Hydrogen-Bonding Cross-Linking Agent-Reinforced Chitosan/Cellulose Composite Films for Fresh Fruit Preservation: An Experimental and Theoretical Study

In this paper, the possible reaction mechanism for grafting chitosan to carboxyl cellulose has been systematically studied by using both experimental and theoretical methods first. The results indicate that the free energy barrier for grafting chitosan to the carboxyl group at C2 and C3 positions in the glucose ring of cellulose chains is about 15 kcal/mol lower in energy than that at the C6 position, indicating high reactivity for C2 and C3 positions relevant to the C6 position in this grafting reaction. Meanwhile, both theoretical and experimental studies showed that proanthocyanidins can be viewed as strong hydrogen-bonding cross-linking agents to enhance the interfacial interaction of chitosan and cellulose. When the mass/volume ratio of proanthocyanidin in the coating solution is 0.4%, the composite film exhibits the optimum comprehensive performance. Its oxygen transmission rate and water vapor transmission rate dropped to 0.0296 ± 0.0015 g/(cm2·24 h·Pa) and 205.41 ± 2.02 g/(m2·24 h), respectively. Its tensile strength (TS) and elastic modulus (EM) can reach 31.68 ± 0.53 and 1064.79 ± 1.25 MPa, respectively. Considering that our composite films were successfully used in the active packing of fresh strawberries (14 days), effectively extending the shelf life, our composite films have the potential to be used as biodegradable packaging materials for fresh fruits.