Melt spun multifilament yarns of carbon nanotubes-based polymeric blends: Electrical, mechanical and thermal properties

Abstract The elaboration of a conductive synthetic multifilament yarn is usually carried out by the processing of a nanocomposite material where conductive nanofillers are incorporated in an insulating matrix. The use of a biphasic blend of immiscible polymers where one phase consists in a multiwalled carbon nanotubes (MWCNT)-polymer composite (selective localization in one polymer) reduces the amount of filler necessary to obtain the properties targeted, and decreases the difficulty to spin the material by a melt spinning process. MWCNT are good candidates for their incorporation in spinnable blends, due to their very high aspect ratio which permits to obtain electrical conductivity with low content without drastic modification of the blend viscosity. These nanofillers have been incorporated in polycaprolactone (PCL) by melt extrusion (4 wt.%), and the resultant nanocomposite has been spun with polypropylene (PP) in several proportions and with different draw ratios. At low concentrations of PCL + 4 wt.% MWCNT the conductive phase is dispersed, whereas with replacing up to 50 wt.% of PP by the conductive phase it gets continuous due to the development of a co-continuous structure. Relationships between morphology and electrical properties, mechanical and thermal properties have been established. A nanofilled PCL proportion of 50 wt.% in PP and a low draw ratio of 1.06 is necessary to obtain a co-continuous morphology and to create a conductive network by “double percolation” in the multifilament yarns. However, the multifilament with such a composition (PP/PCL + 4% MWCNT 50/50) and draw ratio (E = 1.06), has low mechanical properties compared to neat PP multifilament (without MWCNT). A compromise has then to be found in order to combine optimized electrical and mechanical properties of the multifilaments. Concerning the thermal properties, the incorporation of nanofilled PCL and a modification of draw ratio shows a strong influence on crystallisation and thermal stability of the multifilaments.