INFLUENCE OF CHEMICAL CROSS-LINKING ON THE OVER VOLTAGE POSITIVE TEMPERATURE COEFFICIENT OF LINEAR LOW DENSITY POLYETHYLENE/CARBON BLACK/ALUMINUM HYDROXIDE COMPOSITES

摘要

Linear low density polyethylene (LLDPE) with carbon black (CB) and inorganic flame retardant (aluminum hydroxide, Al(OH)_3) composites were prepared by a usual melt-blending method. The effect of cross-linking of blends on the stability of positive temperature coefficient (PTC) and the elimination of negative temperature coefficient (NTC) were investigated. LLDPE was chemically cross-linking with various amounts of dicumyl peroxide (DCP). The resulting of cross-linking structure of composites was analyzed by gel content analysis, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). By the effect of initiator (DCP), not only a high PTC intensity appeared, but also was the NTC effect of the composite eliminated. The PTC intensity reached six orders of magnitude for the LLDPE/DCP(0.10 wt%)/CB(33.7 wt%)/Al(OH)_3(28 wt%) composite, and the PTC transition temperature decreased with increasing of initiator (DCP) content. In addition, the cross-linking of LLDPE gives rise to a decrease in crystallinity, the good reproducibility of PPTC composites were obtained in thermal cycling, and successfully passed the test of over-voltage resistance.