The pyrolysis study of polybutadiene rubber under different structural and process parameters: comparison with polyvinyl chloride degradation

Abstract

The effect of the initial cross-link, as well as process parameters, such as heating rate and temperature, was investigated on the pyrolysis of poly butadiene rubber (PBR) using a semi-batch stirred reactor and a TG equipment. To better evaluate the degradation mechanisms of polybutadiene rubber, the degradation of polyvinyl chloride was also investigated at similar heating rates using TG instrument. The results showed that due to the production of double bonds after HCl release, the pyrolysis of polyvinyl chloride proceeds similar to polybutadiene rubber. It is to note that in PBR pyrolysis, the degradation mechanisms were completely different under fast and slow pyrolysis, i.e., whereas slow pyrolysis follows a cross-linking mechanism and Diels–Alder reactions leading to cyclic products, fast pyrolysis promotes a chain scission mechanism, and therefore more aliphatic products are obtained. While PVC degradation involves three stages of HCl release, cross-link networks creation, and chain scission, respectively, with increasing heating rate, the intermediate stage is almost eliminated and PVC pyrolysis shows two obvious stages. Furthermore, as the cross-link of PBR was more severe, the liquid production was higher and the process time was longer, which significantly promoted char production. Moreover, the TG results of PBR and PVC are evidence that the ratio of cross-link and Diels–Alder over chain scission mechanism decreases as temperature and heating rate are increased. Thus, an increase in heating rate, and so operation under relatively fast pyrolysis conditions (above 90 K min−1), leads to PBR degradation at lower temperatures, which is evidence of the effect polymer structure has on the degradation.