Effect of electron‐beam irradiation on the thermal vulcanization of a natural rubber compound

The influence of electron‐beam irradiation on the thermal vulcanization curing kinetics of a natural rubber compound was investigated by means of rheometric tests [moving die rheometry (MDR)] and differential scanning calorimetry (DSC). Differences in the storage moduli of compounds with different radiation doses were observed and assigned to a plasticizer effect by the zinc stearate mainly formed in the mixing stages; this compound migrated to the interphase region. This fact was confirmed by Fourier transform infrared spectroscopy. From the measurements performed by MDR and DSC testing, the induction time ( t o ) was analyzed in the frame of the Claxton–Liska model, whereas the kinetic behavior of the nonirradiated and pre‐irradiated compounds were satisfactorily fitted with the Isayev–Deng and Kamal–Ryan models. Additionally, both curing characterization techniques corroborated the fact that the pre‐irradiated rubber compound showed an earlier t o and a lower activation energy in comparison with the nonirradiated compound. These facts were attributed to the effect of irradiation on the free sulfur content present in the rubber compound, which promoted more activated precursor species to crosslink with rubber. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136 , 47216.