Effects of environmental exposure on solvent- and water-based epoxy systems

The dielectric properties of latex water-cast and conventional solvent-cast epoxy neat resin systems were investigated under th ree formation conditio ns: solvent-based as-made, waterbased as-made, and water-based following a boiling fluid extraction procedure to remove residual surfactant. Samples f rom each of these three groups were cast, cured, and exposed to controlled humidities in an environmental chamber at room temperature and elevated tem perature, a steam bath at various temperatures, and soaked in boiling water . Composite laminates, press fabricated using solvent and latex-based epoxy impregnated glass cloth, were subjected to similar environmental exposure. The microwave frequency dielectric properties of these materials, after ea ch environmental exposure, were measured at 9.4 GHz. These dielectric measu rements revealed that under identical exposure conditions, waterborne epoxy systems absorbed more water than solvent-based systems and also allowed mo re free water into the samples. Extraction of water and soluble components in the resin had no effect on the dielectric properties of the water-borne samples. The presence of high quantities of free water at moisture fraction s beyond 4.0 wt %, suggests that the differences between the dielectric pro perties of solvent and water-borne epoxy systems are due to void morphology , which was confirmed by optical and electron microscopy. (C) 1999 Kluwer A cademic Publishers.