Cellulosic Functional Bioplastic with Tunable Strength and Toughness Through Heat‐Treatment of Dynamic Covalent Networks

The growing environmental crisis caused by petroleum-based polymers has intensified the development of sustainable alternatives, with many biomass-derived polymers demonstrating potential for degradability, renewability, and low carbon footprints, though these properties can vary depending on structure and processing. However, traditional bio-based systems often lack tunability in mechanical properties, making it challenging to achieve both high strength and ductility. Herein, we report a high-performance, recyclable bio-based film (CAF-L) constructed via Diels-Alder dynamic covalent chemistry between furfuryl-functionalized cellulose acetate and maleimide-modified lignin. Thermally responsive dynamic Diels-Alder bonds, activated through heat-treatment, enable programmable network crosslinking that allows a smooth transition between strength- and ductility-dominated regimes, while maintaining high mechanical performance (tensile strength up to 52.3 MPa and elongation at break up to 545%). Structural characterization and molecular simulations reveal that Diels-Alder bond dynamics drive thermally induced structural reorganization of the polymer network, imparting rare adaptivity to biomass-based systems. In addition, CAF-L films exhibit outstanding UV shielding, oxygen barrier properties, and dual-mode recyclability through solvent dissolution and hot pressing. This work provides a scalable platform for constructing mechanically tunable, structurally reconfigurable, and environmentally resilient cellulosic bioplastic for sustainable packaging and circular material systems.