Carbon nanotube network structure induced strain sensitivity and shape memory behavior changes of thermoplastic polyurethane

Thermoplastic polyurethane (TPU) composites containing different carbon nanotube (CNT) contents ranging from 0.5 to 5 wt% were prepared and the main attention was focused on investigating the relation between the network structure of CNTs and the macroscopic physical properties of the composites. The network structure of CNTs in the TPU/CNT composites was demonstrated through morphological characterization and rheological measurement. Tensile properties, electrical properties, strain sensitivity and shape memory properties were comparatively investigated. The results showed that CNTs at content above 2 wt% formed the percolated network structure in the TPU composites. High content of CNTs exhibited excellent reinforcement effect. Adding a few CNTs greatly reduced the electrical resistivity of the composites. The TPU/CNT composites exhibited good strain sensitivity, and the variation of electrical resistivity during the stretching-restoring process was dependent upon CNT content. At room temperature, CNTs delayed the shape recovery behavior of the composites, especially when the percolated CNT network structure was formed. However, with the aid of electrical actuation, largely accelerated shape recovery behavior was observed for the TPU/CNT sample containing 5 wt% CNTs.