Thermo-chemical rubber devulcanization

ASARO LUCIA; GRATTON, MICHEL; SEGHAR, SAÏD; NOURREDINE AIT HOCINE

Congreso; 3R International Scientific Conference on Material Cycles and Waste Management; 2022

Japan Society of Material Cycles and Waste Management

Rubber parts and tires manufacturing industries are constantly growing. Nonetheless, the inability to recycle their wastes represents a hard environmental problem (Liu et al., 2020). Because of the three dimensional structure of rubbers and their composition that includes numerous components, these kinds of polymers are indeed difficult to recycle (Hejna et al., 2020; Kroll and Hoyer, 2019). One of the alternatives to throw off the mentioned wastes is to accumulate them in stocks, however they are focus of illnesses and fires (Adhikari et al., 2000; Mohajerani et al., 2020). Another way is to use them as an energy source by burning them, but this route is hazardous and generates environmental contamination (Molino et al., 2018). With the aim of reducing this environmental problematic, several processes have been developed, especially the devulcanization technique (Asaro et al., 2018; Bockstal et al., 2019).Rubber devulcanization is a process where poly-, di-, and mono-sulfidic bonds, formed during vulcanization, are totally or partially broken, i.e. a process that causes a selective breakup of sulfidic bonds without degrading the polymer (Isayev, 2013; Asaro et al., 2018). Performing a successful devulcanization is a great challenge, since the energies needed to break the sulfur-sulfur (S-S) and carbon-sulfur (C-S) bonds (227 and 273 kJ/- mol, respectively) are not so different from the energy required to break the rubber main chains i.e. the carbon-carbon (C-C) bonds (348 kJ/mol) (Ramarad et al., 2015). The chemical devulcanization in a pressurized reactor in supercritical carbon dioxide (scCO2)atmosphere has been already analyzed. It is expected that, during the devulcanization process, the supercritical carbon dioxide swell the polymer, facilitating the sulfidic bonds scission. The aim of this work is to develop a novel device allowing performing successful rubber devulcanization, under scCO2 atmosphere. In fact, a triaxial compression reactor was developed. It was integrated into a dynamic hydraulic universal testing machine equipped with a heating chamber. Rubber devulcanization tests were carried out in this reactor, under scCO2 atmosphere, using diphenyl disulfide (DD) as devulcanizing reagent, at different temperatures. The degree and quality of devulcanization of the treated materials were evaluated by the swelling test combined with the Horikx theory.