Vulcanization of EPDM rubber compounds with and without blowing agents: Identification of reaction events and TTT-diagram using DSC data

Abstract

Vulcanization of industrial‐like ethylene propylene diene termonomer rubber compound is studied using a differential scanning calorimetry (DSC). The analysis starts with DSC information to obtain the total transformation heat, followed by an isothermal‐dynamic temperature ramp that captures diffusion‐controlled reaction kinetics. The vulcanization is modeled by an auto‐catalytic Kamal–Sourour model, complemented with a Kissinger model for the prediction of one energy of activation, DiBenedetto's equation for the glass transition temperature, and adjusted reaction constants to include diffusion mechanisms. Two rubber formulations, with and without blowing agents, containing crosslinking agents, primary and secondary accelerators, activators, promoters, and processing aids are studied. The identification and separation of multiple reaction events, occurring during crosslinking of the compound without a blowing agent, is done through a 2k design of experiments. Time–temperature–transformation (TTT) diagrams are calculated, integrating the kinetic model, thereby delineating processability windows, providing avenues for optimization, design, and online processing control. According to the kinetics and the TTT diagrams, the blowing agent induces several differences to the vulcanization reaction: decreases reaction temperatures while increasing reaction heats. It eliminates the exothermic peak before vulcanization and decreases the fully cured resin's glass transition temperature. Therefore, the presence of the blowing agent drives a shift in the vitrification line, resulting in a reduced operational window. POLYM. ENG. SCI., 55:2073–2088, 2015. © 2014 Society of Plastics Engineers

Effect of electron‐beam irradiation on the thermal vulcanization of a natural rubber compound

“…The first region is the induction period, when most of the accelerator reactions occur; this is followed by the curing and postcuring regions. A relationship that describes the dependence of t o on the absolute temperature ( T ) was proposed by Claxton and Liska as follows: where B O is the pre‐exponential factor and A O is a material constant independent of the temperature. The effect of the temperature on t o is reported in Figure , where the test temperatures are given in degrees Kelvin.…”

“…Apart from these proposed curing kinetics models, the relationship between the reaction mechanism and the network structure of the resulting compounds have not yet been conclusively clarified because of the complexity of the chemical reactions that take place during the curing reaction. k 1 characterizes the initial reactivity, including the effect of the catalysts (accelerators and activators in the rubber compound), and k 2 characterizes the autocatalytic effect of the groups generated during the reaction …”

“…Although a few kinetic models that describe the mechanism of crosslinking of rubber compounds under electron‐beam radiation are available in the literature, several researchers have analyzed the thermal vulcanization processes of rubber compounds and have proposed different kinetic models. In general, phenomenological kinetic models have been developed to predict the curing reaction in agreement with obtained results from different curing characterization techniques, such as rheometer tests and differential scanning calorimetry (DSC) under isothermal conditions …”

TTT‐diagram for epoxy film adhesives using quasi‐isothermal scans with initial fast ramps

“…Here, we extended the experimental method proposed by Hernandez‐Ortiz and Osswald and later improved by Restrepo‐Zapata et al . This method to obtain TTT‐diagrams is based on non‐isothermal and quasi‐isothermal DSC measurements.…”

“…The glass transition temperature, T g , is required to model partial diffusion control. This method was used to characterize polyester, linseed‐based epoxy, and ethylene propylene diene monomer (M‐class), EPDM, rubber . This study showed that their method works for epoxy film adhesives.…”