Preparation and properties of emulsifier/N-methylpyrrolidone-free crosslinkable waterborne polyurethane-acrylate emulsions for footwear adhesives. I. Effect of the acrylic monomer content

Stable emulsions of emulsifier/N-methylpyrrolidone-free crosslinkable waterborne polyurethane-acrylates (C-WBPUAs) with various acrylic monomer contents (0, 10, 20, and 30 wt %) for footwear adhesive materials were successfully prepared in this study. The effects of the acrylic monomer content on the shelf stability, mean particle size, and viscosity of the C-WBPUA emulsions; the tensile properties and dynamic mechanical thermal properties of the C-WBPUA film samples; and the adhesive strengths between the upper (synthetic leather) and the sole (ethylene vinyl acetate rubber) in both the dry and wet states of the formulated adhesives (C-WBPUA emulsion-thickener-hardener) were examined. The adhesive strengths of the formulated adhesives for footwear (leather-sole) in both the dry and wet states increased with increasing acrylic monomer content up to 20 wt %; after this, they almost levelled off. Thus, C-WBPUA20 and C-WBPUA30, where the number indicates the acrylic monomer content, can b