Effect of Cellulose-to-Starch Ratio and Sorbitol Concentration on the Mechanical, Physical, and Biodegradation Properties of OPEFB-Based Bioplastics

Abstract

The extensive use of conventional plastics, which are difficult to degrade, has driven the development of environmentally friendly bioplastics derived from oil palm empty fruit bunches (OPEFB). The independent variables were the OPEFB Cellulose-to-Starch ratio (1:2, 1:1, and 2:1) and sorbitol concentration (5%, 10%, 20%, and 30% w/w) in OPEFB-derived cellulose matrices reinforced with cellulose nanocrystals (CNC) and polyvinyl alcohol (PVA). The bioplastics were prepared using the solution casting method. The results indicate that the optimal formulation for water resistance was achieved at a 2:1 cellulose-to-starch ratio with 5% sorbitol, yielding the lowest water absorption of $2.56\% \pm 0.12\%$ and an outstanding water resistance of $97.44\%$. Conversely, the highest tensile strength of $44.16 \pm 1.45 \text{ MPa}$ was obtained at a 1:2 ratio with 30% sorbitol. The highest biodegradability in the soil burial test was observed at 30% sorbitol, with a maximum weight loss of $66.16\% \pm 2.11\%$ within 14 days. FTIR analysis confirmed the typical preservation of polysaccharide functional groups. At the same time, SEM observations at higher magnification revealed a well-distributed nanostructure with a controlled porous morphology that effectively balances mechanical performance and accelerated microbial degradation.