Comparative study of three vulcanization kinetic models for natural rubber/leather wastes composites

In this article, the effect of leather residues from chrome tanning on the vulcanization kinetics and rheometric properties of a natural rubber composite was evaluated using three kinetic models proposed in the literature. Leather wastes were classified according to their size as fine (smaller than 0.6 mm) or coarse (between 0.84 and 2 mm). Subsequently, they were chemically treated with a sodium bicarbonate solution to neutralize their acidic nature derived from the tanning processes. The composites studied in this paper were obtained using a torque rheometer. Fine and coarse leather wastes were added to a natural rubber matrix in proportions of 20, 40, 60, 80, and 100 phr. The rheometric properties of all the composites were monitored during the curing process using a moving die rheometer. The addition of leather wastes increased the vulcanization time and stiffness of the composites; however, materials with fine leather wastes achieved lower vulcanization times than materials with coarse residues. The curves obtained during vulcanization rheometry were fitted to the three kinetic models, which made it possible to determine the kinetic parameters k and n. The fits for the three models were satisfactory based on the R-squared results. The values and trends of the kinetic parameters of each model were analyzed and related to the vulcanization phenomenon of each composite.