Thermally induced performance decay in conductive polymer composites

Abstract

In the course of long‐term service, electrically conductive polymer composites acting as positive temperature coefficient (PTC) materials are faced with performance decay characterized by gradually increased room temperature resistivity and decreased PTC intensity. To reveal the influencing factors and to find appropriate ways for solving the problems, thermal‐cold cycling experiments (which simulate the extreme operating conditions of PTC type materials in a laboratory environment) and electrification tests are carried out in the current work. The results demonstrate that irreversible damage of partial conductive networks and, in particular, oxidation degradation induced crystallizability deterioration of the matrix polymer are responsible for the electrical performance decay. Additionally, an increase in the contact resistance formed at the metallic electrode/composite contacts exerts a negative influence on the service life of the composites. Polym. Compos. 25:270–279, 2004. © 2004 Society of Plastics Engineers.

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

“…The PTC effect strongly depends on the processing condition and thermal history 6, 7. 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…”

A novel polymer composite with double positive‐temperature‐coefficient transitions: effect of filler–matrix interface on the resistivity–temperature behavior

“…When titanate concentration is less than 1 wt%, T c of both first and second transitions increases with increasing titanate concentration. This is because the PTC transition is basically a process of breaking conducting pathways formed by conducting filler particles in composites 4–7, 15, 30–32. Higher titanate concentration indicates better interface adhesion between alloy filler and polymer matrix, which makes it harder for the conducting network to be broken due to the reduced mobility of Sn–Pb alloy particles.…”

In situ melt grafting in carbon black/polyolefin composites and its influence on conductive performance

“…The latter material exhibits an evident unstability with increasing the times of the measurements. It has been known that damage to the partial electrical networks, due to the repeated drastic volume expansion–contraction close to the melting point of the matrix, is responsible for the deterioration of room temperature conductivity and PTC intensity 6. The introduction of chemical bonding into the interphase between CB and the matrix by melt grafting enhances the structural stability of the CB distributed in the composites.…”

“…As a result, degradation in the properties takes place, as characterized by the gradually increased room temperature resistivity and reduced PTC intensity (defined as the ratio of the maximum resistivity to the room‐temperature resistivity, calculated from the temperature‐dependence of the composite resistivity). An earlier study of this problem indicates that the main influencing factors are:6 (i) irreversible damage of the partially conductive networks, (ii) oxidative‐degradation‐induced poor crystallizability of the matrix polymer, and (iii) increased contact resistance formed at the pre‐embedded metallic electrodes/composites contacts.…”