Abstract
Chitosan-citric biomembranes Ch-CA-Gx (x = 0-3) were prepared by a simple cross-linking. The dependence of mechanical property, water-resisting capacity, microstructural characteristic, oxygen barrier ability, and thermal properties of membranes on the content of glycerin was investigated. The results revealed that vacuum drying at 80 °C can lead to low-yield amidation and the Maillard reaction, thus affecting the thermal stability and water resistance of biomembranes. Owing to the ionic cross-linking and amidation, the chitosan-citrate complex showed weaker compatibility when the glycerin content increased, thereby leading to discontinuity of microstructure in the Ch-CA-Gx (x = 1-3) membranes, which was in line with the weaker mechanical properties and water-resisting abilities of membranes, compared to Ch-CA-G0. Chitosan membranes showed interestingly high oxygen barrier capabilities under 40 and 80% relative humidity (RH) conditions, probably attributed to the increased diffusion length arising from the hydrogen-bonding, ionic, and covalent cross-linking. The oxygen transmission rates of Ch-CA-Gx were below 0.1 cm(3) m(-2) day(-1) at 40% RH. The Ch-CA-Gx membranes showed a good elasticity assigned to the reversibly cross-linked structure. The membranes presented strong antibacterial activities against Staphylococcus aureus and Escherichia coli bacteria, probably owing to the citric acids. The results demonstrated that these materials have potential applications as membranes or protecting coatings for food packaging and successful cross-linking by means of amidation, and the Maillard reaction under the condition of vacuum drying can be probably applied as a green and alternative method for the fabrication of mechanically tough and antibacterial membranes, fibers, and gels.