Kinetic mathematical model with induction and reversion for the vulcanization of natural rubber and ethylene propylene diene monomer blend

The complexity inherent in modeling and optimizing rubber cure processes stems from the intricate interplay between “induction” and “reversion” phenomena. During the vulcanization process, rubber compounds undergo a gradual initial decrease in torque in an “induction” phase. Following this, the primary vulcanization reaction triggers a swift surge in cross-link density. Interestingly, the density may peak and subsequently decline, leading to compromised mechanical properties with prolonged curing times. This “reversion” phenomenon is extensively documented in sulfur-cured rubbers at elevated vulcanization temperatures, typically exceeding 140 °C. Moreover, the cure conditions can influence the final structure, mechanical performance, and thermal stability of the network. This paper introduces a kinetic mathematical model that is able to predict the optimal time and temperature for a blend of natural rubber and ethylene propylene diene monomer. This model incorporates considerations for both the induction and reversion phases of the vulcanization process. These considerations prove particularly critical, especially in scenarios involving large rubber items or when the rubber's rheometer curves exhibit a slow pace with significant reversion towards the end. Additionally, the study proposes a novel approach for determining the kinetic variables that concurrently consider all vulcanization temperatures using a standard genetic algorithm.