Effect of Water Spray on Degradation of Styrene-Butadiene-Rubber During Accelerated Weathering Tests

Abstract Accelerated weathering tests using a xenon lamp were performed on styrene-butadiene rubber (SBR) under two conditions: only photo irradiation (photo-irradiated condition) and the addition of intermittent water spraying to photo irradiation (photo-irradiated/water-sprayed condition). Degradation mechanisms under these conditions were evaluated based on changes in chemical structure, hardness, and morphology of the exposed surface during weathering tests. The morphology of the exposed surfaces differed significantly between the two weathering conditions. Random minute cracks, known as crazes, were clearly observed under the photo-irradiated/water-sprayed condition. To clarify the origin of such craze propagation, the temperature change accompanying water spraying was traced. A combination of temperature decrease during water spraying and subsequent increase due to water evaporation was repeated under the photo-irradiated/water-sprayed condition. Such periodic temperature change caused the sample to expand and contract; however, the exposed surface could not follow this dimensional change, resulting in craze. This result indicates that water spraying is a degradation factor for accelerated weathering tests on SBR, especially change of surface shape.