyl (1785–1700 cm�1) and hydroxyl (3400 cm�1)regions. The carbonyl band did not appear as a sharp peakbut as an overlap of various stretching vibration bandsincluding those of aldehydes and=or esters (1710–1725 cm�1) and carboxylic acid groups (1700 cm�1)[42].The mechanism of polyethylene degradation can be seenin Figure 8. CS, as a catalyst, underwent degradation whenexposed to light and heat, through the generation of freeradicals reacting with oxygen to produce peroxides andhydroperoxide[43]. LLDPE can be decomposed into smallermolecules by the functional groups of carbonyl and car-boxylic acids. According to Chiellini et al.[43], chain scissionand macromolecule oxidation are the predominant reac-tions in the presence of oxygen.

Figure 9 demonstrates the carbonyl index of theLLDPE=soya powder blends. As expected, the blends withCS show a higher carbonyl index, and this indicates thatCS was a good catalyst for degrading polyolefin. The car-bonyl index was found to increase with increasing soyapowder content. Thus, it was proven that the soya powderplayed an important role in quickening degradation, asdiscussed in previous section.

There is a strong broad peak at 1644 cm�1, which may bedue to the presence of an overlapping peak corresponding

to the C=C and amine group. The C=C bond was derivedfrom the abstraction of adjacent hydrogen on the hydro-carbon chain through a radical mechanism during degra-dation. The amine group may be due to the proteinderived from the soya powder. Degradation after 6 monthsin the presence of CS showed a shoulder peak in thisregion, implying that the overlapping of these groupsdecreased during the degradation process.

Differential Scanning Calorimetry

DSC thermograms of the melting and cooling of thesamples after weathering are shown in Figures 10 and 11,respectively. From the melting thermogram (Figure 10),the change in the melting temperature for the samples afternatural weathering was not significant. Nevertheless, thearea under the melting thermogram, which indicates thelevel of oxidation, had changed upon exposure. It is expec-ted that the amorphous region underwent degradation,whereas the crystalline region remained unaffected. There-fore, the sample that was subjected to the DSC test afternatural weathering contained a higher volume of crystal-line regions. Indeed, the increase of crystallinity was solelydue to the decrease of the amorphous region and not theformation of new crystalline regions.

The thermal analysis data obtained from DSC is sum-marised in Table 3. The crystallinity of the blends increasedwith increasing soya powder content. The DSC data of theblends before being exposed to natural weathering wasreported in our previous investigation[44]. The DSC dataof the blends showed no significant changes with theaddition of CS before the weathering test. During weather-ing, soya powder leached out easily with moisture and rain-fall. After leaching, the pores were left on the surface of theblends and a bigger surface area was created for the degra-dation process. The leaching effect was more obvious with

FIG. 7. Comparison of the IR spectra of blends with and without CS

after 6 months of natural weathering.

FIG. 8. Mechanism of polyethylene degradation with the addition of

CS[43].

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increasing soya powder content (as shown inFigures 4(b)–(d)and Figures 5(a)–(d)).

Therefore, degradation of the blends was more pro-nounced at higher soya powder content levels. On the otherhand, the crystallinity of the CS added blends was highercompared to blends without CS. This indicates that CS cat-alysed the oxidation reaction during natural weathering.Chain scission in the amorphous phase of PE resulted inincreased crystallinity. The increase in crystallinity afteroutdoor exposure also caused the blends to be brittle[42].This is in agreement with the increase in Young’s modulusafter natural weathering (Figure 6). The embrittlement wasdue to the occurrence of crack initiation from chain scis-sion that gave rise to sufficient chain mobility, producingsecondary crystallisation[42].

Gravimetric Analysis

The weight loss percentage of LLDPE=soya powderblends is shown in Figure 12. The percentage weight lossof the blends increased with increasing soya powder con-tent. A hydrolysis mechanism and leaching effect tookplace on the surface of the blends during weathering. Theweight loss in the soya powder phase might involve hydro-lytic depolymerisation of protein into a lower molecularweight substance and consequently could produce mono-meric amino acid. This smaller unit is more easily con-sumed by microorganisms. Figure 13 shows the proposedmechanism of hydrolytic depolymerisation of peptides insoya powder. Peptides were used to propose the mech-anism. The peptides (made up of mostly glutamine and

FIG. 9. Carbonyl index of the LLDPE=soya powder blends during the 6 month weathering test.

FIG. 10. DSC melting thermogram of LLDPE=soya powder blends after

6 months of outdoor exposure.

FIG. 11. DSC cooling thermogram of LLDPE=soya powder blends after

6 months of outdoor exposure.

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asparagine) underwent hydrolysis in the presence of rainwater during weathering. The peptides were then hydro-lysed into smaller units or amino acids. This is in agree-ment with the study by Kim et al.[45].

They found that depolymerisation of flour occurred inthe presence of moisture during a soil burial test. Besidesthat, the leaching of soya powder during outdoor exposurealso caused a reduction in weight. Higher soya powder con-tent in the blends contributed to a more serious leachingeffect. The addition of the CS also showed a higherreduction in weight loss compared to the blends withoutCS. During weathering, the sunlight and heat resulted inthermal oxidation of polyethylene. The long polymer chainof polyethylene underwent chain scission and was cut down

FIG. 12. Weight loss of LLDPE=soya powder blends after 6 months of natural weathering.

TABLE 3DSC results of LLDPE=soya powder blends after different periods of natural weathering

Tm (�C) Tc (�C) DHf

� Crystallinity (%)

Sample 3 months 6 months 3 months 6 months 3 months 6 months 3 months 6 months

LLDPE 126.3 125.9 104.1 105.0 60.1 63.5 21.8 23.0LLDPE=5% soya powder 125.7 125.6 105.2 105.9 77.9 95.2 28.2 34.5LLDPE=20% soya powder 123.9 124.3 105.9 106.8 102.4 108.7 37.1 39.4LLDPE=40% soya powder 123.3 123.4 106.5 107.5 110.1 115.6 39.9 41.9LLDPE=CS 126.4 126.2 104.9 105.9 62.5 66.8 22.6 24.2LLDPE=5% soya powder= CS 125.9 125.3 106.8 107.7 79.4 100.4 28.8 36.4LLDPE=20% soya powder= CS 123.9 123.6 107.4 109.2 106.3 115.5 38.5 41.8LLDPE=40% soya powder= CS 123.5 123.4 108.0 110.4 114.2 120.3 41.4 43.6

FIG. 13. Proposed mechanism of hydrolytic depolymerisation of

peptides in soya powder.

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to a lower molecular weight segment. This segment waseasily consumed by microorganisms or leached out fromthe surface of the blends. The reduction in the molecularweight is discussed in the following section.

Molecular Weight Changes

Gravimetric analysis was used to investigate the degra-dation of blends, whereas molecular weight analysis wasused to determine the effect LLDPE degradation. The mol-ecular weight data of LLDPE=soya powder blends, withand without the addition of CS as well as after 6 monthsof outdoor exposure, is shown in Table 4. The data inclu-des the number average molecular weight (Mn), weightaverage molecular weight (Mw) and polydispersity. Afterweathering, the Mn and Mw of the LLDPE=soya powderblends decreased due to chain scission. A similar trendwas also reported in montmorillonite filled oxo-biodegrad-able polyethylene[34]. Both Mn and Mw also decreased withincreasing soya powder content. The result agrees with thedegradation mechanism of LLDPE=soya powder blends aspreviously discussed.

The pores on the weathered surface resulted from aleaching effect and microorganism consumption of soyapowder, which created a larger surface area for thedegradation of the LLDPE matrix. Therefore, the averagemolecular weight was reduced more severely with increas-ing soya powder content. As presented in Table 4, theMw of pure LLDPE was 52.1� 103 Da after weathering.The reduction of the Mw of LLDPE was approximately53.7% compared to the control. Addition of soya powderinto the blends further reduced the Mw during weathering.It has been proven that the blends of soya powder withLLDPE can increase the degradability of LLDPE matrix.

The results in Table 4 indicate that the CS added blendscaused a higher Mw reduction after outdoor exposurebecause the chain scission of LLDPE was catalysed byCS and consequently formed segments with lower molecu-lar weight. A comparison of the polydispersity of LLDPE=soya powder blends is shown in Table 4. Polydispersity iscommonly used to describe the molecular weight distri-bution. After weathering, the polydispersity of the weath-

ered samples generally increased. These results indicatethat part of the high molecular weight polymer chain hadbeen fragmented to a lower molecular weight chain. Conse-quently, the MWD was broader after degradation. Thehigher value of polydispersity for CS added blends provesthat the molecular chains of LLDPE degraded into smallersegments compared to blends without CS.

CONCLUSIONS

Our results indicate that the tensile strength and the Ebof LLDPE=soya powder blends decreased after naturalweathering as a result of degradation. However, theYoung’s modulus increased. The addition of CS in theblends increased the degradability of the blends. A numberof pores and fungi were created on the surface of weatheredsamples, thus causing deterioration in the tensile strengthand Eb. The carbonyl indices for the CS added blends werealso higher than blends without CS. The weight loss of theblends increased with increasing soya powder content aswell as the addition of CS. Molecular weight changes indi-cated that LLDPE underwent chain scission after naturalweathering. The addition of CS in LLDPE greatly reducedthe molecular weight of LLDPE.

ACKNOWLEDGMENTS

The authors are thankful for the RU grant (1001=PBAHAN=814008) and USM-RU-PRGS grant fromUniversiti Sains Malaysia. S. T. Sam is also grateful forfinancial support from the USM fellowship.

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TABLE 4Molecular weight and polydispersity of LLDPE=soya powder blends after 6 months outdoor exposure

Blends without CS Blends with CS

Sample Mn (103) Mw(103)Polydispersity(Mn=Mw) Mn (103) Mw (103)

Polydispersity(Mn=Mw)

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