Electron beam irradiation of epoxidized natural rubber: FTIR studies

The effect of irradiation on the structure of epoxidized (50 %) natural rubber (ENR50) has been studied using Fourier transform infrared spectroscopy (FTIR). ENR50 was irradiated using a 3.0 MeV electron beam machine with doses ranging from 20 to 200 kGy. The influence of several additives such as trimethylolpropane triacrylate (TMPTA). Irganox®1010, and tribasic lead sulfate on the irradiation-induced changes of ENR50 is investigated. Upon irradiation, ring opening of epoxide groups, and oxidation and crosslinking of residual double bonds occurred, leading to decreases in the intensities of epoxide and cis double bond bands and an increases in ether, furan and hydroxyl bands. Gel fraction and hardness values have been used to correlate changes in the structure of the rubber upon irradiation. The results show that the increase in gel fraction upon irradiation of pure ENR50 can be associated with irradiation-induced crosslinking, ring opening side-chain reactions of oxirane groups and oxidation at the cis-double bonds. The addition of Irganox®1010 and tribasic lead sulfate inhibits irradiation-induced reactions in ENR50 to a considerable extent. The importance of TMPTA in preventing intramolecular ring opening side-chain reactions is also discussed. However, our studies do not reveal the exact nature of the irradiation-induced reactions involved in ENR.