Synthesis of waterborne polyurethane using snow as dispersant: Structures and properties controlled by polyols utilization

Waterborne polyurethane (WPU) dispersions have gained attention towards environmentally-friendly synthesis. In this article, a series of waterborne polyurethane emulsions was successfully synthesized and extensively characterized in terms of thermal, mechanical properties, hydrophilic behavior and morphology. Snow was chosen as dispersant instead of commonly used water. Preparation parameters such as intrinsic properties and molecular weight of polyols were discussed systematically. A chain structure was confirmed by Fourier transform infrared (FT-IR) spectroscopy. When comparing the nature of the polyols (PPG, PEG and PNA, 2000 g/mol) of this study, as-synthesized polyether waterborne polyurethane provided higher solid content, viscosity and water-resistance. However, polyester waterborne polyurethane performed differently and it exhibited higher thermal stability and crystallinity. When comparing the samples (WPU-N210, WPU-N220, WPU-N230 and WPU-N240) with different molecular weight of the same polyol (PPG) used as soft segment, the emulsion WPU-N220 with molecular weight of 2000 g/mol PPG provided the highest solid content and lowest viscosity. It was observed that particle size was uniform and highly dispersed for all samples from TEM images. Thermogravimetric, differential scanning calorimetry (DSC) and X-ray diffraction results demonstrated that the emulsion WPU-N230 with molecular weight of 3000 g/mol PPG possessed higher thermal stability and crystallinity than the other samples. The reason was that the Tg and thermal stability were increased with increasing molecular weight. When molecular weight increased, the arrangement of soft segment became more regular and so did the regularity of the molecular chains. This work demonstrated that different polyols as soft segment applied could lead to great differences in the structure and property of the resulting WPU.