Preparation and performance of lignin-based waterborne polyurethane emulsion

The unmodified industrial Alkali Lignin (AL) was used as a hydrophilic chain extender to prepare a series of Lignin-based Waterborne Polyurethane (LWPU) emulsions with different lignin contents by step-growth addition polymerization with polypropylene glycol (PPG) and isophorone diisocyanate (IPDI). The lignin content in the series of LWPUs was determined by elemental analysis, with a maximum content of 24.68 wt%. The infrared spectrum and SEM diagram of the LWPU film show that the AL reacts well with isocyanate, the section of the film is flat and smooth, and there are no agglomerated lignin particles in the film, which indicates that the film is homogeneous. With the increase of AL content, the particle size of the LWPU emulsion decreased gradually from 233 nm to 127 nm, the Zeta potential decreased gradually from -44.8 mV to -56.9 mV, and the emulsion has good stability in the pH range of 5–12. The thermogravimetric analysis of the LWPU film show that the introduction of AL can improve the thermo stability of the polyurethane material, and the mechanical properties test results show that the highest tensile strength of the LWPU film can reach 1.29 times that of the pure polyurethane film. Ultraviolet aging test show that the introduction of AL can significantly improve the UV aging resistance of the polyurethane film. The lignin-based waterborne polyurethane emulsion prepared in this study can be used as a new type of bio-based polyurethane material.