High-strength, self-healing waterborne polyurethane elastomers with enhanced mechanical, thermal, and electrical properties

Abstract

Developing elastomers that exhibit both high strength and excellent self-healing efficiency has been a longstanding challenge, as enhancing strength typically compromises fracture elongation and self-healing capabilities. In this work, we balance the mechanical strength and self-healing efficiency of waterborne polyurethane (WPU-SS) elastomers by introducing disulfide bonds as dynamic bonds. Disulfide bonds break and reorganize under external forces, inducing microphase separation in the polyurethane system, enhancing tensile strength and toughness, and promoting molecular chain flow to improve self-healing efficiency. The increased hydrogen bonding content further boosts both self-healing efficiency and mechanical strength. As a result, the maximum fracture strength of the WPU-SS elastomer achieves 26.6 MPa with an elongation at break of 664.6 %.and a self-healing efficiency of 83.4 % under mild heating conditions. By modifying liquid metal (LM) with dopamine and compounding it with WPU-SS, WPU-SS/LM composites are obtained. When the volume content of LM was 15 %, the composite exhibits the most significant improvements in mechanical properties and toughness, with a fracture strength of 43 MPa, which is 160 % times of that of WPU-SS. The thermal conductivity of WPU-SS/LM increases proportionally with the LM content, reaching 583.7 % of that of WPU-SS at 25 % LM content. Further, at 10 % LM content, WPU-SS/LM could be physically sintered to achieve permanent electrical conductivity. This enhanced mechanical, thermal, and electrical performance makes WPU-SS/LM composites promising for applications in conductive elastomers and dynamic switches.