Effect of the concentration of epoxy group in adhesive epoxy primer on cathodic delamination of polyethylene-coated steel pipe

摘要

The cathodic delamination of polyethylene-coated steel pipe was investigated. The steel pipe had three layers of coatings structure; polyethylene, adhesive polyethylene, and amine cured epoxy primer. The cathodic delamination length of polyethylene coating was strongly dependent on the concentration of epoxy group in amine-cured epoxy primer. The polyethylene coating with greater resistance to cathodic delamination was obtained when the concentration of epoxy was higher. In the case that the mixing ratio of epoxide to amine was constant, higher concentration of epoxy group surpressed oxygen permeability through the epoxy primer to the interfacial region between the steel pipe and the epoxy primer because of denser cross-linking of the epoxy primer. In the case that epoxide was in excess against amine curing agent, the cathodic delamination length was also shortened with the increase concentration of epoxy group. The result can not be explained by the cross-linking density or acid-base interaction between amino group and the steel at the interface. The excess of epoxy group was found to promote bonding at the interface with the steel, which resulted in the good resistance for the cathodic delamination.