Pathway for high-quality reclaim by thermal treatment of sulfur-vulcanized SBR

De-vulcanization of SBR (Styrene Butadiene Rubber) is a challenge, as the broken polymer chains tend to re-arrange. This influences the properties of the reclaimed and re-vulcanized rubber, and reduces the quality of the recycled material. Within this study, the breakdown of sulfur-cured SBR in a thermal de-vulcanization process is investigated under various conditions: The temperature range for the de-vulcanization is varied from 180 ºC to 300 ºC, and the treatments are done in air and under oxygen exclusion with nitrogen. Depending on the parameters used, the sol fraction increased as expected, crosslink density first decreased, but increased again above a temperature threshold of 220 ºC. The reasons for this increase in crosslink density are complicated intra-molecular rearrangements of chain fragments due to uncontrolled degradation and oxidation effects. This is confirmed by FT-IR and TGA measurements. Preventing oxidation during thermal treatment reduces the degree of rearrangements and results in significantly improved SBR reclaim properties.