Hygrothermal aging of rubber-modified and mineral-filled dicyandiamide-cured DGEBA epoxy resin. II. Dynamic mechanical thermal analysis

The effects of hydration-dehydration cycling on the dynamic mechanical resp onse of a rubber modified, mineral-filled epoxy resin based on the diglycid yl ether of bisphenol A cured with dicyandiamide are reported. Samples of t he resin were aged in both deionized water and 5% w/w NaCl solution at 65 d egreesC. A dynamic mechanical thermal analyzer was used to detect the chang es in the mechanical spectrum of the material induced by moisture ingress. Water absorbed at weight fractions up to 4.3% caused plasticization of the polymer matrix, and the measured decrease in the glass transition temperatu re could be interpreted in terms of the polymer network-diluent theory. Wat er absorbed at levels >4.3% weight fraction resides in microcavities formed as result of the aging process and did not further affect the dynamic mech anical response of the resin. The dynamic mechanical properties of the mate rial were independent of the previous history of exposure to humidity. In t he presence of NaCl, the microcavity growth was prevented and the amount of water absorbed did not exceed 4.1% weight fraction. (C) 2001 John Wiley & Sons, Inc.