Rubber materials are characterized by great deformability and damping properties, used in various applications such as tires and sealing purposes. To obtain these properties, the vulcanization process promotes the formation of sulfur crosslink bonds between the polymer chains. Recycling rubber materials can be performed through different technological routes. The golden one is the devulcanization route that aims at selectively cleaving the sulfidic crosslink bonds, preserving the polymer chains, which is challenging considering the similar energies of S-S, C-S, and C-C bonds. Among the approaches, chemical devulcanization is considered to permit a higher selectivity by using devulcanizing agents (DA) that can react with the sulfidic bond and cleave it. In the supercritical CO2 (scCO2) assisted chemical devulcanization, the reaction is performed in scCO2 media, which swells the polymeric matrix, stretching the sulfide links, and can carry the DA into the rubber, facilitating the reaction with crosslink bonds. At the end of the reaction, the high-pressure cell is depressurized, and CO2 comes back to its gaseous state, letting the devulcanized rubber free from solvent traces. This project has explored the chemical devulcanization assisted by scCO2 of EPDM, in the frame of a collaboration with EXXON Mobile. EPDM, the third most used rubber, is an ethylene-propylene-diene random terpolymer with low content of unsaturated side chains of diene, that permits vulcanization. To the best of our knowledge, no study has been reported on scCO2-assisted devulcanization. Diphenyl disulfide (DD) was selected as the DA. The operational conditions of the devulcanization were optimized to improve devulcanization efficiency (determined as the decrease of crosslink density, evaluated by swelling tests) and selective cleavage of the crosslink bonds (evaluated by Horikx Model, which expresses the devulcanization percentage as a function of sol fraction). A Design of Experiments was applied to investigate the effect of temperature (100-200 C) and pressure (10-30 MPa), fixing the reaction time (2 h), the depressurization conditions, and the proportion of DD (mass of DD/mass of EPDM at 100 wt.). High devulcanization efficiency and reproducibility were achieved at 200 C and 10 MPa. FTIR spectra showed a decrease of the peak centered at 1262 cm-1, related to sulfidic bonds, which evidenced the crosslink scission after the devulcanization process. The presence of a peak at 690 cm-1, attributed to monosubstituted aromatics, evidences the grafting on EPDM chains. The scCO2-assisted chemical devulcanization of EPDM showed to be a promising recycling process for EPDM compounds.
Comissão Organizadora
Pedro Alves da Silva Autreto
Comissão Científica
Ferramenta completa de submissão, avaliação e publicação de anais para eventos científicos.
