Preparation and properties of emulsifier-/NMP-free crosslinkable waterborne polyurethane-acrylic hybrid emulsions for footwear adhesives (II) – effect of dimethylol propionic acid (DMPA)/pentaerylthritol triacrylate (PETA) content

Stable emulsions (solid content: 38%) of emulsifier-/N-methylpyrrolidone (NMP)-free crosslinkable waterborne polyurethane-acrylic hybrids with a fixed acrylic monomer content (20 wt.%) and different molar ratios (mole%) of dimethylol propionic acid (DMPA)/crosslinkable pentaerythritol triacrylate (PETA)(17/23, 22/17, 27/11, 32/5) were successfully prepared. This study examined the effect of mole% of DMPA/PETA on the stability and viscosity of hybrid emulsions, the tensile properties/dynamic mechanical thermal properties of hybrid film samples and the adhesive strengths of formulated adhesives for footwear at both dry and wet states. The tensile strength/modulus, storage modulus and Tgs increased with increasing PETA content. The adhesive strength at dry state increased with increasing DMPA content up to 27 mole%, and then decreased a little. However, the adhesive strength at wet state decreased with increasing DMPA content. The optimum DMPA/PETA contents were found to be 27/11 mole% to achieve high performance adhesive properties.