The effect of lignin-based polyols on the properties of polyurethane coatings

The aim of this research was to replace petroleum-based polyols with polyols made from lignin and nano-lignin in the production of polyurethane coatings. Lignin and nano-lignin were first reacted with either diethylenetriamine or ethylenediamine. Subsequently, they were modified with propylene carbonate. The lignin- and nano-lignin-derived polyols replaced the conventional acrylic polyol in the production of polyurethane coatings. The results of Fourier transform infrared analysis showed that urethane, isothiocyanate and strong C–N bonds were formed in nano-lignin-based polyurethanes. Moreover, the surface adhesion test of the lignin-based polyurethane coating showed that with increasing lignin content, the adhesion strength of the coating decreased. Mixing lignin nanoparticles into the polyurethane substrate caused the adhesion strength to rise from 1.67 to 4.52 MPa. An increase in the amino nano-lignin content of oil-based polyol of up to 7% improved the curing of the coating and increased the scratch resistance to more than 5 kg. The results showed that lignin from a mechanical pulping process has a direct effect on reducing the smoothness and the glossiness of polyurethane coatings.