Property enhancement of aligned carbon nanotube/polyimide composite by strategic prestraining

Spray winding is a method that draws carbon nanotube sheets from carbon nanotube array, winds them onto rotating mandrel and sprays polymer matrix on each layer of carbon nanotube sheet in the meantime. It is proved to be an effective way to produce aligned carbon nanotubes reinforced polymer composite, in which most of the carbon nanotubes align along the length direction of composite. However, it is found that misalignment and waviness of carbon nanotubes hinder the performance of polymer-nanotube composites in authors' previous study. In order to further improve the carbon nanotube orientation, we demonstrate a methodology employing spray winding followed by a prestraining strategy to enhance the carbon nanotube orientation in a CNT/polyimide composite. Multifunctional carbon nanotube/polyimide composites with high CNT volume fraction were developed with remarkable enhancement in mechanical, thermal and electrical properties. The tensile stress and Young's modulus appreciated by 262% and 205.9%, respectively; upon subjecting the composites to a prestrain of 6%. Significant improvement in the electrical and thermal conductivities was also observed due to prestraining. We attribute the latter to the formation of effective phonon and electron transfer paths resulting from improved carbon nanotube orientation.