Preparation And Characterization Of Lignin-based Polyurethane Elastomer

Polyurethane is a widely used synthetic polymer material in the world today,and one of its reaction materials,petroleum-based polyol,is highly dependent on petroleum resources.Therefore,it is necessary to find a biomass resource to replace petroleum-based polyols to promote the sustainable development of polyurethane industry and to achieve the goal of "double carbon".As the second largest renewable resource in nature after cellulose,lignin is abundant and contains a large number of hydroxyl groups in its structure,which offers the possibility of its use in the synthesis of polyurethane.Partial replacement of petroleum-based polyols by lignin can not only reduce production costs,but also improve the mechanical and biological properties(e.g.antibacterial properties)of polyurethane materials.Lignin sources and species are abundant,among which enzymatic lignin mainly comes from the residue of bio-extracted ethanol from corn straw,and alkali lignin mainly comes from pulp and paper,China’s straw production is huge and the paper industry is developed,so it is of great significance to promote the efficient use of enzymatic lignin and alkali lignin.However,because lignin is a three-dimensional three-dimensional reticulated macromolecule with complex structure and large spatial site resistance,its direct use in polyurethane synthesis suffers from poor compatibility with isocyanates and low reaction efficiency.The second chapter of this thesis addresses the low reactivity of enzymatic lignin and alkali lignin and modifies them using propylene oxide.The alcohol hydroxyl content of enzymatic lignin increased from 3.099 mmol/g to 6.591mmol/g,and that of alkali lignin increased from 9.080 mmol/g to 19.748mmol/g.The reactivity of enzymatic lignin and alkali lignin were modified by propylene oxide,the reactivity with isocyanate was improved;the side chains were extended,the molecular weight distribution became smaller,and the compatibility with isocyanate was improved.Chapters 3 and 4 of this thesis successfully synthesized lignin-based polyurethane elastomers using modified enzymatic lignin and modified alkali lignin as raw materials to replace some polyether polyols,respectively,and systematically investigated the effects of lignin species and their contents on the microstructure and macroscopic properties of polyurethane elastomers,where:(1)The glass transition temperature of polyurethane elastomer increased with the increase of lignin content.Compared with the polyurethane elastomer without added lignin,the tensile strength of the polyurethane elastomer increased from 10.4 MPa to 20.5 MPa and the elongation at break increased significantly from 49% to 249% when 20 wt% modified enzymatic lignin was added;the tensile strength of the polyurethane elastomer increased from 14.0MPa to 16.7 MPa when 10 wt% modified alkali lignin was added,both modified lignin can improve the mechanical properties of polyurethane elastomers through chemical cross-linking and hydrogen bonding.(2)Modified lignin can improve the cytocompatibility and antimicrobial properties of polyurethane elastomers.Without the addition of antimicrobial agents,the lignin-based polyurethane elastomer itself has excellent antimicrobial properties.When modified enzymatic lignin was added at not less than 20 wt%,the polyurethane elastomer inhibited E.coli,S.aureus and C.albicans by more than 99% with universal antibacterial effect;the polyurethane elastomer prepared by modified alkali lignin inhibited the above three bacteria by at least 58%.In addition,the addition of both modified lignin can reduce the cytotoxicity of polyurethane elastomers,which is expected to be applied in the medical field.