Stress-Induced Reduction of Water Uptake in Clay-reinforced Epoxy Nanocomposites

Exfoliated nano-clay/epoxy composites typically contain approximately 1 nm thick layers of clay dispersed in the polymer matrix. Owing to the platy morphology of the silicate layers, exfoliated clay nanocomposites can exhibit dramatically improved barrier and mechanical properties that are not available with conventional composite materials. Since epoxy applications may exist in areas of high moisture content and under mechanically induced stress, the effect of such stressing on water uptake by epoxy-clay nanocomposites is of interest. In this work, low viscosity liquid aromatic diglycidyl ether of bisphenol A (DGEBA) epoxy resin, Epon 815C, was mixed with Montmorillonite nanoclay to produce an exfoliated clay - epoxy resin system containing 0.5% nanoclay by weight. These samples were immersed in water in stressed condition (flexural stress) to assess the effect of stress on the nanocomposite epoxy system's water uptake behavior. Application of the flexural stress affected the water uptake barrier properties for the nanoclay/epoxy nanocomposites, with the stress acting to decrease the rate of absorption as well as to decrease the equilibrium moisture content in the 0.5% loaded nanocomposite. The results revealed up to 33% reduction in water uptake for the stressed samples.