Free volume changes in gamma-irradiated polyethylene and polytetraflourethylene

Positron lifetime spectrum was measured and the change of the free volume w as studied for commercial polyethylene (PE) and polytetrafluoroethylene (PT FE) during gamma-irradiation processing up to 265 kGy. The free volume size increases but the crystallinity decreases as irradiation dose increases in PE. Both qualities (free volume size and crystallinity) in PTFE display an opposite behavior. The fractional free volume reduces monotonically with i ncreasing irradiation dose in both PE and PTFE. The competition between the crosslinking and the splitting decomposition in polymers can be used to un derstand the free volume changes with irradiation dose.