Facile preparation of high solid content waterborne polyurethane and its application in leather surface finishing

High sold content waterborne polyurethanes (WPUs) were prepared based on star-shape prepolymer which was synthesized via arm-first approach using pentaerythritol (PE) as core. With PE content increasing from 0.3% to 1.2%, WPU dispersions presented a decreasing trend in average particle size, whilst size distribution transited from bimodal distribution to monomodal distribution. This may contribute to variation of surfaces roughness of coatings during film formation process. Infrared spectra and atomic force microscope revealed micro-phase separation structure within WPU coatings and hydrogen-bond interactions between soft segments and hard segments. Water swelling ratios of WPU coatings were below 17% and their swelling behaviors were consistent with kinetic first-order equation. Moreover, WPU coatings showed excellent thermal stability and mechanical properties with elongation at break of 400% and breaking strength reaching 15 MPa. It was found that WPU coatings possess optimum damping properties at 50 ℃ which can be regulated by PE content. Notably, application of high solid content WPU dispersions on leather surface resulted in excellent comprehensive performance, implying the potential application of WPU dispersions as leather finishing agents.