阅读说明：本技术 一种可自修复的含木质素聚氨酯弹性体及其制备方法 (Self-repairable lignin-containing polyurethane elastomer and preparation method thereof ) 是由 刘旸 孙楠 李志国 王兆峰 马曦 于 2021-10-08 设计创作，主要内容包括：一种可自修复的含木质素聚氨酯弹性体及其制备方法,它涉及一种含木质素聚氨酯弹性体及其制备方法。本发明要解决现有含木质素聚氨酯弹性体无法实现自修复的问题。可自修复的含木质素聚氨酯弹性体,它由含二硫键和木质素的液态聚酯多元醇、异氰酸酯和扩链剂制备而成；制备方法：一、制备含二硫键和木质素的液态聚酯多元醇；二、含木质素聚氨酯的制备。本发明用于可自修复的含木质素聚氨酯弹性体及其制备。(A lignin-containing polyurethane elastomer capable of self-repairing and a preparation method thereof relate to a lignin-containing polyurethane elastomer and a preparation method thereof. The invention aims to solve the problem that the existing lignin-containing polyurethane elastomer can not realize self-repairing. The self-repairing lignin-containing polyurethane elastomer is prepared from liquid polyester polyol containing disulfide bonds and lignin, isocyanate and a chain extender; the preparation method comprises the following steps: firstly, preparing liquid polyester polyol containing disulfide bonds and lignin; secondly, preparing lignin-containing polyurethane. The invention is used for the self-repairable lignin-containing polyurethane elastomer and the preparation thereof.)

1. A self-repairable lignin-containing polyurethane elastomer is characterized by being prepared from 10 parts by mass of liquid polyester polyol containing disulfide bonds and lignin, 4-7 parts by mass of isocyanate and 1-2.5 parts by mass of chain extender;

the liquid polyester polyol containing the disulfide bond and the lignin is prepared from 0.4 to 2.7 parts of lignin, 10 parts of aliphatic dibasic acid, 4 to 9 parts of dihydric alcohol, 0.9 to 1.35 parts of disulfide and 0.15 to 0.46 part of catalyst in parts by mass; the aliphatic dibasic acid is one or a mixture of adipic acid and sebacic acid; the dihydric alcohol is one or a mixture of more of ethylene glycol, neopentyl glycol, diethylene glycol, 1, 2-propylene glycol and 1, 4-butanediol; the disulfide is bis (2-hydroxyethyl) disulfide; the catalyst is methane sulfonic acid and dibutyltin dilaurate.

2. The self-repairable lignin-containing polyurethane elastomer according to claim 1, wherein the lignin is a byproduct lignin of the ethanol production industry from corn stover.

3. The self-repairable lignin-containing polyurethane elastomer according to claim 1, wherein the isocyanate is one or a mixture of toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate and diphenylmethane diisocyanate.

4. The self-repairable lignin-containing polyurethane elastomer according to claim 1, wherein the chain extender is one or a mixture of more of bis (2-hydroxyethyl) disulfide, ethylene glycol, 1, 4-butanediol, propylene glycol, ethylenediamine, propylenediamine, and lignin.

5. The self-repairable lignin-containing polyurethane elastomer as claimed in claim 1, wherein the mass ratio of methane sulfonic acid to dibutyltin dilaurate in the catalyst is 1 (0.8-1.2).

6. The preparation method of the self-repairable lignin-containing polyurethane elastomer as claimed in claim 1, which is carried out by the following steps:

firstly, preparing liquid polyester polyol containing disulfide bonds and lignin:

weighing:

weighing 0.4-2.7 parts of lignin, 10 parts of aliphatic dibasic acid, 4-9 parts of dihydric alcohol, 0.9-1.35 parts of disulfide and 0.15-0.46 part of catalyst according to the mass parts;

the aliphatic dibasic acid is one or a mixture of adipic acid and sebacic acid; the dihydric alcohol is one or a mixture of more of ethylene glycol, neopentyl glycol, diethylene glycol, 1, 2-propylene glycol and 1, 4-butanediol; the disulfide is bis (2-hydroxyethyl) disulfide; the catalyst is methane sulfonic acid and dibutyltin dilaurate;

② esterification reaction:

sequentially adding 0.4 to 2.7 parts of lignin, 10 parts of aliphatic dibasic acid, 4 to 9 parts of dihydric alcohol and 0.9 to 1.35 parts of disulfide into a reaction device, introducing nitrogen, stirring and reacting for 1 to 2 hours at the temperature of 150 to 155 ℃ and under the nitrogen atmosphere, then heating the temperature from 150 to 155 ℃ to 160 to 170 ℃ under the normal pressure and the nitrogen atmosphere, and stirring and reacting for 3 to 4 hours at the normal pressure, the temperature of 160 to 170 ℃ and the nitrogen atmosphere;

③ polycondensation reaction:

heating the temperature from 160-170 ℃ to 210-230 ℃ under normal pressure and nitrogen atmosphere, stirring and reacting for 3-4 h under the temperature of 210-230 ℃ and nitrogen atmosphere, then vacuumizing until the vacuum degree is-0.04 MPa-0.05 MPa, stirring and reacting for 0.5-1 h under the conditions of nitrogen atmosphere, temperature of 210-230 ℃ and vacuum degree of-0.04 MPa-0.05 MPa, finally introducing nitrogen until the vacuum degree is-0.07 MPa-0.08 MPa, and stirring and reacting for 0.5-1 h under the conditions of nitrogen atmosphere, temperature of 210-230 ℃ and vacuum degree of-0.07 MPa-0.08 MPa;

fourthly, ester exchange reaction:

under normal pressure and nitrogen atmosphere, cooling the temperature from 210-230 ℃ to 90-110 ℃, adding 0.15-0.46 part of catalyst, stirring and reacting for 2-3 h under the condition of 90-110 ℃ and nitrogen atmosphere, and finally cooling to room temperature and discharging to obtain liquid polyester polyol containing disulfide bonds and lignin;

secondly, preparing lignin-containing polyurethane:

weighing 10 parts of liquid polyester polyol containing disulfide bonds and lignin, 4-7 parts of isocyanate and 1-2.5 parts of chain extender in parts by weight, sequentially adding 4-7 parts of isocyanate and 1-2.5 parts of chain extender into 10 parts of liquid polyester polyol containing disulfide bonds and lignin at room temperature, mixing, and reacting for 5-7 hours at the temperature of 60-80 ℃ after uniform mixing to obtain the self-repairable lignin-containing polyurethane elastomer.

7. The preparation method of the self-repairable lignin-containing polyurethane elastomer as claimed in claim 6, wherein the lignin in the first step is lignin which is a byproduct in the ethanol production industry from corn stalks.

8. The preparation method of the self-repairable lignin-containing polyurethane elastomer as claimed in claim 6, wherein the mass ratio of methane sulfonic acid to dibutyltin dilaurate in the catalyst in the first step (i) is 1 (0.8-1.2).

9. The method for preparing the self-repairable lignin-containing polyurethane elastomer according to claim 6, wherein the isocyanate in the second step is one or a mixture of toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate and diphenylmethane diisocyanate.

10. The preparation method of the self-repairable lignin-containing polyurethane elastomer according to claim 6, wherein the chain extender in the second step is one or a mixture of more of bis (2-hydroxyethyl) disulfide, ethylene glycol, 1, 4-butanediol, propylene glycol, ethylene diamine, propylene diamine and lignin.

Technical Field

The invention relates to a lignin-containing polyurethane elastomer and a preparation method thereof.

Background

The rubber and elastomer industry has become one of the important basic industries of national economy. It not only provides daily-use, medical and other light industrial rubber products which are indispensable for daily life, but also provides various rubber production equipment or rubber parts for mining, traffic, building, machinery, electronics and other heavy industries and emerging industries. Among them, polyurethane elastomers have been widely used in tires, seals, biomaterials, soft robots, wearable electronics, sensors, etc. due to their advantages of low modulus, good elongation, easy dyeing, resistance to common chemical solvents, good resilience, etc. However, the polyurethane elastomer is often affected by external environment and additional stress during processing and use to generate unpredictable damage, cracks and even macroscopic fracture, so that the material fails; meanwhile, due to the existence of an irreversible cross-linked structure, the material is difficult to repeatedly process and form, a large amount of waste garbage is generated after the material is invalid, and the waste garbage is difficult to recycle, so that a series of environmental problems and energy waste are brought to people.

Self-repairing is a function of simulating that organisms can spontaneously heal injuries, and is considered as an important characteristic of the next generation of intelligent materials. When the self-repairing material is subjected to the action of external force to generate defects, the self-repairing material can respond spontaneously or under a certain stimulation action so as to repair cracks, so that the structure and the performance of the self-repairing material are consistent with those of the initial crack, the service life of the material is prolonged, and the resource energy loss is reduced. According to different triggering modes, the self-repairing materials can be divided into external aid type self-repairing materials and intrinsic type self-repairing materials. The self-repairing of the externally-applied type mainly utilizes the microcapsule, hollow fiber technology and mesoporous hollow microsphere technology to realize the self-repairing of the material, wherein the microcapsule technology is more widely applied due to the characteristics of high response speed, simple preparation process and the like. However, the extrinsic self-repairing is mainly dependent on the external repairing agent, and the repairing times are limited, so that the intrinsic self-repairing is more concerned. The repairability of the intrinsic self-repairing material mainly depends on dynamic chemical bonds, the intrinsic self-repairing material can be divided into dynamic covalent bonds and dynamic noncovalent bonds according to the difference of the chemical bonds, and the chemical bonds can show reversible association and dissociation capabilities under the action of external stimulation. Chinese patent with application number CN201811343719.X discloses a self-repairable polyurethane elastomer, and a preparation method and application thereof, and the method effectively solves the problem of low repair efficiency of the polyurethane elastomer. However, at present, most raw materials of polyurethane elastomers are derived from petroleum and derivatives thereof, and petroleum and coal resources belong to non-renewable resources. With the gradual decrease of petrochemical resources and the gradual enhancement of environmental protection consciousness of people, research on preparing organic chemicals by replacing non-renewable resources such as petroleum with renewable resources becomes a key point of attention of people.

Lignin is the second largest biomass resource next to cellulose in the plant world, and is also the only natural high molecular polymer containing aromatic structures in plant resources, and is considered to be one of the most abundant green chemical resources at present. Research on the preparation of organic chemicals from biomass resources such as lignin and the like has become a focus of attention. Because the self-repairing performance of the polyurethane elastomer is influenced by the complex chemical structure and the larger steric hindrance of the lignin, no self-repairing report of the lignin polyurethane elastomer is found at present.

Disclosure of Invention

The invention provides a lignin-containing polyurethane elastomer capable of self-repairing and a preparation method thereof, aiming at solving the problem that the existing lignin-containing polyurethane elastomer cannot realize self-repairing.

A self-repairable lignin-containing polyurethane elastomer is prepared from 10 parts by mass of liquid polyester polyol containing disulfide bonds and lignin, 4-7 parts by mass of isocyanate and 1-2.5 parts by mass of chain extender;

the liquid polyester polyol containing the disulfide bond and the lignin is prepared from 0.4 to 2.7 parts of lignin, 10 parts of aliphatic dibasic acid, 4 to 9 parts of dihydric alcohol, 0.9 to 1.35 parts of disulfide and 0.15 to 0.46 part of catalyst in parts by mass; the aliphatic dibasic acid is one or a mixture of adipic acid and sebacic acid; the dihydric alcohol is one or a mixture of more of ethylene glycol, neopentyl glycol, diethylene glycol, 1, 2-propylene glycol and 1, 4-butanediol; the disulfide is bis (2-hydroxyethyl) disulfide; the catalyst is methane sulfonic acid and dibutyltin dilaurate.

A preparation method of a self-repairable lignin-containing polyurethane elastomer comprises the following steps:

firstly, preparing liquid polyester polyol containing disulfide bonds and lignin:

weighing:

weighing 0.4-2.7 parts of lignin, 10 parts of aliphatic dibasic acid, 4-9 parts of dihydric alcohol, 0.9-1.35 parts of disulfide and 0.15-0.46 part of catalyst according to the mass parts;

the aliphatic dibasic acid is one or a mixture of adipic acid and sebacic acid; the dihydric alcohol is one or a mixture of more of ethylene glycol, neopentyl glycol, diethylene glycol, 1, 2-propylene glycol and 1, 4-butanediol; the disulfide is bis (2-hydroxyethyl) disulfide; the catalyst is methane sulfonic acid and dibutyltin dilaurate;

② esterification reaction:

sequentially adding 0.4 to 2.7 parts of lignin, 10 parts of aliphatic dibasic acid, 4 to 9 parts of dihydric alcohol and 0.9 to 1.35 parts of disulfide into a reaction device, introducing nitrogen, stirring and reacting for 1 to 2 hours at the temperature of 150 to 155 ℃ and under the nitrogen atmosphere, then heating the temperature from 150 to 155 ℃ to 160 to 170 ℃ under the normal pressure and the nitrogen atmosphere, and stirring and reacting for 3 to 4 hours at the normal pressure, the temperature of 160 to 170 ℃ and the nitrogen atmosphere;

③ polycondensation reaction:

heating the temperature from 160-170 ℃ to 210-230 ℃ under normal pressure and nitrogen atmosphere, stirring and reacting for 3-4 h under the temperature of 210-230 ℃ and nitrogen atmosphere, then vacuumizing until the vacuum degree is-0.04 MPa-0.05 MPa, stirring and reacting for 0.5-1 h under the conditions of nitrogen atmosphere, temperature of 210-230 ℃ and vacuum degree of-0.04 MPa-0.05 MPa, finally introducing nitrogen until the vacuum degree is-0.07 MPa-0.08 MPa, and stirring and reacting for 0.5-1 h under the conditions of nitrogen atmosphere, temperature of 210-230 ℃ and vacuum degree of-0.07 MPa-0.08 MPa;

fourthly, ester exchange reaction:

under normal pressure and nitrogen atmosphere, cooling the temperature from 210-230 ℃ to 90-110 ℃, adding 0.15-0.46 part of catalyst, stirring and reacting for 2-3 h under the condition of 90-110 ℃ and nitrogen atmosphere, and finally cooling to room temperature and discharging to obtain liquid polyester polyol containing disulfide bonds and lignin;

secondly, preparing lignin-containing polyurethane:

weighing 10 parts of liquid polyester polyol containing disulfide bonds and lignin, 4-7 parts of isocyanate and 1-2.5 parts of chain extender in parts by weight, sequentially adding 4-7 parts of isocyanate and 1-2.5 parts of chain extender into 10 parts of liquid polyester polyol containing disulfide bonds and lignin at room temperature, mixing, and reacting for 5-7 hours at the temperature of 60-80 ℃ after uniform mixing to obtain the self-repairable lignin-containing polyurethane elastomer.

The invention has the beneficial effects that:

the preparation method has the advantages of simple operation, mild conditions, low requirements on raw materials, high repeatability and the like. Aiming at the problems that the existing polyester type polyurethane elastomer is high in cost, not easy to degrade, easy to generate environmental pollution, resource waste and the like, the lignin-containing polyurethane elastomer which is self-repairable based on the dynamic disulfide bonds is prepared by taking lignin as a main raw material. The repair method only needs to align, attach and reheat the fractured or cracked sample. The prepared lignin-containing polyurethane elastomer not only shows good mechanical properties (up to more than 7 MPa), but also shows excellent self-repairing performance (up to more than 93%), thereby greatly expanding the application field of lignin materials and being expected to be applied to the industrial production of lignin elastomers.

The invention relates to a lignin-containing polyurethane elastomer capable of self-repairing and a preparation method thereof.

Drawings

FIG. 1 is a Fourier infrared spectrum of a disulfide bond-free lignin-containing polyester polyol prepared in comparative experiment one and a liquid polyester polyol containing disulfide bonds and lignin prepared in example step one;

FIG. 2 is a stress-strain diagram, wherein a is a lignin-containing polyurethane elastomer without introduced disulfide bonds prepared in comparative experiment one, and b is a self-repairable lignin-containing polyurethane elastomer prepared in example one;

fig. 3 is a graph of tensile strength before and after self-repair, where a is a lignin-containing polyurethane elastomer without introduced disulfide bonds prepared in a comparative experiment one, b is a lignin-containing polyurethane elastomer capable of self-repairing prepared in an example one, 1 is tensile strength before repair, and 2 is tensile strength after repair;

fig. 4 is a graph of repair efficiency before and after self-repair, where a is a lignin-containing polyurethane elastomer without introduced disulfide bonds prepared in comparative experiment one, and b is a lignin-containing polyurethane elastomer capable of self-repair prepared in example one;

FIG. 5 is a graph of a cyclic tensile test in a continuous load-unload cycle of a self-repairable lignin-containing polyurethane elastomer prepared in example one.

Detailed Description

The first embodiment is as follows: the self-repairable lignin-containing polyurethane elastomer is prepared from 10 parts by mass of liquid polyester polyol containing disulfide bonds and lignin, 4-7 parts by mass of isocyanate and 1-2.5 parts by mass of chain extender;

the liquid polyester polyol containing the disulfide bond and the lignin is prepared from 0.4 to 2.7 parts of lignin, 10 parts of aliphatic dibasic acid, 4 to 9 parts of dihydric alcohol, 0.9 to 1.35 parts of disulfide and 0.15 to 0.46 part of catalyst in parts by mass; the aliphatic dibasic acid is one or a mixture of adipic acid and sebacic acid; the dihydric alcohol is one or a mixture of more of ethylene glycol, neopentyl glycol, diethylene glycol, 1, 2-propylene glycol and 1, 4-butanediol; the disulfide is bis (2-hydroxyethyl) disulfide; the catalyst is methane sulfonic acid and dibutyltin dilaurate.

The specific implementation mode comprises the steps of firstly, taking lignin, aliphatic dibasic acid, dihydric alcohol and disulfide as main reaction raw materials, and connecting micromolecular substances through esterification reaction, polycondensation reaction and ester exchange reaction to form macromolecular polyester polyol which is provided with hydroxyl at the end group and contains disulfide bonds and lignin; and then mixing the polyester polyol containing the disulfide bonds and the lignin with a chain extender and isocyanate, and fully reacting to obtain the self-repairable lignin-containing polyurethane elastomer.

The lignin of the embodiment has active groups such as aromatic group, phenolic hydroxyl group, alcoholic hydroxyl group, carbon-based conjugated double bond and the like in the molecular structure, can be subjected to a plurality of chemical reactions such as oxidation, reduction, hydrolysis, alcoholysis, acidolysis, demethoxylation, carboxylation, photolysis, acylation, sulfonation, alkylation, polycondensation or graft copolymerization and the like, and lays a foundation for the lignin to be used as a substitute of an elastomer synthesis raw material. Hydroxyl groups in the lignin can replace hydroxyl groups in dihydric alcohol to react with carboxyl groups in dibasic acid to form polyester polyol connected by ester bonds; it can also replace the hydroxyl groups in the chain extender to react with isocyanate groups to form urethane-linked polyurethane elastomers. Due to the interaction of more aromatic ring structures in the lignin structure and polar groups such as hydroxyl groups in the structure, the introduction of the lignin can improve the mechanical property of the material.

The intrinsic self-repairing material of the specific embodiment is a functional material which realizes self-repairing by means of the interaction of chemical bonds or non-chemical bonds among polymer molecules. The introduction of dynamic Diels-Alder chemical bonds, hydrogen bonds, disulfide bonds or metal ion coordination bonds and the like into materials is a common method for endowing materials with self-repairing performance. Because lignin has a complex chemical structure and large steric hindrance, the molecular chain movement of a polymer and the interaction of chemical bonds can be influenced by the existence of the lignin, so that the self-repairing of the lignin-containing polyurethane elastomer is difficult to realize. However, in the intrinsic self-repairing material, the dynamic disulfide bond (S-S bond) has relatively mild repairing conditions and better self-repairing efficiency. Introduction of disulfides into polyester polyols results in the presence of dynamic disulfide bonds in the structure of lignin-containing polyurethane elastomers. The existence of the disulfide bond not only can endow the material with excellent self-repairing capability, but also can increase the chemical crosslinking effect among molecular chains and improve the mechanical property of the material. However, the variety of disulfides is very large, and not all disulfides can prepare lignin-containing polyurethane elastomers with excellent mechanical properties and self-repairing properties. The disulfide of the specific embodiment is aliphatic disulfide with a more regular and flexible molecular structure, so that the introduction of rigid aromatic rings in a molecular chain is reduced, and the material has excellent self-repairing efficiency while keeping good mechanical properties. Therefore, the preparation of the disulfide bond-based lignin-containing polyurethane elastomer provides a new high-added-value application for lignin, and is expected to be applied to the industrial production of the high-molecular elastomer.

The beneficial effects of the embodiment are as follows:

the preparation method has the advantages of simple operation, mild conditions, low requirements on raw materials, high repeatability and the like. Aiming at the problems that the existing polyester type polyurethane elastomer is high in cost, not easy to degrade, easy to generate environmental pollution, resource waste and the like, the lignin is used as a main raw material, and the lignin-containing polyurethane elastomer capable of self-repairing based on the dynamic disulfide bonds is prepared. The repair method only needs to align, attach and reheat the fractured or cracked sample. The prepared lignin-containing polyurethane elastomer not only shows good mechanical properties (up to more than 7 MPa), but also shows excellent self-repairing performance (up to more than 93%), thereby greatly expanding the application field of lignin materials and being expected to be applied to the industrial production of lignin elastomers.

The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the lignin is byproduct lignin in the ethanol production industry by using corn straws. The rest is the same as the first embodiment.

The third concrete implementation mode: this embodiment is different from the first or second embodiment in that: the isocyanate is one or a mixture of several of toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate and diphenylmethane diisocyanate. The other is the same as in the first or second embodiment.

The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: the chain extender is one or a mixture of more of bis (2-hydroxyethyl) disulfide, ethylene glycol, 1, 4-butanediol, propylene glycol, ethylenediamine, propylenediamine and lignin. The other is the same as in the first or second embodiment.

The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: the mass ratio of the methanesulfonic acid to the dibutyltin dilaurate in the catalyst is 1 (0.8-1.2). The rest is the same as the first to fourth embodiments.

The sixth specific implementation mode: the embodiment provides a preparation method of a self-repairable lignin-containing polyurethane elastomer, which comprises the following steps:

firstly, preparing liquid polyester polyol containing disulfide bonds and lignin:

weighing:

weighing 0.4-2.7 parts of lignin, 10 parts of aliphatic dibasic acid, 4-9 parts of dihydric alcohol, 0.9-1.35 parts of disulfide and 0.15-0.46 part of catalyst according to the mass parts;

the aliphatic dibasic acid is one or a mixture of adipic acid and sebacic acid; the dihydric alcohol is one or a mixture of more of ethylene glycol, neopentyl glycol, diethylene glycol, 1, 2-propylene glycol and 1, 4-butanediol; the disulfide is bis (2-hydroxyethyl) disulfide; the catalyst is methane sulfonic acid and dibutyltin dilaurate;

② esterification reaction:

sequentially adding 0.4 to 2.7 parts of lignin, 10 parts of aliphatic dibasic acid, 4 to 9 parts of dihydric alcohol and 0.9 to 1.35 parts of disulfide into a reaction device, introducing nitrogen, stirring and reacting for 1 to 2 hours at the temperature of 150 to 155 ℃ and under the nitrogen atmosphere, then heating the temperature from 150 to 155 ℃ to 160 to 170 ℃ under the normal pressure and the nitrogen atmosphere, and stirring and reacting for 3 to 4 hours at the normal pressure, the temperature of 160 to 170 ℃ and the nitrogen atmosphere;

③ polycondensation reaction:

heating the temperature from 160-170 ℃ to 210-230 ℃ under normal pressure and nitrogen atmosphere, stirring and reacting for 3-4 h under the temperature of 210-230 ℃ and nitrogen atmosphere, then vacuumizing until the vacuum degree is-0.04 MPa-0.05 MPa, stirring and reacting for 0.5-1 h under the conditions of nitrogen atmosphere, temperature of 210-230 ℃ and vacuum degree of-0.04 MPa-0.05 MPa, finally introducing nitrogen until the vacuum degree is-0.07 MPa-0.08 MPa, and stirring and reacting for 0.5-1 h under the conditions of nitrogen atmosphere, temperature of 210-230 ℃ and vacuum degree of-0.07 MPa-0.08 MPa;

fourthly, ester exchange reaction:

under normal pressure and nitrogen atmosphere, cooling the temperature from 210-230 ℃ to 90-110 ℃, adding 0.15-0.46 part of catalyst, stirring and reacting for 2-3 h under the condition of 90-110 ℃ and nitrogen atmosphere, and finally cooling to room temperature and discharging to obtain liquid polyester polyol containing disulfide bonds and lignin;

secondly, preparing lignin-containing polyurethane:

weighing 10 parts of liquid polyester polyol containing disulfide bonds and lignin, 4-7 parts of isocyanate and 1-2.5 parts of chain extender in parts by weight, sequentially adding 4-7 parts of isocyanate and 1-2.5 parts of chain extender into 10 parts of liquid polyester polyol containing disulfide bonds and lignin at room temperature, mixing, and reacting for 5-7 hours at the temperature of 60-80 ℃ after uniform mixing to obtain the self-repairable lignin-containing polyurethane elastomer.

The seventh embodiment: the sixth embodiment is different from the sixth embodiment in that: the lignin in the first step is byproduct lignin in the ethanol production industry from corn straws. The rest is the same as the sixth embodiment.

The specific implementation mode is eight: the present embodiment differs from one of the sixth or seventh embodiments in that: the mass ratio of the methanesulfonic acid to the dibutyltin dilaurate in the catalyst in the first step is 1 (0.8-1.2). The others are the same as the sixth or seventh embodiments.

The specific implementation method nine: this embodiment differs from one of the sixth to eighth embodiments in that: and the isocyanate in the second step is one or a mixture of several of toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate and diphenylmethane diisocyanate. The others are the same as the embodiments six to eight.

The detailed implementation mode is ten: the present embodiment differs from one of the sixth to ninth embodiments in that: and the chain extender in the second step is one or a mixture of more of bis (2-hydroxyethyl) disulfide, ethylene glycol, 1, 4-butanediol, propylene glycol, ethylenediamine, propylenediamine and lignin. The others are the same as in the sixth to ninth embodiments.

The following examples were used to demonstrate the beneficial effects of the present invention:

the first embodiment is as follows:

a self-repairable lignin-containing polyurethane elastomer is prepared from 10 parts by mass of liquid polyester polyol containing disulfide bonds and lignin, 4.2 parts by mass of isocyanate and 1.19 parts by mass of a chain extender;

the liquid polyester polyol containing the disulfide bond and the lignin is prepared from 0.78 part of lignin, 10 parts of sebacic acid, 3.91 parts of neopentyl glycol, 0.78 part of ethylene glycol, 0.97 part of bis (2-hydroxyethyl) disulfide, 0.17 part of methane sulfonic acid and 0.17 part of dibutyltin dilaurate in parts by mass;

the lignin is a byproduct lignin in the ethanol production industry by using corn straws; the isocyanate is toluene diisocyanate; the chain extender is ethylene glycol.

A preparation method of a self-repairable lignin-containing polyurethane elastomer comprises the following steps:

firstly, preparing liquid polyester polyol containing disulfide bonds and lignin:

weighing:

weighing 0.78 part of lignin, 10 parts of sebacic acid, 3.91 parts of neopentyl glycol, 0.78 part of ethylene glycol, 0.97 part of bis (2-hydroxyethyl) disulfide, 0.17 part of methane sulfonic acid and 0.17 part of dibutyltin dilaurate in parts by mass;

② esterification reaction:

sequentially adding 0.78 parts of lignin, 10 parts of sebacic acid, 3.91 parts of neopentyl glycol, 0.78 parts of ethylene glycol and 0.97 parts of bis (2-hydroxyethyl) disulfide into a reaction device, introducing nitrogen, stirring and reacting for 1.5 hours at the temperature of 150 ℃ in a nitrogen atmosphere, then heating the temperature from 150 ℃ to 160 ℃ in a normal pressure and a nitrogen atmosphere, and stirring and reacting for 3 hours at the normal pressure, the temperature of 160 ℃ in a nitrogen atmosphere;

③ polycondensation reaction:

heating the temperature from 160 ℃ to 220 ℃ under normal pressure and nitrogen atmosphere, stirring and reacting for 3h under the conditions of the temperature of 220 ℃ and the nitrogen atmosphere, then vacuumizing until the vacuum degree is-0.046 MPa, stirring and reacting for 0.5h under the conditions of the nitrogen atmosphere, the temperature of 220 ℃ and the vacuum degree of-0.046 MPa, finally introducing nitrogen until the vacuum degree is-0.078 MPa, and stirring and reacting for 0.6h under the conditions of the nitrogen atmosphere, the temperature of 220 ℃ and the vacuum degree of-0.078 MPa;

fourthly, ester exchange reaction:

under normal pressure and nitrogen atmosphere, cooling the temperature from 220 ℃ to 90 ℃, adding 0.17 part of methanesulfonic acid and 0.17 part of dibutyltin dilaurate, stirring and reacting for 3 hours at the temperature of 90 ℃ and under the nitrogen atmosphere, and finally cooling to room temperature and discharging to obtain liquid polyester polyol containing disulfide bonds and lignin;

secondly, preparing lignin-containing polyurethane:

weighing 10 parts of liquid polyester polyol containing disulfide bonds and lignin, 4.2 parts of isocyanate and 1.19 parts of chain extender in parts by weight, sequentially adding 4.2 parts of isocyanate and 1.19 parts of chain extender into 10 parts of liquid polyester polyol containing disulfide bonds and lignin at room temperature, mixing, and reacting for 7 hours at the temperature of 60 ℃ after uniform mixing to obtain the self-repairing lignin-containing polyurethane elastomer.

Example two: the difference between the present embodiment and the first embodiment is: the liquid polyester polyol containing the disulfide bond and the lignin is prepared from 1.08 parts by mass of lignin, 10 parts by mass of adipic acid, 5.45 parts by mass of neopentyl glycol, 1.08 parts by mass of ethylene glycol, 1.34 parts by mass of bis (2-hydroxyethyl) disulfide, 0.19 part by mass of methane sulfonic acid and 0.19 part by mass of dibutyltin dilaurate. The rest is the same as the first embodiment.

Example three: the difference between the present embodiment and the first embodiment is: the liquid polyester polyol containing the disulfide bond and the lignin is prepared from 0.78 part of lignin, 10 parts of sebacic acid, 3.94 parts of neopentyl glycol, 1.34 parts of diethylene glycol, 0.97 part of bis (2-hydroxyethyl) disulfide, 0.18 part of methane sulfonic acid and 0.18 part of dibutyltin dilaurate in parts by mass. The rest is the same as the first embodiment.

Example four: the difference between the present embodiment and the first embodiment is: the self-repairable lignin-containing polyurethane elastomer is prepared from 10 parts by mass of liquid polyester polyol containing disulfide bonds and lignin, 4.2 parts by mass of toluene diisocyanate, 0.45 part by mass of lignin and 0.74 part by mass of ethylene glycol. The rest is the same as the first embodiment.

Example five: the difference between the present embodiment and the first embodiment is: the self-repairable lignin-containing polyurethane elastomer is prepared from, by mass, 10 parts of liquid polyester polyol containing disulfide bonds and lignin, 4.2 parts of toluene diisocyanate, 0.43 part of lignin, 0.72 part of ethylene glycol and 0.66 part of bis (2-hydroxyethyl) disulfide. The rest is the same as the first embodiment.

Example six: the difference between the present embodiment and the first embodiment is: the self-repairable lignin-containing polyurethane elastomer is prepared from 10 parts by mass of liquid polyester polyol containing disulfide bonds and lignin, 4.2 parts by mass of toluene diisocyanate and 1.73 parts by mass of 1, 4-butanediol. The rest is the same as the first embodiment.

Example seven: the difference between the present embodiment and the first embodiment is: the self-repairable lignin-containing polyurethane elastomer is prepared from, by mass, 10 parts of liquid polyester polyol containing disulfide bonds and lignin, 4.06 parts of hexamethylene diisocyanate and 1.19 parts of ethylene glycol. The rest is the same as the first embodiment.

Example eight: the difference between the present embodiment and the first embodiment is: the self-repairable lignin-containing polyurethane elastomer is prepared from 10 parts by mass of liquid polyester polyol containing disulfide bonds and lignin, 5.36 parts by mass of isophorone diisocyanate and 1.19 parts by mass of ethylene glycol. The rest is the same as the first embodiment.

Example nine: the difference between the present embodiment and the first embodiment is: the self-repairable lignin-containing polyurethane elastomer is prepared from 10 parts by mass of liquid polyester polyol containing disulfide bonds and lignin, 6.03 parts by mass of diphenylmethane diisocyanate and 1.19 parts by mass of ethylene glycol. The rest is the same as the first embodiment.

Comparative experiment: taking the first example in the patent "an environment-friendly polyurethane elastomer containing lignin" (CN110183615B) as a comparative experiment, the liquid polyester polyol containing lignin obtained by repeating the experiment is the lignin-containing polyester polyol without introducing disulfide bonds, and the obtained environment-friendly polyurethane elastomer containing lignin is the lignin-containing polyurethane elastomer without introducing disulfide bonds.

Comparative experiment two: the comparative experiment differs from the first example in that: the liquid polyester polyol containing the disulfide bond and the lignin is prepared from 0.78 part of lignin, 10 parts of sebacic acid, 3.94 parts of neopentyl glycol, 0.78 part of ethylene glycol, 1.56 parts of 4,4' -diaminodiphenyl disulfide, 0.17 part of methane sulfonic acid and 0.17 part of dibutyltin dilaurate in parts by mass. The rest is the same as the first embodiment.

Fig. 1 is a fourier infrared spectrum, a is a lignin-containing polyester polyol without introduced disulfide bonds prepared in comparative experiment one, and b is a liquid polyester polyol containing disulfide bonds and lignin prepared in example step one. As can be seen, the infrared spectra of a and b are similar. At 3519cm^-1The stretching vibration peak of O-H appears, and the vibration peaks of the two samples are almost the same at the O-H, which shows that the disulfide sufficiently participates in the esterification reaction of acid and alcohol in the polyester polyol, and the polyester polyol with the same content of hydroxyl end capping is obtained. Curves of a and b at 1374cm^-1And 1236cm^-1Both the syringyl aromatic nucleus vibrational peak of lignin and its characteristic stretching vibrational peak of-C ═ O appear, indicating that lignin has been successfully incorporated into polyester polyol. Curve b at 603cm^-1A stretching vibration absorption peak of S-S was observed, confirming that disulfide bonds have been introduced into the polyester polyol.

The polyurethane elastomers prepared in comparative experiments one to two and examples one to nine were cut into dumbbell test pieces using a cutter. The polyurethane elastomer is subjected to tensile test through a universal mechanical testing machine, and the experimental tensile speed is 200 mm/min. Tensile strength of the polyurethane elastomer was tested as measured by GBT528-1998 elastomer tensile strength.

Fig. 2 is a stress-strain diagram, wherein a is a lignin-containing polyurethane elastomer without introduced disulfide bonds prepared in the first comparative experiment, and b is a lignin-containing polyurethane elastomer capable of self-repairing prepared in the first example. As can be seen from the figure, the tensile strength of the lignin-containing polyurethane elastomer without introducing disulfide bonds is 5.01MPa, and the tensile strength of the self-repairable lignin-containing polyurethane elastomer prepared in the first example is 8.71 MPa. The introduction of disulfide bonds obviously improves the tensile strength of the polyurethane elastomer, because S atoms and S atoms are close to each other to form dynamic disulfide bonds, and when the material is acted by external force, the dynamic chemical bonds are broken to dissipate energy, so that the tensile strength of the material is improved.

In order to quantitatively evaluate the self-repair efficiency of the polyurethane elastomer, the dumbbell type polyurethane elastomer was completely cut into two pieces. The fractured dumbbell sample was then realigned at the fracture and placed in an oven at 60 ℃ for 24 h. And calculating the tensile strength of the repaired polyurethane elastomer according to the stress-strain curve. The self-healing efficiency is the ratio of the tensile strength of the repaired polyurethane elastomer to the tensile strength of the original polyurethane elastomer.

Fig. 3 is a graph of tensile strength before and after self-repair, where a is a lignin-containing polyurethane elastomer without introducing disulfide bonds prepared in a comparative experiment one, b is a lignin-containing polyurethane elastomer capable of self-repairing prepared in an embodiment one, 1 is tensile strength before repair, and 2 is tensile strength after repair. Fig. 4 is a graph of repair efficiency before and after self-repair, where a is a lignin-containing polyurethane elastomer without disulfide bonds prepared in the first comparative experiment, and b is a lignin-containing polyurethane elastomer capable of self-repair prepared in the first embodiment. As can be seen from the figure, the tensile strength of the lignin-containing polyurethane elastomer without introducing the disulfide bond before repair is 5.01MPa, the tensile strength after repair is 2.80MPa, and the self-repairing efficiency is 55.89%; the tensile strength of the polyurethane elastomer containing disulfide bonds and lignin prepared in the first embodiment before repair is 8.71MPa, the tensile strength after repair is 8.13MPa, and the self-repairing efficiency is 93.34%. The data show that the self-repairing capability of the lignin-containing polyurethane elastomer introduced with the disulfide bonds prepared in the first embodiment is greatly improved compared with the lignin-containing polyurethane elastomer not introduced with the disulfide bonds, and the self-repairing capability is better. This is mainly because when the material is subjected to an external force, the unstable dynamic disulfide bonds in the molecular chain are first broken and dissipate energy, thereby improving the tensile strength of the material. In addition, when the material is fractured by external force, the molecular chains at the fractured ends of the material move under the external stimulation, the fractured disulfide bonds are recombined, and the material is healed.

The tensile strengths of the polyurethane elastomers were 5.01MPa (comparative experiment one), 5.97MPa (comparative experiment two), 8.71MPa (example one), 7.98MPa (example two), 7.67MPa (example three), 6.98MPa (example four), 14.99MPa (example five), 8.76MPa (example six), 9.28MPa (example seven), 10.77MPa (example eight), and 16.76MPa (example nine), respectively, and the self-repairing efficiencies were 55.89% (comparative experiment one), 39.8% (comparative experiment two), 93.34% (example one), 89.90% (example two), 87.90% (example three), 72.47% (example four), 55.97% (example five), 90.79% (example six), 93.40% (example seven), 93.02% (example eight), and 80.82% (example nine), respectively, and the experiments demonstrated that the polyurethane elastomers containing disulfide bonds and lignin were prepared in examples one to nine, the introduction of the disulfide bond not only endows the polyurethane elastomer material with self-repairing capability, but also improves the tensile strength of the material. Solves the problem that the existing lignin-containing polyurethane elastomer is difficult to self-repair.

The disulfide bond and lignin containing polyurethane elastomer prepared according to comparative example experiment two had a low self-healing efficiency (< 40%) although it also had a good tensile strength (>5 MPa). The main reason is that the 4,4' -diamino diphenyl disulfide raw material has a rigid benzene ring structure, so that the movement of a polyurethane molecular chain is difficult, and the self-repairing capability of the polyurethane elastomer is greatly influenced although the mechanical property of the material can be improved. And the introduction of 4,4' -diaminodiphenyl disulfide makes the polyurethane material hard and brittle, and the elongation at break is low (< 150%), which influences the use of the polyurethane elastomer in practical application.

FIG. 5 is a graph of a cyclic tensile test in a continuous load-unload cycle of a self-repairable lignin-containing polyurethane elastomer prepared in example one. Shows that the self-repairable lignin-containing polyurethane elastomer prepared in the first example has 120 percent strain and the tensile rate of 20mm & min^-1Four consecutive cycles of load-unload tensile curve under the conditions of (a). As can be seen, when the second cycle was repeated immediately after the first cycle, the residual strain was 28.53% and the hysteresis energy was significantly reduced. With the increase of the cycle number, the hysteresis energy gradually approaches to a stable value of 1.78 MJ.m after the 4 th cycle^-3The material shows good fatigue resistance. This is because the dynamic chemical bonds in the polyurethane elastomer break and dissipate energy, thereby rendering the material exhibit better fatigue resistance.