Permeation of Gases through Electron-Beam-Irradiated Polymer Films

Abstract

The permeation of CO2, CH4, O2, N2, SF6, and He was measured at 35°C in electron-beam-irradiated polymer films such as 1,2-polybutadiene (PB), polycarbonate (PC), polydimethylsiloxane (PDMS), poly(ethylene terephthalate) (PET), poly(4-methylpentene-1) (PMP), and polypropylene (PP). The permeability coefficients of the gases in PB decreased and those in PP increased with increasing irradiation dose, while those of PC, PDMS, PET, and PMP were virtually unaffected by irradiation. These results were attributed to the radiation effects of crosslinking in PB and degradation in PP. PC, PDMS, PET, and PMP were insensitive to radiation, which accounts for the little change in permeation behavior. The decreases in permeability coefficients of the gases in irradiated PB films were attributed to changes in diffusivity, while solubility was not greatly affected. The dependence of permeability coefficients on crosslinking density of the irradiated PB films was also discussed. Decreases in permeability and diffusion coefficients were interpreted as due to decrease of free-volume content by crosslinking. The diffusion coefficient showed an approximately exponential relationship to the reciprocal of the average molecular weight between crosslinks (Mc) over a range of Mc between 200 and 20000. This suggests that the free-volume of the crosslinked polymer may be proportional to Mc.