Morphology and electric conductivity of cross-linked polyethylene-carbon black blends prepared by gelation/crystallization from solutions

Ultra-high-molecular-weight polyethylene (UHMWPE)-carbon black (CB) blends were prepared by gelation/crystallization from PE dilute solutions containing CB particles. The UHMWPE/CB composition chosen were 1/0.15, 1/0.25, 1/0.5, 1/0.75, 1/1, 1/3, 1/5, and 1/9, etc. The crosslinking of PE chains was performed by chemical reaction of dicumylperoxide at 160 OC. X-ray diffraction patterns indicate that the crystallinity of PE within the blends decreased drastically through the chemical reaction at high temperature. The sample preparation method by gelation/crystallization provided the UHMWPE-CB system with various CB contents up to 90% and the conductivities for the resultant specimens were in the range from 10(-9) to 1 Omega(-1) cm(-1) corresponding to the electric conductivity range of semiconductors. The blends assured thermal stability of electric conductivity by cross-linking of PE chains, although the mechanical property such as the storage and loss moduli were very sensitive to temperature. The conductivity of the blends with CB content greater than or equal to 20% were almost independent of temperature up to 220 degrees C and the values in the heating and cooling processes were almost the same. On the other hand, for the UHMWPE-CB blends with 13% CB content corresponding to the critical one, temperature dependence of electric resistivity showed positive temperature coefficient (PTC) effect. The PTC intensities for non-crosslinked and cross-linked materials were lower than that of the corresponding low-molecular-weight-polyethylene (LMWPE)-CB blend but the maximum peak appeared at 160 degrees C which is higher than the peak temperature of LMWPE-CB blend.