A polyimine vitrimer/cellulose nanofibrils composite film with excellent biodegradability and recyclability for plastic substitute.

Plastic pollution has been one of the biggest challenges to the ecological environment. Polyimine vitrimer (PI) synthesized by dynamic imine chemistry is degradable and closed-loop recyclable, making it a promising candidate to replace conventional nondegradable plastics. However, most PIs exhibit poor mechanical properties, which seriously weaken their application potential. Herein, a high strength PI/CNFs composite film (PI/CNFs film) was successfully developed by reinforcing PI using cellulose nanofibrils (CNFs). The resulting PI/CNFs film exhibited excellent mechanical properties with the tensile strength, toughness, and Young's modulus of 71 MPa, 33.7 MJ m-3, and 1.4 GPa, respectively. The PI/CNFs film also showed good waterproof capability, as well as excellent shape stability in water, ethanol, and alkali solution. The dynamic exchange character of PI endowed the PI/CNFs film with excellent re-healing, remolding, and reshaping capabilities. The PI/CNFs film could be chemically degraded and recycled because of the reversibility of imine bonds. Moreover, the PI/CNFs film could completely biodegrade in natural soil within two months. Therefore, this PI/CNFs film represents a novel and environmentally friendly plastic substitute.