Robust, Thermo-Malleable, and Closed-Loop Recyclable Mulberry Paper/Polyimine Composite Films Enabled by Dynamic Covalent Interpenetrating Networks.

The persistence of petrochemical plastics necessitates high-performance and recyclable alternatives, yet balancing mechanical robustness with component-level closed-loop recovery remains challenging for biomass-based plastic-replacement films. Here, a high-performance, thermo-malleable, and closed-loop recyclable composite film is constructed by integrating a highly crystalline enzyme-treated mulberry paper (Enzyme-MP) fiber network with an in situ formed polyimine (PI) vitrimer network via capillary-assisted infiltration. This process induces densification and extensive interfacial hydrogen bonding, forming a confined interpenetrating architecture that enhances stress transfer and restricts chain mobility. As a result, the composite film achieves a tensile strength of 70.3 MPa and a Young's modulus of 2.37 GPa, together with excellent thermomechanical stability over a broad temperature range. The dynamic imine exchange enables thermo-malleability, allowing seamless self-welding and thickness-scalable lamination at 120 °C. The dense structure also acts as an effective barrier, reducing water uptake to 14.3% and providing resistance to various organic solvents. Furthermore, full-component closed-loop recycling is realized via room-temperature transimination, enabling selective depolymerization of the matrix while preserving the crystalline cellulose fiber network. This work demonstrates a viable strategy to integrate high-strength film performance, processability, and chemical recyclability in biomass-based composite films, while providing a basis for future cradle-to-cradle material circulation in recyclable plastic-replacement films.