Adhesion of surface-treated EVA to polychloroprene adhesive containing different polyisocyanate content

Different surface treatments for EVA copolymers, such as corona discharge and low pressure gas plasma, have been proposed to improve wettability, and thus enhanced adhesion. However, the effectiveness of those teratments is limited by the vinyl acetate content in the EVA. Different amounts of a polyisocyanate (3-5 wt%) were added to a polychloroprene (PCP) adhesive to determine their influence on the adhesion properties of an ethylene vinyl acetate copolymer containing 12 wt% vinyl acetate (EVA12). EVA12 was treated with sulphuric acid to increase its adhesion, and improved wettability, creation of carbon-oxygen moieties and roughness were achieved. The thermal, rheological and surface properties of the PCP and polyisocyanate mixtures were obtained. The higher the polyisocyanate content in the PCP, the higher the peel strength value of sulphuric acid-treated EVA 12 adhesive joints. By increasing the polyisocyanate content in the adhesive, the locus of failure changed from adhesion to mixed (adhesion + cohesion in EVA 12). The ageing of the sulphuric acid-treated EVA12/PCP+polyisocyanate adhesive joints produced a decrease in T-peel strength, although always a cohesive failure in the EVA 12 was obtained.