The effect of percent hydrogenation and vulcanization system on ozone stability of hydrogenated natural rubber vulcanizates using Raman spectroscopy

The ozone stability of partially hydrogenated natural rubbers (HNRs) was evaluated. HNRs with the hydrogenation levels of 14, 33 and 65 mol% including with vulcanization systems of peroxide and sulfur on ozone stability comparing with natural rubber (NR) and ethylene-propylene-diene-rubber (EPDM) vulcanizates were studied. The chemical structures of rubber vulcanizates were characterized by Raman spectroscopy. The surface cracks were observed by Raman optical microscopy. The results clearly exhibited that the ozone stability of HNRs vulcanizates was much greater than that of the NR vulcanizates. The difference between the integral intensities of C=C bonds of isoprene units in rubber chains by Raman spectroscopy before and after ozone exposed was minimized with the degree of hydrogenation. The depth of cracking observed by three-dimensional (3D) modes clearly decreased with an increase in the degree of hydrogenation, while no cracks on the surface of EPDM were found. These findings indicated that ozone stability increased with the degree of hydrogenation. Regarding the effect of vulcanizing systems, sulfur cure showed greater resistance to ozone degradation than peroxide cure.