Construction of polyurethane composites incorporating borate ester and B-N coordinative bonds: Achieving ultra-high fracture energy, self-healing property, and facile recyclability for wearable sensors

Abstract

In recent years, there has been a notable surge in research focusing on the utilization of polyurethane (PU) in flexible wearable electronic devices. Consequently, it is essential to incorporate attributes such as high stretch, self-healing, and easy recyclability into PU. However, the suboptimal compatibility of PU with conductive fillers poses a significant challenge. This paper details the synthesis of a highly stretchable, self-healing, and easily recyclable PU elastomer, utilizing borate ester bonds and B-N mating bonds as the composite matrix. Highly conductive flexible composites were fabricated, employing multi-walled carbon nanotubes (CNTs) and graphene nanosheets (GNSs) as fillers. These composites exhibit excellent fracture energy, self-healing ability, and tensile strength due to the synergistic interaction of borate bonds, B-N ligand bonds, and hydrogen bonds. The fracture energy achieves an impressive 109.4 KJ·m−2, with a noteworthy 79% self-healing efficiency. Furthermore, the materials demonstrate mechanical properties, including a tensile strength of 66.5 MPa and an exceptionally high elongation at break of 2792%. The flexible conductive composites present high electrical conductivity (6.86 S/m) and sensitivity (GF：9.45). In its capacity as a flexible conductive composite, it can accurately detect human behaviors, such as finger flexion, facial expressions, throat articulation tests, and more. Therefore, it has potential applications in various fields, including wearables, robotic skin, and health monitoring.