Nonisothermal cure experiments

For nonisothermal cure experiments it is not necessary to perform the experiment in heat-only conditions. However, for curing experiments, it is advisable to use larger modulation amplitudes with low underlying heating rates, to improve the accuracy of the heat capacity measurement. The amplitude of the temperature modulation should not exceed a certain value in order to limit its effect on the cure kinetics. Typical modulation amplitudes range within 0.1-1 °C. 

The basis of the method described by Hands and HorsfaU [1] consists of calculating the tanperature distribution as a function of lime first, thoi evaluating the dis-ttibution of the cure. Taking a temperature profile, a technique is described enabling the evaluation of the state of cure. When the form of the relationship between cure and temperature history is known, the basic cure parameters can be obtained from experiments in which temperature varies with time. When the relationship is not known, it is preferable to conduct experiments at various fixed temperatures in order to separate the dependence on time and temperature. An apparatus was built for measuring cure as a function of time at a constant temperature. The data obtained from this isothermal apparatus and a new mathematical model of cure was used to predict the cure distribution obtained in nonisothermal experiments. 

Thns, by working in terms of equivalent time instead of cure, the dependence of on c is eliminated. For a nonisothermal experiment, Equation 1.4 can be integrated ... 

Figure 2.110. Nonisothermal experiment (l°C/min underlying heating rate l°C/60s modulation, two consecutive heatings) on the 30-min Devcon glue, showing initial glass transition (at T, o), heat capacity increase at Tgo [ACp(T g,o)], reaction enthalpy (AHj) and glass transition of fully cured thermoset (at Tg ), heat capacity increase at Tg [AC ,(rg )], and reaction heat capacity (ArCp) (Swier, unpublished results).

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