Complete relaxation map of polyethylene: filler-induced chemical modifications as dielectric probes

Abstract

Low-density polyethylene (LDPE) filled with a small amount of titanium dioxide proves to be very suitable for studying the molecular motion of polyethylene by means of dielectric spectroscopy. The titanium dioxide acts as an oxidizing agent that introduces a small concentration of polar carbonyl groups, which does not alter molecular motion, but couples it to the alternating electric field. The frequency and temperature dependences of molecular-motion processes in LDPE are determined from both isochronal and isothermal loss plots. In particular, the temperature dependence of the β process connected with the glass-rubber transition in polyethylene obeys the Vogel-Fulcher-Tammann-Hesse law, which indicates co-operative behaviour. For pure LDPE, a glass-transition temperature of -31 °C is determined dielectrically. It increases with increasing titanium dioxide content.