An investigation on changes in chemical properties of pure ethylene-propylene-diene rubber in aqueous acidic environments

The influence of two aqueous acidic environments on two types of pure ethylene-propylene-diene (EPDM) rubber (i.e., elastomer) thin films is studied. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) results revealed the formation of several oxygenated species on the surface after exposure. Raman spectroscopy along with ATR-FTIR results confirmed the vulnerability of the olefinic double bonds (CC) of 5-ethylidene-2-norbornene (ENB) in acidic environments. In addition, the aggressive nature of 20% Cr(VI)/H2SO4 was also observed through an increase in oxygenated species formation on the surface of EPDM rubbers compared to 20% H2SO4 under identical conditions. Complex formation on the surface of EPDM samples exposed to 20% Cr(VI)/H2SO4 through reactions of carboxylic groups (generated due to EPDM degradation) with Cr(III) (formed due to reduction of Cr(VI)) was also evident in ATR-FTIR. Finally, all the oxygenated species combined to form crosslinking as observed by the increase in gel fraction with exposure time. Effect of molar mass on chemical changes was noticed as samples with higher molar masses were found to form relatively higher amount of gel upon exposure. However, no significant effect of long chain branching was noticed. On this basis, plausible surface degradation mechanisms are proposed.