Effect of thermal annealing on the electrical conductivity of high-strength bicomponent polymer tapes containing carbon nanofillers

A new concept is described that creates highly oriented multifunctional polymer nanocomposite tapes (or fibres) that combine high stiffness and strength with good electrical properties and a low percolation threshold of conductive nanofillers. The concept is based on a bicomponent construction consisting of a highly oriented polymer core together with conductive polymer composite skins based on a polymer with lower melting temperature than the core. This construction allows for a thermal annealing process that can be applied selectively to the skins to improve their conductivity through a kinetic re-aggregation process while retaining the mechanical properties of the core and hence those of the overall tape or fibre. In the current study this generic concept was applied to bicomponent tapes based on a polypropylene homopolymer core and a multi-wall carbon nanotube or carbon black filled polypropylene copolymer skin. The conductivity of the bicomponent tape containing 5.3 wt.% of MWNTs in its outer skins increased from 1.3E−6 to 1.5 S/cm after annealing while the percolation threshold in the copolymer skins of highly drawn bicomponent tapes could be decreased from 5.3 to 1.1 wt.%. To the best of the authors’ knowledge this is the lowest percolation threshold reported in literature for highly drawn polymer nanocomposites fibres or tapes. In fact, the percolation threshold is as low as 0.1 wt.% when considered on the overall tape as the conductive skins account for only 10% of the total volume of these bicomponent tapes.