Unleashing the potential of water-insoluble Cu2+-crosslinked chitosan nanocomposite film for enhanced antibacterial and flame-retardant properties.

Chitosan (CS) has received widespread attention in various fields due to its excellent antimicrobial properties, inherent biodegradability and biocompatibility. However, the water swelling property of chitosan films reduces their performance and becomes a major obstacle for their practical application. Herein, we develop a water-insoluble montmorillonite/chitosan nanocomposite film (CS/MMT-Cu) with anti-bacterial and fire-retardant properties via Cu2+-crosslinking technique. Cu2+ ions are coordinated with amino and hydroxyl groups to crosslink the chitosan chains and bind to the montmorillonite (MMT) via electrostatic forces. As a result, the content of MMT has a significant effect on the mechanical and flame-retardant properties of CS/MMT-Cu films, in which the maximum tensile strength and finite oxygen index are 30.6 MPa and 40.5 %, respectively. In addition, the CS/MMT-Cu films exhibit good anti-bacterial properties. Overall, the prepared CS/MMT-Cu films have a broad application prospect in various fields, such as flame-retardant material, packaging and coatings.