Chitosan-based Self-Adaptive Crosslinker-Driven Functional Integration of Polyurethane Foam: High Strength, Intrinsic Flame Retardancy, and Upcycling

Semi-rigid polyurethane foam plays an indispensable role in the field of safety protection. However, its widespread use has brought challenges of unsustainability and potential fire hazards. Bio-based foams offer a new path to solve these problems, but the complexity of traditional manufacturing processes and their insufficient performance hinder their industrialization. This study synthesized a chitosan-based multifunctional crosslinking agent using a scalable one-pot method, which was subsequently utilized to construct a bio-based semi-rigid polyurethane foam (SPUR/CS-D) that integrates flame retardancy, recyclability, and high performance. The foam exhibits exceptional mechanical properties, capable of withstanding loads exceeding 9,000 times its own weight without significant deformation. Furthermore, SPUR/CS-D possesses excellent flame retardancy, maintaining structural stability under sustained flame attack at around 1200°C. Notably, based on the dynamic exchange behavior of urethane bonds and ester bonds catalyzed by tertiary amines, SPUR/CS-D can be rapidly recycled and upgraded into a high-performance transparent film through simple process. Furthermore, the multifunctional composite material formed by stacking the film with graphene exhibits an ideal electromagnetic shielding effect. This study successfully addressed the comprehensive challenges of traditional foams in terms of sustainability, manufacturing complexity, fire risk, and mechanical properties through green design and structural innovation.