Surface treatment of vulcanized latex soles to improve their adhesion performance in shoe manufacturing

Vulcanized latex sole materials in footwear are difficult to join with polyurethane adhesives and although chlorination is widely used, the nature of the modifications produced is not fully understood. In this study, the effects produced by treatment of two different vulcanized latex soles with ethyl acetate solution of 3 wt% trichloroisocyanuric acid (TCI) (3 wt% TCI-EA) were studied. On the other hand, new more environmentally friendly alternative treatment with UV radiation was also carried out. Surface modifications of the vulcanized latices by treatment with 3 wt% TCI/EA or UV radiation were analyzed by contact angle measurements (in water at 25°C), ATR–FT-IR spectroscopy and Scanning Electron Microscopy (SEM). T-peel tests on surface-treated vulcanized latex/polyurethane adhesive + 5 wt% polyisocyanate/leather joints were carried out to quantify the adhesive strength. Chlorination with 3 wt% TCI/EA improved the wettability, created roughness, produced polar moieties (C—Cl, C—O), and removed antiadhesion moieties from the vulcanized latices' surfaces. These modifications led to improved adhesive strength. However, the UV treatment of the vulcanized latices was not so effective and only moderate adhesive strength was obtained, likely due to the presence of antiadhesion moieties and surface crosslinking, which constitute a weak boundary layer in which the joint failed.