Dusting Thermoplastic Polyurethane Granules with Carbon Nanotubes toward Highly Stretchable Conductive Elastomer Composites

Abstract

Improving the electrical conductivity of elastomer composites while maintaining their favorable mechanical properties is crucial in a wide range of applications such as strain sensors for wearable devices and electronic skins. Herein, a facile and scalable strategy, i.e., dusting technology, is proposed to fabricate conductive elastomer composites (CECs) using multiwalled carbon nanotubes (CNTs) filler and thermoplastic polyurethane (TPU) elastomer. The TPU granules with various sizes are dusted with CNTs, and then the excess fillers not attached to the granules are removed prior to the compression molding, resulting in CECs with extremely low filler content. This fabrication strategy leads to a segregated structure at certain sizes of TPU granules and significantly enhances the electrical properties of resulting CECs, i.e., 5–6 orders of magnitude change at TPU particle sizes of above 1400 μm. It is shown that the larger the TPU particle size is, the more robust the conductive network is, leading to higher electrical conductivity. The tensile strength and elongation at break of TPU composites remain almost unchanged compared to the neat TPU. The results also reveal that the proposed method is capable of tuning the piezoresistive behavior of strain sensors using various TPU granule sizes. The gauge factors obtained for these composites are 81, 194, 160, and 202 for strain ranges of 0–10, 10–25, 50–75, and 125–150%, which opens up many interesting applications in wearable sensors.