Breakage of sulfur crosslinks in styrene-butadiene rubber by zinc(II) dithiocarbimate derivative

The chemical structure of rubbers makes reprocessing quite difficult. In this work, the chemical regeneration was used for styrene-butadiene rubber recycling. As a first step, the rubber was compounded with commercial vulcanization additives on a roll mill. Rheometric and rheological parameters were obtained in a Rubber Process Analyzer (RPA 2000), and the composition was vulcanized and molded in a hydraulic press. The cured samples were characterized by mechanical tests (tensile strenght, tear resistance and hardness). Following this first step, zinc(II) dithiocarbimate complex was then mixed with the vulcanized rubber and devulcanization was carried out. Finally, the regenerated composition was revulcanized and properties obtained before and after the regeneration and revulcanization processes were compared. The results showed that low concentrations of zinc(II) dithiocarbimate complex favored its action as a vulcanization accelerator, producing elastomers with high values of torque, viscosity, modulus, hardness, tear resistance, and stress at break. Amounts in the range 4.0–8.0 phr favored its performance as a regeneration agent, giving rise to rubbers with low values of the already mentioned properties. Lastly, it was also observed that above 8.0 phr of the complex, the properties were further increased, indicating a supression of the regenerating efficiency of zinc(II) dithiocarbimate complex.