Soutenance de thèse Petros Mubari

The management of end-of-life tyres remains a critical issue, given the regulations requiring used tyres to be recovered, reused and recycled. Carbon black is a manufactured product of petrochemical origin whose production process is energy-intensive and polluting, it is the main mechanical reinforcement filler of rubber in tyres. Recovering carbon black and reintroducing it into the formulation of new tyres is a major challenge for the circular economy. Currently, only chemical (toxic organic solvents) or thermochemical techniques are capable of isolating carbon black from vulcanised rubber.
In the manufacture of tyres, carbon blacks ensure mechanical strength, while the increasing addition of silica reduces rolling resistance and increases service life. At the end of the pyrolysis process in the presence of steam, the elastomer is degraded and the solid phase is made up of carbon black, silica and ash (zinc, sulphur). In this thesis, the physical and chemical properties of carbon black recovered from model tyre tread mixtures are analysed using several complementary techniques. At present, recovered carbon black does not have properties close enough to those of the original material that is used in the elastomer industry, because it is not sufficiently dispersed. In order to better assess the modifications induced by the thermochemical process, as well as the role of ash from the formulation, physical techniques such as X-ray diffraction, which shows the fraction of the additional carbon deposit, have been used. Chemical techniques such as gas adsorption and desorption at programmed temperatures have highlighted the change in porosity and the gain in oxygen-containing surface functional groups. This made it possible to differentiate more clearly between the original N330 carbon black and the recovered carbon black. Other experiments focusing on the dispersibility of the recovered material in various media highlighted the complexity of the material's behaviour. In order to improve the incorporation of the recovered carbon blacks into the elastomer, functionalisation tests were carried out by depositing crystalline nano-cellulose and reducing the oxygen-containing surface functional groups by hydrogen treatment. These results represent a major contribution to the understanding of the physico-chemical properties of recovered carbon blacks, and form part of a virtuous objective to promote the circular economy and reduce pollutant emissions.