CN115386063A

CN115386063A - Lignin-based waterborne polyurethane and preparation method thereof

Info

Publication number: CN115386063A
Application number: CN202211137496.8A
Authority: CN
Inventors: 石聪灿; 朱伯承; 王韬; 唐桂明; 江瑶; 江学亮
Original assignee: Guangdong Tuopu Synthesis Technology Co ltd
Current assignee: Guangdong Tuopu Synthesis Technology Co ltd
Priority date: 2022-09-19
Filing date: 2022-09-19
Publication date: 2022-11-25
Anticipated expiration: 2042-09-19
Also published as: CN115386063B

Abstract

The invention relates to the field of high added value utilization of biomass resources, and particularly discloses lignin-based waterborne polyurethane and a preparation method thereof. The lignin-based waterborne polyurethane is prepared from the following raw materials in parts by weight: 80-120 parts of oligomer polyol, 70-90 parts of polyisocyanate, 5-20 parts of chain extender, 5-20 parts of organic amine compound, 30-80 parts of oxime compound, 1-5 parts of emulsifier, 100-120 parts of isocyanate modified lignin and 300-800 parts of deionized water. According to the invention, lignin is modified with isocyanic acid and used as a filler of polyurethane, so that the chemical bond binding sites of lignin and polyurethane are increased, and the mechanical property of the polyurethane film is improved.

Description

Lignin-based waterborne polyurethane and preparation method thereof

Technical Field

The invention belongs to the technical field of biomass resource high added value utilization and polyurethane intersection, and particularly relates to lignin-based waterborne polyurethane and a preparation method thereof.

Background

In the field of coating applications, biobased materials, particularly vegetable oils, have been widely used to prepare novel green and environmentally friendly coatings. The vegetable oil has the characteristics of no toxicity, low volatility, biodegradability, abundant and easily obtained raw materials and the like. Since the 19 th century, a series of studies have been conducted on plant oil-based polymers. For example, triglyceride in vegetable oil is subjected to glycerolysis to obtain monoglyceride for preparing alkyd resin; firstly, drying oil or fatty acid is subjected to maleic anhydride esterification, and then is subjected to ester exchange reaction with an epoxy prepolymer to prepare a fatty acid modified epoxy coating; the soybean oil is subjected to epoxidation treatment and then is combined with acrylate to prepare epoxidized soybean oil acrylate resin; monoglyceride is also a polyol, and can react with diisocyanate to prepare polyurethane, and vegetable oil for preparing water-based polyurethane includes sunflower oil, castor oil, rapeseed oil, soybean oil, etc.; the tung oil is thermally cross-linked and polymerized to directly form a biodegradable coating.

Lignin is a complex class of organic polymers that forms an important structural material in the supporting tissues of vascular plants and some algae. Lignin is particularly important in the formation of cell walls, particularly in wood and bark, because it imparts rigidity and is not prone to decay. Chemically, lignin is a cross-linked phenolic polymer. The lignin is a biopolymer with a three-dimensional network structure formed by mutually connecting 3 phenylpropane units through ether bonds and carbon-carbon bonds, contains rich active groups such as aromatic ring structures, aliphatic and aromatic hydroxyl groups, quinone groups and the like, and is a second largest biomass resource with the second reserve in the plant world next to cellulose. As a typical biomass material, lignin is one of the few renewable resources in aromatic compounds. Lignin, as a biomass material of the second largest resource after cellulose in the plant world, produces about 5000 million tons per year worldwide, with about 10-20% lignin from agricultural residues and about 20-30% lignin from forest biomass materials, widely available and in enormous quantities.

Lignin has a molecular structure containing active groups such as aromatic groups, phenolic hydroxyl groups, alcoholic hydroxyl groups, and carbon-based conjugated double bonds, and thus can undergo many chemical reactions such as oxidation, reduction, hydrolysis, alcoholysis, acid hydrolysis of methoxy groups, carboxyl groups, photolysis, phthalylation, sulfonation, alkylation, halogenation, nitration, polycondensation, or graft copolymerization. Wherein, the reactivity of oxidation, phthalylation, sulfonation, polycondensation, graft copolymerization and the like is used for playing an important role in the application of the lignin research, and is also an important way for expanding the application of the lignin. In the process, the sulfonation reaction is the basis and precondition of lignin application, and the lignin is mostly utilized in the form of lignosulfonate until now. A large amount of black liquor is generated in the pulping and papermaking process, and a large amount of lignin is contained in the night, so that the method has very important practical application value for separating, recovering and utilizing the lignin. The lignin and the derivatives thereof can be used as a reinforcing filler of the coating, and can also be used as a synthetic raw material or a film-forming substance of coating resin. The technology and research of the utilization of the bio-based resources in China are far behind those of developed countries such as the United states. Therefore, the research on novel renewable and environment-friendly coatings has profound and important significance for the development of the coating industry in China.

Chinese patent [ 202111492704.1 ] discloses a lignin-modified waterborne polyurethane film and a preparation method thereof, wherein the waterborne polyurethane film comprises oligomer polyol, polyisocyanate, a hydrophilic chain extender, an oxime compound, a polyamine compound, an acid compound, an organic solvent and lignin. According to the invention, lignin is introduced into the synthesized polyurethane emulsion in a water-phase in-situ adding manner, so that the in-situ nano dispersion effect of the lignin in a water-based polyurethane system is realized, the water-based polyurethane film is obtained by heating and curing, the mechanical property is greatly improved, the self-repairing function is effectively reserved, and the recycling performance of the material is improved. However, the invention only uses lignin as a filler, and does not form a chemical bond with stronger bonding force, so that the strength performance of the prepared polyurethane film has a larger improvement space.

Chinese patent [ 202010334761.6 ] discloses a preparation method of a modified lignin-based polyurethane coating with high flame retardance, in particular to a preparation method of a reaction type flame retardant modified lignin, which comprises the following steps: (1) Adding alkali lignin into a 1, 4-dioxane solvent, uniformly dispersing by ultrasonic waves, adding a catalyst 4-dimethylaminopyridine, slowly dropwise adding diphenylphosphinic chloride by using an automatic injector, heating to 80-100 ℃, reacting for 15-20h, removing the solvent, washing and drying to prepare the phosphorized lignin; (2) Adding the phosphorylated lignin into an N, N-dimethylformamide solvent, uniformly dispersing by ultrasonic, adding 1, 5-naphthalene diisocyanate, tetrachloro phosphorus trioxide and a catalyst pyridine, heating to 100-120 ℃, reacting for 12-18h, filtering, washing and drying to prepare the isocyanate grafted polyphosphorated modified lignin. The modification process of the invention is complex, a large amount of organic matters with toxic action are used, and a large amount of pollutants can be generated in the production process, so that the large-scale production is not facilitated.

Therefore, the invention proposes that the lignin is subjected to micro-nano treatment, then isocyanic acid modification is carried out on the lignin, and finally the lignin-based polyurethane is prepared. The process is simple, water is used as a solvent, the reaction process is relatively green and environment-friendly, and the method has the potential of large-scale production.

Disclosure of Invention

The invention aims to provide lignin-based waterborne polyurethane and a preparation method thereof, in particular to bio-based waterborne polyurethane produced by taking lignin as a raw material.

The specific technical scheme is as follows:

a lignin-based waterborne polyurethane is composed of the following raw materials in parts by weight: 80-120 parts of oligomer polyol, 70-90 parts of polyisocyanate, 5-20 parts of chain extender, 5-20 parts of organic amine compound, 30-80 parts of oxime compound, 1-5 parts of emulsifier, 100-120 parts of isocyanic acid modified lignin and 300-800 parts of deionized water.

In some embodiments, the lignin-based polyurethane comprises the following components in parts by weight: 90-120 parts of oligomer polyol, 70-90 parts of polyisocyanate, 5-20 parts of a chain extender, 10-20 parts of an organic amine compound, 40-80 parts of an oxime compound, 1-5 parts of an emulsifier, 100-120 parts of isocyanate modified lignin and 300-800 parts of deionized water.

In some of these embodiments, the oligomer polyol is polytetrahydrofuran ether glycol, polypropylene glycol, and the polyester polyol includes at least one of polyhexamethylene glycol adipate, polycarbonate diol, polybutylene adipate, polycaprolactone diol, and polypropylene glycol.

In some of these embodiments, the polyisocyanate is at least one of hexamethylene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, polymethylene polyphenyl polycyanate.

In some of these embodiments, the chain extender is at least one of ethylene glycol, propylene glycol, 1, 4-butanediol, diethylene glycol, glycerol, trimethylolpropane, 1, 4-cyclohexanediol, 2-dimethylolbutyric acid, 2-dimethylolpropionic acid, oleic acid diethanolamide.

In some embodiments, the organic amine compound is at least one of diethanolamine, triethanolamine, methyldiethanolamine, diisopropylamine, 1, 2-dimethylpropylamine, 1, 2-propylenediamine, 1, 4-butylenediamine, and hexamethylenediamine.

In some of these embodiments, the oxime based compound is at least one of acetaldoxime, dimethylketoxime, butyraldoxime.

In some of these embodiments, the emulsifier is one or more of sodium lauryl sulfosulfate, 2-para-nonylphenoxy-ethyl ammonium sulfate, sodium 2-acrylamido-methyl-propyl sulfate, and ammonium 2-acrylamido-methyl-propyl sulfate.

In some of these embodiments, the step of preparing the isocyanated modified lignin comprises:

(1) Micro-nano treatment of lignin: dispersing 200-300 parts of lignin in 500-600 parts of polyvinyl alcohol, carrying out constant temperature treatment for 1-3 hours at 80-100 ℃, filtering to remove filtrate, sequentially crushing filter residue by an oil press and a colloid mill, dispersing the filter residue in 400-600 parts of methyl ethyl ketone, and carrying out ultrasonic treatment for 1-3 hours at a power of 400-500W to obtain a dispersion liquid of the micro-nano lignin in the methyl ethyl ketone;

(2) Isocyanic acid modification of lignin: adding the micro-nano lignin methyl ethyl ketone dispersion liquid obtained in the step (1) into a multifunctional reaction kettle, sequentially adding 300-450 parts of polybasic isocyanate and 1-3 parts of dibutyltin dilaurate, heating the mixture to 80-100 ℃ and reacting for 24 hours, cooling the reacted mixture to 25 ℃, adding 200-500 parts of n-hexane into the mixture under stirring at the stirring speed of 1000-2000 r/min, continuously stirring for 0.5-1 hour, finally, filtering the mixture, washing with the n-hexane for at least three times, and drying at 50-80 ℃ for 10-12 hours to obtain the dry isocyanate modified lignin.

In some of the embodiments, the polyisocyanate in the step (2) is at least one of hexamethylene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, toluene diisocyanate, and isophorone diisocyanate.

The invention also provides a preparation method of the lignin-based waterborne polyurethane, which comprises the following steps:

firstly, introducing nitrogen for 5-20 minutes to remove air in a reaction kettle, sequentially adding deionized water, an emulsifier and isocyanic acid modified lignin into the multifunctional reaction kettle according to the weight of the formula, stirring at the stirring speed of 500-1000 revolutions per minute for emulsification, rapidly heating to 80-100 ℃, and keeping the temperature for 0.5-1 hour; adding the polyisocyanate and the oligomer polyol into the mixture to react, heating the mixture to 110-120 ℃, reacting the mixture for 1-3 hours at constant temperature, adding the chain extender, quickly heating the mixture to 120-150 ℃, adding the oxime compound, continuing reacting the mixture for 1-2 hours at constant temperature, adding the organic amine compound, continuing reacting the mixture for 1-3 hours, measuring the viscosity of the reaction solution every half an hour, and cooling the reaction solution to 50-60 ℃ when the viscosity is 5-30S/25 ℃, and keeping the temperature; then introducing nitrogen for 20-30 minutes, removing water vapor in the reaction kettle, pouring reactants out of the reaction kettle, dispersing and emulsifying in a high-speed dispersion machine, and removing water by reduced pressure distillation to obtain lignin-based waterborne polyurethane emulsion; and coating the lignin-based waterborne polyurethane emulsion on a glass plate and curing to obtain the lignin-based waterborne polyurethane film.

The invention has the following advantages:

(1) Water is used as a solvent, so that the reaction process is relatively green and environment-friendly, and the VOC emission of the subsequent polyurethane in the use process can be reduced;

(2) The strength performance of the polyurethane can be enhanced by carrying out isocyanic acid modification on lignin and taking the lignin as a reactant to react instead of simply taking the lignin as a filler;

(3) The lignin is subjected to high-value utilization and is converted into biomass resources, so that the pollution of the lignin to the environment in the paper industry is reduced, and the carbon emission is reduced.

Drawings

FIG. 1 Electron micrograph of isocyanic acid-modified lignin prepared in example 1;

FIG. 2 is an infrared spectrum of lignin before and after modification with isocyanic acid prepared in example 1;

FIG. 3 is a drawing graph of a polyurethane film prepared in example 2;

FIG. 4 the stretch profile of the polyurethane film prepared in example 3;

FIG. 5 stretch profile of polyurethane film prepared in example 4

FIG. 6 stretch profile of polyurethane film prepared in example 5

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings, technical process steps, specific implementation conditions and materials in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.

Example 1

Dispersing 200g of lignin in 500g of polyvinyl alcohol, carrying out constant temperature treatment at 90 ℃ for 2 hours, filtering to remove filtrate, sequentially crushing filter residues through an oil press and a colloid mill, dispersing the filter residues in 500g of methyl ethyl ketone, and carrying out ultrasonic treatment at 500W for 3 hours to obtain a dispersion liquid of the micro-nano lignin in the methyl ethyl ketone. Adding the obtained micro-nano lignin methyl ethyl ketone dispersion liquid into a multifunctional reaction kettle, sequentially adding 450 parts of diphenylmethane diisocyanate and 2 parts of dibutyltin dilaurate, heating the mixture to 100 ℃ and reacting for 24 hours, cooling the mixture to 25 ℃ after the reaction, adding 400 parts of n-hexane into the mixture under stirring at a stirring speed of 1500 revolutions per minute, continuously stirring for 1 hour, finally, filtering the mixture, washing with the n-hexane for at least three times, and drying at 50 ℃ for 12 hours to obtain the dry isocyanate modified lignin. Scanning electron microscope testing is carried out on the prepared lignin isocyanate particles, and the result is shown in figure 1; the infrared spectrum characterization was performed as shown in FIG. 2. Comparing the infrared spectrograms before and after lignin modification, 1680, 1100 and 910cm ^-1 Vibration of C = C, C-C and C-H, respectively; and 1480cm ^-1 Is the vibration of C-N, and the peak intensity is strong after the modificationIn the unmodified lignin, the isocyanic acid modified lignin was shown to be successful.

Example 2

The embodiment provides lignin-based waterborne polyurethane and a preparation method thereof, wherein the raw material composition is shown in table 1:

table 1 raw material ratios of example 2

Tetrahydrofuran ether glycol	90 portions of
		Hexamethylene diisocyanate	70 portions of
Propylene glycol	5 portions of
		Triethanolamine	5 portions of
Dimethyl ketoxime	30 portions of
		Sodium lauryl sulfate	5 portions of
Isocyanic acid modified lignin	100 portions of
		Deionized water	500 portions

In this example, the isocyanate-modified lignin was the isocyanate-modified lignin prepared in example 1.

The lignin-based waterborne polyurethane and the preparation method thereof in the embodiment are as follows: firstly, introducing nitrogen for 5-20 minutes to remove air in the reaction kettle, sequentially adding deionized water, sodium lauryl sulfate and isocyanic acid modified lignin into the multifunctional reaction kettle according to the weight of the formula, stirring at the stirring speed of 1000 revolutions per minute for emulsification, rapidly heating to 90 ℃, and keeping the temperature constant for 1 hour; adding hexamethylene diisocyanate and tetrahydrofuran ether glycol into the mixture to react, heating the mixture to 110 ℃, reacting the mixture at a constant temperature for 1 to 3 hours, adding propylene glycol, quickly heating the mixture to 120 to 150 ℃, adding dimethyl ketoxime, continuing to react at the constant temperature for 1 to 2 hours, adding triethanolamine, continuing to react for 3 hours, measuring the viscosity of the reaction solution every half an hour, and cooling the reaction solution to 50 ℃ and preserving the temperature when the viscosity is 5 to 30S/25 ℃; then introducing nitrogen for 20 minutes, removing water vapor in the reaction kettle, pouring reactants out of the reaction kettle, dispersing and emulsifying in a high-speed dispersion machine, and removing water by reduced pressure distillation to obtain lignin-based waterborne polyurethane emulsion; and coating the lignin-based waterborne polyurethane emulsion on a glass plate and curing to obtain the lignin-based waterborne polyurethane film. Tensile strength of the film measured by a universal tensile tester is shown in FIG. 3, which is a strength of about 172MPa.

The VOC of the prepared alkyd resin is tested according to GB/T23985-2009 determination difference method of content of Volatile Organic Compounds (VOC) of colored paint and varnish, and the result is that the VOC is less than or equal to 229.

Example 3

The embodiment provides lignin-based waterborne polyurethane and a preparation method thereof, wherein the raw material composition is shown in table 2:

table 2 raw material ratios of example 3

Polypropylene glycol	100 portion of
		Toluene diisocyanate	90 portions of
Diethylene glycol	10 portions of
		Methyldiethanolamine	15 portions of
Butyraldehyde oxime	30 portions of
		2-para-nonylphenoxy-ethyl ammonium sulfate	5 portions of
Isocyanic acid modified lignin	110 portions of
		Deionized water	600 portions of

In this example, the isocyanate-modified lignin was isocyanate-modified lignin prepared in example 1.

The lignin-based waterborne polyurethane and the preparation method thereof in the embodiment are as follows: firstly, introducing nitrogen for 5-20 minutes to remove air in the reaction kettle, sequentially adding deionized water, 2-p-nonylphenoxy-ethyl ammonium sulfate and isocyanic acid modified lignin into the multifunctional reaction kettle according to the weight of the formula, emulsifying while stirring at the stirring speed of 500-1000 revolutions per minute, rapidly heating to 80 ℃, and keeping the temperature for 0.5 hour; adding toluene diisocyanate and polypropylene glycol into the mixture to perform a mixing reaction, heating the mixture to 120 ℃, performing a constant temperature reaction for 2 hours, adding diethylene glycol, quickly heating the mixture to 150 ℃, adding butyraldehyde oxime, continuing the constant temperature reaction for 1 hour, adding methyldiethanolamine, continuing the reaction for 2 hours, measuring the viscosity of the reaction solution every half hour, and cooling the reaction solution to 50 ℃ and preserving the temperature when the viscosity is 5-30S/25 ℃; then introducing nitrogen for 20 minutes, removing water vapor in the reaction kettle, pouring reactants out of the reaction kettle, dispersing and emulsifying in a high-speed dispersion machine, and removing water by reduced pressure distillation to obtain lignin-based waterborne polyurethane emulsion; and coating the lignin-based waterborne polyurethane emulsion on a glass plate and curing to obtain the lignin-based waterborne polyurethane film. Tensile strength of the film measured by a universal tensile tester is shown in FIG. 4, which is about 153MPa.

The VOC of the prepared alkyd resin is tested according to GB/T23985-2009 determination difference method of Volatile Organic Compound (VOC) content of colored paint and varnish, and the result is that the VOC is less than or equal to 187.

Example 4

The embodiment provides lignin-based waterborne polyurethane and a preparation method thereof, wherein the raw material formula is shown in table 3:

table 3 raw material ratios of example 4

Polycarbonate diol	120 portions of
		Dicyclohexylmethane diisocyanate	90 portions of
2, 2-dimethylolpropionic acid	20 portions of
		1, 2-dimethylpropylamine	5 portions of
Dimethylglyoxime	30 portions of
		2-acrylamido-methyl-propyl ammonium sulfate	5 portions of
Isocyanic acid modified lignin	120 portions of
		Deionized water	800 portions of

The lignin-based waterborne polyurethane and the preparation method thereof are as follows: firstly introducing nitrogen for 20 minutes to remove air in a reaction kettle, sequentially adding deionized water, 2-acrylamide-methyl-propyl ammonium sulfate and isocyanic acid modified lignin into a multifunctional reaction kettle according to the weight of a formula, stirring at the stirring speed of 1000 revolutions per minute for emulsification, rapidly heating to 100 ℃, and keeping the temperature for 1 hour; adding dicyclohexylmethane diisocyanate and polycarbonate diol into the mixture to react, heating the mixture to 110 ℃, reacting the mixture at constant temperature for 1 hour, adding 2, 2-dimethylolpropionic acid, quickly heating the mixture to 150 ℃, adding dimethylglyoxime, reacting the mixture at constant temperature for 2 hours, adding 1, 2-dimethylpropylamine, reacting the mixture for 1 hour, measuring the viscosity of the reaction solution every half an hour, and cooling the reaction solution to 50-60 ℃ and keeping the temperature when the viscosity is 5-30S/25 ℃; then introducing nitrogen for 30 minutes, removing water vapor in the reaction kettle, pouring reactants out of the reaction kettle, dispersing and emulsifying in a high-speed dispersion machine, and removing water by reduced pressure distillation to obtain lignin-based waterborne polyurethane emulsion; and coating the lignin-based waterborne polyurethane emulsion on a glass plate and curing to obtain the lignin-based waterborne polyurethane film. Tensile strength of the film measured by a universal tensile tester as shown in FIG. 5, the strength was about 168MPa.

The VOC of the prepared alkyd resin is tested according to GB/T23985-2009 determination difference method of content of Volatile Organic Compounds (VOC) of colored paint and varnish, and the result is that the VOC is less than or equal to 221.

Example 5

The embodiment provides lignin-based waterborne polyurethane and a preparation method thereof, wherein the raw material composition is shown in table 4:

the lignin-based waterborne polyurethane and the preparation method thereof are as follows: introducing nitrogen for 20 minutes to remove air in the reaction kettle, sequentially adding deionized water, sodium lauryl sulfate and isocyanic acid modified lignin into the multifunctional reaction kettle according to the weight of the formula, stirring at the stirring speed of 1000 revolutions per minute for emulsification, rapidly heating to 100 ℃, and keeping the temperature for 1 hour; adding hexamethylene diisocyanate and polybutylene adipate into the mixture to react, heating the mixture to 90 ℃, reacting the mixture at constant temperature for 1 hour, adding trimethylolpropane, quickly heating the mixture to 150 ℃, adding acetaldehyde oxime, continuing to react at constant temperature for 2 hours, adding 1, 2-propane diamine, continuing to react for 3 hours, measuring the viscosity of the reaction solution every half hour, cooling the reaction solution to 50 ℃ when the viscosity is 5-30S/25 ℃, and keeping the temperature; then introducing nitrogen for 30 minutes, removing water vapor in the reaction kettle, pouring out the reactant from the reaction kettle, dispersing and emulsifying in a high-speed dispersion machine, and removing water by reduced pressure distillation to obtain lignin-based waterborne polyurethane emulsion; and coating the lignin-based waterborne polyurethane emulsion on a glass plate and curing to obtain the lignin-based waterborne polyurethane film. Tensile strength of the film measured by a universal tensile tester is shown in FIG. 6, and the strength is about 134MPa.

The VOC of the prepared alkyd resin is tested according to GB/T23985-2009 determination difference method of Volatile Organic Compound (VOC) content of colored paint and varnish, and the result is that the VOC is less than or equal to 203.

Table 4 raw material proportioning for example 5

Polybutylene adipate	120 portions of
		Hexamethylene diisocyanate	90 portions of
Trimethylolpropane ester	20 portions of
		1, 2-propanediamine	20 portions of
Acetaldoxime	80 portions
		Sodium lauryl sulfate	5 portions of
Isocyanic acid modified lignin	120 portions of
		Deionized water	800 portions

The skilled person should know that: although the present invention has been described in terms of the above-described embodiments, the inventive concept is not limited thereto, and any modification that utilizes the inventive concept is intended to be included within the scope of the appended claims.

Claims

1. The lignin-based waterborne polyurethane is characterized by comprising the following raw materials in parts by weight: 80-120 parts of oligomer polyol, 70-90 parts of polyisocyanate, 5-20 parts of chain extender, 5-20 parts of organic amine compound, 30-80 parts of oxime compound, 1-5 parts of emulsifier, 100-120 parts of isocyanate modified lignin and 300-800 parts of deionized water.

2. The lignin-based aqueous polyurethane according to claim 1, wherein the oligomeric polyol is polytetrahydrofuran ether glycol, polypropylene glycol, polyester polyol mainly comprises at least one of polyhexamethylene adipate, polycarbonate diol, polybutylene adipate, polycaprolactone diol, polypropylene glycol.

3. The lignin-based aqueous polyurethane according to claim 1, wherein the polyisocyanate is at least one of hexamethylene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and polymethylene polyphenyl polyisocyanate.

4. The lignin-based aqueous polyurethane according to claim 1, wherein the chain extender is at least one of ethylene glycol, propylene glycol, 1, 4-butanediol, diethylene glycol, glycerol, trimethylolpropane, 1, 4-cyclohexanediol, 2-dimethylolbutyric acid, 2-dimethylolpropionic acid, oleic diethanolamide.

5. The lignin-based aqueous polyurethane according to claim 1, wherein the organic amine compound is at least one of diethanolamine, triethanolamine, methyldiethanolamine, diisopropylamine, 1, 2-dimethylpropylamine, 1, 2-propanediamine, 1, 4-butanediamine, and hexanediamine.

6. The lignin-based aqueous polyurethane according to claim 1, wherein the oxime-based compound is at least one of acetaldoxime, dimethylketoxime, dimethylglyoxime, butyraldehyde oxime.

7. The lignin-based aqueous polyurethane of claim 1, wherein the emulsifier is one or more of sodium lauryl sulfosulfate, 2-p-nonylphenoxy ethyl sulfate, sodium 2-acrylamido-methyl-propyl sulfate, and ammonium 2-acrylamido-methyl-propyl sulfate.

8. The lignin-based aqueous polyurethane according to claim 1, wherein the isocyanate-modified lignin is prepared by a process comprising:

9. The lignin-based aqueous polyurethane according to claim 8, wherein the polyisocyanate in step (2) is at least one of hexamethylene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, toluene diisocyanate, and isophorone diisocyanate.

10. The method for preparing lignin-based waterborne polyurethane according to any one of claims 1 to 9, wherein the method comprises the following steps:

firstly, introducing nitrogen for 5-20 minutes to remove air in the reaction kettle, sequentially adding deionized water, an emulsifier and isocyanic acid modified lignin into the multifunctional reaction kettle, stirring at the stirring speed of 500-1000 revolutions per minute for emulsification, rapidly heating to 80-100 ℃, and keeping the temperature for 0.5-1 hour; adding the polyisocyanate and the oligomer polyol into the mixture to react, heating the mixture to 110-120 ℃, reacting the mixture for 1-3 hours at constant temperature, adding the chain extender, quickly heating the mixture to 120-150 ℃, adding the oxime compound, continuing reacting the mixture for 1-2 hours at constant temperature, adding the organic amine compound, continuing reacting the mixture for 1-3 hours, measuring the viscosity of the reaction solution every half an hour, and cooling the reaction solution to 50-60 ℃ when the viscosity is 5-30S/25 ℃, and keeping the temperature; then introducing nitrogen for 20-30 minutes, removing water vapor in the reaction kettle, pouring out the reactant from the reaction kettle, dispersing and emulsifying in a high-speed dispersion machine, and removing water by reduced pressure distillation to obtain lignin-based waterborne polyurethane emulsion; and coating the lignin-based waterborne polyurethane emulsion on a glass plate and curing to obtain the lignin-based waterborne polyurethane film.