Combined model-free and model-based devolatilisation kinetics of tyre rubbers

• The devolatilisation kinetics of four typical tyre rubbers was modelled.
• Two subsequent devolatilisation zones have been identified.
• These zones were kinetically modelled as two consecutive reactions.
• Model-free and model-based kinetics were successfully combined.
• Butadiene and styrene-butadiene rubbers started to boil around 450 °C.

The pyrolytic devolatilisation behaviour of four rubbers, which are predominantly used in tyre manufacturing, has been studied using combined model-free and model-based kinetics. Natural rubber, synthetic polyisoprene, butadiene and styrene-butadiene rubbers were investigated experimentally using a TGA–DTA instrument. For all of these rubbers two distinct zones of weight loss (here termed as devolatilisation reactions) were observed, i.e., primary depolymerisation/condensation and secondary (consecutive) degradation of the condensed product. Moreover, the DTG and DTA results indicated that the two butadiene rubbers started to boil around 450 °C. Next, fixed values of the activation energy, derived from two different isoconversional methods, were implemented as fixed values in a model-based kinetic procedure. The values of the apparent activation energies for the rubber devolatilisation reactions were between 200 and 440 kJ mol−1. This kinetic strategy resulted in a decrease of the degrees of freedom of the model-based multivariate nonlinear regression procedure. Therefore, the estimated kinetic parameters are less dependent on the initial guesses. Furthermore, the interdependence of the two consecutive devolatilisation reactions has also been successfully incorporated in the model, further improving the regression. This combined kinetic approach resulted in very accurate predictions of the experimental data.