WO2023045981A1

WO2023045981A1 - Solvent-free lignin-based polyurethane elastomer capable of being repeatedly processed and preparation method therefor

Info

Publication number: WO2023045981A1
Application number: PCT/CN2022/120288
Authority: WO
Inventors: 刘伟峰; 邱学青; 黄锦浩; 杨东杰; 楼宏铭; 庞煜霞; 秦延林; 欧阳新平; 林绪亮
Original assignee: 华南理工大学; 广东工业大学
Priority date: 2021-09-26
Filing date: 2022-09-21
Publication date: 2023-03-30
Also published as: CN113817130A; CN113817130B

Abstract

Disclosed in the present invention are a solvent-free lignin-base polyurethane elastomer capable of being repeatedly processed and a preparation method therefor. According to the present invention, lignin with a specific molecular weight and a short-chain polyol are prepared into a lignin-polyol mixed dispersion liquid, and then the dispersion liquid is reacted with a polyurethane prepolymer to prepare a lignin-based polyurethane elastomer. According to the present invention, the lignin with a specific molecular weight is extracted by using an organic solvent with a low boiling point and low toxicity, which is suitable for the industrial large-scale production of low-molecular-weight lignin. The low-molecular-weight lignin has a high reaction activity and better compatibility with a polyurethane matrix, the lignin-based polyurethane elastomer is synthesized by using a solvent-free method, such that the introduction of a high-boiling-point or volatile toxic organic solvent in the synthesis process of the polyurethane elastomer is avoided, and the synthesis process is green and environmentally friendly and has industrial application prospects. The solvent-free lignin-based polyurethane elastomer of the present invention can be recycled multiple times and repeatedly processed and utilized, and the problems whereby a traditional thermosetting lignin-based polyurethane elastomer is difficult to recycle and cannot be reprocessed are overcome.

Description

A kind of reprocessable solvent-free lignin-based polyurethane elastomer and preparation method thereof

technical field

The invention belongs to the technical field of polyurethane elastomers, in particular to a reprocessable solvent-free lignin-based polyurethane elastomer and a preparation method thereof.

Background technique

Polyurethane elastomer is a block copolymer polymer material synthesized from polyol and isocyanate. Because of its superior wear resistance, high toughness, high stability, and easy processing, it is widely used in construction, automotive, electronics, and medical industries. However, polyurethane elastomers have the disadvantages of high cost, difficult degradation and recycling, and the raw materials are heavily dependent on petrochemical resources. In order to achieve sustainable development, it is urgent to find renewable resources that can replace petrochemical polyols to produce polyurethane elastomers.

Renewable green lignin is cheap and rich in hydroxyl groups. If it can partially replace petrochemical polyols for the production of polyurethane elastomers, it will not only realize the high-value utilization of lignin, reduce the production cost of polyurethane elastomers, but also endow polyurethane with elasticity The biodegradability of the body part and excellent thermal stability, anti-ultraviolet and thermal-oxidative aging properties.

Patent CN101845146A discloses a method of using liquefied lignin polyol solution to prepare lignin-based polyurethane elastomer. Although the molecular weight of the liquefied lignin decreases and the reactivity increases, the prepared polyol solution has a high hydroxyl value and viscosity, which is not conducive to the reaction, and the lignin treatment process conditions are relatively harsh and dangerous. The synthesized polyurethane elastomer is cross-linked. The degree of connection is also high, and heavy processing cannot be carried out.

Patent CN109485824A discloses a method for depolymerizing lignin under alkaline conditions, and uses it to prepare a recyclable lignin-based polyurethane elastomer. Although the prepared elastomer has good recycling processing performance, the chemical modification process of lignin increases the cost of the polyurethane elastomer synthesis process, and introduces high boiling point toxic organic solvents into the polyurethane synthesis. Environmentally friendly, it is not suitable for the actual industrial production of polyurethane elastomers.

At present, the use of lignin to synthesize polyurethane elastomers has the following three problems: First, the chemical modification or liquefaction modification of lignin not only increases the cost of the synthesis process, but also has a high hydroxyl value of lignin after modification, which is difficult to control , resulting in a high degree of crosslinking of the synthesized polyurethane elastomer materials, all of which are thermosetting materials, which are difficult to reprocess; second, the currently synthesized lignin-based polyurethane elastomers need to dissolve lignin in volatile or high-boiling toxic organic solvents , in order to allow lignin to react well with isocyanate, which is not conducive to actual production.

Contents of the invention

In order to solve the shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a method for preparing a solvent-free lignin-based polyurethane elastomer that can be repeatedly processed.

The lignin-based polyurethane elastomer prepared by the invention is synthesized under solvent-free conditions, and the synthesized elastomer has high strength, toughness and elasticity, good solvent resistance and aging resistance, and can be processed and utilized repeatedly. The invention overcomes the problems of low strength or poor toughness of traditional lignin-based polyurethane elastomers, low lignin reactivity and easy agglomeration, the need to use high boiling point or volatile toxic organic solvents in the synthesis process, and difficult repeated processing and utilization of materials. In addition, unlike methods such as liquefaction and chemical modification of lignin, the lignin extraction process in the present invention is simple and easy to operate, and is suitable for industrial mass production; at the same time, in the process of synthesizing polyurethane elastomers, there is no need to introduce volatile or The high-boiling-point toxic organic solvent is suitable for industrial production of high-performance and reprocessable lignin-based polyurethane elastomers.

Another object of the present invention is to provide a reprocessable solvent-free lignin-based polyurethane elastomer prepared by the above method.

The object of the invention is achieved through the following technical solutions:

A method for preparing a reprocessable solvent-free lignin-based polyurethane elastomer, comprising the following steps:

(1) Mix industrial lignin with an organic solvent, stir at 20-100°C for 1-10 hours, filter and separate, take the filtrate, remove the solvent, and dry to obtain lignin with a specific molecular weight;

(2) Mix lignin with specific molecular weight and short-chain polyol, and stir at 60-130° C. for 1-3 hours to obtain a mixed dispersion of lignin-polyol, wherein the mass fraction of lignin in the dispersion is 10-60 wt %;

(3) Vacuum dehydrate long-chain polyols at 110-130°C, then cool down to 60-80°C, add catalyst and isocyanate to synthesize polyurethane prepolymer, and then add lignin polyol mixed dispersion to polyurethane prepolymerization In the mixture, stirring and reacting for 4-6 hours, the obtained product was cured at 40-70°C for 12-36 hours, and hot-pressed at 130-180°C to obtain a thermosetting lignin-based polyurethane elastomer;

In step (3), the molar ratio of the NCO of the isocyanate to the total OH in the polyol and lignin is 1:1 to 1.8:1, and the polyol includes long-chain polyols and short-chain polyols; lignin polyol mixed dispersion The mass ratio to long-chain polyols is 10:90 to 60:40.

Preferably, the mixing concentration of the industrial lignin and the organic solvent in step (1) is 200-1000 g/L.

Preferably, the industrial lignin in step (1) is at least one of enzymatic lignin extracted from ethanol by fermentation of wood fiber, alkali lignin by-product of alkaline pulping and organic solvent lignin extracted from wood fiber kind.

Preferably, the weight-average molecular weight of the specific molecular weight lignin obtained in step (1) is between 700 and 3500, and the molecular weight distribution index is less than 2.5; more preferably less than 2.0.

Preferably, the organic solvent described in step (1) is at least one of tetrahydrofuran, acetone, methyl ethyl ketone, methanol, isopropanol, ethyl acetate, ethanol, ether and hexane or is at least one of these solvents mixed with water of the mixture.

Preferably, the drying temperature in step (1) is 40-80°C.

Preferably, the short-chain polyol in step (2) is 1,4-butanediol, pentaerythiol, glycerin, ethylene glycol, polypropylene glycol (molecular weight 100-1000), propylene glycol, glycerol, polyethylene glycol At least one of diol (molecular weight 100-1000), isopropanol, castor oil, soybean oil and palm oil.

Preferably, the mass fraction of the lignin in step (2) in the dispersion liquid is 50wt%.

Preferably, the mass ratio of the lignin polyol mixed dispersion to the long-chain polyol in step (3) is 80-90:10-20.

Preferably, the molar ratio of the NCO of the isocyanate in step (3) to the total OH in the polyol and lignin is 1.4:1˜1.8:1.

Preferably, the long-chain polyol in step (3) is polyethylene glycol (molecular weight 1000-6000), polytetrahydrofuran ether glycol (molecular weight 1000-6000), polypropylene glycol (molecular weight 1000-4000), polypropylene glycol-poly At least one of a copolymer of ethylene glycol (molecular weight 1000-4000) and polycaprolactone diol (molecular weight 1000-6000).

Preferably, the isocyanate described in step (3) is pentamethylene diisocyanate (PDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), 4,4'-dicyclohexylmethane At least one of diisocyanate (HMDI) and hexamethylene diisocyanate trimer.

Preferably, the catalyst described in step (3) is a conventional tin catalyst, which can be dibutyl tin dilaurate, dibutyl tin oxide, di(dodecylsulfur) dibutyl tin, stannous octoate and monobutyl At least one of tin oxide; the amount of the catalyst accounts for 0.3-0.8% of the total mass of polyols (including short-chain and long-chain polyols) and specific molecular weight lignin.

Preferably, the vacuum dehydration time in step (3) is 2-3 hours.

Preferably, the time required for synthesizing the polyurethane prepolymer in step (3) is 2-3 hours.

Preferably, the pressure of the hot press forming in step (3) is 10-12 MPa, and the time is 15-20 min.

The invention provides a reprocessable solvent-free lignin-based polyurethane elastomer prepared by the above method.

Compared with untreated industrial lignin raw materials, the specific molecular weight lignin prepared by the present invention has smaller molecular weight and more uniform distribution, higher content of phenolic hydroxyl groups, higher reactivity, and better compatibility with polyurethane matrix. Its rigid aromatic ring structure also has a reinforcing effect on polyurethane elastomers. In the polyurethane synthesis process, the lignin-based polyurethane elastomer is synthesized by using the lignin-polyol mixed dispersion liquid to replace part of the long-chain petrochemical polyol raw materials, and there is no need to use tetrahydrofuran, acetone, N,N-dimethylformamide, etc. in the synthesis process Volatile or high-boiling toxic solvents are beneficial to actual industrial production. Due to the higher content of phenolic hydroxyl groups in the prepared specific molecular weight lignin, under high temperature conditions, organometallic tin catalysts can catalyze the cleavage and reconstruction of phenolic hydroxyl-type carbamate bonds, thereby obtaining cross-linked lignin-based polyurethane elastomers Repeat processing performance many times. The phenolic hydroxyl type urethane bond formed by lignin and isocyanate is easier to reconstruct than the urethane bond formed by traditional aliphatic polyols, which is conducive to reprocessing. After repeated processing, the thermosetting lignin-based polyurethane elastomer still maintains Good mechanical properties. In addition, the specific molecular weight lignin prepared by the present invention also endows the polyurethane elastomer with better anti-ultraviolet radiation and anti-aging properties.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. The present invention uses a low-boiling point and low-toxicity organic solvent to extract lignin with a specific molecular weight. The process is simple and easy to operate, and is suitable for industrialized large-scale production of low-molecular-weight lignin. It overcomes the disadvantages of time-consuming, labor-intensive and high-cost conventional chemical modification of lignin.

2. In the synthesis process of lignin-based polyurethane, the present invention uses short-chain polyols to disperse lignin without using additional organic solvents, which overcomes the disadvantage of using high boiling point or volatile toxic organic solvents in conventional synthesis, and the synthesis process is green and environmentally friendly , and easy to industrial production.

3. The specific molecular weight lignin prepared by the present invention has a higher phenolic hydroxyl content, and the prepared lignin-based polyurethane elastomer has more phenolic hydroxyl type carbamate bonds, and the phenolic hydroxyl type carbamate bonds The characteristics of reversible fracture and reconstruction under the action of high temperature and organometallic tin catalysts can realize the good performance of multiple reprocessing of elastomers, and overcome the difficulty of recycling and repeated cycle processing of traditional lignin-modified thermosetting polyurethane elastomers However, the properties of the lignin-based polyurethane elastomer synthesized in the present invention remain basically unchanged after repeated processing.

4. The lignin raw material of the present invention is rich in output, low in price, wide in source, green and renewable, non-toxic and degradable. Compared with the polyurethane elastomer prepared by traditional polyether polyol or polyester polyol, the lignin-based polyurethane elastomer of the present invention is biodegradable and has lower cost. In addition, lignin also endows polyurethane elastomers with better mechanical properties, anti-ultraviolet and anti-aging properties, and thermal stability.

Detailed ways

The present invention will be further described in detail below with reference to the examples and drawings, but the implementation of the present invention is not limited thereto.

In the embodiment of the present invention, if no specific conditions are indicated, it is carried out according to the conventional conditions or the conditions suggested by the manufacturer. The raw materials, reagents, etc. of manufacturers not indicated are all conventional products that can be purchased from the market.

The materials involved in the following examples are all available from commercial sources.

Tensile test conditions: the elastic body after hot pressing is cut into a standard dumbbell-shaped spline with a length of 50mm, a narrow width of 4mm, and a thickness of 0.5mm, and the tensile gauge length is selected as 20mm. A CMT electronic universal testing machine is used, the test temperature is room temperature, and the tensile rate is 200mm/min.

According to the treatment conditions in Table 1, 1000 parts by mass of alkali lignin was dissolved in 5L of ethanol aqueous solution, stirred at 20-90°C for 4 hours, filtered and separated, the filtrate was taken, the solvent was removed, and dried to obtain lignin with specific molecular weight.

The productive rate of obtained lignin under different treatment conditions of table 1

It can be found from Table 1 that when alkali lignin (AKL) is extracted at room temperature, the smaller the volume fraction of ethanol in the ethanol aqueous solution, the yield of lignin increases first and then decreases. The effect of ethanol and water on lignin The extraction had a synergistic effect; and when the volume fraction of ethanol was constant, the higher the stirring temperature during the extraction process, the lower the lignin yield.

GPC test conditions for lignin:

(1) Before the test, the lignin sample was dried in a vacuum oven at 50°C for 24 hours.

(2) Dissolve the dried lignin in chromatographically pure THF to a concentration of about 1 mg/mL, and then filter the prepared solution with a 0.22um organic phase filter. The filtrate was poured into a gel permeation chromatograph, the mobile phase was chromatographically pure THF, and the flow rate was 1.0 mL/min.

Table 2 GPC data before and after extraction of alkali lignin

The molecular weight of the obtained lignin was measured, and it can be found from Table 2 that the relative molecular weight and dispersion coefficient of the extracted lignin were significantly reduced. When alkali lignin was extracted at room temperature, the weight average molecular weight of the obtained lignin products showed a trend of first increasing and then decreasing with the decrease of ethanol volume fraction in the extract, which was consistent with the change trend of the obtained lignin yield.

Example 1

(1) Dissolve 1000 parts by mass of alkali lignin in 5 L of absolute ethanol solution to prepare a 200 g/L alkali lignin solution. After stirring at room temperature for 4 hours, dry at 50°C for 48 hours, grind and sieve to obtain specific molecular weight alkali lignin AOH100-25 with a particle size of 100 μm.

(2) AOH100-25 and polyethylene glycol 200 were stirred at 120° C. for 1 h to obtain a polyol solution with a lignin mass fraction of 50 wt %.

(3) 9 parts by mass of polytetrahydrofuran 2000 were vacuum-dried at 120° C. for 2 hours, and after cooling to 70° C., 0.05 parts by mass of dibutyltin dilaurate was added and stirred evenly. Then 1.94 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to total OH in polyol and lignin is 1.4) was added, and the mixture was kept at 70° C. for 2 hours. Then add 1 mass part of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The tensile test shows that the elongation at break of the sample is 1123%, the tensile strength is 35.3 MPa, the Young's modulus is 5.4 MPa, the absorbed energy at break is 125.5 MJ/m ³ , and the elastic recovery rate is 97.8%.

(4) Shred the lignin-based polyurethane elastomer broken during the mechanical property test, keep the same hot-pressing conditions as in step (3), and hot-press with a flat vulcanizer to obtain a reprocessed lignin-based polyurethane elastomer. The tensile test shows that the elongation at break of the sample is 1315% (the retention rate of elongation at break is 117.2%), and the tensile strength is 38.3 MPa (the retention rate of tensile strength is 108.5%).

Example 2

Step (1) is with embodiment 1.

Step (2) is the same as in Example 1.

Step (3) is as follows: vacuum-dry 8 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then add 2.703 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.4), and keep at 70° C. for 2 h. Then add 2 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The tensile test shows that the elongation at break of the sample is 938%, the tensile strength is 37.2MPa, the Young's modulus is 9.3MPa, the absorbed energy at break is 129.4MJ/m ³ , and the elastic recovery rate is 97.3%.

Step (4) is the same as in Example 1. The tensile test shows that the elongation at break of the sample is 830% (the retention rate of tensile strength is 88.5%), and the tensile strength is 29.8 MPa (the retention rate of elongation at break is 79.9%).

Example 3

Step (1) is with embodiment 1.

Step (2) is the same as in Example 1.

Step (3) is as follows: vacuum-dry 6 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then add 4.229 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.4), and keep at 70°C for 2h. Then add 4 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 370%, and the tensile strength was 17.6 MPa.

Step (4) is the same as in Example 1. The tensile test shows that the elongation at break of the sample is 348% (the retention rate of tensile strength is 93.8%), and the tensile strength is 17.5 MPa (the retention rate of elongation at break is 99.3%).

Example 4

Step (1) is with embodiment 1.

Step (2) is the same as in Example 1.

Step (3) is as follows: 4 parts by mass of polytetrahydrofuran 2000 were vacuum-dried at 120° C. for 2 hours. After cooling to 70° C., 0.05 parts by mass of dibutyltin dilaurate was added and stirred evenly. Then add 5.755 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.4), and keep at 70° C. for 2 hours. Then add 6 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 252%, and the tensile strength was 26.9 MPa.

Example 5

Step (1) is with embodiment 1.

Step (2) is the same as in Example 1.

Step (3) is as follows: vacuum-dry 8 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then add 2.317 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.2), and keep at 70°C for 2h. Then add 2 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 904%, and the tensile strength was 18.6 MPa.

Example 6

Step (1) is with embodiment 1.

Step (2) is the same as in Example 1.

Step (3) is as follows: vacuum-dry 8 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then 2.124 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.1) was added and kept at 70°C for 2 hours. Then add 2 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 962%, and the tensile strength was 12 MPa.

Example 7

Step (1) is with embodiment 1.

Step (2) is the same as in Example 1.

Step (3) is as follows: vacuum-dry 8 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then 1.931 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.0) was added and kept at 70°C for 2 hours. Then add 2 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 1024%, and the tensile strength was 7.9 MPa.

Example 8

(1) Dissolve 1000 parts by mass of alkali lignin in 5 L of ethanol aqueous solution (volume fraction of ethanol is 55%) to prepare a 200 g/L alkali lignin solution. After stirring at room temperature for 4 hours, dry at 50°C for 48 hours, grind and sieve to obtain specific molecular weight alkali lignin AOH55-25 with a particle size of 100 μm.

(2) AOH55-25 and polyethylene glycol 200 were stirred at 120° C. for 1 h to obtain a polyol solution with a lignin mass fraction of 50 wt %.

Step (3) is as follows: vacuum-dry 8 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then add 2.803 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.4), and keep at 70° C. for 2 hours. Then add 2 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 1055%, and the tensile strength was 40.1 MPa.

Example 9

(1) Dissolve 1000 parts by mass of alkali lignin in 5 L of aqueous ethanol (volume fraction of ethanol is 75%) to prepare a 200 g/L alkali lignin solution. After stirring at room temperature for 4 hours, dry at 50°C for 48 hours, grind and sieve to obtain specific molecular weight alkali lignin AOH75-25 with a particle size of 100 μm.

(2) AOH75-25 and polyethylene glycol 200 were stirred at 120° C. for 1 h to obtain a polyol solution with a lignin mass fraction of 50 wt %.

Step (3) is as follows: vacuum-dry 8 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then 2.792 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.0) was added and kept at 70°C for 2 hours. Then add 2 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 1015%, and the tensile strength was 43.2 MPa.

Example 10

Step (1) is with embodiment 1.

Step (2) AOH100-25 and polyethylene glycol 200 were stirred at 120° C. for 1 h to obtain a polyol solution with a lignin mass fraction of 30 wt %.

Step (3) is as follows: vacuum-dry 6.667 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then add 3.529 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.2), and keep at 70°C for 2h. Then add 3.333 parts by mass of the lignin polyol mixed dispersion, and continue the reaction for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 1161%, and the tensile strength was 10.5 MPa.

Example 11

Step (1) is with embodiment 1.

Step (2) is the same as in Example 10.

Step (3) is as follows: vacuum-dry 5 parts by weight of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by weight of dibutyltin dilaurate and stir evenly. Then add 4.789 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.2), and keep at 70° C. for 2 h. Then add 5 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 969%, and the tensile strength was 19.2 MPa.

Example 12

Step (1) is with embodiment 1.

Step (2) is the same as in Example 10.

Step (3) is as follows: vacuum-dry 6.667 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then add 4.117 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.4), and keep at 70° C. for 2 h. Then add 3.333 parts by mass of the lignin polyol mixed dispersion, and continue the reaction for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 829%, and the tensile strength was 30.6 MPa.

Example 13

Step (1) is with embodiment 1.

Step (2) is the same as in Example 10.

Step (3) is as follows: vacuum-dry 5 parts by weight of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by weight of dibutyltin dilaurate and stir evenly. Then add 5.587 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.4), and keep at 70° C. for 2 h. Then add 5 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 854%, and the tensile strength was 36.7 MPa.

Example 14

Step (1) is with embodiment 1.

Step (2) is the same as in Example 10.

Step (3) is as follows: vacuum-dry 8.333 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then add 3.026 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.6), and keep at 70° C. for 2 h. Then 1.667 parts by mass of lignin polyol mixed dispersion was added, and the reaction was continued for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 1003%, and the tensile strength was 33.6 MPa.

Example 15

Step (1) is with embodiment 1.

Step (2) is the same as in Example 10.

Step (3) is as follows: vacuum-dry 6.667 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then add 4.705 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.6), and keep at 70° C. for 2 h. Then add 3.333 parts by mass of the lignin polyol mixed dispersion, and continue the reaction for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 726%, and the tensile strength was 35.3 MPa.

Example 16

Step (1) is with embodiment 1.

Step (2) is the same as in Example 10.

Step (3) is as follows: vacuum-dry 5 parts by weight of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by weight of dibutyltin dilaurate and stir evenly. Then 6.386 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.6) was added and kept at 70°C for 2 hours. Then add 5 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 505%, and the tensile strength was 26.5 MPa.

Example 17

Step (1) is with embodiment 1.

Step (2) is the same as in Example 10.

Step (3) is as follows: 3.333 parts by mass of polytetrahydrofuran 2000 was vacuum-dried at 120° C. for 2 hours. After cooling to 70° C., 0.05 parts by mass of dibutyltin dilaurate was added and stirred evenly. Then 8.066 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.6) was added and kept at 70°C for 2 hours. Then 6.667 parts by mass of lignin polyol mixed dispersion was added, and the reaction was continued for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 471%, and the tensile strength was 30.5 MPa.

Example 18

Step (1) is with embodiment 1.

Step (2) is the same as in Example 10.

Step (3) is as follows: vacuum-dry 6.667 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then 5.293 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.8) was added and kept at 70°C for 2 hours. Then add 3.333 parts by mass of the lignin polyol mixed dispersion, and continue the reaction for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 563%, and the tensile strength was 21 MPa.

Comparative example 1

(1) Stir the alkali lignin raw material AKL and polyethylene glycol 200 at 120° C. for 1 h to obtain a polyol solution with a lignin mass fraction of 50 wt %.

(2) 8 parts by mass of polytetrahydrofuran 2000 were vacuum-dried at 120° C. for 2 hours. After cooling to 70° C., 0.05 parts by mass of dibutyltin dilaurate was added and stirred evenly. Then 2.601 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.4) was added, and the mixture was kept at 70° C. for 2 hours. Then add 2 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The tensile test shows that the elongation at break of the sample is 895%, the tensile strength is 24.5 MPa, the Young's modulus is 11 MPa, the absorbed energy at break is 102.5 MJ/m ³ , and the elastic recovery rate is 97.2%.

Step (3) is the same as step (4) in Example 1. The tensile test shows that the elongation at break of the sample is 884% (the retention rate of elongation at break is 98.8%), and the tensile strength is 25.5 MPa (the retention rate of tensile strength is 104.2%).

Comparative example 2

Step (1) is the same as Comparative Example 1.

Step (2) is as follows: vacuum-dry 6 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then add 4.024 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.4), and keep at 70° C. for 2 hours. Then add 4 parts by mass of lignin polyol mixed dispersion, and continue to react for 4 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 262%, and the tensile strength was 7.9 MPa.

Comparative example 3

Step (1) is the same as embodiment 2 step (3). The difference is that 1,4 butanediol is used instead of lignin polyol to mix and disperse. The elongation at break of the sample obtained from the tensile test was 170%, and the tensile strength was 14.9 MPa.

Step (2) is the same as embodiment 2 step (4). The tensile test obtained that the elongation at break of the sample was 43% (the retention rate of the tensile strength was 25%), and the tensile strength was 6.8 MPa (the retention rate of the elongation at break was 45.3%).

Comparative example 4

Step (1) is the same as embodiment 2 step (3). The difference is that polyether glycol PEG200 is used instead of lignin polyol mixed dispersion. The elongation at break of the sample obtained from the tensile test was 61%, and the tensile strength was 2.4 MPa.

Comparative example 5

Step (1) is with embodiment 1.

Step (2) is the same as in Example 1.

Step (3) is as follows: vacuum-dry 8 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then add 2 parts by mass of lignin polyol mixed dispersion and 1.931 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to the total OH in polyol and lignin is 1.0), and keep at 70°C for 6h. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 982%, and the tensile strength was 10.3 MPa.

Comparative example 6

Step (1) is with embodiment 1.

Step (2) is the same as in Example 1.

Step (3) is as follows: vacuum-dry 8 parts by mass of polytetrahydrofuran 2000 at 120° C. for 2 hours, and after cooling to 70° C., add 0.05 parts by mass of dibutyltin dilaurate and stir evenly. Then 2 parts by mass of lignin polyol mixed dispersion and 2.703 parts by mass of hexamethylene diisocyanate (the molar ratio of NCO of isocyanate to total OH in polyol and lignin is 1.4) were added, and kept at 70°C for 6 hours. After the reaction, the product was poured out and solidified under vacuum at 50° C. for 24 hours. Using a flat vulcanizer, press the sample under the conditions of 165°C and 10MPa for 20 minutes to obtain a solvent-free lignin-based polyurethane elastomer. The elongation at break of the sample obtained from the tensile test was 778%, and the tensile strength was 20 MPa.

The polyurethane elastomer mechanical property parameter of table 3 comparative example 6 and embodiment 2

Table 3 shows the mechanical property parameters of the polyurethane elastomer prepared by the two-step method (Example 2) and the one-step method (Comparative Example 6) when the lignin substitution amount is 10% and the isocyanate index is 1.4. It can be found that compared with the polyurethane elastomer prepared by directly mixing short-chain long-chain polyols and specific molecular weight lignin at one time, the tensile strength and elongation at break of the polyurethane elastomer prepared by the two-step method are significantly greater, and the elasticity The recovery rate is also higher, which is due to the more regular structure of the polyurethane elastomer prepared by the two-step method, and the soft segment can be better dispersed in the hard segment.

Table 4 The polyurethane elastomer reprocessing performance parameters of Example 1 and Comparative Example 3

Table 4 shows the test results of the reprocessing tensile test of the solvent-free lignin-based polyurethane elastomer prepared in the present invention. It can be seen from the table that even after repeated reprocessing, the lignin-based polyurethane elastomer prepared in Example 1 still retains high tensile strength and elongation at break, and its comprehensive mechanical properties are still far better than those of Comparative Example 3. The strengthening and toughening effect of the element on the polyurethane elastomer is remarkable. In addition, after the second reprocessing of the solvent-free lignin-based polyurethane elastomer prepared by the present invention, its tensile strength and elongation at break are significantly better than those of the prior art CN201811189140 (the second reprocessing of the patent example 1 Properties: tensile strength is 22.6MPa, elongation at break is 1193%).

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims

A kind of preparation method of reprocessable solvent-free lignin-based polyurethane elastomer, is characterized in that, comprises the following steps:

(1) Mix industrial lignin with an organic solvent, stir at 20-100°C for 1-10 hours, filter and separate, take the filtrate, remove the solvent, and dry to obtain lignin with a specific molecular weight;

(2) Mix lignin with specific molecular weight and short-chain polyol, and stir at 60-130° C. for 1-3 hours to obtain a mixed dispersion of lignin-polyol, wherein the mass fraction of lignin in the dispersion is 10-60 wt %;

(3) Vacuum dehydrate long-chain polyols at 110-130°C, then cool down to 60-80°C, add catalyst and isocyanate to synthesize polyurethane prepolymer, and then add lignin polyol mixed dispersion to polyurethane prepolymerization In the mixture, stirring and reacting for 4-6 hours, the obtained product was cured at 40-70°C for 12-36 hours, and hot-pressed at 130-180°C to obtain a thermosetting lignin-based polyurethane elastomer;

In step (3), the molar ratio of the NCO of the isocyanate to the total OH in the polyol and lignin is 1:1 to 1.8:1, and the polyol includes long-chain polyols and short-chain polyols; lignin polyol mixed dispersion The mass ratio to long-chain polyols is 10:90 to 60:40;

The industrial lignin in step (1) is at least one of enzymatic lignin extracted from ethanol by fermentation of lignocellulosic fibers, alkali lignin by-product of alkaline pulping, and organic solvent lignin extracted from lignofibers;

The weight-average molecular weight of the specific molecular weight lignin obtained in step (1) is between 700 and 1953, and the molecular weight distribution index is less than 2.5;

The short-chain polyhydric alcohol described in step (2) is 1,4-butanediol, pentaerythiol, glycerin, ethylene glycol, polypropylene glycol, propylene glycol, glycerol, polyethylene glycol, isopropanol, castor oil , at least one of soybean oil and palm oil; wherein the molecular weight of polypropylene glycol is 100-1000, and the molecular weight of polyethylene glycol is 100-1000;

The long-chain polyhydric alcohol described in step (3) is at least one in polyethylene glycol, polytetrahydrofuran ether glycol, polypropylene glycol, polypropylene glycol-polyethylene glycol copolymer and polycaprolactone glycol, wherein poly The molecular weight of ethylene glycol is 1000-6000, the molecular weight of polytetrahydrofuran ether diol is 1000-6000, the molecular weight of polypropylene glycol-polyethylene glycol copolymer and polypropylene glycol is 1000-4000, and the molecular weight of polycaprolactone diol is 1000 ~6000.
According to the preparation method of a kind of reprocessable solvent-free lignin-based polyurethane elastomer according to claim 1, it is characterized in that,

The isocyanate described in step (3) is pentamethylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate and hexamethylene diisocyanate trimer at least one of the
A method for preparing a reprocessable solvent-free lignin-based polyurethane elastomer according to claim 1, wherein the mixing concentration of industrial lignin and organic solvent in step (1) is 200-1000g/L .
According to the preparation method of a kind of reprocessable solvent-free lignin-based polyurethane elastomer according to claim 1, it is characterized in that the mass ratio of the lignin polyol mixed dispersion liquid and the long-chain polyol in step (3) 1:9 or 2:8; the molar ratio of the NCO of the isocyanate to the total OH in the polyol and lignin is 1.4:1-1.8:1.
A method for preparing a reprocessable solvent-free lignin-based polyurethane elastomer according to claim 1, wherein the mass fraction of the lignin in step (2) in the dispersion is 50 wt%.
A method for preparing a solvent-free lignin-based polyurethane elastomer that can be repeatedly processed according to claim 1, wherein the time required for synthesizing the polyurethane prepolymer in step (3) is 2 to 3 hours; The pressure of the hot press forming is 10-12 MPa, and the time is 15-20 minutes.
According to the preparation method of a kind of reprocessable solvent-free lignin-based polyurethane elastomer according to claim 1, it is characterized in that,

The organic solvent described in step (1) is at least one of tetrahydrofuran, acetone, methyl ethyl ketone, methanol, isopropanol, ethyl acetate, ethanol, ether and hexane or is a mixed solution of at least one of these solvents and water .
According to the preparation method of a kind of solvent-free lignin-based polyurethane elastomer that can be repeatedly processed according to claim 1, it is characterized in that, the catalyst described in step (3) is a tin catalyst; 0.3-0.8% of the total mass of alcohols, long-chain polyols and specific molecular weight lignin.
According to the preparation method of a kind of reprocessable solvent-free lignin-based polyurethane elastomer according to claim 8, it is characterized in that, the tin catalyst is dibutyl tin dilaurate, dibutyl tin oxide, dibutyl tin oxide, At least one of (dodecylsulfur)dibutyltin, stannous octoate and monobutyltin oxide.
A method for preparing a reprocessable solvent-free lignin-based polyurethane elastomer according to claim 1, wherein the drying temperature in step (1) is 40 to 80° C.; the vacuum in step (3) The dehydration time is 2-3 hours.
A reprocessable solvent-free lignin-based polyurethane elastomer obtained by the preparation method described in any one of claims 1-10.