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

Abstract 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.