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

- Polycarbonate/CNT fibers were successfully melt-spun.
- Mechanical, electrical and piezoresistive properties were evaluated on the fibers.
- Enhanced mechanical and electrical properties were achieved starting at 1 wt% CNT.
- Increasing draw down ratio & lowering CNT wt% enhances the strain sensitivity.
- Gage factors (strain sensitivity) as high as 16 were obtained from the fibers.

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 (φc) for the bulk material was <1 wt% and ∼1 wt% for the undrawn-extruded rods, for the melt-spun fibers φc 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 SGF) was estimated for fibers with MWCNTs amounts that range from 3.5 to 6 wt%. The highest SGF ∼16 was found at 3.5 wt% and the lowest SGF ∼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.

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