Publication: Preparation and properties of rubber toughened polylactic acid/kenaf biocomposite
Date
2022-02-01
Authors
Alias, Nur Fazreen
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Abstract
Development of biopolymers and biocomposites has been driven by several environmental factors such as depletion of fossil fuels sources, pollutions and lack of landfill. Researches are growing continuously to achieve optimum properties of green polymeric materials with respects to the applications. In this research, polylactic acid (PLA) was used as main matrix, while rubber was incorporated to toughen PLA via melt blending in internal mixer, followed by compression moulding. Simultaneously, kenaf fiber was added at various loading from 0 phr up to 20 phr. The properties of biocomposites investigated were mechanical properties, thermal properties, physical properties and chemical properties, and biodegradation via soil burial. In the first stage of study, three types of rubber were used, which were natural rubber (NR), styrene butadiene rubber (SBR) and nitrile butadiene rubber (NBR). Comparing the effect of rubber type, PLA/NR/kenaf showed highest mechanical properties than PLA/SBR/kenaf and PLA/NBR/kenaf biocomposites. However, in term of kenaf loading, the mechanical properties deteriorated with increasing of kenaf loading due to poor interfacial adhesion, as proven via morphological study. On the other hand,
kenaf addition contributes to higher water absorption percentage and enhanced degradation of biocomposite. This is attributed by presence of abundant hydroxyl group from natural filler. The second stage of study aimed to improve interfacial adhesion and compatibility within PLA/NR/kenaf biocomposites by addition of polymethyl methacrylate (PMMA) and epoxidized natural rubber (ENR) as co compatibilizer. Tensile properties and impact strength of biocomposites were improved upon compatibilization. On the other hand, due to enhanced interfacial adhesion, water absorption and biodegradability of biocomposite decreased. Substitution of NR by liquid natural rubber (LNR) at fixed ratio was carried out in
third stage of study. Based on the results, tensile properties of PLA/NR/LNR/KF biocomposites was enhanced. However, impact strength did not show positive effect.
Lower molecular weight of LNR resulted in better compatibility to PLA. Besides that, it would ease the processability as substituting LNR resulted in lower processing and
stabilization torque. Similar findings were recorded in second stage, in which better interfacial adhesion led to decrement of water absorption capability and biodegradability. Another approach to enhance the properties of biocomposite was via filler hybridization. In fourth stage of study, microcrystalline cellulose (MCC) was gradually hybridized in biocomposite at highest filler loading, 20 phr. It was found that kenaf-MCC hybridization resulted in synergistic effect especially in mechanical properties. Highest tensile strength, elongation at break and impact strength were recorded for biocomposite with combination of 5 phr kenaf and 15 phr MCC. From morphological study, interfacial adhesion between filler and matrix was improved in hybrid biocomposite compared to biocomposite with one. In biodegradability aspect, addition of kenaf facilitate to higher biodegradation process compared to MCC. The hybrid biocomposites showed intermediate water absorption and biodegradability properties.