Electron beam irradiation of epoxidized natural rubber: FTIR studies

The effect of irradiation on the structure of epoxidized (50%) natural rubb er (ENR50) has been studied using Fourier transform infrared spectroscopy ( FTIR). ENR50 was irradiated using a 3.0MeV electron beam machine with doses ranging from 20 to 200 kGy. The influence of several additives such as tri methylolpropane triacrylate (TMPTA). Irganox((R))1010, and tribasic lead su lfate on the irradiation-induced changes of ENR50 is investigated. Upon irr adiation, 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 hyd roxyl bands. Gel fraction and hardness values have been used to correlate c hanges in the structure of the rubber upon irradiation. The results show th at the increase in gel fraction upon irradiation of pure ENR50 can be assoc iated with irradiation-induced crosslinking, ring opening side-chain reacti ons of oxirane groups and oxidation at the cis-double bonds. The addition o f Irganox((R))1010 and tribasic lead sulfate inhibits irradiation-induced r eactions in ENR50 to a considerable extent. The importance of TMPTA in prev enting intramolecular ring opening side-chain reactions is also discussed. However, our studies do not reveal the exact nature of the irradiation-indu ced reactions involved in ENR. (C) 2000 Society of Chemical Industry.