Corrosion Behavior of Epoxy Resin Cured with Different Amount of Hardener in Corrosive Solutions

Abstract

Epoxy resin systems with different amounts of hardener were prepared. Bisphenol A type epoxy resin prepolymer was used and the hardener was m-xylylenediamine.Specimens were immersed in water, 10wt% resistance to water and sodium hydroxide solution regardless of the amount of hardener.On the other hand, color changed layers were observed on the both surfaces of specimen uniformly in sulfuric acid solution. Sulfuric acid did not penetrate into color unchanged layer. From the results of weight change in sulfuric acid solution, it was suggested that the larger the amount of hardener, the faster was the penetration of sulfuric acid solution. Especially for specimen cured with the largest amount hardener, cracks and defects were observed.The flexural strength, which was measured immediately after taking from sulfuric acid solution, decreased as immersion time increased. The flexural strength recovered by drying. However, the specimen with the largest amount of hardener indicated irreversible degradation due to formation of cracks. The results suggested that excess hardener promote the penetration of sulfuric acid solution. The amount of hardener must be determined carefully in order to avoid corrosion.

Non-destructive evaluation by terahertz spectroscopy for penetration of acid solutions into epoxy resin

“…The depth also increases linearly with square root of time and leveled off at 150 hours because the acid penetrates to whole thickness at this immersion time. These observations are consistent with other reports [4][5][6]. In addition, epoxy resin itself scarcely changes in respect of the molecular structure or chemically degrade despite the penetration of sulfuric acid [5].…”

“…The ñ increased with the fraction of the sulfuric acid in the specimen. As mentioned in section 3.2, the sulfuric acid does not cause the chemical decomposition of the epoxy network by hydrolysis and other reactions [5]. From these results, it is guessed that the change of the ñ can be attributed mainly to the sulfuric acid in epoxy resin.…”

“…In addition to water, sulfuric acid solutions are also known to penetrate into the EP network [4][5][6]. Therefore, EP specimens after immersion in the sulfuric acid solution and after drying are studied gravimetrically and spectroscopically.…”

“…In acid aqueous solutions, the water and acid could penetrate into the immersed resin specimen with time [4][5][6]. In order to evaluate the amounts of penetrants, the mass of the specimen was measured soon after removal from the solution (m wet ) and after drying in air at 50°C (m dry ).…”

“…In particular, the amine-cured epoxies can cure at ambient conditions and are known as the most common coatings for metal equipment and concrete constructions under corrosive environments [1]. When these coatings are used in chemical solutions such as process fluids in chemical plants and sewage water in communities, the water and solute molecules gradually penetrate into the epoxy resins, especially under low pH acid conditions [2][3][4][5][6][7]. After the penetrants reach the interface between the resin coating and the substrate, the substrate can be corroded by the penetrants.…”