Complex hygrothermal effects on the glass transition of an epoxy-amine thermoset.

Anomalous hygrothermal behavior in an epoxy-amine thermoset was observed in terms of increases in glass-transition temperatures (T(g)) after immersion in water at different temperatures. Fourier transform near-infrared (FT-NIR) spectroscopic measurements showed that an increase in conversion was responsible for the increase in glass transition, while plasticization occurred simultaneously, rendering the hygrothermal behavior to be complex. To consider other factors affecting this complex hygrothermal behavior, a relationship between T(g) and conversion was constructed for the unexposed system and compared to the corresponding T(g) values for the exposed system at the same point of each conversion value. With this method, the conversion was successfully excluded to compare the T(g) values directly between the unexposed and exposed systems. This indicates the effects of other factors are negligible compared with the large plasticization effect. The plasticization effect was also evaluated quantitatively by observing T(g) differences between the unexposed and the exposed system as a function of absorbed water amount estimated by a characteristic water peak in the NIR spectra. The result indicates that there is additional anomalous behavior in which DeltaT(g) changes independently of the water amount at higher exposure temperatures.