Tensile Properties and Water Absorption of Recycle Polypropylene (rPP) Oil Palm Empty Fruit Bunch (OPEFB) Composites: The Effect of Maleic Anhydrate-g-Polypropylene (MAPP) Addition

Green Building, Materials and Civil Engineering – Kao, Sung & Chen (Eds)
 2015 Taylor & Francis Group, London, ISBN 978-1-138-02669-8

Tensile properties and water absorption of recycle polypropylene (rPP) / oil palm empty fruit
bunch (OPEFB) composites: the effect of maleic anhydrate-g-polypropylene (MAPP)
addition
Halimatuddahliana Nasution
Department of Chemical Engineering, Faculty of Engineering, Universitas Sumatera Utara,Medan, Indonesia
h_dahliana@yahoo.com
ABSTRACT: The effects of maleic anhydrate (MAPP) as compatibilizer on tensile properties and water absorption of
recycle polypropylene (rPP)/oil palm empty bunch fruit (OPEFB) composites were investigated. Several contents of
MAPP viz. 2, 4, 6, 8 wt.% were prepared. Corresponding rPP/OPEFB composite without MAPP addition was also
made for comparison.The OPEFB composition was fixed at 30 wt.%, while rPP was 70 wt.% and reduced
correspondingly on the addition of MAPP. Composites were prepared in extruder with temperatur of 190oC. Results
indicated an improvement in tensile strength and elongation at break were obtained on the addition of MAPP up to 6
wt.%. It was also revealed that the water absorption was significantly decreased as the MAPP was increased up to 6%.
However, the addition of 8 wt.% MAPP was found to reduce these properties. Scanning electron microscopy (SEM)
images from the tensile fracture surface supported that the improvement on interface region between matrix and filler
have occurred.
KEYWORDS: recycle polypropylene, oil palm empty fruit bunch, maleic anhydrate-g-polypropylene, tensile strength,
water absorption.


1. INTRODUCTION
Production of plastic waste in Indonesia was
ranked as the second producer of domestic waste that is
equal to 5.4 million ton per year. Based on statistical data
of domestic Indonesian waste, the amount of plastic
waste that is 14% of the total waste production in
Indonesia [1]. It comprises mostly plastics used in food
packaging such as PET, PVC, LDPE, HDE, and PP. One
of the most popular plastic packaging is plastic cup for
sparkling beverages which is made from PP. Since Incineration method is not a good solution because it raises
the pollutions, the only alternative left for easy disposal
of this huge plastic waste is recycling to obtain value
added products. Therefore, it is a promising way of use
recycle PP (rPP) as matrix to obtain composite and a perfect choice due to its low cost and the resulting protection of environment. Plastic recycling is a process which
basically comprises the following steps: collection, separation, cleaning and pelletizing. Adhikary [2] and
Bhaskar [3] have published studies dealing with rPP
composites.
On the other hand, in general the use of fillers in
composites aim to reduce costs, provide color, strengthen

or reinforce composite materials. As a filler, natural fibers have several advantages compared to inorganic fillers such as lower density, renewability, improvement in
the mechanical properties, increase in range of
application, biodegradability, greater deformability, en-

hanced energy recovery and relatively lower cost [4].
Several studies of natural fibers used as filler in composites such as jute, kenaf, banana, and bamboo [5-8] has
been done. One of natural fibers which can be potentially
used is fiber of empty fruit bunch palm oil (EFBPO).
The utilization of fiber of EFBPO as fillers had been studied using thermoplastic matrix [9-11].
However, the interfacial adhesion between natural
fiber and thermoplastics is usually very weak due to the
high interfacial tension. This leads to undesirable properties of the composites. The process of modifying interfacial properties of an incompatible polymer blend leading
to the creation of polymer blend is called compatibilization [12]. Physical compatibilization is a modification of
polymeric structure to enhance miscibility, control of
crystallization as a means to lock-in developed morphology and addition of compatibilizing agents [13]. Maleic
anhydrate-g-polypropylene (MAPP) is the
most
common compatibilizer/coupling agent which is expected to give good compatibility between the natural
fiber and the thermoplastic by formation of stronger linkages in the interfaces and reducing filler-matrix surface
tension. Some researchers have published studies dealing

with MAPP addition on composites [10, 14-16].
In the present study the effect of MAPP addition
on tensile properties and water absorption of rPP/OPEFB
composites were investigated.

635

2. EXPERIMENTAL
To carry out this experiment, fixed quantities of
rPP, EPOFB, and calculated quantities of MAPP were
measured. In the formulations where the MAPP had added, the rPP mass was reduced correspondingly thus, the
total proportion of the rPP and the MAPP was 70%. The
composition of the systems are shown in Table 1. The
mixture was fed into extruder machine, and processed at
temperature of 190 oC. Composites were then compression molded using hot press at 190 oC. In hot press, composites were preheat for 5 minutes and followed by 5 minutes compression time at the same temperature. The
specimens were allowed to cool under pressure for
another 5 minutes.

Figure 1. Plot of tensile strength versus MAPP content for
rPP/OPEFB composites


The lowest tensile strength of composite without
the addition of MAPP could be attributed to the poor
interfacial interaction between the polymeric matrix dan
filler, not allowing efficient stress transfer between the
two phases of the material. Poor interfacial bonding
causes partially separated micro-spaces between the filler
particles and the polymer matrix, this causes stress propagation when tensile stress is loaded and induce increased brittleness [15]. This leads to undesirable tensile
resistance of the composite.
Nevertheless, the addition of compatibilizer
(MAPP) has improved interfacial bonding between the
filler and the matrix and improved the tensile strength.
The application of the MAPP as compatibilizer increased
hydrophobicity of the composites. Other investigations
noted, the increase in the tensile strength of the composites on addition of MAPP was caused by maleic anhydride from the MAPP molecule which reacts with the
hydroxyl groups (-OH) of cellulose or hemicellulose, the
two main constituents in OPEFB [11]. The reaction of
the hydrophilic –OH groups from the filler and the acid
anhydride groups from MAPP, forming ester linkages.
Here, the anhydride moieties of functionalized polyolefin

compatibilizer entered into esterification reaction with
the surface hydroxyl groups of OPEFB. Upon the esterification reaction, the polyolefin backbone chain of the
compatibilizer was exposed on the surface of OPEFB. It
is believed that these exposed polyolefin chains diffused
into the PP matrix phase and entangled with rPP molecules during processing creating a bridge at the interface
between the OPEFB and the rPP matrix [2]. As was
noticed above, further increase in the MAPP up to 6
wt.% has significantly increased the tensile strength of
the composites. Fuqua and Ulven [17] have investigated the different MAPP loading (0, 5 and 10 wt.%) effects on tensile properties of corn chaff fiber reinforced
PP composites. It was found that 5 wt.% MAPP yielded
the optimum value for the composites in term of tensile
strength.

Table 1. Formulation of rPP/EPOFB composite
Sample
EPOFB wt.%
rPP wt%
MAPP wt.%
1.
30

70
0
2.
30
68
2
3.
30
66
4
4.
30
64
6
5.
30
62
8

Tensile tests were carried out according to ASTM

D638 using a Universal Testing Machine GOTECH AL7000M. One mm thick dumbbell specimens were cut
from the moulded sheets with a dumbbell cutter. The
tensile test was performed at constant rate (20 mm/min)
at room temperature. The results were quoted based on
the average value of five specimens for each system.
For water absorption test, small blocks of 1×5×5
cm were cut from the sheet and oven dried at 103±2°C to
determine dry weights. The blocks were immersed in distilled water at room temperature and weighed after 2, 4,
6, 12 and 24 hours of soaking to determine their wet
weights. Prior to weighed, speciments were wiped with
tissue to make sure all their surfaces dried. Water absorption was calculated according to Equation (1).

where: w and wo indicate wet weight and dry weight of
the specimens (g), respectively.

3. RESULTS AND DISCUSSION
3.1 The Effect of MAPP addition on the tensile strength
and elongation at break of rPP/OPEFB composites.
The effect of MAPP addition on tensile strength of
rPP/OPEFB composites are shown in Figure 1. It was

found that the addition of MAPP until 6 wt (%) resulted
in an increase of tensile strength.

638

However, the tensile strength reduction observed
with 8 wt.% MAPP content. It could be attributed to a
plasticizing effect exerted by MAPP on the composites
since it is possible that MAPP has a lower molecular
weight compared to the matrix PP [11].
The effect of MAPP additions on the elongation at
break of RPP/OPEFB composites are showed in Figure
2.

Figure 3. Plot of water absorption versus MAPP content
for rPP/OPEFB composites
The current composite consists of hydrophilic
(OPEFB) and hydrophobic (rPP) parts. The hydrophilicity of cellulose and hemicellulose within the OPEFB is
the main cause of water absorption. They contain numerous hydroxyl groups (–OH) and carboxyl groups (–
COOH) which had tendency to interact with water molecules via hydrogen bonding. Under water immersion, the

water molecules resided in the unfilled pores and voids
in the composites, and formed hydrogen bonds with the
components of cellulose and hemicellulose. On the
addition of MAPP, the anhydride moieties in the MAPP
reacted with the surface hydroxyl groups of OPEFB
(ester linkage). Therefore, application of the MAPP decreased the surface tension in composites and it caused
the hydrophilic part less accessible for the water molecules due to good encapsulation of the OPEFB by the
hydrophobic part as well as decreased number of hydroxyl groups in the OPEFB part. Similar to our findings,
Chinomso et.al [11] who studied OPEFB Filled HDPE
reported that the amount of water absorbed was found to
decrease with increase in MAPP content.
However, the composites containing 8 wt. %
MAPP exhibited slightly higher water absorption compared with the composites with 6 wt. % MAPP. It is
possible that unreacted MAPP increased the hydrophilicity of the composites since the MAPP contains a low
content of polar groups in contrast to the non-polar rPP
matrix.

Figure 2. Plot of elongation at break versus MAPP content for
rPP/OPEFB composites


An examination of Figure 2 reveals that the elongation at break of rPP/OPEFB composites were significantly improved as content of MAPP increase until 6 wt.
%. This could be related to improvement adhesion
between OPEFB fiber and rPP. Without addition of
MAPP, the elongation at break of composite shows the
lowest value. This could be attributed to the lack
adhesion on filler-matrix interface. On the addition of
MAPP, as in the case of tensile strength, improving the
adhesion between OPEFB and rPP has enhanced the
elongation at break. At high MAPP content (8 wt.%), decreases on elongation at break were however observed
for the rPP/OPEFB composite. This could be related to
the migration of too much of the compatibilizer around
the fibers, causing self entanglement among the compatibilizers rather than the polymer matrix, resulting in slippage [11].
3.2 The Effect of MAPP Addition on Water Absorption
of rPP/OPEFB Composites
Figure 3 shows the effect of MAPP addition on
water absorption of rPP/OPEFB composites. It shows the
water absorption was decreased due to the addition of
compatibilizer (MAPP) to the rPP/OPEFB composites.

3.3 Morphology

Microstructure of the fractured surface for
rPP/OPEFB composite specimens tested in tensile is examined using scanning electron microscopy (SEM). Images of the composites without and with compatibilizer
(MAPP) are shown in Figures 4a and 4b, subsequently,
in 1000× magnification.

637

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a
b
Figure 4. SEM micrographs of fractured surfaces of composites
rPP/EPOFB. a) without MAPP addition; b) with MAPP
addition (6 wt.%)

Figure 4a shows there was fiber pull out leaving
holes behind on uncompatibilized
rPP/OPEFB
composite. It is clearly indicating weak interfacial
region and damage mainly occured along the loose and
weak interface between OPEFB fiber and rPP matrix. As
mention before, the hydrophilic nature of OPEFB fiber
filled hydropobic rPP is believed to be responsible for
the poor interfacial adhesion between OPEFB and
rPP.This image has become evidence the low value tensile strength and high degree of water absorption of composite. However, as seen on Fig 4b, the presence of
MAPP in rPP/EPOFB composite reduced the holes
turned more difficult fiber pull-out during brittle fracture.
The surface of fiber displayed a rough morphology confirming its effect on promoting adhesion in the interfacial
region, indicating stress transfer from the matrix to the
fiber, resulting in enhanced tensile in response to stress.
Interface bonding between the fillers and the matrix is
the key to transfer the stress from the matrix into the fillers across the interface [11].

4. CONCLUSION
Tensile strength and elongation at break of oil
palm empty fruit bunch (OPEFB) fiber filled recycle
polypropylene (rPP) have shown improvement with increasing of maleic anhydrate g-polypropylene (MAPP)
up to 6 wt.% content. The addition of MAPP into
rPP/OPEFB composites was found to significantly improve surface adhesion between filler and matrix. SEM
images of the fractured surfaces confirmed that an addition of the MAPP compatibilizer improved the interfacial
bonding between the rPP and the OPEFB fiber for the
rPP based composites.

REFERENCES
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2. Adhikary, K. B. 2008.Wood flour recycled polymer
composite panels as building materials. Thesis. Chemical and Process Engineering, University of Canterbury
3. Bhaskar, J. Haq, S. Pandey, A. K. & Srivastava, N.
2012. Evaluation of properties of propylene-pine
wood Plastic composite J . Mater. Environ. Sci.
3(3):605-612
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