ADHESION OF POLYURETHANE TO SURFACE-MODIFIED STEEL

A number of procedures for cleaning the surface of steel have been tested. By washing with different solvents, ultrasonic solvent cleaning, sand-blasting or grinding, and desorption of organic contamination in an oxygen plasma, the degree of cleaning increased successively, as detected by XPS. The adhesion of polyurethane to steel measured in terms of the tensile shear strength could even approach the critical shear strength of the polyurethane itself. The highest adhesion strengths were obtained by using a combination of cleaning methods, including oxygen plasma treatment. A composite of optimally pretreated steel, a phenolic resin primer, and a polyurethane showed fracture far from the interface to steel in the boundary layer comprised of polyurethane and primer. Strong interactions between the phenolic resin and steel were indicated by the shift of the Fe 2p3/2 Peak to a binding energy of 712.7 eV. The strong adhesion-promoting effect of the hydrogen plasma pretreatment was produced by another effect. With the carbon incorporated in the steel, a thin adhesion-promoting plasma polymer layer was formed. Tests with model primers, instead of the phenolic resin and chemical modification of the phenolic resin, showed that the interaction between the phenolic resin primer and the polyurethane involved the phenolic hydroxyl groups.