Ordinary Speaker
International Symposium on Advanced Polymeric Materials 2016 (ISAPM 2016)
Modification of Pineapple Leaf Fibre to Reinforce Polylactic Acid Composite with
Improved Mechanical Properties
Mathivanan, D.B.1,*, Siregar, J.P.1, Mat Rejab, M.R.1, Bachtiar, D.1, and Tezara, C2
1
Faculty of Mechanical Engineering, Universiti Malaysia Pahang
26600 Pekan, Pahang, Malaysia
2
Department of Mechanical Engineering, Faculty of Science, Technology, Engineering and
Mathematics, INTI International University 71800 Nilai, Negeri Sembilan, Malaysia
*
davindrabrabu@gmail.com
ABSTRACT
Natural fibres play a significant role in mass industries such as automotive, construction and
sports. Many researchers have found that the natural fibres are the best replacement for the
synthetic fibres in terms of cost, safety, and degradability due to the shortage of landfill and
ingestion of non biodegradable plastic by animals. This study mainly revolved around
pineapple leaf fibre (PALF) which is available in abundance in tropical countries and for its
excellent mechanical properties. The composite fabricated in this study is highly compostable
as both fibre and matrix is from natural based material. The matrix used which is polylactic
acid (PLA) is made from corn starch, which gives the upper hand as both materials are
renewable resources are easier to degrade by bacteria or enzyme. The PALF is treated with
different alkaline percentage to remove excessive moisture in the fibre for better interfacial
bonding with PLA. Thereafter the PALF is washed with distilled water several times before
placing in vacuum oven. The dried PALF were later mixed with PLA through extrusion using
fibre in percentage of 30 by weight for better bonding and afterwards the products of the
mixture were pelletized using pelletizer. The pellets were placed in the specimen sized mould
for hot compression and subsequently were cold pressed. The specimens were tested for
tensile and flexure strength and the result was remarkable where a fluctuating graph can be
seen for both tensile and flexure strength where 5% alkaline treatment showed the highest
tensile and flexure strength among the alkaline solution. It can be concluded that the alkaline
concentration affects the strength of the composite and the 5% NaOH solution is the best
percentage of alkaline treatment for PALF.
Keywords: alkaline treatment; composite; mechanical properties; natural fibres
Introduction
Each year, million tonnes of plastics are being produced and a portion of it always finds its
way to the ocean. In a groundbreaking study “Plastic waste inputs from land into the
ocean”, published in the journal Science estimated that in 2010 alone, almost 8 million tonnes
of plastics were washed into the ocean from 192 coastal countries. The non biodegradability
characteristic of the plastic has made it harmful to the environment. However, there are many
studies being conducted on various material to find the suitable substitute for plastics[1]. The
biocomposite found to be a better replacement for plastics in term of biodegradability, cost,
and safety[2]. Biocomposite is made of two or more materials combined to achieve a better a
multiphase material with desired properties and can be degraded by enzyme or bacteria[3].
In this study, Pineapple leaf fibres (PALF) were used as the fibre and polylactic acid
(PLA) as matrix for PALF acts a good reinforcement material for this biocomposites due to
the high cellulose content in the fibre compared to other plant fibers and the chemical
similarities between the material[4]. Moreover pineapple leaf can be easily acquired in
tropical countries like Malaysia[5].
Experimental details
Materials and methods
The PALF was washed, grind and sieved, subsequently placed in sodium hydroxide ((NaOH)
solutions with 3%, 5%, and 7% alkaline concentration for 6 hours under room temperature.
The PALF were later dried under sunlight for 24 hours and then placed in vacuum oven for
24 hours under the temperature of 80oC.
Composite Processing
Table 1 PALF/PLA mixing ratio
Alkaline concentration in PALF /PLA Mixture PALF PLA Resin
Untreated PALF reinforced PLA composite plate 30% 70%
3% PALF reinforced PLA composite plate 30% 70%
5% PALF reinforced PLA composite plate 30% 70%
7% PALF reinforced PLA composite plate 30% 70%
The fibre and matrix were mixed in the amount of 30% by weight, for all samples using
extrusion technique then pelletized using pelletizer. The temperature of the extrusion machine
for all zones were maintained at 170oC. The pellets were later hot pressed to specimen size
using specimen sized mould under the temperature of 170oC at 8Mpa for 5 minutes, then was
cold pressed under room temperature at 8Mpa for 5 minutes. The mould was prepared
according to the ASTM D638 and D790.
Testing
Tensile test
The test was carried out accordingly to ASTM 638 at room temperature using Instron
Universal Testing machine. 7 replicates from each sample were tested with a crosshead speed
of 1 mm/min.
Flexure test
Flexure test was performed under room temperature following the ASTM D790 standards
using Instron Universal Testing machine. 7 replicates from each sample were tested with a
crosshead speed of 2 mm/min.
Result and discussion
From figure 1, it can be seen that the tensile and flexural strength of the composite increases
as the fibre content increases. The tensile strength of untreated fibre reinforced recorded
36.24 MPa which increases by 14% when the fibre treated with 3% concentration and
increased 12.7% at 5% concentration. The flexural strength shows 19.7% increase after
80
67.66
70
56.30
60
47.03 46.66
50
36.24 41.37 AVERAGE TENSILE
37.65
40 STRENGTH
32.37
30 AVERAGE FLEXURE
STRESS
20
10
0
UNT PALF/PLA3% PALF/PLA5% PALF/PLA7% PALF/PLA
Figure 1 Effect of alkaline concentration on tensile and flexural strength of PALF/PLA composite
2.80
2.575 2.633
2.60
2.40
2.409 2.343 2.456
2.20 2.103
1.985 1.934
2.00
1.80
1.60 AVERAGE TENSILE
1.40 MODULUS [Gpa]
1.20
1.00 AVERAGE FLEXURE
0.80 MODULUS [Gpa]
0.60
0.40
0.20
0.00
UNT 3% 5% 7%
PALF/PLA PALF/PLA PALF/PLA PALF/PLA
Figure 2 Effect of alkaline concentration on tensile and flexural modulus of PALF/PLA composite
treated at 3% concentration and 20% more at 5% concentration. However, the tensile and
flexural strength drastically drops at the highest concentration of alkaline solution where it
can be seen a reduction of 30% for tensile and 44% for flexure strength. The modulus graph
also potrays the same fluctuating pattern
This is because alkaline treatment removes the wax and the pectin offering more cellulose to
be exposed, increasing the chances for more reactions. Moreover, the treatment also increases
the surface roughness resulting in better mechanical interlocking. However, at the 7%
alkaline treatment excess delignification of the fibre occurs, resulting in weaker or damaged
fibre. Similar result was observed by M.S.Meon et al, the author reported that the high
concentration treatment damages the fibers inter-laminar bonding[6].
Conclusion
From the study, it can be concluded that the pineapple leaf fibre as reinforcement for PLA
was successfully developed and the concentration of alkaline effects the tensile and flexural
strength of the composite. The 5% alkaline solution is the optimum concentration for 30%
PALF reinforced PLA composite.
Acknowledgement
This research was funded by the Ministry of Higher Education, Malaysia under the grant
number FRGS140120.
References
1. Munawar, R.F., et al., Development of Green Composite: Pineapple Leaf Fibers
(PALF) Reinforced Polylactide (PLA). Applied Mechanics and Materials, 2015. 761:
p. 520-525.
2. Huda, M.S., et al., Effect of chemical modifications of the pineapple leaf fiber
surfaces on the interfacial and mechanical properties of laminated biocomposites.
Composite Interfaces, 2008. 15(2-3): p. 169-191.
3. Asim, M., et al., A Review on Pineapple Leaves Fibre and Its Composites.
International Journal of Polymer Science, 2015. 2015: p. 1-16.
4. Kaewpirom, S. and C. Worrarat, Preparation and properties of pineapple leaf fiber
reinforced poly(lactic acid) green composites. Fibers and Polymers, 2014. 15(7): p.
1469-1477.
5. Abd Razak, S.I., et al., Impregnation of Poly(lactic acid) on Biologically Pulped
Pineapple Leaf Fiber for Packaging Materials. BioResources, 2015. 10(3).
6. Meon, M.S., et al., Improving Tensile Properties of Kenaf Fibers Treated with Sodium
Hydroxide. Procedia Engineering, 2012. 41: p. 1587-1592.
