Surface modifications of EVA copolymers by using RF oxidizing and non-oxidizing plasmas

Ethylene vinyl acetate copolymer (EVA20, 20 wt.% of vinyl acetate, VA, content) has been treated with low pressure RF plasma of non-oxidizing (Ar, N2) and oxidizing gases (Air, a mixture of 4N2:6O2(v/v), O2 and CO2). The enhancement of the surface chemistry of EVA20 was more noticeable by treatment with non-oxidizing plasmas than with oxidizing ones, the higher the reactivity, the lower the difference with respect to the as-received EVA surface, as it is shown by contact angle measurements and XPS. The surface etching produced with the non-oxidizing plasmas, giving rise to a high roughness, depends on the different resistance of VA (low) and PE (high) to the non-oxidizing plasma particles bombardment. The adhesion properties obtained by using a polyurethane adhesive (PU) showed improved T-peel strength values and an adhesion failure in the joints produced with EVA20 treated with oxidizing plasmas, and lower T-peel strength values with those of non-oxidizing plasmas. The poor adhesion properties of the EVA20 treated with non-oxidizing plasmas were due to the removal of surface moieties by brushing with the solvent of the polyurethane adhesive (methyl ethyl ketone). Furthermore, the joints produced with oxidizing plasmas treated EVA surfaces showed adequate resistance to ageing under high relative humidity and temperature.