Effect of Curing Conditions on the Glass-Transition Temperature

4 Effect of Curing Conditions on the Glass-Transition Temperature 

Gillhami ] [72] developed a time-temperature transformation ( ITT) diagram (Fig. 2.18) to represent the curing process. The ITT diagram is a plot of the log of time on the x-axis versus the curing temperature on the y-axis. There are five distinct regions in the diagram  

GelTg the temperature at which gelation and vitrification occur simultaneously 

In isothermal cures, at temperatures between the gel Tg and Tg the resin undergoes gelation followed by vitrification. Since Tg is a function of both the degree of cure and the cross-link density, it increases to a point at which all polymer reaction sites have been consumed. At that point, the Tg reaches a plateau and does not increase further with temperature until the decomposition temperature where a char region occurs (Fig. 2.18). An example of the effect of cure conditions on Tg and CTE values was shown by Konarskil who varied the cure cycles of an anhydride-cured epoxy from 130°C to 175°C as shown in Table 2.10. The value of continued to increase while the expansion coefficient decreased with increasing cure temperature. 

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Effect of curing conditions on the glass-transition temperature 68... 

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