Corrosion Behavior of Epoxy and Unsaturated Polyester Resins in Alkaline Solution

The effect of temperature and concentration on corrosion behavior and corrosion mechanism of epoxy and polyester resins in NaOH solution were studied, and were discussed by considering their structures. Resins used were two types of epoxy resins cured with anhydride and amine and iso-phthalic type polyester resin. Different behaviors and mechanisms were clearly recognized between these resins. Epoxy resin cured with amine showed no degradation during immersion because of its stable crosslinks. Epoxy resin cured with anhydride showed the uniform corrosion with the softening and dissolution of the surface and also behaved similar to the oxidation corrosion of the metal at high temperature obeying linear law. Iso-phthalic polyester resin was corroded with the formation of the color changed surface layer and corrosion rate of the resin were controlled by diffusion process of the solution through the layer. Thus similar behavior was observed to oxidation corrosion of metal obeying Wagner's parabolic law. The difference of behaviors of these resins were mainly due to the position of ester bonds in the structures. Method to predict the retention of the strength of resins after immersion was also proposed by applying the concept of corrosion mechanism in metal.