Publication: Physicochemical, tensile, thermal and biodegradation studies of chitosan-filled polylactic acid biocomposites
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Date
2022-06-01
Authors
Kamaludin, Nor Helya Iman
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Abstract
Environmental problems associated with the use of synthetic polymer have encouraged researchers to tune to the biopolymer through the development of biodegradable composite material or biocomposites. Hence, efforts have been established to produce such composite by the addition of polysaccharide chitosan (Cs) into the polylactic acid (PLA) via melt compounding and compression molding techniques. This study investigated the effect of filler loadings of 2.5, 5, 7.5, and 10 parts per hundred parts of polymer (php) on the physicochemical, tensile, thermal, antimicrobial, and biodegradability properties consecutively. A comparison of properties after water absorption and soil burial was also conducted. Series 1 involved the preparation of PLA/Cs biocomposites at various predetermined Cs loadings, which serve as a control for the other proposed series. The tensile analysis demonstrated that the Cs inclusion of 2.5 php showed an optimal filler loading based on a slight increment in tensile properties, but further addition up to 10 php resulted in a significant decrease of tensile strength by approximately 56%, which was ascribed by a weak filler-matrix interfacial adhesion. A similar reduction trend was presented by thermal stability through Cs addition, which suggested poor thermal resistance of the Cs component. In order to cater for the deficiencies encountered by the prepared PLA/Cs biocomposites, two modification strategies were implemented. In Series 2, halloysite nanotubes (HNTs) was introduced as a hybrid filler to Cs component for the fabrication of PLA/Cs/HNTs hybrid
biocomposites. The results showed that the combined loading of 1 php Cs and 1.5 php HNTs hybrid fillers into PLA produced the best performance in all properties. The findings demonstrated that at this optimal formulation, the thermal stability of the non-hybrid PLA/2.5Cs biocomposites increased by ~12%, and attained the maximum tensile strength and elongation at break of 59 MPa and 2.72%, respectively. Series 3 involves the surface treatment of Cs filler with bioactive phenolic compounds of tannic acid (TA). Through the structural analysis, TA-treated Cs showed a decrease in the hydroxyl group’s absorption band, implying the decrease in the hydrophilic character of the treated Cs, which is beneficial in improving the compatibility with PLA. This concurs well with the enhancement of tensile strength and better interfacial adhesion between Cs-TA and PLA in the TA-treated biocomposites as compared to the untreated. Moreover, the TA-treated Cs showed a positive effect on thermal stability correlated to a higher decomposition temperature. An investigation established a significant inhibition percentage of more than 90% against food-pathogenic bacterial of B. subtilis and E. coli, which support a strong antibacterial activity of the prepared PLA/Cs biocomposites. Interestingly, the modified specimens presented a higher inhibition percentage than that of control attributed to the interaction of specific components with the cell membrane. The biodegradation studies by water absorption and soil burial indicated that the control sample of PLA/Cs biocomposites showed the highest water uptake and weight loss of 3.9% and 21%, respectively, after 50 days of water immersion and 12 months of soil burial. However, all modified biocomposites presented relatively lower degradability and lesser properties’ deterioration, which signified structural improvement due to their respective modification. In fact, all studied properties were diminished with increasing filler loadings and prolonging exposure time to 10 php and 12 months, respectively. Lastly, the microbial-samples. Four unknown strains (F1, F2, F3, and F4) were isolated from the biocomposites. The morphological observation indicated that the isolated strains were originated from fungi based on the presence of hyphae, phialides,conidiophores, and conidia. Indeed, internal transcribed spacer (ITS) sequencing revealed that three fungal species are responsible for the PLA/Cs degradation, namely Clonostachys rosea (F1), Aspergillus aculeatus (F3), and Bionectria sp. (F4), based on the constructed phylogenetic tree.