Dielectric relaxations in titanium-dioxide-filled polyethylene: Filler-induced chemical modifications provide the dielectric response

Low-density polyethylene (LDPE) filled with a small amount (1 to 10 wt.%) of titanium-dioxide (TiO₂) powder 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 induces a small concentration of polar carbonyl groups, which do not alter molecular motion, but couple it to the alternating electric field, The frequency and temperature dependences of molecular-motion processes in LDPE are determined. In particular, it is shown that 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. The dielectrically determined glass-transition temperatures are close to the literature value of about -30°C. The unrelaxed permittivity increases with TiO₂ content by a factor of 1.45 at 35 wt.% TiO₂. This is lower than expected from models for the permittivity of heterogeneous mixtures. It points towards an inhomogencous TiO₂ -particle distribution