A study on electrically conductive blends of polycarbonate/ liquid crystalline polymer/ multi-walled carbon nanotubes

摘要

A thermotropic liquid crystalline polymer (LCP) was introduced into the composites of polycarbonate (PC) and multi-walled carbon nanotube (CNT) with the goal of improving electrical conductivity and mechanical properties. It was hypothesized that double percolation networks would be produced first from aligned, continuous fibrils of LCP and then by CNT networks within LCP fibrils. Two grades of LCP were chosen: Vectra A950 (VA950), and Vectra V400P (V400P) from Hoechst Celanese. The CNT used was Baytubes, C-150P and the PC used was Lexan 121. The compounds were prepared by melt-blending in a twin-screw mini-compounder and injection molded using a mini-injection molder. The LCP content was kept at 20 wt% and the CNT contents were varied from 0.5 to 15 wt%. Only PC/VA950 blend showed fibrils of LCP. However, these fibrils turned into droplets with the addition of CNT. Results from TEM showed that CNT preferentially located inside the LCP domains as predicted from the value of spreading coefficient. The electrical conductivity showed the following order (the numbers in parenthesis are electrical percolation threshold): PC/CNT (2%) > PC/VA950P/CNT (3%) > PC/V400P/CNT (4%). The resulting discontinuity of the LCP droplet phase with CNTs located inside disrupted the electrically conductive pathways and resulted in lower electrical conductivity values. The value of storage modulus showed improvement by the addition of CNT and VA950.