Positive temperature coefficent (PTC) behaviors of carbon black (CB)-filled polypropylene (PP)/ultra-high molecular weight polyethylene (UHMWPE) composites prepared by a coventional melt-mixing method

Positive temperature coefficent (PTC) effect in polymers was first discovered by Frydman in 1945 for low density polyethylene loaded with carbon black (CB). After Frydman, many investigators have studied the PTC effect in polymers extensively. Most past works are based on the experimental results from CB-filled polymers especially CB-filled single semicrystalline polymer composites due to their potential industrial applications. It has been found that non-crosslinked CB-filled semicrystalline polymer composites exhibit a sharp negative temperature coefficient(NTC) effect, which is a great disadvantage for their application in over-temperature protections. To eliminate the NTC effect, one successful approach is to crosslink the semicrystalline polymer matrix by peroxide, Gamma radiation or electron beam. Another method is to use extremely high viscosity polymer matrix such as UHMWPE. Recently, Chan et al used UHMWPE as polymer matrix and prepared CB-filled UHMWPE composites by a sintering method. They found that the CB-filled UHMWPE composites are good PTC materials which do not show NTC effect even though they are not crosslinked. This is a new approach to prepare polymer PTC materials. However, the sintering method has its disadvantage──low production rate. To overcome the problem, the coventional melt-mixing method can be used to prepare CB-filled UHMWPE based composites. The objective of this paper is to prepare the CB-filled PP/UHMWPE composites by the conventional melt-mixing method and to study the effect of the PP/UHMWPE weight ratio and the CB content on the PTC behaviors of the composite