Environmental weathering of (linear low-density polyethylene)/(soya powder) blends compatibilized with polyethylene-grafted maleic anhydride

Environmental Weathering of (Linear Low-DensityPolyethylene)/(Soya Powder) Blends Compatibilizedwith Polyethylene-Grafted Maleic Anhydride

Sam Sung Ting, Hanafi Ismail, Zulkifli AhmadSchool of Materials and Mineral Resources Engineering, Universiti Sains Malaysia,Nibong Tebal, Penang 14300, Malaysia

Blends containing various percentages of linear low-density polyethylene and soya powder were prepared.The effects of polyethylene-graft-(maleic anhydride)(PE-g-MA) as a compatibilizer and soya powder con-tent on the natural weathering were investigated.Blends without PE-g-MA were used as controls. Thesoya powder was varied from 5 to 40 wt% of theblends, and PE-g-MA was used at 50 wt% based onsoya powder content. The samples were exposed tonatural weathering in the northern part of Malaysia for1 year. Higher decreases in tensile strength and elon-gation at break of the controls were observed as com-pared to those of the PE-g-MA compatibilized blendsafter the natural weathering. The Young’s modulus ofboth controls and compatibilized blends increasedover the environmental exposure period. A controlsample lost 8.8% of its original weight after 1 year ofweathering, whereas a compatibilized blend lost 7.5wt% during the same period. J. VINYL ADDIT. TECHNOL.,18:57–64, 2012. ª 2012 Society of Plastics Engineers

INTRODUCTION

Research on biodegradable polymers has been very

active in recent years. The objective of the research was

to reduce the environmental pollution by solid waste dis-

posal. Invention of biopolymer is one of the important

developments in helping to solve the environmental prob-

lem. It has been utilized in surgical implants, sutures and

controlled-released drug [1]. However, it is difficult to

implement the use of biopolymer in packaging application

as the biopolymer is far more expensive compared to con-

ventional petroleum based polymer such as polyethylene

(PE), polypropylene (PP), polystyrene and poly(vinyl

chloride) (PVC).

One of the alternatives to produce degradable polymeris to incorporate degradable natural polymer into the non-degradable polymer. Starches are abundant, renewableand inexpensive natural polymers that are commonly usedin blends with conventional plastic such as PE and PP.Many publications on various starch filled polyolefin havebeen reported in the literature [2–5]. Soya powder is aremaining product after soy bean oil removal. From theliterature search, introduction of soya powder into thermo-plastic is a novel investigation. It is a biodegradable, inex-pensive and abundant protein based natural polymer [6].Nevertheless, the common polyolefin is immiscible withsoya powder due to their different polarity. Therefore,compatibilizer acts as a linkage between the petroleumbased polymers and protein based polymers. The compati-bilization effect on PE and several hydrophilic filler andpolymer blends has been proven in several investigations[6–9].

The degradation of a polymer can sometimes occur if

the main chain of the polymer consists of a hydrolyzable

group. The advantage of the incorporation of hydrophilic

natural polymer such as starch or soya powder into petro-

leum based polymer is to promote larger surface for the

degradation activities. When the blends of protein based

polymer and petroleum based polymer are exposed to the

environment, the microorganism only consumes the pro-

tein based natural polymer and leaving the petroleum

based polymer intact. However, the consumption of the

natural polymer forms pores on the surface of the blends.

The petroleum based polymer can be further degraded by

UV irradiation, thermal oxidation and thermo-oxidative

degradation [10, 11].

In the current study, soya powder was blended with

linear low-density polyethylene (LLDPE). Polyethylene-

grafted maleic anhydride (PE-g-MA) was used as a com-

patibilizer in the blends. The degradability of LLDPE/

soya powder blends was evaluated by exposing the sam-

ples to the environment of Penang, Malaysia for a period

of 1 year. The tensile properties, morphology, chemical

structure, and weight loss of the specimens were investi-

gated after the exposure.

Correspondence to: H. Ismail; e-mail: [email protected]

Contract grant sponsor: Research University Grant; contract grant num-

ber: 814008; contract grant sponsor: USM-RU-PRGS; contract grant

numbers: 8042039; contract grant sponsor: USM fellowship from Uni-

versiti Sains Malaysia.

DOI 10.1002/vnl.20292

Published online in Wiley Online Library (wileyonlinelibrary.com).

� 2012 Society of Plastics Engineers

JOURNAL OF VINYL & ADDITIVE TECHNOLOGY——2012

EXPERIMENTAL

Materials

The LLDPE (ETILINAS LL0209SA) was supplied by

Polyethylene Malaysia Sdn. Bhd. Soya powder with a

melt flow index of 1.0 g (10 min)21 was purchased from

Hasrat Bestari (M) Sdn Bhd. The moisture content was

3.12% and the average granular size was 12 lm. The pro-

tein content was 60%. PE-g-MA with appropriate 3 wt%

grafted level was supplied by Aldrich Chemical Com-

pany, Inc (Milwaukee, WI).

Blending of LLDPE/Soya Powder

LLDPE was blended with soya powder, varying soya

powder content between 5 and 40 wt%, using a Haake

Reodrive 5000 internal mixer maintaining the operating

temperature at around 1508C and rotor speed of 50 rpm.

The ratio of blends is shown in Table 1. The concentra-

tion of PE-g-MA was 50 wt% based on soya powder con-

tent. LLDPE/soya powder blends were compression

molded by using a hot press. The hot press temperature

was maintained at 1508C. Molded samples were cut into

dumbbell shapes according to ISO 527 before being

exposed to the environment.

Outdoor Weathering Test

Outdoor weathering tests were performed by exposing

dumbbell samples of LLDPE and soya powder blends to

sunlight. The tests were conducted in Universiti Sains

Malaysia (latitude 5880N, longitude 1008290E), for a pe-

riod of 1 year, from May 2008 to April 2009. The mete-

orology data such as average temperature, rainfall, and

relative humidity were obtained from the nearest meteor-

ology station in Butterworth (latitude 58280N, longitude

1008230E). Figures 1 and 2 show the data obtained from

the meteorology station, average of the data for each

month was taken. The test was carried out based on ISO

877.2. The dumbbell samples of the blends were arranged

on an exposure rack facing to the south and at an inclina-

tion angle of 458. After the exposure period, the samples

were subjected to further mechanical and analytical test.

The samples were washed with distilled water, dried and

weighed after drying to constant weight in an air-drying

oven, maintained at 708C.

ANALYTICAL METHODS

Tensile Properties

Five dumbbell-shaped samples were subjected to ten-

sile test after exposing to the environment. As a control,

the samples were also tested before the environmental ex-

posure. The tensile tests were carried out with an Instron

Universal Testing Machine (Model Instron 3366) with a

crosshead speed of 50 mm min21. Five samples were

tested and the average were taken. The parameters

obtained were tensile strength, elongation at break (Eb)

and Young’s modulus. The retention of these properties

was calculated as follow equation:

retention ð%Þ ¼ value after degradation

value before degradation3100%: (1)

Fourier Transform Infrared Analysis

A Fourier transform infrared (FTIR) spectrometer

(Perkin-Elmer Model Series 2) was used to obtain the IR

spectra. The equipment was operated with a resolution of

TABLE 1. Composition of LLDPE/soya powder blends.

Materials Formulation (wt%)

LLDPE 100% LLDPE

LLDPE/5 soya powder 95% LLDPE þ 5% soya powder






Similar series of LLDPE/soya powder blends were prepared with PE-

g-MA as compatibilizer. 50% of PE-g-MA based on soya powder con-

tent was used. FIG. 1. Variation of temperature during outdoor natural weathering

test.

FIG. 2. Variation of mean relative humidity and rainfall during outdoor

natural weathering test.

58 JOURNAL OF VINYL & ADDITIVE TECHNOLOGY——2012 DOI 10.1002/vnl

4 cm21 and a scanning range from 4000 to 400 cm21.

Thin sample sheets with a 1-mm thickness were tested by

the attenuated reflection method. Carbonyl index (CI) was

used as a parameter to observe the degree of degradation

of LLDPE/soya powder blends. CI was calculated accord-

ing to the baseline method i.e. the ratio of absorption

bands at 1720 and 2910 cm21.

Weight Loss

After the exposure to the natural weathering, the sam-

ples were rinsed thoroughly using distilled water and

dried to a constant weight in oven. The weight loss per-

centage was calculated as following equation.

% Weight loss ¼ Wi �Wf

Wi

3100: (2)

Wi and Wf are weight before weathering and weight after

weathering, respectively.

Morphological Study

Scanning electron microscopy (SEM) was performed

to examine the surface changes of the samples after deg-

radation tests. The surface of the sample was sputtered

with gold and analyzed with an electron microscope

(VPFESEM), Model SUPRA 35VP, by applying a voltage

of 10 kV.

RESULTS AND DISCUSSION

Tensile Properties

As a control, the tensile strength of the blends without

the compatibilizer is shown in Fig. 3. Figure 4 shows the

tensile strength of LLDPE/soya powder blends compatibi-

lized with PE-g-MA after 3 months, 6 months and 1 year

natural weathering. The tensile strength of all the blends

decreased over the period of environmental exposure due

to the effect of polymer degradation. The reduction of the

tensile strength could be attributed to the chain scission

which results in the oxidation under UV exposure [12].

The samples exposure area, Malaysia, is near the latitude

of the equator, the temperatures are high year round

(Fig. 1). Therefore, the thermal oxidation also took place

in the degradation and resulted deterioration in the me-

chanical properties of the blends. For uncompatibilized

LLDPE/soya powder blends, the samples with 30 and 40

wt% soya powder are degraded and broken down to

smaller pieces after 1 year natural weathering. Therefore,

LLDPE/30 soya powder and LLDPE/40 soya powder

blends could not be subjected to tensile test after exposing

to environment for 1 year. Table 2 shows the comparison

of tensile properties retention between the compatibilized

and uncompatibilized blends. The retention of the tensile

strength decreased with an increase in soya powder con-

tent in LLDPE/soya powder blends. The reduction

was due to the rapid degradation of soya powder in the

blends compared to LLDPE. This is because soya powder

FIG. 3. Tensile strength and retention versus soya powder loading for

uncompatibilized blends after weathering.

TABLE 2. Retention of tensile properties for LLDPE/soya powder blends after 1 year weathering.

Sample

Retention of uncompatibilized blends (%) Retention compatibilized blends (%)

Tensile

strength

Elongation

at break

Young’s

modulus

Tensile

strength

Elongation

at break

Young’s

modulus

LLDPE 41.01 38.32 191.57 — — —

LLDPE/5 soya powder 37.94 13.29 229.64 38.75 18.34 129.27


LLDPE/40 soya powder Fragmented Fragmented Fragmented 23.00 6.12 138.35

FIG. 4. Tensile strength and retention versus soya powder loading for

compatibilized blends after weathering.

DOI 10.1002/vnl JOURNAL OF VINYL & ADDITIVE TECHNOLOGY——2012 59

is a natural polymer that consists of different types of

protein fraction [13]. Figure 5 show the tensile strength

comparison between uncompatibilized and compatibilized

blends after 1 year natural weathering. The tensile

strength of compatibilized blends was higher than uncom-

patibilized blends over different degradation period. This

might be due to the strong esterification reaction estab-

lished between hydroxyl group in soya powder and maleic

anhydride of PE-g-MA [14].

Variation in elongation at break (Eb) after 1 year

weathering of uncompatibilized and compatibilized

LLDPE/soya powder blends are shown in Figs. 6 and 7,

respectively. The plot shows that there is a decrease on

the addition of soya powder into the blends. Early study

[14] confirmed that the reduction was due to the incom-

patibility between LLDPE and soya powder. As can be

seen in Fig. 6, the value of Eb for the uncompatibilized

blends of LLDPE/30 soya powder and LLDPE/40 soya

powder cannot be measured due to the fragmentation. The

fragmentation was due to the degradation occurred in

soya powder phase in the blends. Figure 8 demonstrate

the comparison between uncompatibilized and compatibi-

lized blends after 1 year natural weathering exposure.

Again, the Eb for compatibilized blends are slightly

higher than uncompatibilized blends for the all the blends

ratio. The stronger interfacial adhesion in compatibilized

blends resulted in the blends become less susceptible to

thermal and photo degradation under sunlight. Morphol-

ogy of blends explains better the Eb of the samples of nat-

ural weathering. Figures 9a–9d and 10a–10d show the

surface morphology of the uncompatibilized LLDPE/soya

powder blends after 6 months and 1 year natural outdoor

weathering, respectively. The micrographs for every deg-

radation period indicated that the presence of soya powder

resulted in higher degradation rate in the blends. As can

be seen in Fig. 9a, the fungus only attached on the surface

of LLDPE whereas the surface LLDPE/soya powder was

occupied by fungus and micro pores was formed as

shown in Fig. 9b–9d. Therefore, the Eb retention for the

blends decreased with the increase of soya powder con-

tent in the blends. The degradation was pronounced for

the uncompatibilized blends after 1 year outdoor weather-

ing as shown in Fig. 10a–10d. A small crack was found

in LLDPE sample after 1 year natural weathering. This

indicates that the matrix was attacked by thermal and UV

degradation. As the content of the soya powder increased,

more fungus colonized on the surface of the samples and

larger pores was observed. Similar observation was also

FIG. 5. Comparison of tensile strength after 1 year natural weathering.

FIG. 6. Eb and retention versus soya powder loading for uncompatibi-

lized blends.

FIG. 7. Eb and retention versus soya powder loading for compatibilized

blends.

FIG. 8. Comparison of Eb after 1 year natural weathering.


found by previous investigation in thermoplastic/starch

system [15, 16]. Figure 11a–11d demonstrated the surface

degradation of the PE-g-MA compatibilized blends after 6

months natural weathering. As can be seen in Fig. 11a

and 11b, cracks can be found throughout the blends sur-

face, indicating the occurrence of photo and thermal deg-

radation. The increase in CI as discussed in following sec-

tion indicates the occurrence of the photo and thermal

degradation. However, biodegradation by fungus was

obviously shown in Fig. 11c. Higher soya powder content

caused more fungus colonized on the surface of the

blends. The appearance of the pores on the surface might

be due to the localized consumption by the organism. The

surface morphology of compatibilized blends after 1 year

FIG. 9. SEM micrographs (5003) of weathered surface for uncompatibilized blends with soya powder con-

tent a) 0 wt%, b) 5 wt%, c) 20 wt%, and d) 40 wt% after 6 months weathering.

FIG. 10. SEM micrographs (5003) of weathered surface for uncompatibilized blends with soya powder

content a) 0 wt%, b) 5 wt%, c) 20 wt%, and d) 40 wt% after 1 year weathering.


natural weathering is presented in Fig. 12a–12c. More

pronounced degradation effect can be seen on the surface

of the blends compared to 6 months weathering. More

fungus and larger cracks was observed after 1 year natural

weathering exposure.

Figures 13 and 14 demonstrate the Young’s modulus

of the samples over a period of 3 months, 6 months and 1

year natural weathering for uncompatibilized and compa-

tibilized blends, respectively. After weathering, both

uncompatibilized and compatibilized blends experienced

an increase in modulus value and retention. This was

attributed to the embrittlement effect of the samples over

the period of outdoor exposure. As comparison between

uncompatibilized and compatibilized blends, the Young’s

modulus 1 year natural weathering is presented in Fig. 15.

After weathering, the uncompatibilized blends have higher

Young’s modulus compared to the compatibilized blends

in high soya powder content (above 30 wt%). This is

attributed to the embrittlement effect of the uncompatibi-

lized blends was higher compatibilized blends as previ-

ously discussed.

Carbonyl Indices

The degraded samples were further analyzed by using

FTIR to verify the structural changes that occurred in the

samples as a result of natural weathering. The FTIR spec-

tra of the LLDPE/soya powder blends over different peri-

ods of degradation are shown in Fig. 16. The unweathered

blends that were used as controls showed an additional

peak at 1710 cm21 (carbonyl stretching vibration). The

spectra of the samples also generated a peak at 3395

cm21, corresponding to the hydroxyl group. Formation of

carbonyl groups after weathering confirms that photo-

degradation took place and that the chemical structure of

the polymers was changed. Figure 17 shows the spectra

for the compatibilized blends after natural weathering.

Carbonyl group and hydroxyl group were also generated

for the compatibilized blends. For neat LLDPE, the

change of FTIR is not significant. The representative

spectra were shown in our previous investigation [14].

The carbonyl indices for the blends with different soya

powder ratio are shown in Fig. 18. It was found that the

CI increased with increasing soya powder content. As dis-

FIG. 11. SEM micrographs (5003) of weathered surface for PE-g-MA

compatibilized blends with soya powder content a) 5 wt%, b) 20 wt%,

and c) 40 wt% after 6 months weathering.

FIG. 12. SEM micrographs (5003) of weathered surface for PE-g-MA

compatibilized blends with soya powder content a) 5 wt%, b) 20 wt%,

and c) 40 wt% after 1 year weathering.


cussed in previous section, the surface of the blends was

consumed by the microorganism and left the pores on the

surface. The consumption increases the soya powder con-

tent. The pores increased the surface area for photodegra-

dation. The CI for compatibilized blends was slightly

lower than uncompatibilized blends. This is due to the

formation of strong ester bond during blending which was

not susceptible to degradation in the compatibilized

blends.

Weight Loss

The percentage of weight loss for compatibilized and

uncompatibilized LLDPE/soya powder blends is shown in

Table 3. With increasing the soya powder content, the

FIG. 13. Young’s modulus and retention versus soya powder loading

for uncompatibilized blends.

FIG. 14. Young’s modulus and retention versus soya powder loading

for compatibilized blends.

FIG. 15. Comparison of Young’s modulus after 1 year natural weather-

ing.

FIG. 16. IR spectra of uncompatibilized blends over 1 year natural

weathering.

FIG. 17. IR spectra of compatibilized blends over 1 year natural weath-

ering.

FIG. 18. CI for the uncompatibilized and compatibilized blends over a

period of weathering for 1 year.


weight loss of the blends increased. The weight loss

might was due to the hydrolytic polymerization of the

protein to lower molecular weight material. The smaller

unit of the material, amino acid, was consumed by the

microorganism, finally resulting in overall weight loss of

the blends. A similar finding has been reported by Kim

et al. [17], in that the cellulosic materials in agro-flour

were degraded into a lower-molecular-weight compound,

which was the monomeric glucose unit. As can be seen in

Table 3, the compatibilized blends show lower weight

loss compared to uncompatibilized blends. Again, the bet-

ter interfacial adhesion of the compatibilized blends gave

better resistance to the microorganism and photodegrada-

tion. The weight losses for the uncompatibilized and com-

patibilized blends with 40% soya powder content were

8.8 and 7.5 wt%, respectively.

CONCLUSIONS

1. The retention of tensile strength and elongation at break

for compatibilized LLDPE/(soya powder) blends was

higher than for uncompatibilized blends over 1 year of

natural weathering.

2. The Young’s modulus for both uncompatibilized and

compatibilized blends increased because of the embrittle-

ment effect after 1 year of degradation.

3. The surface of both uncompatibilized and compatibilized

blends was colonized by fungus during the weathering test.

4. The CI for the blends increased after outdoor weathering

exposure. Uncompatibilized blends showed a higher CI

compared to that of compatibilized blends.

5. The weight loss after the degradation period for uncompa-

tibilized blends was higher than that for compatibilized

blends.

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TABLE 3. Weight loss of compatibilized and uncompatibilized LLDPE/soya powder blends.

Sample

Uncompatibilized blends Compatibilized blends

3 months 6 months 1 year 3 months 6 months 1 year

LLDPE 0.17 0.17 0.18 — — —








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Environmental weathering of (linear low-density polyethylene)/(soya powder) blends compatibilized with polyethylene-grafted maleic anhydride