Abstract
Dimethyl phthalate is widely used as a diluent of hardener for an unsaturated polyester resin. It was investigated that the effect of dimethyl phthalate on corrosion behavior and its mechanism of isophthalic type unsaturated polyester resins. Four kinds of specimens with the different contents of dimethyl phthalate were used for a corrosion test which were performed by immersing them in 30wt% nitric acid solutions at 80°C, The more the dimethyl phthalate content, the less was the flexural strength and modulus of specimens. The corrosion behavior and its mechanism of these specimens changed in the following three steps; physical degradation by swelling, formation of pits, and hydrolytic corrosion. The corrosion depth of these specimens initially increased linearly with the square root of immersion time, then the following a rapid increase with the formation of blisters near the surface of specimens. The reaction of dimethyl phthalate with nitric acid was one of the causes of pit and blister formation. The higher the content of dimethyl phthalate, the lager corrosion rate of the resin. In conclusion, it was clarified that the corrosion behavior of the isophthalic type unsaturated polyester resin was strongly affected with the content of dimethyl phthalate used as a diluent of hardener.
