SURFACE MODIFICATIONS ON EVA TREATED WITH SULPHURIC ACID

In this study, treatment with sulphuric acid was used to increase the adhesion of an ethylene-vinyl acetate copolymer containing 20 wt% vinyl acetate (EVA20). The treatment with sulphuric acid improved the wettability of EVA20 due to thecreation of different oxygen and sulphonic acid moieties on the surface. The treatment also created cracks and heterogeneities on the EVA20 surface, and enhanced T-peel strength values of EVA20/polychloroprene adhesive+5 wt% isocyanate joints were obtained. The loci of failure of the joints were mixed, i.e. , adhesional and cohesive in the adhesive. Peel strength values of both as-received and sulphuric acid-treated EVA20/polychloroprene adhesive joints increased after ageing at 50°C and 95 wt% relative humidity for 72 because the complete cure of the adhesive was thereby was produced. The durability of the EVA20 treated with sulphuric acid was monitored between 15 min and 5 years. High peel strength values were obtained for times up to 61 days; the joints produced with the treated EVA20 five years after treatment showed lower peel strength value due to the creation of a weak boundary layer produced by reaction of the residual sulphuric acid on the surface with EVA20. On the other hand, different experimental variables in the treatment of EVA20 with sulphuric acid were considered. The optimum treatment conditions for EVA20 were obtained by immersion in highly concentrated sulphuric acid (96 wt%) for one minute followed by neutralisation with ammonium hydroxide.