A Study of the Vulcanization Kinetics of an Accelerated-Sulfur SBR Compound

Abstract

Vulcanization kinetics for a SBR compound was studied by using both curemeter and DSC methods by a kinetic approach. A simplified but realistic model reaction scheme was used to simulate both induction and curing periods simultaneously. Model parameters were extracted from isothermal curemeter experiments. The model prediction demonstrated a good agreement with isothermal curemeter data over a temperature range of 120°C to 180°C. The variation of equilibrium modulus with temperature, observed from cure curves, can also be predicted. However, DSC experiments showed a different reaction behavior in the curing period as compared to model calculations. This was explained by the assumption that the reaction heat observed in DSC is due to all possible exothermal reactions, and the formation of crosslinks is only a part of these reactions. Hence, the curemeter can provide a good indication of crosslink formation, while DSC displays the entire reaction heat released during the vulcanization process. The kinetic approach allows one to incorporate vulcanization kinetics into the practical simulation of reactive processing operations.

Sulfur Vulcanization of Natural Rubber for Benzothiazole Accelerated Formulations: From Reaction Mechanisms to a Rational Kinetic Model

“…The formation of these dead ends and elastically ineffective loops occurs throughout the cure process; however, the rate of crosslink formation is initially much greater than the rate of loop formation so that the concentration of Vu increases for times less than 6 minutes. The PBE model results shown in Figure 13 qualitatively agree with the lumped parameter simulations of Coran 21 and Ding et al 24,25 However, in contrast to the lumped parameter models of Coran and coworkers, which require the initial concentration of A as input, the population-balance model predicts the formation of A from the initial concentrations of accelerator and sulfur. In addition the population-balance model is consistent with the experimental observation that sulfur is totally consumed at the end of the reaction.…”

“…6. Using the model parameters reported by Ding et al 24 , more degradation product D is formed via the side reaction than crosslinks that are formed by the main vulcanization reaction. It is difficult to accept a kinetic scheme where the major product is from a side reaction.…”

“…The rate constants k 1 , k 2 and k 3 capture the kinetics of the initial accelerator chemistry and crosslinking chemistry while the reaction with rate constant k 4 accounts for the scorch-delay observed in sulfenamide accelerators. This basic kinetic model was later extended by Ding et al 24 to include a competitive side reaction to explain the variation of equilibrium modulus with cure temperature; specifically,…”

“…The kinetic models developed by Coran and coworkers [19][20][21][22][23][24][25] describe some of the experimental ODR data and have significantly extended the state of the art; nevertheless, they have the following shortcomings:…”

Evaluation of injection‐molding simulation tools to model the cure kinetics of rubbers

“…Although mechanistic kinetics models have been developed and described in the literature, 42,43,[46][47][48][49] the use of phenomenological or empirical models is more common, as is the case with both simulation tools.…”