Synthesis And Properties Of HBS Lignin Modified Polyurethane

The HBS (high boiling solvent) lignin is a new, environment friendly natural material, which contains a lot of phenolic and aliphatic hydroxyl groups with high reactivity. HBS lignin can be used to synthesize polyurethane without any modification. It is found that HBS lignin can dissolve in poly(ethylene glycol)(PEG), and the HBS lignin-polyurethane can be prepared without solvent by one-step technique, which provide great advantage to the application of HBS lignin in polyurethane industry. The lignin-based polyurethane was characterized by mechanical test, swelling resistance test, infrared spectra (IR), thermogravimetric analysis (TG),differential scanning calorimetry (DSC) and scanning electron microscope(SEM). The results show that the structure of HBS lignin affects the properties of lignin-based polyurethane. HBS lignin brings polyurethane higher hardness because of its phenyl groups and can be seen as hard segment in polyurethane. The decomposition temperature of polyurethane shifts to higher temperature with increasing the lignin content, and the lower degradation on ratio of polyurethane below 500℃ also indicate that HBS lignin can improve the thermal stability of lignin-polyurethane. As a three-dimension polyol of better thermodynamics consistent to the PEG, HBS lignin can reduce the interfacial energy between phases, giving a finer dispersion and stability against large-scale hard segment aggregation, and thus the amount of hydrogen bond decreased in hard segments but increased between hard segments and soft segments. The tensile strength of polyurethane was improved while HBS lignin content increasing. With a structure of polyol, the HBS lignin can bring a higher crosslink density of polyurethane; in consequence the swelling property was improved while the elongation at break decreased. It was found that better lignin-based polyurethane can be obtained by using PEG of molecular weight 400, the tensile strength of the polyurethane was raised up to 36MPa and the swelling weight gain mass fraction even decreased to 1.25% while the ultimate strain weren't lower much or even higher at NCO/OH molar ratio lower 1.6; HBS lignin was used as crosslink agent to synthesize polyurethane containing between 18.9% to 25.9% lignin, and the tensile strength of the lignin-based polyurethane was lower than 10MPa and breaking elongation lower than 325%. When PU elastomer was synthesized using 7.20% of HBS lignin to replace PEG, it was found that: 1)In comparison with the polyurethanes derived from 1,6-hexamethylene diisocyanate (HDI) and toluene diisocyanate(TDI), better HBS lignin-based polyurethane was obtained by using 4,4'-diphenylmethane diisocyanate(MDI). The tensile strength can raised up to 39MPa while polyurethane from TDI was 9.88MPa, and the breaking elongation was 319.78%, the swelling weight gain mass fraction was decreased to 42.46%, the beginning decomposition temperature corresponding to the polyurethane rigid block was also increased with about 58℃(from260℃ to 318℃) compared to polyurethane from TDI; 2) The mechanical properties of lignin-based polyurethane can be improved by adding polytetramethylene glycol(PTMG), which has high polarity. While adding PTMG to replace 1/4 amount of PEG, the tensile strength was raised up to 37.66 MPa, elongation up to 325.89% and the swelling weight gain mass fraction maintained at 79.79%。...