Combined experimental and numerical kinetic characterization of NR vulcanized with sulfur, N-terbutyl, 2-benzothiazylsulfenamide, and N,N-diphenylguanidine

A comprehensive experimental and numerical analysis aimed at investigating the rheometer behavior of Natural Rubber (NR) vulcanized with sulfur and two accelerators [N,N-diphenylguanidine (DPG) and N-terbutyl, 2-benzothiazylsulfenamide (TBBS)] is presented. To fit experimental data, the general reaction scheme proposed by Han and co-workers for vulcanized sulfur NR is re-adapted and suitably modified, taking into account DPG and TBBS single contributions. An ad hoc interactive software based on GUI technology is utilized to fit experimental data, allowing estimating kinetic constants also by unexperienced users. Chain reactions initiated by the formation of macrocompounds responsible for the formation of the instable crosslinked polymer are accounted for. In the presence of two accelerators, reactions are assumed to proceed in parallel, making the hypothesis of negligible interactions, being their concentrations rather similar. From the kinetic scheme adopted, a closed form solution is found for the crosslinking density, with the only limitation that the induction period is excluded from computations.