Studies on Biodegradability and Mechanical Properties of

International Journal of Scientific & Engineering Research Volume 3, Issue 8, August-2012 1 ISSN 2229-5518

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Studies on Biodegradability and Mechanical Properties of High Density

Polyethylene/Corncob Flour Based Composites

Obasi, Henry .C.

Department of Polymer and Textile Engineering, Federal University of Technology, Owerri, P.M.B. 1526,

Imo State, Nigeria.

Corresponding author: Obasi, H.C., [email protected]; Tel: +2348039478014

Abstract

In this study, corncob flour obtained from a waste product of corn threshing processing was blended with high

density polyethylene via melt extrusion to produce HDPE/Corncob biodegradable composites. Plastics

composites filled with corncob flour are materials that offer a credible alternative for using this botanical

resource considering the production of low dense materials with some specific properties. The composite

sample showed a decrease in tensile strength and elongation at break and an increase in Young’s Modulus as

the filler content increases. PE graft- maleic anhydride (PE-g-MA) was added as a coupling agent. The

presence of PE-g-MA gave rise to better properties for modified corncob flour composite (HDPE/CCF1) than

the unmodified corncob flour composite (HDPE/CCF) indicating better dispersion and homogeneity of corncob

flour to the PE-g-MA matrix. High water absorption resistance and low biodegradation rate of HDPE/ CCF1 as

compared with HDPE/CCF showed the effect of coupling agent on the composite. However, water absorption

and weight loss of composites buried in soil indicated that both were biodegradable, even at high levels of

corncob flour substitution.

Keywords: Corncob flour, HDPE, PE-g-MA, Mechanical properties, Biodegradability.

1. INTRODUCTION

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Synthetic polymeric materials have been

extensively used globally due to their

excellent chemical, physical and mechanical

properties. These properties on the other

hand have made them very resistant to

microorganisms and other natural

degradation forces, so they remain in the

environment after disposal. This had led to

environmental problems and also in addition

to the land shortage problems for solid waste

management [1]. Almost everywhere, plastic

waste can be seen thereby creating increased

costs on the collection and disposal of solid

municipal wastes.

Recycling is seen as an attractive and

alternative approach to solve this waste

problem. However, not all plastics are

recyclable and most end up in municipal

burial sites. The production and use of

biodegradable polymers are considered as

possible route to produce the dependence on

landfills in solving solid waste problems.

Many attempts have been made on the

compounding of petroleum based polymers

with natural biopolymers such as cellulose,

starch, lignin, chitin and chitosan to produce

new products with improved properties and

as a way to accelerate polymer

biodegradation [2], [3], [4], [5], [6], [7].

These natural biopolymers are abundant,

cheap, renewable and completely

biodegradable. Using natural biopolymers as

fillers to reinforce the composite materials

offers the following benefits when compared

with mineral fillers [8], [9]: light weight,

strong and rigid, environmentally friendly,

economical, renewable and abundant

resource. On the contrary, the demerits of

the materials are [10]: degradation by

moisture, poor surface adhesion to

hydrophobic polymers, non-uniform filler

sizes, not suitable for high temperature

application and its susceptibility to fungal

and insect attack.

Biocomposites consist of a polymer

(degradable or non-degradable) which is a

matrix polymer and cellulose material which

act as the reinforcing filler. However, blends

of biopolymer and polymer in addition to

being susceptible to water absorption exhibit

inferior mechanical properties because the

hydrophilic character of the biopolymer

leads to poor adhesion with the hydrophobic

polymer.

There have been many studies on the use of

biofillers as reinforcers in biodegradable

polymer biocomposite systems. These

reinforcing materials can be naturally

degraded by microorganisms and play a

major role in degrading natural organic

substances in the ecosystem [11], [12]. We

have studied the application of corncob flour

(CCF) as reinforcing filler in the

biocomposites. Corncob flour (CCF) is an

abundant waste product obtained from the

woody core of a maize ear that has limited

industrial applications. The use of CCF as

reinforcing material for biocomposite can

represent the conversion to industrially

useful biomass energy [13].

The purpose of this study was to produce

composites of high density polyethylene

(HDPE) and corncob flour (CCF). However,

properties of HDPE become significantly

worse when blended with biofiller due to the

poor compatibility between the two phases.

This condition requires a compatibilizer

and/or a coupling agent to enhance the


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compatibility between the two immiscible

phases and to improve the mechanical

properties of the composites. In this present

study, the incorporation of additive in the

corncob based HDPE composites has been

considered as a means of improving the

mechanical properties and biodegradability

of plastic materials made from these blends.

In this regard, the effect of filler loading and

maleic anhydride as a coupling agent on the

mechanical properties and biodegradability

of corncob filler/HDPE blend has been

investigated.

2. EXPERIMENTAL

2.1 Materials

The high density polyethylene (HDPE)

matrix used in this study was supplied by

Ceeplast Industry Ltd, Aba, Nigeria. It is a

product of Indorama Group, a subsidiary of

Eleme Petrochemical Company Ltd Nigeria

with a density of 0.965g/cm3 and a melt

flow index (MFI) of 16g/10 min.

Polyethylene graft maleic anhydride (PE-g-

MA) was obtained from Sigma-Aldrich

chemical corporation. The bio-flour used as

the reinforcing filler was corncob flour

(CCF) was obtained from Agro-produce

market, Aba as woody core of maize ear and

then processed to obtain corncob flour. The

CCF mesh size used was 300mm.

2.2 Sample Preparation

The CCF was melt-blended with HDPE in

an extruder. The filler was first oven dried

as 90˚C for 24 h to adjust its moisture

content and then stored in a polyethylene. A

laboratory size extruder Haake Rheomex

CTW 100p was used for compounding

corncob flour and high density PE. The

screw speed was 50 rpm and the temperature

range varied from 150 to 170˚C. CCF

loadings were from 40, 45, 50, 55 and 60 wt.

(%). PE-g-MA was used at an amount of 2

wt (%) based on the weight of filler. The hot

press process involved preheating at 170˚C

for 10 min followed by compression at the

same temperature for 4minutes. After this,

the sample was allowed to cool down at

ambient temperature and the samples were

carefully removed from the moulds.

2.3 Mechanical Testing

Tensile tests were carried out using a

universal Instron tensile tester 3366

according to ASTM D 638 with the samples

obtained as described. Tensile properties

were measured at room temperature at

5mm/min crosshead speed to obtain the

tensile strength, elongation at break and

Young’s modulus.

2.4 Water Absorption Study

The water absorption tests were conducted

for the various sample specimens. Each

sample was weighed prior to immersion in

distilled water. Weight gains were recorded

by periodic removal of the specimens from

the water. Moisture on the surface of the

sample was removed with filter paper, re-

weighed and the percentage water

absorption calculated. Results were recorded

every 1 week for 9 weeks. The percentage

water absorption was calculated according

to the equation:


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Where, W0 and W1 are the weights of dried

sample and the sample after exposure to

water absorption respectively.

2.5 Soil Burial Test

Biodegradation of the samples was studied

by the soil burial test method. Blend samples

with 3.0 x 3.0 x 1.5 mm dimensions were

dried and weighed to obtain a dry weight.

These samples were then buried in the test

soil at depth of 15 cm from the surface for 9

weeks. After 1-week, the samples were

carefully washed with water and dried to

obtain a new weight. The percentage weight

loss was calculated using the equation:

Where, W2 and W3 are the weights of dried

sample before and after burial in the soil.

3. RESULTS AND DISCUSSION:

3.1 Mechanical Tests

Mechanical properties are great significance

for all bio-filled polymer composites

applications. Figs 1-3 show the effect of

filler loading on tensile strength, elongation

at break and Young’s modulus for

HDPE/CCF1 and HDPE/CCF composites.

We observed that the tensile strength for

HDPE/CCF decreased continuously with

increasing filler loading (Fig. 1). It was thus

clear that the mechanical incompatibility of

the two phases was great and would increase

with the filler content. This behavior has

been described in similar studies and has

been explained by the increase of the

interfacial area with filler loading [14], [15].

Though lower tensile strength at break was

observed for HDPE/CCF1 composites

compared with neat HDPE, this decrease

was smaller than that of the HDPE/CCF

composites. The absolute value of tensile

strength for all compatibilized HDPE/CCF1

composites was higher than that of

uncompatibilized HDPE/CCF composites.

This behaviour could be attributed to the

reaction of the hydrophilic –OH groups from

the filler and the acid anhydride groups from

PE-g-MA, thus forming ester linkage, as

established in the literature works [16]. The

reaction fosters strong adhesion between

filler and matrix interface creating thus a

better stress transfer from the matrix to the

filler leading to higher tensile strength [17].

Simple adhesion of the polymer to the filler

through weak bonding or induction

interactions is experienced in the absence of

chemical modification.

Incorporation of the filler resulted in a

decrease in elongation at break. Fig. 2 shows

the effect of filler loading on the elongation

at break of HDPE/CCF1 and HDPE/CCF

composites. We observed that the elongation

at break for the composites decreases with

increasing filler loading. The reduction of

the elongation at break with the increasing

filler loading indicates the inability of the

filler to support the stress transfer from

polymer matrix to filler. It can be seen that

the elongation at break for HDPE/CCF1 is

lower than for HDPE/CCF. These

observations were in agreement with the

results presented by researchers [18], [19].

However, the effect of the compatibilizer

was not evident on this property.


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Results obtained from Young’s modulus

determination indicated that increasing filler

loading showed a tendency to increase the

composite stiffness for HDPE/CCF1 and

HDPE/CCF composites (Fig.3).

The increase in modulus was observed

because as starch content is increased, filler-

filler interaction becomes more pronounced

than filler-matrix interaction. Again, the

increased modulus corresponds to more

filler where its intrinsic properties as a

request agent exhibit high stiffness

compared to polymeric material [20]. This is

in agreement with the result reported by

Ardhyananta et al [21]. Some researchers

have also related the increase in composites

rigidity with the reduction in polymer chains

mobility in the presence of the filler [22].

The Young’s modulus for HDPE/CCF1 with

the addition of compatibilizer showed a

higher modulus than the uncompatibilized

HDPE/CCF. This result might be due to the

compatibilizing effect of the PE-g-MA in

the composites which enhanced high

interfacial interaction between the fillers and

PE matrix in which the fillers strengthen the

composite materials.

3.2 Water Absorption

The effects of corncob flour on water

absorption of the blends for the

compatibilized HDPE/CCF1 and

uncompatibilized HDPE/CCF composites

after immersion in water for 1-week interval

of time for 9 weeks are shown in figs. 4 and

5. From the figures, water absorption for

both compatibilized and uncompatibilized

composites increased with the increase in

corncob loading. This is due to the

hydrophilic nature of the corncob flour by

virtue of the presence of an abundant

hydroxyl groups which are available for

interaction with molecules. Again, as the

filler loading increases, agglomerate

formation increases thus creating difficulties

in achieving a homogenous dispersion of

filler in the composite. This results in water

molecules penetration into the composites

through voids created by agglomeration

which increases water absorption of the

composites [23], [24].

The figures showed lower percentage of

water absorption by HDPE/CCF1 as

compared to the HDPE/CCF composites.

The compatibilized HDPE/CCF1 composite

has better adhesion between the matrix and

the filler, reducing the formation of

agglomerates. Thus modification of the

corncob flour led to the decrease in the

number of free hydroxyl groups on the

surface, reducing the percentage of water

absorption.

3.3 Soil Burial Test

The biodegradability of corncob flour

blended with HDPE was estimated using

soil burial test method. Figs. 6 and 7 show

changes in weight ratio (initial

sample/buried sample) with time for the

HDPE/CCF1 and HDPE/CCF buried in the

soil. In the soil, water diffuses into the

composite sample, causing swelling and

enhancing biodegradation. The weight loss

of the sample after burial in the soil for 9

weeks was determined. The weight was

observed at each time point over the period

of study was larger with increasing starch

content in the composite. This means that

percent weight loss of both compatibilized


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and uncompatibilized composite increases

continuously with increase in the number of

weeks indicating that the samples

continuously degrade with increase in the

length of time and suggested that

microorganisms consume starch and create

pores in the PE matrix. However,

HDPE/CCF1 had a lower weight loss ratio

than the HDPE/CCF. The higher

biodegradation of HDPE/CCF may be

caused by the same factors leading to its

higher water absorption and lower

mechanical properties.

4. CONCLUSION

Woody core of a maize ear was milled, dried

and used as filler in HDPE composite. It was

observed that it is plausible to use this waste

product of the maize grain cob as low cost

filler, in view of the properties obtained

from the products. The composites stiffness

was seen to increase with increasing filler

loading. Though tensile strength decreased

slightly, they were improved in the presence

of the coupling agent PE-g-MA due to the

formation of an ester linkage not present in

HDPE/CCF. This account for the differences

in properties and behaviour showed by the

two composite materials.

Both HDPE/CCF1 and HDPE/CCF

demonstrated increase in water absorption

and weight loss with increase in starch

content. High water resistance and low

biodegradation loss rate of HDPE/CCF1,

however, were observed when compared

with HDPE/CCF composites.

ACKNOWLEDGMENT: The research

received no specific grant from any funding

agency in the public, commercial or not-for-

profit sectors

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FIGURES

Fig 1: Effect of filler loading on the tensile strength of CCF-filled HDPE composites

Fig 2: Effect of filler loading on the elongation at break of CCF-filled HDPE composites

0

2

4

6

8

10

12

14

16

18

0 40 45 50 55 60

Ten

sile

Str

en

gth

(MP

a)

Filler loading (% wt)

HDPE

HDPE/CCF1

HDPE/CCF

0

2

4

6

8

10

12

14

16

0 40 45 50 55 60

Elo

nga

tio

n a

t b

reak

(%

)


HDPE

HDPE/CCF1

HDPE/CCF


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Fig 3: Effect of filler loading on the Young’s modulus of CCF-filled HDPE composites

Fig 4: Water absorption versus time of HDPE/CCF1 at different filler loadings

110

115

120

125

130

135

140

145

150

155

0 40 45 50 55 60

Yo

un

g's

Mo

du

lus

(MP

a)


HDPE

HDPE/CCF1

HDPE/CCF

0

2

4

6

8

10

12

14

16

1 2 3 4 5 6 7 8 9

Wat

er a

bso

rpti

on

(%)

Time (Weeks)

HDPE

HDPE/40 CCF1

HDPE/45 CCF1

HDPE/50 CCF1

HDPE/55 CCF1

HDPE/60 CCF1


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Fig 5: Water absorption versus time of HDPE/CCF at different filler loadings

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9

Wat

er

abso

rpti

on

(%)

Time (Weeks)

HDPE

HDPE/40 CCF

HDPE/45 CCF

HDPE/50 CCF

HDPE/55 CCF

HDPE/60 CCF


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Fig 6: Weight loss versus time of HDPE/CCF1 at different filler loadings

0

2

4

6

8

10

12

14

16

18

20

1 2 3 4 5 6 7 8 9

Wei

ght

Loss

(%)

Time (Weeks)

HDPE

HDPE/40 CCF1

HDPE/45 CCF1

HDPE/50 CCF1

HDPE/55 CCF1

HDPE/60 CCF1


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Fig 7: Weight loss versus time of HDPE/CCF at different filler loadings

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9

Wei

ght

Loss

(%

)

Time (Weeks)

HDPE

HDPE/40 CCF

HDPE/45 CCF

HDPE/50 CCF

HDPE/55 CCF

HDPE/60 CCF

Studies on Biodegradability and Mechanical Properties of

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