Radiation Effects on Thermal Properties of Polymers. I. Polyethylene (contd.)

The information about radiation effects on the thermal properties of polymeric materials is of special interest as: (1) the temperature regime of technical structural units operated in the radiation fields is determined in many respects by the values of the material thermal constants and the rate of their degradation (2) the temperature and dose dependencies of heat conductivity and, especially, heat capacity characterize the polymer structure. The data on radiation effects on the thermal conductivity, heat capacity and diffusivity, linear thermal expansion, density, degree of crystallinity, heat and temperature of phase transitions were presented in the first part of this paper [Nucl. Instr. Meth. in Phys. Res. B 185 (2001) 116–122] for polyethylene of high and low density, as a well-known and typical partly-crystalline polymer that is very convenient for investigation of the radiolysis processes. This part of the review examines such problems as reversible radiation effects on heat capacity, analytical models of the radiation-induced changes and anisotropy effects on the thermal conductivity, accumulated radiation energy (‘heat defect’) and important problems of specific action of different kinds of radiation on the thermal properties of the polymer and dose-rate effects, especially under vacuum.