Kinetics of the Cure Reaction

The cure of vulcanization of elastomers is a process whereby chemical crosslinks are introduced between the elastomer chains, resulting in the formation of a three-dimensional network. Overall, the chemistry accompanying snlfnr vulcanization is extremely complex and althongh several techniqnes have been developed to monitor the process and to analyze the prodncts formed, most are time-consnming and tedious. 

There are various ways to determine the parameters of the kinetics of the cure reaction. The parameters to consider are the cure enthalpy, which is the heat evolved from the overall cnre reaction the order of the reaction which is concerned with the concentration of active agent remaining free during the reaction at time t and the two parameters that allow defining of the effect of the temperature on the rate of the reaction, that is, the energy of activation and a constant that depends only on the compound, by following the Arrhenius expression. Thus, by considering aU these parameters, the cure of rubbers is considered a simple reaction. 

Various techniques have been developed in turn the Mooney viscometer, the Wallace-Shawbury curometer, the oscillating disc rheometer (ODR), and the moving disc rheometer (MDR), in addition to the calorimetry techniques. The isothermal calorimetry and its counterpart in scanning mode, the isothermal moving disc rheometer (MDR), and the improvement of this last technique with the rubber process analyzer run in scanning mode, are considered. 

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Finally, using the above results and theoretical consideration, the kinetics of the cure reaction was established and used for evaluating either the profiles of temperature developed through the material or the corresponding profiles of state of cure [10-12], At that time the kinetics of the cure reaction was determined by calorimetry run under isothermal conditions and finally in scanning mode with a constant temperature program. As the enthalpy of the cure reaction is rather low for rubbers, the problem was tedious, leading to resnlts with sometimes a low level of accuracy. 

The kinetics of the cure reaction, expressed in terms of either the heat evolved or the torque modulus obtained by the MDR and RPA... 

The data published by various authors are given so as to help readers make their own calculations. They concern the valnes that deal with the heat transfer and the kinetics of the cure reaction, or with the diffnsion of Uqnids through the rubbers. In each case, the references of the authors are given in the nsnal way. 

Using Eq. (14.13), we can now predict the viscosity of unsaturated polyester during cure once information on a during cure is available to us. In order to use Eq. (14.13) to describe the variation of r/ during cure of unsaturated polyester, one must have an expression describing the kinetics of the cure reactions. Below, we present experimental methods that can be used to determine an expression for cure kinetics. 

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