Roles of Heat and Radiation in the Degradation of Polymers in Nuclear Power Plant Environments II. Flame-retardant Cross-linked Polyethylene

摘要

Sheets of flame-retardant cross-linked polyethylene (FR-XLPE) were aged thermally at 80,100, 135, and 155°C for various periods from 100 to 800 h. They were also aged concurrently by heat and gamma-rays at the same temperatures for the same periods at a dose rate of 100 Gy/h. For these sheets, we measured complex permittivity, FT-MIR spectra, absorption spectra at THz frequencies, and indenter modulus. As a result, it has become clear that the aging at 135°C makes FR-XLPE hard regardless of the presence of concurrent irradiation of gamma-rays. This makes the transport of charge carriers difficult. Therefore, both the real and the imaginary parts of complex permittivity decrease, which is significant if the measurement frequency is low. However, this tendency becomes opposite as the samples are aged at 155°C by heat or concurrently by heat and radiation. This means that the heat plays a dominant role in the property change of FR-XLPE. On the other hand, the samples aged at 155°C concurrently by heat and radiation show larger values in the indenter modulus and in two parts of complex permittivity than the samples aged at the same temperature only by heat. This is probably due to the oxidative degradation induced by the cooperative reaction of heat and radiation.