Effects of thermal aging on morphology, resistivity, and thermal properties of extruded high‐density polyethylene/carbon black heating elements

Abstract

Abstract Various output heating elements were extruded with carbon black (CB)‐filled high‐density polyethylene (HDPE) composites. After thermal aging near melting point of HDPE, the effects of thermal aging on the morphology, resistivity, and thermal properties of the extruded and electron beam (EB)‐irradiated heating elements were examined using scanning electron microscopy (SEM) megohmmeter and differential scanning calorimetry, respectively. The heating element was insulated with a polytetrafluoroethylene tape wrap. The SEM image of HDPE is covered with microvoids that leave a dimple‐like structure on the surface. As the percolation threshold is achieved, CB aggregates are usually located in oval cavities larger than the particles themselves. During the resistivity–temperature cycling test, significant change in resistivity was observed for extruded and EB‐irradiated heaters. In case of thermal‐aged samples at 140°C for 120 h, both heaters showed good stability without pronounced changes in resistivity after resistivity–temperature cycling test. After thermal aged at 140°C for 120 h, the Heater02‐EB composite recovered the oval cavity structure, whereas for Heater02, the amorphous region became narrower and formed a more electroconductive pathway. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers