Cure reaction factors, evaluation

All these setups work under isothermal conditions. In the MDR, a thin sheet (around 2 mm) is placed between the two dies kept at the desired temperature the lower disc oscillates and a reaction torque/pressure transducer is positioned above the upper die. It has been found that the MDR gives shorter times of cure than the ODR because of better heat transfer and higher torque values owing to the die design. The MDR is run at three temperatures to allow evaluation of the kinetic parameters of the cure reaction. Thus, the activation energy and the preexponential factor can be calculated from the fractional modulus time values obtained with this apparatus. The modulus value is assumed to vary with time following first-order kinetics, and the rate constant varies with temperature according to the Arrhenius equation. 

Van Mele et al. (1995) describe a mobility factor that can be measured by MTDSC and approximates the diffusion factor in Eq. (2.90) see Section 2.13 on modulated temperature DSC. Kenny and Trivisano (1991) and Kenny et al. (1992) present a phenomenological approach to the shift from chemical control to diffusion-control of the cure reaction. Schawe (2002) also presents a phenomenological approach that uses model-free kinetics to evaluate the chemically controlled kinetics and introduces a diffusion-controlled function. 

The maximum exothermic temperature reached, the time required for the reaction to attain peak exothermic temperature, and the time of gelation are important factors to be considered when selecting a resin. Reactivity tests provide a method for determining the behavior, uniformity, and curing characteristics of a resin. The use of a resin for a specific application often depends on the reactivity of the resin. Measurements of reactivity are helpful in the evaluation of accelerator, catalysts, and other materials that must be considered for the correct use of the resin. 

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