EFFECT OF WATER AND ITS ACTIVITY ON TRANSPORT-PROPERTIES OF GLASS EPOXY PARTICULATE COMPOSITES/

Silane coated glass microspheres embedded in an epoxy polymer matrix h ave been employed as a model system to investigate water sorption at t hree water activities. Composites containing soda-lime-silica (A) glas s in the range 0-25% by volume were tested in deionized water, saturat ed NaCl and saturated MgCl2, at 40 degrees C. Increase in water activi ty led to a decrease in the effective water diffusivity due to trappin g, especially at interfaces ruptured by osmotic pressure. Higher water activities favoured interfacial water transport, whereas lower water activities favoured water transport through the bulk of the polymer. E lectrical resistance and water permeation tests suggested very rapid p referential water transport through areas of low cross-link density, e ven in the pure polymer, enhanced by the introduction of interfaces. E ffective diffusivity calculations during water absorption and desorpti on, together with electrical resistance measurements and water uptake measurements in saturated NaCl, suggested the formation of a pecolatin g liquid channel network for composites containing more than 15% glass . Electrical resistance measurements using silver-coated A-glass/epoxy composites located the percolation threshold at 16% glass. Similar wa ter sorption effects were observed with uncoated A-glass filled epoxy composites. (C) 1997 Elsevier Science Limited.