Hybrid polylactide acid (PLA) composites reinforced with palm empty fruit bunch (EFB) and chopped strand E-glass (GLS) fibres were investigated. The hybrid fibres PLA composite was prepared through solution casting followed by pelletisation and subsequent hot compression press into 1 mm thick specimen. Chloroform and dichloromethane were used as solvent and their effectiveness in dissolving PLA was reported. The overall fibre loading was kept constant at volume fraction,
Fibre reinforced composites based on carbon, glass, and Kevlar have been widely used in the aviation, automotive, marine, sport, and defence industries, attributed to their high strength to weight ratio, easy formability, and high tensile and fracture resistance. However, synthetic fibres are generally manufactured through energy intensive processes that produce toxic by-products while their reinforced composites are difficult to recycle and resistant to biodegradation [
Biodegradable polymeric resins generally can be categorised into two groups depending on their origin, natural biopolymers (polymer derived from natural resources such as starch, cellulose, gelatine, casein, wheat gluten, silk, wool, plant oils, and polylactic acid), and synthetic biopolymers (mineral based biopolymer synthesised from crude oil with example including aliphatic polycaprolactone, aromatic polybutylene succinate terephthalate, and polyvinyl alcohols) Amongst the many natural-origin biodegradable polymers, polylactic acid (PLA), a corn-based biodegradable polyester obtained from fermentation of sugar feedstock, is gaining its popularity in the scientific community [
Motivated by the growing concerns on sustainability and product life cycle of polymer composites, natural fibre with its relatively high specific strength and stiffness, lightweight, and renewable, biodegradable, and low cost manufacture has received significant attention to be developed as an alternative reinforcement in polymer composites [
Owing to the inherently much weaker mechanical performance of EFB fibre [
Rozman et al. revealed that increasing the volume fraction,
To yield a more sustainable composite with reasonable mechanical properties and to reduce environmental impact, PLA hybrid composite reinforced with randomly oriented oil palm EFB and chopped strand GLS fibres was studied, whereby a large proportion of the ingredients (i.e., PLA, EFB) are harnessed from renewable sources. Homogeneous mixture of the PLA resin and EFB fibres was first prepared using solvent dissolution method and the solidified compound was shredded into pellets. Measured quantity of GLS fibre with predefined length was evenly distributed amongst the PLA-EFB pellets prior to hot compression press into specimen of 1 mm in thickness. The effects of synthetic fibre length, solvent type, and fibre volume fraction on the mechanical properties of the hybrid fibres PLA composite were reported.
The EFB fibres used in this research were supplied by Malaysian Palm Oil Board (MPOB). The fibres have an average length of 4 to 13 mm (Figure
Varying length of the EFB fibres.
SEM micrograph showing the various diameters of EFB fibres.
The EFB fibres were first washed and sieved under running water to remove sand, mud, and residue from pulverized fibre. The cleaned fibres were subsequently dried at 70°C for a minimum of 24 hours. On the other hand, the PLA pellets were dried in an oven at 50°C for a period of 24 hours to remove moisture content. The conditioned PLA pellets were then weighed into the required masses and sealed by batch into plastic bags containing silica gel to prevent moisture reabsorption prior to solvent dissolution.
The dried PLA pellets were dissolved in solvent at a ratio of 60 g resin to 200 mL solvent within a 500 mL Erlenmeyer. The PLA pellets were continuously stirred with a magnetic stirrer for a minimum of 6 hours to ensure complete dissolution. Dried EFB fibres were subsequently introduced into the Erlenmeyer and mixing continues until a homogenous fibre distribution was achieved. The resulting PLA-EFB mixture was then spread out in metal trays precoated with silicone mould release agent and left to dry within a fume hood for a period of 24 hours. The solidified mixture was obtained and shredded into pellets form before being placed in an oven maintained at 60°C for further drying over a period of 24 hours. Figure
The chopped solidified PLA-EFB pellets.
A stainless steel mould (cavity 200 × 150 × 3 mm) with a 2 mm steel plate insert incorporated was used to produce 1 mm thick specimen sheets. The PLA-EFB pellets and GLS fibres of specific length were mixed and evenly spread into the cavity of the mould. The material was then pressed at 165°C, that is, slightly above the crystalline melt temperature of PLA using a hydraulic hot press. Two different pressure settings, 4.4 MPa and 8 MPa, were employed. The material was then cooled under controlled pressure within the mould prior to demoulding of the solidified specimen plate.
The effects of fibre loading (ranging from 0 to 20%
Experimental parameters investigated in this work.
Sample designation* | Volume fraction, |
Solvent type | Length of E-glass (GLS) fibre (mm) | |
---|---|---|---|---|
E-glass (GLS) fibre | Empty fruit bunch (EFB) fibre | |||
CH003 | 0 | 20 | Chloroform | 3 |
CH053 | 5 | 15 | Chloroform | 3 |
CH103 | 10 | 10 | Chloroform | 3 |
CH153 | 15 | 5 | Chloroform | 3 |
CH203 | 20 | 0 | Chloroform | 3 |
DC003 | 0 | 20 | Dichloromethane | 3 |
DC053 | 5 | 15 | Dichloromethane | 3 |
DC103 | 10 | 10 | Dichloromethane | 3 |
DC153 | 15 | 5 | Dichloromethane | 3 |
DC203 | 20 | 0 | Dichloromethane | 3 |
DC056 | 5 | 15 | Dichloromethane | 6 |
DC106 | 10 | 10 | Dichloromethane | 6 |
DC156 | 15 | 5 | Dichloromethane | 6 |
DC206 | 20 | 0 | Dichloromethane | 6 |
“CH” and “DC” refer to the solvent type used for the processing (CH = chloroform; DC = dichloromethane); “XX” corresponds to the volume fraction of GLS fibre (ranging from 0 to 20%
Specimens with EFB: GLS fibre loading of 20 : 0, 10 : 10, and 0 : 20%
The tensile specimens were milled to ASTM D638-02a Type 1 standard. The specimens were kept in sealed plastic bags with silica gel for a minimum of 24 hours to remove traces of surface moisture prior to testing. All specimens were tested to failure under constant crosshead speed of 5 mm/min using Lloyd Instruments LR50k tensile testing machine. At least three specimens were tested for each formulation.
The flexural specimens of size 75 × 12.7 mm were prepared with the aid of a vertical bandsaw. The deflection point was set in accordance with ASTM D790-03 standards and crosshead speed of 1 mm/s was employed in the test. The specimens were sealed into plastic bags with silica gel to remove traces of surface moisture prior to testing. Flexural modulus and flexural strength were calculated based on constitutive equations.
Figure
Tensile strength of the pure EFB, hybrid EFB-GLS, and pure GLS fibre PLA composite at various %
The specimens which were produced using chloroform as the solvent performed significantly better (between 50 and 150%) than the specimens which were produced using dichloromethane. For the specimens with dichloromethane, the 6 mm GLS specimens generally exhibit lower tensile strength compared to the 3 mm GLS specimens (except for specimens with 10%
The specimens’ percentage elongation at break is shown in Figure
Elongation at break (%) against various %
The flexural strength and modulus of the composite subjected to 3-point bending are shown in Figures
Flexural strength against various
Flexural modulus against various
In terms of the flexural modulus, all specimens showed a drop in flexural modulus from 15% to 20%
In general the tensile and flexural tests showed that mechanical properties of the hybrid composite increase with increasing GLS fibre loading, that is, with decreasing concentration of EFB fibres. The result is consistent with existing literature on the performance of oil palm EFB lignocellulosic/thermoplastic composites [
A major contributing factor to the strength of fibre reinforced composite could be attributed to the interfacial adhesion between the fibres and the resin matrix [
The tensile fracture surface of a specimen (15% 3 mm GLS fibre, 5% EFB).
The tensile fracture surface of a specimen (5% 3 mm GLS fibre, 15% EFB).
There are two major factors which could contribute to weak interfacial bonding between the fibre-matrix interfaces: the wetting of the fibres and the fibre distribution within the composite [
Comparing to the hybrid fibres composite at 15% GLS fibre loading, the recorded lower tensile strength of the homo-GLS fibres PLA composite (i.e., 20% GLS, 0% EFB) may be attributed to the specimen preparation procedure needed to preserve the GLS fibre length, which causes reduced fibres wetting, fibre agglomeration, and poor interfacial adhesion between GLS fibre and PLA matrix interface.
The composite produced with chloroform as the solvent displayed a significantly higher tensile and flexural strength than specimen prepared through dichloromethane. The viscosity of the resin solution with different solvents could have affected the degree of fibre wetting; that is, lower viscosity is more effective in fibres wetting, thereby improving the interfacial bond between the fibres and the matrix. In accordance with the Hansen Solubility Index [
The use of EFB and GLS fibres as reinforcement in a hybrid PLA composite produced results that are outlined as follows. The tensile and flexural strength of the hybrid composite generally improved with increased GLS fibre loading, up to 15% PLA specimens filled with GLS fibres alone (20% GLS, 0% EFB) depict poorer mechanical properties compared to EFB-GLS fibres hybrid PLA composites. The use of chloroform to compound EFB fibres in PLA resin improved the tensile and flexural properties of the specimens by 50 to 150% compared to dichloromethane.
The authors declare that there is no conflict of interests regarding the publication of this paper.