Microwave-assisted Modification of Cellulose as a Compatibilizer for PLA and MCC Biocomposite Film: Effects of Side Chain Length and Content on Mechanical and Thermal Properties

This research focused on the utilization of modified banana leaf sheath (BS) to be used as the compatibilizer for biocomposite films based on poly(lactic acid) (PLA) and 40 wt.% banana leaf sheath microcrystalline cellulose (BS MCC). Two types of cellulose ester, i.e. cellulose butyrate and cellulose laurate were used as a compatibilizer. The cellulose esters were prepared via acylation process under microwave heating. The proper condition for preparing cellulose butyrate was 180 sec of reaction time and 80 watt of microwave power, while the suitable condition for preparing cellulose laurate was 150 sec of reaction time and 160 watt of power output, respectively. These optimum conditions led to the highest percentage of weight increase (%WI) and the absence of the degradation of cellulose. The butyrate and laurate were successfully grafted on the BS MCC which was confirmed by FT-IR and NMR spectroscopy techniques. For biocomposite films, although the increase of cellulose laurate or cellulose butyrate induced the decrease in Young's modulus of 40 wt.% BS MCC/PLA composite, the elongation at break of 40 wt.% BS MCC/PLA composite was increased. Likewise, the presence of 5 wt.% cellulose butyrate or cellulose laurate contributed to the highest tensile properties, especially in elongation at break, when compared to other contents of cellulose ester. According to SEM micrographs, the presence of both cellulose esters can improve the compatibility between PLA and MCC as evidenced by the disappearance of many holes in 40 wt.% BS MCC/PLA composites. Comparatively, cellulose butyrate is an effective compatibilizer for improving the elongation at break of 40 wt.% BS MCC/PLA since it had better compatibility with BS MCC and PLA matrix than cellulose laurate. However, the addition of both cellulose esters, i.e. cellulose butyrate or cellulose laurate, led to the decrease in the degradation temperature (Td) of 40wt.% BS MCC/PLA, particularly when adding cellulose laurate.