Effect of Acrylic Acid on the Mechanical Properties of Coconut Shell Filled Low Density Polyethylene (LDPE) Composites

The 1st International Conference on Sustainable Technology Development
"Sustainable Technology Based on Environmental and Cultural Awarenes"

Effect of Acrylic Acid on the Mechanical Properties of Coconut Shell
Filled Low Density Polyethylene (LDPE) Composites
Mhd. Hendra S Ginting l , Salmah

I,

Halirnatuddahliana l , Tengku Faisal

z. H2,

I Departemen

Teknik Kimia, USU
2Fakultas Teknik UMA
ABSTRACT: The effects of chemical modification of coconut shell (CS) with acrylic acid (esterification)
and filler content on mechanical properties and morphology of LDPEICS composites were studied. Results
show that the increasing content of coconut shell in composites has increased the tensile strength and Young's
modulus but decreased elongation at break. The esterification treatment has improved the tensile strength,

elongation at break, and Young's modulus of composites. The scanning electron microscopy (SEM) study of
the tensile fracture surface of the esterified composites indicates that the presence of acrylic acid increased the
interfacial interaction between coconut shell and LDPE matrix.
Key Words: coconut shell, low density polyethylene, chemical modification, acrylic acid, composites.

t\
'.

The use of natural plant fibres as reinforcement
iIi polymer composites for making low cost
engineering materials has generated much interest
in recent years. The advantages of natural plant
fibres over traditional glass fibres are acceptable as
good specific streng-ills and modulus, economical
viability, low density, reduced tool wear, enhanced
energy recovery, reduced dermal and respiratory
irritation and good biodegraJability (Bolton J,
I 995).However, natural plant fibre reinforced
polymeric
composites,

also
have
some
disadvantages such as the incompatibility between
the hydrophilic natural fibres and hydrophobic
thermoplastic and thermoset matrices requiring
appropriate use of physical and chemical
treatments to enhance the adhesion between fibre
and the matrix (GasSaD. J et ai, 2000).
Chemical modification will be defined as a
chemical reaction between some reactive part of a
lignocellulosic cell wall polymer and a simple
single chemical reagent, with or without catalyst,
to form a covalent bond between the two (Rowell
et aI, 1993). The most important chemical
modification involves coupling methods. The
coupling agent used contains a chemical group,
which can react with the fiber and the polymer
(Salmah et al, 2005). Esterification is one of the
. chemical modifications undergone by the natural

fiber. Most of the research conducted on esterified
natural fiber have focused on improving the
mechanical properties polymer composites
(Mwaikarnbo et al, 2002, Marcovich et all, 200 I,
Cantiro et aI, 2003)
Coconut shell is one of the most important
natural fillers produced in tropical countries like
Malaysia, Indonesia, Thailand, and Sri Lanka.
Many works have been devoted to use of other
natural fillers in composites in the recent past and
coconut shell filler is a potential candidate for the
development of new composites because of their
high strength and modulus properties. Composites
of high strength coconut filler can be used in the
broad range of applications as, building, materials,
marine cordage, fishnets, furniture, and other
household appliances (Sapuan et aI, 2003).
This article reports the result of an
investigation on the effect of esterification of

coconut shell on mechanical properties and
morphology of of Coconut Shell Filled Low
Density Polyethylene (LDPE) Composites
EXPERIMENTAL

Materials
Low density polyethylene used in this study
was of injection molding grade, from The Polylefin
Company (Singapura) Pte. Ltd (code F41 0-1) with

Faculty of Engineering, Udayana University
7 - 8 October 2010, Denpasar Oty campus

C- 44

The 1st International Conference on Sustainable Technology Development
·Sustainable Technology Based on Environmental and Cultural Awarenes"

MFI value of 5 glI0 min at 111°C and density
0.923 glcm3• Acrylic acid was obtained from

Fluka, and Ethanol from Fisher Scientific Sdn.
Bhd, Malaysia. Coconut Shell (CS) was obtain
from local grocer, Pedis, Malaysia. Coconut shell
was cleaned from waste and crushed into small
pieces. After soaked in water for 2 weeks, coconut
shell pieces dried in a vacuum oven at 80°C for 24
h to remove moisture and then ground to a powder.
A Ball mill and Endecotts sieve was used to obtain
the average filler sizes of 44 pm (density, 2.2
glcm3). The formulation of LDPEICS composites
used in this study is shown in Table 1.
Mixing Procedure
Composites were prepared in a Z-Blade
mixer. Mixing was done at 180°C and 50 I]Jm.
LDPE was first charged to start the melt mixing.
After 12 min, the filler was added and mixing
continued until 25 min. At the end of 25 min, the
composites were taken out and sheeted through a
laboratory mill at 2.Omm nip setting. The sample
of composites was taken compression molded in an

electrically heated hydraulic press. Hot-press
procedures involved preheating at 180°C and 150
kglcm2 for 6 min followed by compressing for 4
min at the same temperature and subsequent
cooling under pressure for 4 min.
Table I . Formulation of LDPEICS composites with
esterification treatment.
Composite 1

Materials
LDPE(phr)

Ccconut

Shell

les

Composite 1

(without

(with

Esterification)
100

Esterification)
100

0,15,30,45,60

15.30, 45,60

(wt'Io)

Acrylic Acid (wt'Io)

3

Table 2. Chemical Composition of Coconut Shell
Composition

Wt(%)

Cellulose
Lignin
Pentosans
Solvent Extractives
Uronic Anhydrides
Moisture
.

26,6
29,40
27,70
4,20
3,50
8,0
0,6

Ash

Esterification
Coconut shell was esterified using 3% acrylic
acid in ethanol 95%, keeping the filler to solvent
ratio at 3 : 97 (v/v), and stirred for 1 h. The

Coconut shell was filtered out, washed with ~ater
and dried in oven at 80_C for 24 h.

Measurement o/Tensile Properties
Tensile tests were carried out according to
ASTM D-638 on an Instron 5582. Dumbbell
specimens, Imm thick, were cut from the molded
sheets with a Wallace die cutter. A cross head
speed of 50 mm1min was used and the test was
performed at 25±3°C.

Morphology Study .

Studies on the mOI]Jhology of the tensile
fracture surface of the composites were carried out
using a scanning electron microscope (SEM),
model JEOL ISM 6460 LA. The fracture ends of
the specimens were mounted on aluminum stubs
and sputter coated with a thin layer of paladium to
avoid electrostatic charging during examination.

RESULTS AND DISCUSSION
The effect of filler loading on the tensile
strength of untreated filler and esterified filler on
LDPEICS composites are shown in Figure 1. It can
be seen that the tensile srrength of the composites
increases with increasing filler loading. The tensile
strength of the composites increases due to the
ability of the filler to support stress transferred
from the matrix. Coconut shell as a filler has a
high toughness and high lignin content
(www.reade.com). The bio-flour materials are
mainly composed of a complex network of three

polymers: cellulose, hemicellulose and lignin
(Marti-Ferrer et ai, 2005). According to Hee-Soo
Kim et aI (2007), lignin not only holds the bioflour together, but also acts as a stiffening agent for
the cellulose molecules within bio-fIour cell wall.
Therefore, the lignin and cellulose content of CS
has an influence on the strength of CS and the
tensile strength of composites. At a similar filler
loading, esterified composites exhibit higher
tensile strengths than untreated composite. This
indicates that the chemical modification of coconut
shell with esterification has resulted in an
improvement of the interfacial bonding and
dispersion between the filler and matrix as shown
later in SEM mOI]Jhology.

Faculty of Engineering, Udayana University
7 - 8 October 2010, Denpasar City Campus

C - 45

The 1st International Conference on Sustainable Technology Development
'Sustainable Technology Based on Environmental and Cultural Awarenes"

,

has a higher stiffuess than the matrix can increase
the modulus of the composites. At a similar filler
loading, Young's modulus of esterified composites
exhibits the highest value than that of untreated
composites. lIDs result provides evidence that the
stiffuess of the LDPE/CS composites increases
with the introduction of chemical treatment.

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Figure L Effect of filler loading on tensile strength of
untreated and esterified LDPEICS composites.

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