The effect of electron beam irradiation on the tensile and dynamic mechanical properties of epoxidized natural rubber

The effect of irradiation on the tensile and dynamic mechanical properties of ENR50 (ENR: epoxidized natural rubber) was investigated. 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), Irganox1010 and tribasic lead sulfate (TBLS) on the irradiation-induced changes of ENR50 was investigated. The general improvement on the tensile, as well as dynamic mechanical properties with irradiation indicates the formation of irradiation-induced crosslinks. An appreciable increase in T-g is observed with irradiation while the enhancement in stress at break is found to be marginal. This observation agrees well with the relatively small increase in storage modulus occurred beyond the T-g of the irradiated ENR. This in return reveals that only a small degree of crosslinking is achieved through irradiation. Based on these factors it can be inferred that the gradual increase in T-g upon irradiation of ENR50 could be associated with the occurrence of irradiation-induced ring opening side chain reaction of the oxirane group and irradiation-induced oxidation at the cis double bond along with the irradiation-induced crosslinking. From the observation in the properties studied it confirms that TMPTA is efficient in enhancing the irradiation-induced crosslinking of ENR50. The addition of Irganox 1010 and TBLS are found to impart considerable stability to ENR50, although the antioxidant did cause some inhibition of crosslinking. The acceleration of crosslinking by the TMPTA as well as the inhibition of crosslinking the added stabilizing additives were further confirmed by using gel fraction data. However, the studies did not reveal the exact nature of irradiation-induced reactions involved in ENR. (C) 2001 Elsevier Science Ltd. All rights reserved.