Acidic Ethanol/Water Casting Approach to Improve Chitin Nanofibril Dispersion and Properties of Propionylated Chitin Biocomposites

A fabrication process using acidic ethanol/water as a medium was developed to achieve homogenous dispersion of chitin nanofibrils (ChNFs) in a chitin propionate (CP) solution to form ChNF-reinforced CP nanocomposites. CP was prepared by propionylation of chitin to improve its dissolution in green organic solvents. ChNFs were extracted from chitin via partial alkali deacetylation in water. An acidified ethanol/water mixture as a medium was found to dissolve CP and disperse ChNF suspensions simultaneously, forming clear and stable formulations. The degree of ChNF dispersion and compatibility between ChNF and CP in the acidified ethanol/water mixture yielded transparent ChNF-reinforced CP nanocomposites with a moderate UV-blocking capability of up to 76%. The tensile strength and modulus of 15% ChNF-filled nanocomposites were enhanced by 66 and 97%, respectively, when compared to the neat films. In addition, the maximum degradation temperature was increased by 40 °C. The increase in storage modulus was more pronounced above the glass transition temperature. These results demonstrated that ChNFs had substantial reinforcing effects on the cast CP nanocomposites.