Quasi-analytical kinetic model for natural rubber and polybutadiene rubber blends

A very simple kinetic model for natural rubber (NR) and polybutadiene (PB) blends is presented. The model is characterized by a completely uncoupled curing between NR and PB, NR being modeled with a primary vulcanization and a subsequent de-vulcanization and PB only by a simple first order model of vulcanization. The assumptions made are roughly in agreement with the actual experimental behavior of the constituent materials in a rheometer chamber, where PB exhibits a quite stable behavior even at high curing temperatures and long vulcanization times. As a result of the simplifications assumed into the curing model adopted, the numerical approach uses only on three kinetic constants, two for NR and one for PB. Such assumptions allow for a quite straightforward determination of the kinetic constants by means of a simple semi-analytical approach. The reliability of the procedure proposed is benchmarked on some 70% NR- 30% PB blends with two different accelerants (N-terbutyl, 2-benzothiazylsulfenamide TBBS and N,N-diphenylguanidine DPG) in different concentrations tested experimentally on a standard rheometer chamber at 170 and 180 °C. Quite good match is found between numerical predictions and normalized rheometer curves, with a clear practical impact into the Finite Element FE modelling of vulcanization of real items