A ductile and strong bioplastic film based on biodegradable polyurethane nanoparticle-crosslinked chitosan

Abstract

The widespread use and disposal of petroleum-derived plastic films contribute significantly to environmental pollution, affecting water, soil, and air quality and leading to microplastic contamination. In response, extensive research has focused on developing biodegradable chitosan-based films with enhanced mechanical properties as alternatives to conventional plastics. However, balancing ductility and strength in chitosan-based materials remains a significant challenge because these two mechanical properties are intrinsically mutually exclusive. This study presents a facile strategy for fabricating chitosan/polyurethane nanoparticle (PU NP) bioplastic films that simultaneously enhance both ductility and strength. The chitosan/PU NP bioplastic film exhibits a unique and novel elastic node–grid structure, where PU NPs serve as crosslinkers (elastic nodes) within an entangled chitosan network. Notably, incorporating 20 wt% PU NPs results in a failure strain of 37.47%, a tensile strength of 64.98 MPa, and a tensile work to fracture of 17.50 MJ m⁻³, representing increases of 311%, 23%, and 350%, respectively, compared with pure chitosan films. These remarkable mechanical properties are attributed to the deformation of the elastic nanoscale PU NPs under load and dynamic hydrogen bonding interactions between PU NPs and chitosan molecules. Furthermore, the bioplastic film is recyclable through a simple process without noticeable loss of mechanical performance and is compostable and biodegradable in soil within three months. This innovative bioplastic film holds promise for developing strong, ductile, and tough biopolymer materials, paving the way for sustainable alternatives to conventional plastic films and diverse future applications.