Strain sensing, electrical and mechanical properties of polycarbonate/multiwall carbon nanotube monofilament fibers fabricated by melt spinning

Polycarbonate (PC)/multiwall carbon nanotube (MWCNT)/composites were prepared by melt mixing and subsequently melt spun to monofilament fibers. Electrical, mechanical and piezoresistive (strain sensing) properties of the fibers were evaluated as a function of the MWCNT weight concentration, which was varied up to 6 wt%. After the incorporation of MWCNTs, a decrease in electrical resistivity of the fibers was found for MWCNT concentrations as low as 2 wt%. Furthermore, an important effect of the draw down ratio (DDR) on the electrical properties of the fibers was observed. While the electrical percolation threshold (phi(c)) for the bulk material was <1 wt% and similar to 1 wt% for the undrawn-extruded rods, for the melt-spun fibers phi(c) was found to be highly dependent on the DDR. Stiffness and offset yield stress of the MWCNT/PC fibers were increased starting with the addition of 1 wt% of MWCNTs. However, decreased spinnability was observed for fibers with MWCNT concentrations above 4 wt%. The coefficient that relates the electrical resistance changes to the mechanical strain (strain gage factor S-GF) was estimated for fibers with MWCNTs amounts that range from 3.5 to 6 wt%. The highest S-GF similar to 16 was found at 3.5 wt% and the lowest S-GF similar to 2.5 at 6 wt% MWCNT. Smart multifunctional textiles, made from such conductive fibers, have wide applications such as structural health monitoring, detection of gases and liquids, sensor arrays and flexible sensors. (C) 2015 Elsevier Ltd. All rights reserved.