Effect of γ‐radiation on the thermal conductivity of polypropylene

Abstract

SynopsisThe effect of W o 7-radiation on the thermal conductivity of polypropylene (PP) has been studied over the temperature range 0-160°C. for radiation doses of 600 and 1800Mrad. The conductivity of unirradiated specimens rises from 4.5 X lo-' cgs units (cal./cm.-sec.-"C.) a t 0°C. to 4.8 X cgs units a t 80°C. and subsequently decreases with temperature to a value of about 3.1 X 10-4 cgs units a t 160OC. Upon irradiation to 600 Mrad the thermal conductivity is lowered over the (t15OOC. temperature range. Above 90°C. the conductivity decreases with temperature and becomes relatively constant a t 3.4 X lo-' cgs units from 120 to 160°C. Differential scanning calorimeter (DCS) measurements from 30 to 200°C. show that irradiation to 600 Mrad lowers the energy associated with crystalline melting and shifts the endotherm melting peak from about 160 to 105°C. Irradiation to 1800 Mrad results in additional lowering of the thermal conductivity over the 50-160OC. range, a further decrease in area of the endothermic peak and a shift of its maximum peak position to about 75°C. The effects of radiation on the thermal conductivity of polypropylene are compared and correlated with the observed effects of radiation on the dynamic mechanical behavior.