Improving Wet Performance of Chitosan-xylan Bioplastic Using a Biobased Additive

Abstract

The objective of this study was to improve the water stability and wet strength performance of chitosan-xylan polymer using citric acid as a green and biobased crosslinking agent. Aqueous solution containing chitosan and xylan was added with citric acid at different dosages (0, 0.2, 0.4, 0.8, and 1.6 mmol per gram of polymer). The solution was cast into films for Fourier transform infrared spectroscopic (FTIR) studies, tensile tests, and 24-hour water soaking experiments. The tensile results showed 40% higher wet strength as the citric acid dosage were increased from 0 to 0.4 mmol/g. Higher citric acid dosages (i.e., 0.8 and 1.6 mmol/g), however, resulted in films that were too weak to be tested wet. FTIR results verified the presence of amide linkages, which increased as the citric acid dosage were increased to 0.2 and then to 0.4 mmol/g. The inferred crosslinking was supported by the lower water absorption of the films; the moisture content of the soaked films reduced from 90% (no citric acid) to 52-54%. Additionally, the wet stiffness (modulus of elasticity) of the crosslinked films was improved from 1.2 GPa (control) to 1.6 GPa (citric acid 0.4 mmol/g). An attempt to improve the dry-state ductility (flexibility) of the crosslinked films using adipic acid in partial substitution of citric acid, however, did not turn out to be conclusive under the conditions examined. Overall, findings from this study suggest that the wet mechanical properties and water resistance of chitosan-xylan polymer can be improved through citric acid crosslinking.