Kinetic model for S-TBBS-DPG NR vulcanization: Extrapolation from S-TBBS and S-DPG experimental data

A robust extrapolation model requiring few input parameters to predict the kinetic constants characterizing the curing behavior of NR vulcanized in presence of sulfur and two accelerants (TBSS and DPG) at different concentrations is discussed. The numerical model based on the reproduction of rheometer curves by means of the well-known Han's kinetic model, which describes with kinetic base the most important NR vulcanization phases, namely curing initiation, formation of matured crosslinked polymer and reversion. The derived mathematical model is a closed form exponential function depending on only three kinetic constants. The procedure proposed is a two-step one. In the first step, kinetic constants of NR in the presence of single activators (i.e. either only with S and TBBS or S and DPG) are estimated by means of an interactive trial and error optimization software (GURU) that proceeds in approximating more and more strictly normalized experimental rheometer curves with Han's function. Four different concentrations of S and TBSS (or S and DPG) are assumed as calibration points. In the second step, from the results obtained previously, kinetic constants for NR with any S-TBBS-DPG concentration of technical relevance are deduced by means of standard mathematical extrapolation. The procedure is benchmarked on 16 different S-TBBS-DPG concentrations at two temperatures (150°C and 180°C), for which both experimental data are available and kinetic constants are previously derived with GURU. Quite good agreement is found, meaning that the approach may be useful for practical purposes, because expensive and cumbersome experimental investigations can be avoided.