Influence of plasma duty cycle during plasma polymerization in adhesive bonding

Junctions between aluminium substrates and ethylene-co-propylene-co-diene terpolymer (EPDM) have been strengthened by depositing alkene functionalized plasma polymers on the aluminium side. The double bonds in the plasma polymer layer were able to covalently bond to the EPDM during the crosslinking step with peroxide. Variations in the peel strength were observed by varying of the plasma duty cycle during plasma polymer deposition. The higher peel strength was obtained with low duty cycles. Analysis of the failure after peel tests showed a cohesive rupture in the EPDM substrate. The differences were explained by analysing the respective concentration of alkene groups in the plasma polymer layer.