Preparation and characterization of high boiling solvent lignin-based polyurethane film with lignin as the only hydroxyl group provider

A novel diisocyanate-modified lignin-based polyurethane (LPU) film was facilely prepared using renewable lignin as the only hydroxyl group provider at ambient temperature and pressure for the first time. The lignin was extracted through a modified high boiling solvent (HBS) method with 1,4-dioxane as the solvent, and then dried through freeze drying. The ash content of the HBS lignin sample was about 0.25%, which was lower than for other lignins. The HBS lignin had a large number of hydroxyl groups, which indicated the potential value in substitution of polyols in the synthesis of polyurethane (PU). From the results, the LPU film possessed high performance in hardness, solvent resistance and hydrophilicity with no need for further modification. The LPU film also had high tensile strength with a maximum value of 41.6 MPa. In order to investigate the thermal properties of the LPU film, thermal gravimetric analysis (TGA) and thermogravimetric infrared analysis (TGA-FTIR) were performed, and the LPU film was stable at 114 degrees C in air and an N-2 atmosphere. This study developed a novel LPU film which could show promising future applications as a coating and base.