Self-healing thermoplastic elastomer blends with hybrid fillers for piezoresistive and humidity sensing applications

Abstract

Sustainable, flexible electronics are promising for soft robotics, wearable devices, and e-skin, but soft substrates and sensors are vulnerable to damage. Incorporating self-healing functionality provides a promising strategy to overcome this limitation, enhancing durability and extending the operational lifetime. In this study, a hybrid filler based on carbon black and zinc oxide endows flexible thermoplastic polyurethane (TPU) ethylene vinyl acetate (EVA) blend with humidity sensing capabilities. Due to the thermoplastic nature of the TPU-EVA blend, namely the weakening of intramolecular forces above a critical softening temperature, recovering the mechanical properties upon structural damage is possible at 110 °C. In addition, the thermoplastic nature of the TPU-EVA blend allows shaping by thermoplastic processing techniques, like extrusion, injection molding and material extrusion additive manufacturing (MEX-AM). For the TPU-EVA blend 68 % recovery of the ultimate strength was achieved after self-healing at 110 °C. Nonetheless, for the sensing properties an 83 % recovery was achieved after the healing process. Finally, the self-healing capability of 3D printed TPU-EVA stips with embedded hybrid filler humidity sensors was investigated. It was exhibited fusing strips of the self-healing substrate with the integrated sensing elements preserved their electrical conductivity after fusing. This new type of flexible environmental sensor combines mechano- and hygroreception abilities and compatibility with thermoplastic processing, like MEX-AM. • Hybrid carbon black–ZnO filler enables humidity sensing in TPU–EVA blends. • TPU–EVA substrate shows self-healing with 68 % recovery of mechanical strength. • Humidity sensing performance recovers up to 83 % after healing above 100 °C. • Blend is compatible with thermoplastic shaping, including 3D printing (MEX-AM).