Conducting bicomponent fibers obtained by melt spinning of PA6 and polyolefins containing high amounts of carbonaceous fillers

Abstract

Melt spinning of conductive polymer composites (CPCs) is coupled with some difficulties such as a decrease of conductivity upon drawing and a reduced spinnability with increasing filler concentration. Applying bicomponent technology may provide the possibility to produce fibers from CPCs with a high filler concentration. A pilot-scale bicomponent melt spinning set-up was used to produce core/sheath fibers with fiber titers between 13 and 47 dtex. The sheath material was polyamide 6 (PA6) or polypropylene (PP) and the core material was a CPC. Two CPCs were used, polypropylene (PP) with carbon black (CB), denoted by PP/CB, and polyethylene (PE) with multiwalled carbon nanotubes (MWNT), denoted by PE/MWNT. The results showed that both materials could be used with a filler concentration of 10 wt % to obtain melt draw ratios up to 195. The volumetric fraction of core material in the bicomponent structure was 28%. A heat treatment of PP/CB fibers restored the conductivity to the level of the undrawn material, corresponding to an increase in conductivity by a factor 5. The same heat treatment had a positive effect on the conductivity of PE/ MWNT fibers although the conductivity was not restored.

Electrically conductive polymeric bi‐component fibers containing a high load of low‐structured carbon black

“…The electrical volume conductivity of the fibers containing 18 vol % CB was reduced from 1 S/cm for the undrawn strand to 0.47 S/cm for fibers produced with MDR = 101, SSDR = 1, and to 0.15 S/cm for MDR = 33, SSDR = 3. Previous studies have shown that SSDR had a stronger influence on the electrical properties of the fibers than MDR which is in line with the present findings.…”

“…Thus, there are good arguments for seeking other ways of making textile fibers conductive. Our research group has recently investigated the possibility of using conductive polymer composites in the manufacturing of melt‐spun textile fibers . Conductive carbon nanoparticles, carbon black (CB), carbon nanotubes (CNT) and, recently, graphite nanoplatelets (GNP), have gained intense attention during the last decades.…”

“…Thus CB, although its lower inherent conductivity compared to CNT and GNP, would be the most favourable option for melt spinning applications since it is less affected by flow orientation effects. Furthermore, the decrease in conductivity of a polymer/CB composite during the drawing can be restored by heat treatment, which is not the case for polymer/CNT or polymer/GNP composites …”

“…This has a negative effect on the fiber spinning in terms of spin line instabilities, fiber diameter variations and ultimately, as the melt draw ratio increases, spin line breakage . To overcome some of these difficulties it was recently proposed to use bi‐component technology, where the fibers have a conductive composite in the core surrounded by a fiber forming polymer in the sheath. The main part of the spin line stress is then taken up by the sheath polymer relieving some of the requirements on spinnability of the CPC core material.…”

“…The main part of the spin line stress is then taken up by the sheath polymer relieving some of the requirements on spinnability of the CPC core material. Bi‐component fibers with a PA6 sheath and a core material of CB filled HDPE with a conductivity of 0.35 S/cm in the core were then produced …”