IMPROVED OZONE RESISTANCE OF STYRENE-BUTADIENE RUBBER CURED BY A COMBINATION OF SULFUR AND IONIZING-RADIATION

The ozone resistance of filled styrene-butadiene rubber (SBR) samples, cured by a combination of sulfur and ionizing radiation, was investig ated. The ozone resistance of similar filled samples, but fully cured by sulfur or peroxide, was also studied. The influence of the filler ( carbon black) on the optical density measurements of these SBR formula tions was investigated. In addition, the influence of the absorbed dos e on the ozone resistance for samples with formulations containing par tial levels of sulfur was determined. Fourier-transform infrared studi es performed in this work indicate that the high ozone resistance of S BR formulations, cured by a combination of sulfur and ionizing radiati on, is associated with unusually high vinyl concentration. On the othe r hand, sulfur cured SBR formulations with low vinyl concentration hav e poor ozone resistance. Curing with peroxides, which involves chemist ry similar to that of radiation curing, also leads to high vinyl conce ntration (relative to sulfur curing) and high ozone resistance. Increa sing the absorbed dose in sulfur-radiation cured samples decreased the high vinyl content to a point where the ozone resistance declined gre atly.