Characterization of waterborne polyurethane adhesives containing different soft segments

Waterborne polyurethane (WBPU) adhesives were prepared by the pre-polymer process using different polyester polyols (M n = 2000), namely poly(tetramethylene adipate glycol) (PTAd) and poly(caprolactone glycol) (PCL), and polyether polyols (M n = 2000), namely poly(tetramethylene oxide glycol) (PTMG) and poly(propylene glycol) (PPG), as soft segments. This study focused on the effect of various soft segments on the physical, mechanical and thermal properties, as well as adhesive strength of WBPUs. All of the WBPU dispersions showed small particle size and high viscosity. PTAd-based WBPU shows higher thermal stability, mechanical properties and adhesive strength than PCL-R, PTMG- and PPG-based WBPUs. During preparation of adhesive-bonded samples the optimum pressing temperature and pressure, which were the same for all samples, were found to be 100°C and 15 kg/cm2, respectively. However, it was found that only PTAd-based WBPU had good adhesive strength under moderately high temperature (100°C) compared to all other polyol (PCL/PTMG/PPG)-based WBPUs.