Effect of deep eutectic solvent pretreatment on devulcanization of waste rubber powder

ABSTRACT The recycling of waste rubber is very important for environmental protection, but the compatibility problem restricts the recycling and application of waste rubber powder (WRP). Devulcanization of WRP has been proven to be an effective method to improve the solubilization effect. The use of environmentally friendly nontoxic solvents can not only improve the devulcanization effect but also avoid secondary pollution. Thus, in this article, an environmentally friendly deep eutectic solvent (DES) is first prepared and then applied to the devulcanization treatment of WRP. The results show that the prepared DES has a positive devulcanization effect, and the devulcanization rate can reach 50%. The devulcanization mechanism can be divided into two aspects: (1) adsorption and removal of sulfur-containing low-molecular compounds and (2) destruction of the crosslinking structure and improvement of fluidity. Observation of the microstructure showed that the rougher the surface of the desulfurized rubber powder, the more conducive to the crosslinking reaction with the matrix material to form a uniform whole. The devulcanization mechanism of DES is divided into destroying the sulfur-containing cross-linked structure and adsorbing the sulfur-containing low-molecular compounds. The surface of WRP after DES treatment is rougher and more porous, which is beneficial to the crosslinking reaction with the matrix material. Finally, the optimum process conditions for the de-crosslinking effect are determined by orthogonal test as follows: liquid-solid ratio 15∶1, temperature 120°C, time 0.5 h.