Thermal, electrical and mechanical properties of ultra-high molecular weight polypropylene and carbon filler composites

isotactic ultra-high molecule weight polypropylene (UHMWPP) composites filled with multi-wall carbon nanotubes (MWNTs), vapor growth carbon fibers (VGCFs) and short carbon fibers (CFs) were prepared by gelation/crystallization from solutions, in which these aspect ratios of MWNTs, VGCFs and CFs chosen were 5001000, 50-300 and 5-20, respectively. The thermal, electrical and mechanical properties of these composites were studied in terms of their aspect ratios of the three kinds of fillers. The admixture of the three kinds of carbon filter provided better improvement of thermal property in comparison with neat UHMWPP, and the effect was the most significant for the admixture of MWNTs with the highest average aspect ratio. The electrical conductivity by the admixture of carbon fillers was also sensitive to the aspect ratio. Namely, the electrical conductivity of undrawn UHMWPP-MWNT composite film was the highest, when the filler content of the composites was the same. The conductivities of UHMWPP-VGCF and UHMWPP-CF composites decreased drastically by elongation up to 5 times (lambda = 5), while the conductivity of UHMWPP-MWNT maintained ca. 10(-3) S/cm at lambda = 5 but further elongation up to lambda = 20 caused a gradual decrease of the conductivity. Young's modulus of the UHMWPP-VGCF composites was higher than that of neat UHMWPP films in undrawn and drawn states, while that of UHMWPP-MWNT composites became lower when the composite with 3 wt% MWNT content was elongated up to lambda = 20. These phenomena indicated that a number of entanglement points of MWNTs within the composite assure electric channels in drawn state but hamper the smooth orientation of UHMWPP chains.