Strength of adhesive joints from functionalized polyethylene and metals

LDPE and functionalized LDPE (FLDPE) adhesive interaction with copper, steel and aluminum was studied. Polyethylene grafted with a non-saturated dicarboxylic acid displays elevated adhesion to all metals. The maximum adhesion strength is shown by joints with steel. The reasons of FLDPE effect on adhesion are discussed proceeding from regularities observed at structural and chemical transformations in the adhesive and metal boundary layers and the analysis is proposed of differences in destruction topography in LDPE and LDPE-g-IA adhesive capability are determined by oxidative transformations going at the metal-adhesive interface at the stage of the contact formation, than by their physical structure. Carboxylic group grafting to LDPE macromolecules results in acceleration of macromolecules oxidation in the adhesive boundary layers on copper and steel, and its inhibition. For aluminum substrates an oxidation process for LDPE-g-IA and LDPE is practically identical, though concentration of carboxylic groups is higher in the first one. At a mild heat regime of the adhesive contact formation with copper (low temperature of the contact formation) the oxidation degree is lower for LDPE-g-IA than for the initial polyethylene. When adhesive joints from FLDPE and metal are broken, a predominantly cohesive character is observed along the adhesive boundary layer. Topography of the polymer layer remaining on the metal surface is determined by the latter nature. Continuous layers are formed on steel and aluminum without a noticeable structural flaw. Copper shows overlayer from hollow micro drops 100-400 nm high, 1000-2000 nm long and 30-150 nm cavity depth. Change of adhesive strength in LDPE-g-IA at varying technological conditions is caused mainly by the altered concentration of low-molecular substances in the contact zone. The presence of a non-grafted IA in the adhesive layer leads to the reduction of adhesive strength. (C) 1998 Elsevier Science Ltd. All rights reserved.