Measurement of Tg in epoxy resins by DSC - effects of residual stress

Abstract

Differences in the glass transition temperatures (Tg) of epoxy resins were observed when their samples for differential scanning calorimetry (DSC) measurements were prepared by two different methods. The differences (in Tg) are believed to be due to the effects of interfacial residual stress, which is present only in the samples of lower Tg prepared with the formation of a `chemical' contact between epoxy resin and aluminum (pan) which have mismatched thermal expansion coefficients. Both types of the samples also showed, respectively, lower Tg when they were prepared by a fast-cooling process than when they were prepared by a slow-cooling process. This suggests that matrix residual stress, which is present in both types of the samples, as well as interfacial residual stress, has similar effects on the Tg of epoxy resins. This conclusion is substantiated by the results of the change of contact pattern and the freezing stress experiments.