High-Biomass-Loading, High-Performance, Closed-Loop Recyclable, and Easily Processable Wheat Straw-Polyimine Biocomposites

Biocomposites derived from agricultural waste and traditional polymers enable the valorization of biomass waste while reducing reliance on petroleum-derived feedstocks. However, achieving high biomass loading while maintaining excellent performance, recyclability, and processability remains a challenge. Herein, the gelation behavior of a polyimine vitrimer was regulated to achieve excellent casting flowability and rapid postcasting gelation, enabling the fabrication of biocomposites containing 80 wt % wheat straw waste. The biocomposites exhibited a well-dispersed microstructure and strong hydrogen-bonding interactions, resulting in mechanical properties superior to those of reported biocomposites at similar filler loadings. Their glass transition temperature reached 183 °C, exceeding that of commercial wood-plastic composites, while the coefficient of thermal expansion was reduced by 8–12-fold. They demonstrated outstanding solvent resistance, healing capability, and recyclability, retaining over 95% of tensile strength. They could also be readily processed into daily-use and decorative products through casting and hot pressing. This study promoted the utilization of agricultural wastes.