Improvement of conductive network quality in carbon black‐filled polymer blends

Abstract

Heat treatment of polymer-based composites is critical for the enhancement of both stability and long-term service life, especially when the materials function under an inconstant temperature environment. The present article discusses the effect of heat-treatment conditions on the electrically conductive properties of carbon black (CB)-filled low-density polyethylene (LDPE) and ethylene-vinyl acetate copolymer (EVA) composites, which are candidates for positive temperature coefficient (PTC) materials. It was found that the dispersion mode of CB particles changes as a function of the matrix morphology. When the composites are irradiated to form crosslinked networks in the matrix for the elimination of negative temperature coefficient (NTC) behavior, some of the produced free radicals are also entrapped for quite a long time after the irradiation treatment. These residual radicals further enhance the interaction between CB and the matrix and further induce the crosslinking of the matrix so that the composites' conductivity changes with time as a result of the continuous variation in the contacts between the conductive fillers. To improve the quality of the conduction paths in the composites, appropriate post-heat treatment should be carried out, which speeds up the formation of the above-mentioned two kinds of crosslinked structures within a limited time. Annealing at 75 o C for more than 10 h is believed to be an effective way. After the treatment, a balanced performance characterized by reduced roomtemperature resistivity and improved PTC intensity was obtained. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2768 -2775, 2002

Influence of annealing on conduction of high‐density polyethylene/carbon black composite

“…The composites undergoing heating–cooling cycles usually show poor reproducibility of resistivity due to redistribution of particles in the matrix as a result of repeated melting and crystallization 8, 9. Improvement of the reproducibility of resistivity might be achieved through postheat treatment of the composites 4, 10, 11…”

Room temperature resistance relaxation behavior for carbon black filled conductive polymer composites

“…The PTC effect strongly depends on the time related thermal history, 19,20 so that thermal aging is becoming a common method to eliminate the thermal history and to stabilize the conduction behavior. 21,22 Tao et al 23 and Park et al 24 found that annealing at temperatures below and above T m has different influences on the redistribution of filler aggregates in the matrix and also on the PTC/NTC behavior of CPCs. Their observations were confirmed by Song and Zheng,20 and were explained with respect to the breakdown and reformation of the percolation network at lower temperatures, as well as the agglomeration of carbon black (CB) aggregates and formation of percolation network in the melts.…”

“…4,5 As most of these mechanisms are actually involved with kinetic processes, CPCs often exhibit time-dependent resistance changes at constant temperatures, stresses, or strains. [19][20][21][22][23][24][25][26][27][28][29][30] Many CPCs exhibit a drastic increase in electric resistivity over a temperature range around the melting point (T m ) of the semicrystalline matrix as is termed as positive temperature coefficient (PTC) effect of resistivity, which is usually followed by a rapid resistivity decrease named negative temperature coefficient (NTC) effect. The PTC effect strongly depends on the time related thermal history, 19,20 so that thermal aging is becoming a common method to eliminate the thermal history and to stabilize the conduction behavior.…”

Effects of layer-multiplying process on conducting properties of multilayer composites consisting of alternating layers of carbon black/polypropylene and polyamide 6/polypropylene

“…Numerous methods can be used to influence the selective distribution of CB particles within the continuous phase, and the introduction of a polar component is generally regarded as one of the most convenient and effective methods []. For example, Foulger [] decreased the percolation threshold of the CB‐filled co‐continuous poly(ethylene‐ co ‐vinyl acetate) (EVA)/HDPE composites to ∼4 wt% by selectively localizing CB particles within the EVA phase.…”