Structure and process-dependent properties of solid-state spun carbon nanotube yarns

The effects of processing conditions and apparent nanotube length on properties are investigated for carbon nanotube yarns obtained by solid-state drawing of an aerogel from a forest of multi-walled carbon nanotubes. Investigation of twist, false twist, liquid densification and combination methods for converting the drawn aerogel into dense yarn show that permanent twist is not needed for obtaining useful mechanical properties when nanotube lengths are long compared with nanotube diameters. Average mechanical strengths of 800 MPa were obtained for polymer-free twist-spun multi-walled carbon nanotube (MWNT) yarns and average mechanical strengths of 1040 MPa were obtained for MWNT yarns infiltrated with 10 wt% polystyrene solution. Strategies for increasing the mechanical properties are suggested based on analysis of intra-wall, intra-bundle and inter-bundle stress transfer.