Using chitosan for future food packaging: An investigation into the effect of metal crosslinking on chitosan films’ mechanical, water barrier, and antimicrobial properties

Active, biodegradable food packaging offers a solution to conventional plastic pollution and food waste. Chitosan is derived from chitin, the second most abundant polymer found in nature after cellulose, and is antimicrobial, film-forming, non-toxic, renewable, and biodegradable. In order to make chitosan films viable for food packaging, crosslinking methods can be employed to improve its functional properties. This research explores the mechanical, water barrier, and antimicrobial properties of three chitosan-based films: non-crosslinked chitosan, crosslinked copper(II)-chitosan, and iron(III)-chitosan. This comparative study found that: 1) crosslinked chitosan films had the weakest elasticity but no increase in tensile strength, 2) crosslinking had no measurable effect on the water-vapor permeability, and 3) crosslinking enhanced the antimicrobial properties of the films. Despite showing promise as an active packaging material to replace low-density polyethylene, none of the films had all the functional properties needed for food packaging. Yet, inspiring research suggests that other active chitosan-based food packaging could replace passive conventional plastics to reduce plastic pollution, greenhouse gas emissions, food-waste, and disease transmission. The functional properties of chitosan-based films could be improved via biomimetic engineering and combining chitosan with other agricultural waste streams as part of the circular economy.