Comprehensive kinetic numerical model for NR and high-cis poly-butadiene rubber blends

A simple but robust kinetic mathematical model to predict the mechanical/thermal behaviour of NR and high-cis polybutadiene rubber blends is presented. The benchmark blend is a 70% NR with 30% high-cis polybutadiene blend vulcanized in presence of sulphur at 1 phr and single accelerants TBSS or DPG at concentrations equal to 1-0 and 0-1 respectively. Experimental rheometer curves are at disposal for both the NR-PB blend and single NR/PB rubbers at 170°C and 180°C. Rheometer curves at 150°C are utilized as reversion free references to normalize experimental data. The numerical model is based on a modification of Han's kinetic approach, where a linear interaction between NR and PB is accounted for. The determination of kinetic constants is possible by means of a constrained minimization approach that uses Sequential Quadratic Programming and fits through standard least-squares normalized rheometer curves. The procedure is benchmarked on 1-1-0 and 1-0-1 concentrations of S-TBBS-DPG at 170°C and 180°C. Quite good agreement is found against experimental data, with values of kinetic constants addressing a reduction of vulcanization rate with respect to pure NR and a beneficial reversion decrease due to PB contribution.