Biomass-derived dynamic polyurethanes: Enhanced self-healing and recyclability through reversible cross-linking

Chemically cross-linked polyurethanes (CCPUs), renowned for their superior solvent resistance, high strength, and exceptional thermostability, have emerged as extensively used polymeric materials. Despite their advantages, CCPUs face a significant limitation that their stable cross-linked structures can preclude healing and recycling once damaged. This limitation underscores the urgent need for a new CCPUs variant that offers selfhealing and recyclability to extend service life. In this work, a new type of cross-linked polyurethanes (CPUs) was designed and synthesized by incorporating the biomass-derived castor oil (CO) as a cross-linking agent and dynamic disulfide bond into a traditional polyurethane without using any catalysts. These newly developed CPUs exhibit superior mechanical performance with an impressive tensile strength of 29.37 MPa and a remarkable maximum elongation at break of 769.9%. Notably, our recycled CPU-2 can retain a tensile strength of 22.40 MPa and an elongation at break above 604.8 % even after four thermal recycling cycles. Furthermore, the addition of conductive carbon black (CB) into this CPU matrix imparts remarkable self-healing properties to the polyurethanes/carbon black composite (CPU-2/CB), activated solely by near-infrared light. This inventive approach effectively enhances the functionality of traditional CCPUs, broadening their application potential.