Piezoresistive response and damage evolution of CNT/TPU/ABS nanocomposites under tensile loading

We investigated the piezoresistive performance and damage evolution of carbon nanotube (CNT) reinforced polymer composites suitable for deformable electronics. CNT/TPU (Thermoplastic Polyurethane)/ABS (Acrylonitrile Butadiene Styrene) nanocomposites (TPU/ABS weight ratio: 4/1) were manufactured via solution-casting and hot-pressing. A low electrical percolation threshold of 0.1 wt% and a 70% improvement in the elastic modulus at 1 wt% CNT loading were achieved, indicating effective CNT distribution and interfacial interaction. To study the mechanism governing the piezoresistive responses of CNT/TPU/ABS, specimens underwent monotonic, stiffness-sensing, and progressive cyclic tests. The nanocomposite resistance exhibited three distinct responses to deformation under progressive cyclic tests. Notably, the volumetric conductivity results, which decoupled the effects of applied strain and variation in conductivity on the electrical resistance, revealed the negative piezoresistivity of CNT/TPU/ABS during the unloading and reloading processes in the cyclic tests. This finding helps explain the resistance-strain response of similar nanocomposites based on the competition between the intrinsic piezoresistive effect and geometric changes. Furthermore, the in-situ electromechanical X-ray computed tomography (CT) test directly correlated the macroscopic electrical responses of CNT/TPU/ABS with its microstructural damage evolution. After void nucleation, the resistance was found to continue increasing during stress relaxation.