Effect of Aging Environment on Degradation of Glass-Reinforced Epoxy

The effects of immersing coupons of glass-reinforced epoxy in four different liquid media at two separate temperatures were investigated in this study which is aimed at examining the durability of fiber-reinforced plastics currently being used in the construction industry. A commercially available epoxy resin was reinforced with 47% by weight of an epoxy-compatible, E-glass woven fabric. Composite samples were soaked for up to 5 months in distilled water, a saturated salt solution (30g/100 cc NaCl), a 5-molar NaOH solution, and a 1-molar hydrochloric acid solution. Aging was conducted at room temperature and at 60°C. Samples were harvested periodically and their tensile and fracture properties determined. The fracture surfaces were also examined using scanning electron microscopy. Results show that commercial epoxy resins used in glass fiber-reinforced polymers are fairly durable. It was found that all the solutions marginally degraded the mechanical properties of the neat resin, especially at the higher temperature; this was mainly the result of polymer hydrolysis. The strength of the composites, however, was reduced by more than 70% by the acid at room temperature and by the alkali at the elevated temperature. Water immersion was less damaging than either acid or alkali soaking, and immersion in brine had the least effect on mechanical properties. As evidenced by SEM micrographs, the worst cases of damage involved attack on the glass fibers in acid at 60°C compared to room temperature. Therefore, reinforcing glass fibers have to be protected from attack by liquid media to improve the durability of composites.