Barrier properties of electron-beam-modified EPDM rubber

EPDM rubber was surface and bulk-modified with varying concentrations of trimethylol propane triacrylate (TMFTA) in the presence of a constant electron-beam irradiation dose of 100 kGy and over a wide range of irradiation doses from 0 to 200 kGy at a fixed TMPTA concentration (10%). The permeation rate and absorption of three homologous nonpolar solvents, namely, n-hexane, n-heptane, and n-octane, along with an aromatic solvent, toluene, and a polar solvent, trichloroethylene, through unirradiated, unmodified control, and modified rubber membranes (approximate to 150 mu m) were studied. It was found that both the permeation rate and absorption decrease progressively with increase in the TMPTA concentration up to 10% for both the surface and bulk-modified rubbers, With increase in the radiation dose, there also is an initial drop in the values up to 50 kGy for the control and surface-modified rubbers and up to about 100 kGy for the bulk-modified one, The control rubber shows the highest absorption and permeation for all the solvents except trichloroethylene, followed by the bulk-modified rubber membrane. Trichloroethylene is, however, absorbed and permeated most by the surface-modified sample. The observations are explained in terms of the structural modifications of the rubber, crosslinking, changes in the relevant thermodynamic properties such as surface energy, the penetrant size, and the transport mechanism of the penetrants. The influence of temperature on the permeability characteristics of the control and modified rubbers was also studied. (C) 2000 John Wiley & Sons, Inc.