Analysing the modifications of carbon black and other fillers after pyrolysis of model tyres

Abstract

Carbon blacks (CBs) that are used as fillers to reinforce rubber contribute to tyre recycling issues. Although recovered carbon black (rCB) produced from the thermoconversion of waste tyres has poor reinforcing abilities in non-polar rubbers, the exact origin of the difference between rCBs and CBs is not elucidated. The characteristics of the rCBs produced from the steam pyrolysis of model laboratory-reinforced rubbers, with or without silica added, were analysed and compared to the pristine CB. X-Ray Diffraction revealed that the quantity of unorganised carbon in the rCB increased by about 25% after pyrolysis, revealing the occurrence of carbonaceous deposits originating from rubber carbonisation. They affected the filler texture, and part of the ultra-microporosity (i.e., pores within the diameter range 0.34–0.76 nm), which had a three-fold decrease in the rCB sample. The recovered fillers, with and without silica, had more oxygenated functional groups than the CB. The dispersibility and stability of the colloidal suspensions were affected by the increased surface oxygen functional groups. Reductive hydrogenation was utilised to remove the excess oxygen allowing an improved understanding of the rCBs. This is a promising method to maximise material reutilisation in the circular value chain of tyres.