Diffusion controlled radiochemical oxidation of low density polyethylene

LDPE samples of 0.6mm thickness were exposed to reactor radiation at 0.7 Gy/s dose rate and analysed after respectively 0.1, 0.5 and 1 MGy irradiation. Infrared spectrophotometry and differential scanning calorimetry were made on microtome sections of 20 μm thickness. It appeared clearly that the depth distribution of carbonyl concentration, melting point and enthalpy of fusion can be explained by a double competition between processes having opposite consequences: at a chemical level-oxidative chain scission and crosslinking, and at a morphological level-chemicrystallisation induced by chain scission and inhibited by crosslinking, and crystal destruction which is presumably independent of the chemical changes in the amorphous phase. (author)