Surface modification of polyethylene to improve its adhesion to aluminum

Abstract

The effects of surface modification of polyethylene (PE) and aluminum on the adhesion strength have been investigated. PE was modified by KMnO4/H2SO4 treatment followed by adsorption of different cations, Ca2+, Ba2+, and Zn2+. The aluminum surface was treated with alkali and was also modified by adsorption of titanates. The surfaces were characterized by means of multiple internal reflection (MIR) IR and ESCA. The adhesion strength was measured by the T-peel test. Both ESCA and MIR analyses show the presence of hydroxyl, carbonyl, ester, and carboxyl groups on the KMnO4/H2SO4-treated PE surface. In addition, sulfate and sulfonate groups are present. The sulfonate groups are apparently localized in crevices extending beneath the ESCA sampling depth of 50 A. Vinylidene groups are also present on the surface. Cation adsorption on the oxidized PE surface seems to be determined by the solubility constant of the corresponding sulfate salts and is in the order Ba2+ > Ca2+ > Zn2+. Adsorption of Ca2+ and Ba2+ increases the relative concentration of oxygen-containing groups on the KMnO4/H2SO4-treated surface. A further increase is seen after annealing. KMnO4/H2SO4 treatment almost doubled the adhesion strength of PE to aluminum. Ca2+ adsorption on the surface prior to lamination increased the adhesion strength nearly three times and caused cohesive failure in the T-peel test. However, when Zn2+ was adsorbed, the adhesion strength decreased drastically. Alkaline treatment of the aluminum surface had only a minor effect on adhesion. The chemical structure of the adsorbed titanates has a great influence on the adhesion strength.