Synthesis And Properties Of Polyurethane Materials Prepared From Modified Soda Lignin

Polyurethane is a new and important organic high-molecular material,which was used widely.The polyol components used in the preparation of polyurethanes are mainly from petrochemical products currently.Considering the issue of renewable resources,people try to use biomass materials to replace part of pertroleum.As the second most abundant natural biopolymer,and the main source of aromatic structures on earth,lignin has drawn the attention of many scientists for several years.Due to its complexity,nonuniformity,and conjunctive bonding to other substances,lignin has been difficult to isolate without modification and difficult to convert into useful consumer products,and its structure has been difficult to determine.The soda lignin macromolecule carries multiple functional groups: hydroxyl groups,either phenolic or aliphatic,so it can be used as a source of OH groups,able to react with diisocyanates to yield polyurethanes.In this paper,polyhydric aminated lignin containing both amino and hydroxyl groups was prepared by a new two-step method: hydroxylation and amination.The polyurethane film containing polyhydric aminated lignin was prepared and compared with those of polyurethane film using soda lignin.Furan and maleimide ring were bounded onto soda lignin respectively by functional modify,then the functional modified lignin was used in preparation of polyurethane film.The mechanical properties,thermal properties and self-healing ability of various polyurethane materials were evaluated.The main contents and conclusions of this paper are listed as follows:1.Preparation of polyhydric aminated lignin: The polyhydric aminated lignin possessing amine groups was synthesized through a two-step process,and the effects of reaction conditions on the target product have been discussed.For hydroxylation reaction,the optimum reaction conditions were at 60 °C,mass ratio of H2O2/lignin=1.2,ferric hydroxide/lignin(mass ratio)=0.01 and the reaction time was 60 min.For amination reaction,the optimum reaction conditions were at 75 °C,reaction time of 3 h,and the mass ratio of DETA/lignin and formaldehyde/lignin was 0.9 and 0.6,respectively.The result of 1H-NMR test confirmed that hydroxyl groups in soda lignin were increased from 5.10% to 8.19%.The results of qualitative amine color test and elements analysis proved that the introduction of primary amine groups.The TGA revealed good thermal-mechanical performance of the products.2.Polyhydric aminated lignin used in preparation of polyurethane film: The polyhydric aminated lignin was used in preparation of polyurethane film.The thermal stability ?mechanical properties?water absorption and solvent resistance properties of polyurethane film containing polyhydric aminated lignin were researched and compared with those of polyurethane film using soda lignin.The results of study confirmed that the modifications of lignin not only allow the increased addition of lignin in polyurethane but also increased the tensile strength of polyurethane film.The thermal stability? water absorption and solvent resistance properties of polyurethane film were also improved.3.Preparation of functionalized lignins: Soda lignin was modified with furan and maleimide ring respectively.The structure of funtionalized lignin and reversible crosslinking of funtionalized lignin via the furan–maleimide Diels–Alder reaction were studied.The results of 1H-NMR?FTIR and elements analysis indicated that furan ring and maleimide ring were attached into lignin.The furan-and maleimide-grafted lignins were then combined to generate a mixture suitable for crosslinking via the Diels–Alder(DA)[4 + 2] cycloaddition.The lignin solutions in DMSO turned into a gel at 70 °C as a result of the crosslinking,and quickly turned back into the liquid state after generating the retro-DA reaction at 120 °C.After conducting the retro reaction at 120 °C,the solutions were cooled to room temperature and the gels were formed again at 70 °C,thus confirming the full reversibility of the crosslinking.4.Functionalized lignins used in preparation of polyurethane film: The functionalized lignins were used in preparation of polyurethane film.The thermal stability? mechanical properties and self-healing properties of polyurethane film containing functionalized lignins were researched and compared with those of polyurethane film using soda lignin.The results of research demonstrated that the thermal stability and the tensile strength of polyurethane film were improved.The functionalized lignins bring self-healing ability to polyurethane film.