Hygrothermal aging of rubber modified and mineral filled dicyandiamide cured digylcidyl ether of bisphenol A epoxy resin. I. Diffusion behavior

The effect of hydration-dehydration cycling on the properties of a rubber m odified, mineral filled epoxy resin is reported. This resin was based on di glycidyl ether of bisphenol A and cured with dicyandiamide. The material wa s aged in deionized water and a 5% (w/w) NaCl solution at 65 degreesC. Grav imetric measurements, transmission electron microscopy, and diffusive refle ctance IR Fourier transform spectroscopy were used to monitor the water sor ption and physical and chemical changes occurring in the material. Two-stag e absorption was observed with deionized water, and the quasiequilibrium-st ate water content was independent of the hygrothermal history. The equilibr ium weight after dehydration depended on the hygrothermal history due to th e presence of irreversibly absorbed water and leaching of material. The fir st stage of the absorption was found to be Fickian and was interpreted as b eing related to the process of saturation of the epoxy matrix. The driving force for the second stage was the osmotic pressure, and it was not observe d when the material was aged in NaCl solution. The water caused irreversibl e damage to the resin through microcavity formation, and part of the water was molecularly dispersed in the epoxy matrix and part resided in microcavi ties. Absorption-desorption cycling resulted in an increased rate of absorp tion during subsequent rehydration. (C) 2001 John Wiley & Sons, Inc.