Thermal curing to improve properties of genipin-crosslinking chitosan film

Importance of the work: Chitosan film as a natural biodegradable packaging material has limited food applications due to its high moisture permeability and poor mechanical strength. Crosslinking with genipin, a natural crosslinker, and thermal curing were applied to eliminate these drawbacks. Objective: To study the effect of the genipin concentration and thermal curing on the chemical structure and properties of chitosan film. Materials & Methods: Chitosan (CS, 1.5 g) solution were prepared crosslinked with genipin at 0.5%, 1.0% or 1.5 (all weight per weight, w/w of chitosan) % and cured at 25 °C, 80 °C or 105 °C. Film properties were investigated: water vapor permeability (WVP), tensile strength (TS), elongation at break (EAB), Young’s modulus (YM), thermal stability, crystallinity and contact angle. Results: Increasing the genipin concentration significantly increased the degree of crosslinking, TS and YM of the films, with the best film obtained at 1.5% w/w genipin (CS1.5G). The CS1.5G film with curing at 105 °C (CS1.5G-105) had the highest (p < 0.05) TS (36.45 MPa), YM (315.99 N/m²) and thermal stability due to a high conjugation of C double bonding between the genipin molecules in the chitosan chains. However, CS1.5G-105 decreased the crystallinity, EAB and WVP, while the contact angle value increased. Main finding: Improving properties, such as the mechanical strength and moisture barrier of the genipin-crosslinked film, could be achieved by thermal curing, thus increasing the potential of the film for use as food packaging in the food industry.