High-hydrophobicity and high-mechanical-strength bio-based waterborne polyurethane and preparation method thereof

Abstract

The invention belongs to the technical field of waterborne polyurethane, and particularly relates to high-hydrophobicity and high-mechanical-strength bio-based waterborne polyurethane and a preparation method thereof. The lignin, the polyol, the castor oil and the diisocyanate are used as main raw materials, the tannic acid is used as a cross-linking agent to change the cross-linking degree of the polyurethane material, the hydrophobicity and the mechanical strength of polyurethane are effectively improved through the synergistic effect of multiple components, meanwhile, the proportion of the lignin, the castor oil and other bio-based materials is high, and the polyurethane material has the advantages of being environmentally friendly and free of toxic and side effects. The consumption of a petroleum-based raw material is greatly reduced, so that the environmental friendliness of the waterborne polyurethane material is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of waterborne polyurethane, and in particular relates to a bio-based waterborne polyurethane with high hydrophobicity and high mechanical strength and a preparation method thereof. Background Art

[0002] Driven by the current trends of green chemistry and sustainable development, the coatings industry is accelerating its transformation toward environmentally friendly, high-performance solutions. As a key alternative to traditional solvent-based coatings, waterborne polyurethane (WPU) coatings, using water as a dispersion medium, offer significant advantages such as low volatile organic compound (VOC) emissions and safety and non-toxicity. They hold broad application prospects in the leather finishing field. Leather products are widely used in various areas of daily life and industrial production, and the performance requirements for their surface coatings are increasingly stringent.

[0003] However, traditional waterborne polyurethane coatings still have the following technical bottlenecks: 1. Limitations of Bio-Based Substitution Technologies: In recent years, bio-based raw materials (such as lignin and castor oil) have been used to replace petroleum-based polyols to reduce environmental burdens. However, existing technologies still face multiple challenges: (1) The substitution rate of bio-based raw materials is low (generally <30wt%), making it difficult to achieve large-scale emission reductions; (2) The introduction of lignin can easily lead to material brittleness, requiring reliance on petroleum-based toughening agents, which weakens the environmental advantages; (3) The hydrophobicity of bio-based waterborne polyurethanes is insufficient, making it difficult to meet the daily application requirements of leather coatings.

[0004] Second, high water absorption leads to performance degradation: Conventional waterborne polyurethane coatings, due to the presence of hydrophilic groups in their molecular chains, absorb high water rates in humid environments, significantly reducing the coating's mechanical strength (such as tensile strength and elongation at break). Furthermore, they struggle to maintain stability under dynamic stress or in hot and humid environments, leading to easy peeling or blistering of the coating, which impacts the lifespan of leather products. This drawback severely limits the widespread use of waterborne polyurethane coatings in applications such as shoe uppers and sofas that are subject to frequent moisture exposure or deformation.

[0005] At present, many studies have been devoted to the preparation and performance improvement of waterborne polyurethane coatings.

[0006] Patent publication number CN119505161A describes a method for preparing a solvent-free lignin-modified waterborne polyurethane. The method involves first reacting an isocyanate, a polyol, and a liquefied lignin sulfonate alcohol to form a prepolymer. The prepolymer is then dispersed in water and reacted with a post-chain extender to produce the final product. While this method improves environmental friendliness and the mechanical properties of the product, facilitating its application in leather finishing, it lacks significant research into its hydrophobic properties. Consequently, the resulting coating may not meet the waterproofing requirements of leather in high humidity or frequent water exposure environments.

[0007] Patent publication CN115386063A describes a lignin-based waterborne polyurethane and its preparation method. Lignin is first micronized and modified with isocyanate before reacting with other components to produce the polyurethane. This method increases the number of chemical bonding sites between lignin and polyurethane, improving the mechanical properties of the polyurethane film. However, the method is not specifically optimized for leather finishing. This may result in defects such as poor hydrophobicity when applied to leather, impacting the service quality and lifespan of leather products.

[0008] Patent publication number CN119331505A describes a lignin-modified waterborne polyurethane strippable coating and its preparation method. By modifying the molecular structure of the base resin and filler, the coating's crosslinking density, outdoor aging resistance, and corrosion resistance are enhanced. However, the patent primarily focuses on the coating's strippability and corrosion resistance, lacking sufficient utilization of bio-based raw materials and assessing the suitability of waterborne polyurethane as a leather coating.

[0009] Therefore, how to screen suitable bio-based materials as the main raw materials, cooperate with the synergistic effect of other components such as cross-linking agents, and prepare bio-based water-based polyurethanes that have excellent environmental friendliness while obtaining good hydrophobic properties and mechanical strength has become a direction that needs to be studied. Summary of the Invention

[0010] In response to the deficiencies in the prior art, the present invention aims to provide a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane and a preparation method thereof. The present invention uses lignin, polyols, castor oil and diisocyanate as main raw materials, utilizes tannic acid as a cross-linking agent to change the cross-linking degree of the polyurethane material, and effectively improves the hydrophobicity and mechanical strength of the polyurethane through the synergistic effect of multiple components. At the same time, bio-based materials such as lignin and castor oil account for more than 30wt% of the main raw materials, greatly reducing the consumption of petroleum-based raw materials, thereby significantly improving the environmental friendliness of the waterborne polyurethane material.

[0011] The first aspect of the present invention provides a method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane, comprising the following steps: (1) mixing lignin, polyol, castor oil and diisocyanate to carry out a first polymerization reaction to obtain a first prepolymer; (2) mixing the first prepolymer obtained in step (1) with the first chain extender and tannic acid, and performing a second polymerization reaction to obtain a second prepolymer; (3) mixing the second prepolymer obtained in step (2) with an organic metal catalyst and performing a third polymerization reaction to obtain a third prepolymer; (4) adding a neutralizing agent dropwise to the third prepolymer obtained in step (3) to carry out a neutralization reaction to obtain a fourth prepolymer; (5) adding the auxiliary agent to water and mixing evenly, then adding the fourth prepolymer obtained in step (4) and mixing evenly, and performing an emulsification reaction to obtain a polyurethane emulsion; (6) The polyurethane emulsion obtained in step (5) is mixed with the second chain extender to carry out a chain extension reaction to obtain a bio-based waterborne polyurethane with high hydrophobicity and high mechanical strength.

[0012] As a preferred technical solution of the present invention, the weight proportions of the raw materials are: 50-70 parts of lignin, 30-50 parts of polyol, 3-8 parts of castor oil, 40-60 parts of diisocyanate, 5-9 parts of a first chain extender, 1-4 parts of tannic acid, 0.05-0.3 parts of an organometallic catalyst, 4-7 parts of a neutralizer, 450-650 parts of water, 1.8-5.3 parts of an additive, and 2-4 parts of a second chain extender.

[0013] As a preferred technical solution of the present invention, the weight percentage of the lignin is preferably 55 to 65 parts, more preferably 60 to 65 parts. The lignin of the present invention is one of the main raw materials for preparing polyurethane and can partially replace petroleum-based polyols to synthesize bio-based polyurethane materials, which has the advantages of being green, environmentally friendly and low-cost.

[0014] As a preferred technical solution of the present invention, the lignin is enzymatically hydrolyzed lignin, with a residual sugar content of ≤3.0%, an ash content of ≤5.0%, a moisture content of ≤12.0%, and a phenolic hydroxyl content of ≥3.0%. The Longli Bio-enzymatic Lignin LIG-II selected for this invention is extracted from the residue left after functional sugars are produced from corncobs. It is a novel, low-carbon, and environmentally friendly material that aligns with the concept of ecological recycling. Furthermore, after enzymatic hydrolysis, the enzymatically hydrolyzed lignin has shorter molecular chains and a more even distribution of polar groups, which promotes uniform dispersion of the lignin and a more complete reaction with isocyanates, thereby improving the material's resistance to tensile failure.

[0015] As a preferred technical solution of the present invention, the weight proportion of the polyol is preferably 35 to 45 parts.

[0016] As a preferred technical solution of the present invention, the polyol is polypropylene glycol and / or polytetrahydrofuran, and the molecular weight of the polyol is 900 to 4000 g / mol. The polyol of the present invention is one of the main raw materials for preparing polyurethane, which can provide a soft segment structure for polyurethane, alleviate the material brittleness problem caused by adding lignin, improve the mechanical properties of the material, and make it show more excellent comprehensive performance in practical applications. The present invention controls the molecular weight of the polyol to be 900 to 4000 g / mol. Through the soft segment of moderate length, it can provide a certain flexibility without causing the molecular chain to slip out of control due to excessive flexibility, thereby obtaining good tensile strength; if the molecular weight is too small, the segment is too short, resulting in insufficient flexibility of the soft segment and increased brittleness; if the molecular weight is too large, the soft segment is too flexible and easily causes the molecular chain to slip, which will reduce the mechanical properties of the polyurethane.

[0017] As a preferred technical solution of the present invention, the weight proportion of castor oil is preferably 4 to 6 parts; the castor oil of the present invention, as the second bio-based material, is one of the main raw materials for preparing polyurethane. Its molecular structure contains abundant linear segments, which can provide a bio-based soft segment structure for polyurethane, effectively reduce brittleness, and improve the overall performance of the material.

[0018] As a preferred technical solution of the present invention, the castor oil is hydrogenated castor oil with a hydroxyl value of 150 mgKOH / g and a saponification value of 178 mgKOH / g. The present invention uses hydrogenated castor oil from Weiyu Biotechnology. Hydrogenated castor oil has a long and rigid molecular chain, which can form a dense hydrophobic network. Hydrogenation also reduces the polarity of double bonds and hydroxyl groups, lowering the surface energy of the material and improving its hydrophobicity. Furthermore, when hydrogenated castor oil is introduced into the polyurethane system, the long-chain hydrophobic groups form "hydrophobic microdomains" within the material, reducing the contact points between the molecules and water molecules, thereby reducing the material's hydrophilicity.

[0019] As a preferred technical solution of the present invention, the weight proportion of the diisocyanate is preferably 50 to 60 parts.

[0020] As a preferred technical solution of the present invention, the diisocyanate is selected from one or more of isophorone diisocyanate, hexamethylene diisocyanate, and hydrogenated phenylmethane diisocyanate. In the present invention, the diisocyanate serves as the core raw material for preparing polyurethane. The isocyanate groups in its molecular structure undergo an addition reaction with hydroxyl-containing materials to form urethane bonds, thereby building the molecular backbone of the polyurethane. The rigid segments (such as aromatic rings and aliphatic carbon chains) remaining after the reaction of the diisocyanate constitute the hard segment structure of the polyurethane, effectively improving the mechanical properties of the material.

[0021] As a preferred technical solution of the present invention, the weight proportion of the first chain extender is preferably 6 to 8 parts.

[0022] As a preferred technical solution of the present invention, the first chain extender is 2,2-dimethylol propionic acid and / or dimethylol butyric acid.

[0023] As a preferred technical solution of the present invention, the weight portion of the organic metal catalyst is preferably 0.1 to 0.2 parts.

[0024] As a preferred technical solution of the present invention, the organic metal catalyst is an organic silver catalyst and / or an organic bismuth catalyst; the present invention selects an organic silver catalyst and an organic bismuth catalyst as the organic metal catalyst for polyurethane, wherein the empty silver orbital in the organic silver catalyst forms a strong coordination bond with the carbonyl oxygen of isocyanate, thereby enhancing the electrophilicity of the carbon atom and promoting the nucleophilic attack of the hydroxyl group; the bismuth in the organic bismuth catalyst simultaneously coordinates the carbonyl oxygen of isocyanate and the oxygen of the alcohol hydroxyl group through the empty orbital, forming a six-membered ring transition state and reducing the reaction activation energy; the organic metal catalyst achieves efficient catalysis of the polymerization reaction by significantly reducing the reaction activation energy of isocyanate and active hydrogen groups such as hydroxyl groups, thereby accelerating the synthesis of polyurethane.

[0025] As a preferred technical solution of the present invention, the weight proportion of the neutralizing agent is preferably 5 to 6 parts.

[0026] As a preferred technical solution of the present invention, the neutralizing agent is triethylamine and / or triethanolamine; the neutralizing agent of the present invention reacts with the group introduced by the first chain extender to form a salt, thereby improving the dispersibility of the polyurethane in water and its overall stability.

[0027] As a preferred technical solution of the present invention, the weight proportion of the second chain extender is preferably 2 to 3 parts.

[0028] As a preferred technical solution of the present invention, the second chain extender is selected from one or more of ethylenediamine, isophoronediamine or hydroxyethylethylenediamine; the present invention can regulate the molecular weight and the ratio of soft segments to hard segments of the polyurethane through the second chain extender, thereby obtaining good mechanical properties.

[0029] As a preferred technical solution of the present invention, the weight proportion of the water is preferably 500 to 600 parts; in the present invention, water serves as a dispersion medium to ensure sufficient reaction and also promote chain extension to obtain bio-based polyurethane.

[0030] As a preferred technical solution of the present invention, the auxiliary agent includes a defoaming agent, a wetting agent and a leveling agent.

[0031] As a preferred technical solution of the present invention, the 1.8-5.3 parts of the auxiliary agent include: 0.1-0.3 parts of a defoaming agent, 0.7-2.0 parts of a wetting agent and 1.0-3.0 parts of a leveling agent; the auxiliary agent in the present invention can eliminate the foam generated during the production and construction of water-based polyurethane, and is conducive to quickly wetting the substrate and improving the film smoothness of the water-based polyurethane.

[0032] As a preferred technical solution of the present invention, the first polymerization reaction in step (1) includes: first mixing and stirring lignin, polyol, and castor oil, heating to 60-80°C, and evacuating for 30 minutes; then adding diisocyanate, stirring and heating, and performing a first polymerization reaction to obtain a first prepolymer.

[0033] As a preferred technical solution of the present invention, the temperature of the first polymerization reaction is 70-90°C, more preferably 80-90°C, and more preferably 83-87°C; the time of the first polymerization reaction is preferably 0.5-2 hours, more preferably 0.8-1.6 hours. The present invention first mixes lignin, polyol, castor oil, and diisocyanate for the first polymerization reaction, which facilitates the formation of a controllable prepolymer structure and lays the foundation for the introduction of functional groups or the optimization of cross-linking density.

[0034] As a preferred technical solution of the present invention, the time of the second polymerization reaction in step (2) is 0.5~1h; the present invention can introduce active groups and cross-linking points into the polyurethane by mixing the first prepolymer, the first chain extender and tannic acid, thereby obtaining a water-based polyurethane having a cross-linked network structure.

[0035] As a preferred technical solution of the present invention, the temperature of the third polymerization reaction in step (3) is 80-85°C, and the time is 0.8-2h; the reaction degree is controlled to be 80-90%, and the reaction degree is more preferably 85-90%; the reaction degree of the third polymerization reaction of the present invention is determined by measuring the residual isocyanate group (NCO) content by the di-n-butylamine method.

[0036] As a preferred technical solution of the present invention, the dropwise addition time of the neutralizing agent in step (4) is 5 to 15 minutes; the temperature of the neutralization reaction is 55 to 60° C., and the time is 1 to 1.5 hours; the third prepolymer of the present invention mixed with the neutralizing agent can neutralize the hydrophilic groups introduced by the chain extender in the polyurethane, thereby improving the stability of the waterborne polyurethane.

[0037] As a preferred technical solution of the present invention, the conditions of the emulsification reaction in step (5) are: under stirring conditions, the reaction temperature is 10~20℃, and the reaction time is 0.5~1h; preferably, the reaction temperature is 15~20℃, and the reaction time is 0.6~0.8h; the emulsification reaction of the present invention can make the hydrophobic parts on the waterborne polyurethane molecules fold, curl and gather at the core position of the colloid particles, while the hydrophilic parts are distributed on the surface of the colloid particles and extend to the peripheral water phase. This unique molecular arrangement further enhances the overall stability of the waterborne polyurethane system.

[0038] As a preferred technical solution of the present invention, the chain extension reaction step in step (6) includes slowly adding a second chain extender to the aqueous polyurethane emulsion at a stirring speed of 1000 to 1500 rpm, and a chain extension reaction time of 0.5 to 1 hour. The present invention can regulate the molecular weight and the ratio of soft segments to hard segments of the aqueous polyurethane through the chain extension reaction, thereby ensuring good tensile strength of the material.

[0039] The second aspect of the present invention provides a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane prepared by the preparation method described in the first aspect.

[0040] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses lignin, polyols, castor oil, and diisocyanate as the main raw materials, and utilizes tannic acid as a cross-linking agent to change the cross-linking degree of the polyurethane material. Through the synergistic effect of multiple components, the hydrophobicity and mechanical strength of the polyurethane are effectively improved. At the same time, bio-based materials such as lignin and castor oil account for more than 30wt% of the main raw materials, which greatly reduces the consumption of petroleum-based raw materials, thereby significantly improving the environmental friendliness of the water-based polyurethane material. When the bio-based water-based polyurethane of the present invention is applied to the surface of leather, it can impart good hydrophobicity and mechanical strength to the leather surface, and maintain good durability even in a wet environment and after friction, which not only extends the service life of the leather surface, but also promotes the green and sustainable development of the leather finishing industry; (2) The enzymatically hydrolyzed lignin used in the present invention is extracted from the residue after functional sugars are prepared from corn cobs. It is a new, low-carbon, and environmentally friendly material that conforms to the development concept of ecological circulation. At the same time, after the enzymatic hydrolysis process, the molecular chain of the enzymatically hydrolyzed lignin is shorter and the polar groups are more evenly distributed, which can promote the uniform dispersion of lignin and more complete reaction with isocyanate, thereby improving the material's ability to resist tensile damage; (3) The hydrogenated castor oil selected in the present invention has a long and rigid molecular chain, which can form a dense hydrophobic network. At the same time, hydrogenation reduces the polarity of double bonds and hydroxyl groups, lowers the surface energy of the material, and improves the hydrophobicity. In addition, when hydrogenated castor oil is introduced into the polyurethane system, the long-chain hydrophobic groups will form "hydrophobic micro-regions" inside the material, reducing the contact sites between the molecules and water molecules, thereby reducing the hydrophilicity of the material. (4) The tannic acid of the present invention is a bio-based environmentally friendly material. The molecule is connected to the side chain of the pyranose heterocycle, hydroxyl group and ester group. Tannic acid is added in different proportions as a cross-linking agent, and the special structure of tannic acid is used to modify the polyurethane to improve the hydrophobicity and mechanical properties of the polyurethane. The presence of tannic acid can promote the formation of a dense cross-linked network in the waterborne polyurethane film, reduce the distance between the molecular chains, make it difficult for water molecules to penetrate, and thus reduce the hydrophilicity of the waterborne polyurethane. On the other hand, the cross-linked network structure of the waterborne polyurethane encapsulates some hydrophilic groups to a certain extent, and the hydrophobic groups extend outward, thereby enhancing the hydrophobicity of the waterborne polyurethane film. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0042] Figure 1 The water absorption test data of the embodiments of the present invention and the comparative examples are shown in FIG.

[0043] Figure 2 The water contact angle test data of the embodiments of the present invention and the comparative examples are shown in FIG.

[0044] Figure 3 The tensile strength test data of the embodiments of the present invention and the comparative examples are shown in FIG. DETAILED DESCRIPTION

[0045] For the convenience of understanding the present invention, the present invention is given below with examples. It should be understood by those skilled in the art that the examples are only for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0046] The sources of some components in the Examples and Comparative Examples are as follows: Commercially available lignin, product number 8068-05-1, was purchased from Tai'an Jiangzhou Biotechnology Co., Ltd. Enzymatic lignin LIG-Ⅱ, residual sugar ≤ 3.0%, ash ≤ 5.0%, moisture ≤ 12.0%, phenolic hydroxyl content ≥ 3.0%, was purchased from Shandong Longli Biotechnology Co., Ltd.; Polypropylene glycol A, product number P103208, molecular weight 2000 g / mol, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Polypropylene glycol B, product number P103209, molecular weight 400 g / mol, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Polytetrahydrofuran A, product number P816778, molecular weight 2000 g / mol, was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. Polytetrahydrofuran B, product number P903557, molecular weight 250 g / mol, was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; Commercially available castor oil, product number C110663, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Hydrogenated castor oil, hydroxyl value 150 mgKOH / g, saponification value 178 mgKOH / g, was purchased from Inner Mongolia Weiyu Biotechnology Co., Ltd. Isophorone diisocyanate, product number I109582, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Hexamethylene diisocyanate, product number H106723, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Hydrogenated phenylmethane diisocyanate, CAS No. 5124-30-1, was purchased from Shanghai Minshi Chemical Co., Ltd.; 2,2-Dihydroxymethylpropionic acid, CAS No. 4767-03-7, was purchased from Sinopharm Chemical Reagent Co., Ltd.; Dihydroxymethylbutyric acid, CAS No. 10097-02-6, was purchased from Sinopharm Chemical Reagent Co., Ltd.; Tannic acid, CAS No. 1401-55-4, was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; Organic silver catalyst, model ESCAT 100Ag, was purchased from Qieke New Materials Technology (Shanghai) Co., Ltd. Organic bismuth catalyst, model NIAX MC-710, was purchased from Momentive, USA; Triethylamine, CAS No. 121-44-8, was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; Triethanolamine, CAS No. 102-71-6, was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; Ethylenediamine, CAS No. 107-15-3, was purchased from Sinopharm Chemical Reagent Co., Ltd.; Isophorone diamine, CAS No. 2855-13-2, was purchased from Sinopharm Chemical Reagent Co., Ltd. Hydroxyethylethylenediamine, CAS No. 111-41-1, was purchased from Nantong Runfeng Petrochemical Co., Ltd.

[0047] Example 1: This example provides a method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane, comprising the following steps: (1) Add 65 parts of lignin, 40 parts of polypropylene glycol A (product number P103208, molecular weight 2000 g / mol), and 5 parts of castor oil into a reactor, mix and stir, heat to about 75°C, and evacuate for 30 minutes; then add 50 parts of isophorone diisocyanate, stir and heat, and control the temperature at about 85°C to react for 1.2 hours to obtain the first prepolymer; (2) 8 parts of dimethylolpropionic acid and 1 part of tannic acid were added to the first prepolymer, mixed and stirred, and reacted for 0.8 hours to obtain a second prepolymer; (3) adding 0.2 parts of an organic silver catalyst to the second prepolymer, controlling the temperature at about 85°C to react for 1.5 hours to obtain a third prepolymer; (4) The residual NCO content in the third prepolymer was determined by the di-n-butylamine method. When the reaction degree reached 90%, the third prepolymer was cooled to 60°C, and then 6 parts of triethylamine were slowly added. The addition process took about 10 minutes. Then, the temperature was controlled at about 60°C for a neutralization reaction for 1.2 hours to obtain a fourth prepolymer. (5) Prepare 600 parts of water in a dispersion kettle in advance and add 0.2 parts of defoamer, 1.5 parts of wetting agent and 2.0 parts of leveling agent into the water, mix and stir. Quickly add the fourth prepolymer into the dispersion kettle, control the reaction temperature at about 18°C, and emulsify for 0.8h to obtain a waterborne polyurethane emulsion. (6) Under stirring conditions, an aqueous solution of ethylenediamine was slowly added to the aqueous polyurethane emulsion, wherein the solution contained 3 parts of ethylenediamine and the concentration was 35 wt%. The dispersion was continued under high-speed stirring at 1500 rpm for 0.8 h to carry out a chain extension reaction to obtain a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane.

[0048] Example 2: The difference between this example and Example 1 is that the amount of tannic acid in step (2) is changed from 1 part to 2 parts.

[0049] Example 3. The difference between this example and Example 1 is that the amount of tannic acid in step (2) is changed from 1 part to 3 parts.

[0050] Example 4: This example provides a method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane, comprising the following steps: (1) 70 parts of enzymatically hydrolyzed lignin LIG-Ⅱ, 50 parts of polytetrahydrofuran A (product number P103209, molecular weight 400 g / mol), and 8 parts of castor oil were added to a reactor, mixed and stirred, heated to about 75°C, and vacuumed for 30 minutes; then 60 parts of hexamethylene diisocyanate were added, stirred and heated, and the temperature was controlled at about 90°C for 0.5 hours to obtain a first prepolymer; (2) 9 parts of dimethylolbutyric acid and 1 part of tannic acid were added to the first prepolymer, mixed and stirred, and reacted for 0.5 hours to obtain a second prepolymer; (3) adding 0.3 parts of an organic bismuth catalyst to the second prepolymer, controlling the temperature at about 80°C to react for 2 hours to obtain a third prepolymer; (4) The residual NCO content in the third prepolymer was determined by the di-n-butylamine method. When the reaction degree reached 80%, the third prepolymer was cooled to 55°C, and then 7 parts of triethanolamine was slowly added. The addition process took about 15 minutes. Then, the temperature was controlled at about 55°C for a neutralization reaction for 1.5 hours to obtain a fourth prepolymer. (5) Prepare 650 parts of water in a dispersion kettle in advance and add 0.3 parts of defoamer, 2.0 parts of wetting agent and 3.0 parts of leveling agent into the water, mix and stir. Quickly add the fourth prepolymer into the dispersion kettle, control the reaction temperature at about 20°C, and emulsify for 0.5 hours to obtain a waterborne polyurethane emulsion. (6) Under stirring conditions, an aqueous solution of isophorone diamine was slowly added to the aqueous polyurethane emulsion, wherein the solution contained 4 parts of isophorone diamine and the concentration was 30 wt %. The dispersion was continued under high-speed stirring at 1000 rpm for 1 hour to carry out a chain extension reaction to obtain a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane.

[0051] Example 5. This example provides a method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane, comprising the following steps: (1) Add 50 parts of lignin, 50 parts of polypropylene glycol A (product number P103208, molecular weight 2000 g / mol), and 3 parts of hydrogenated castor oil into a reactor, mix and stir, heat to about 75°C, and evacuate for 30 minutes; then add 40 parts of hydrogenated phenylmethane diisocyanate, stir and heat, and control the temperature at about 70°C for 2 hours to obtain a first prepolymer; (2) Add 5 parts of 2,2-dihydroxymethylpropionic acid and 1 part of tannic acid to the first prepolymer, mix and stir, and react for 1 hour to obtain a second prepolymer; (3) adding 0.05 parts of an organic silver catalyst to the second prepolymer, controlling the temperature at about 85°C to react for 0.8h to obtain a third prepolymer; (4) The residual NCO content in the third prepolymer was determined by the di-n-butylamine method. When the reaction degree reached 85%, the third prepolymer was cooled to 60°C, and then 4 parts of triethylamine were slowly added. The addition process took about 5 minutes. Then, the temperature was controlled at about 60°C for a neutralization reaction for 1 hour to obtain a fourth prepolymer. (5) Prepare 450 parts of water in a dispersion kettle in advance and add 0.1 parts of defoamer, 0.7 parts of wetting agent and 1.0 parts of leveling agent into the water, mix and stir. Quickly add the fourth prepolymer into the dispersion kettle, control the reaction temperature at about 10°C, and emulsify for 1 hour to obtain a waterborne polyurethane emulsion. (6) Under stirring conditions, an aqueous solution of hydroxyethylethylenediamine was slowly added to the aqueous polyurethane emulsion, wherein the solution contained 2 parts of hydroxyethylethylenediamine at a concentration of 40 wt %. The solution was then dispersed under high-speed stirring at 1200 rpm for 0.8 h to carry out a chain extension reaction, thereby obtaining a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane.

[0052] Example 6: This example provides a method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane, comprising the following steps: (1) Add 65 parts of enzymatically hydrolyzed lignin LIG-Ⅱ, 20 parts of polypropylene glycol A, 20 parts of polytetrahydrofuran A, and 5 parts of hydrogenated castor oil into a reactor, mix and stir, heat to about 75°C, and evacuate for 30 minutes; then add 50 parts of isophorone diisocyanate, stir and heat, and control the temperature at about 85°C to react for 1.2 hours to obtain a first prepolymer; (2) 4 parts of 2,2-dihydroxymethylpropionic acid, 4 parts of dihydroxymethylbutyric acid, and 1 part of tannic acid were added to the first prepolymer, mixed, stirred, and reacted for 0.8 hours to obtain a second prepolymer; (3) Adding 0.1 parts of an organic silver catalyst and 0.1 parts of an organic bismuth catalyst to the second prepolymer, controlling the temperature at about 85°C to react for 1.5 hours, to obtain a third prepolymer; (4) The residual NCO content in the third prepolymer was determined by the di-n-butylamine method. When the reaction degree reached 90%, the third prepolymer was cooled to 60°C, and then 3 parts of triethylamine and 3 parts of triethanolamine were slowly added. The addition process took about 10 minutes. Then, the temperature was controlled at about 60°C for a neutralization reaction for 1.2 hours to obtain a fourth prepolymer. (5) Prepare 600 parts of water in a dispersion kettle in advance and add 0.2 parts of defoamer, 1.5 parts of wetting agent and 2.0 parts of leveling agent into the water, mix and stir. Quickly add the fourth prepolymer into the dispersion kettle, control the reaction temperature at about 18°C, and emulsify for 0.8h to obtain a waterborne polyurethane emulsion. (6) Under stirring conditions, an aqueous solution of ethylenediamine was slowly added to the aqueous polyurethane emulsion, wherein the solution contained 3 parts of ethylenediamine and the concentration was 35 wt%. The dispersion was continued under high-speed stirring at 1500 rpm for 0.8 h to carry out a chain extension reaction to obtain a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane.

[0053] Comparative Example 1 The difference between this comparative example and Example 1 is that tannic acid is not added in step (2).

[0054] Comparative Example 2 The difference between this comparative example and Example 1 is that polypropylene glycol B (article number P103209, molecular weight 400 g / mol) is used instead of polypropylene glycol A (article number P103208, molecular weight 2000 g / mol).

[0055] Comparative Example 3 The difference between this comparative example and Example 1 is that polytetrahydrofuran B (article number P903557, molecular weight 250 g / mol) is used instead of polypropylene glycol A (article number P103208, molecular weight 2000 g / mol).

[0056] The performance of the above embodiments and comparative examples was tested using the following method: (1) Water absorption 10 g of the aqueous polyurethane dispersion prepared in the Examples and Comparative Examples was weighed and placed in a 9 cm diameter watch glass to form a uniform thin film on the bottom of the dish. The film was first dried at room temperature for 12 hours, then dried in a vacuum drying oven at 50°C for 12 hours, and then carefully peeled off after cooling to room temperature to obtain an aqueous polyurethane film. Three 2 cm × 2 cm specimens were cut from the aqueous polyurethane film obtained in each Example and Comparative Example, and each specimen was weighed. The specimens were soaked in deionized water at room temperature for 24 hours, then removed, the surface moisture was quickly blotted, and then weighed. The water absorption rate of the aqueous polyurethane film was calculated as follows: in, m 0 is the weight of the dry film sample, m 1 is the weight of the membrane sample after it was taken out of deionized water and immediately dried with filter paper. The water absorption rate of the waterborne polyurethane membrane obtained in each example and comparative example is the average of the water absorption rates of three samples; (2) Water contact angle test Water contact angle tests were conducted with reference to GB / T 30693-2014 "Measurement of the Contact Angle of Water with Plastic Films." During the tests, the waterborne polyurethanes obtained in different Examples and Comparative Examples were evenly sprayed onto a leather surface. To avoid the effects of leather finishing on the test, untreated wet blue leather was used to prepare the samples. The water contact angles of the leather surfaces coated with the waterborne polyurethanes obtained in each Example and Comparative Example were averaged over three samples. (3) Tensile strength After the waterborne polyurethane film sample was vacuum-dried, the sample was made into a dumbbell-shaped specimen using a mold and a tensile test was performed at room temperature using a universal (tensile) testing machine with a tensile rate set to 200 mm / min. The mechanical properties of the waterborne polyurethane films obtained in each embodiment and comparative example were the average mechanical properties of the three samples.

[0057] The above performance test data is shown in Table 1.

[0058] Table 1 Performance test results .

[0059] From the above content, it can be seen that the present invention uses lignin, polyols, castor oil and diisocyanate as the main raw materials, and uses tannic acid as a cross-linking agent to change the cross-linking degree of the polyurethane material. Through the synergistic effect of multiple components, the hydrophobicity and mechanical strength of the polyurethane are effectively improved. At the same time, the high proportion of bio-based materials such as lignin and castor oil greatly reduces the consumption of petroleum-based raw materials, thereby significantly improving the environmental friendliness of the water-based polyurethane material.

[0060] Compared with Example 1, the amount of tannic acid in step (2) of Example 2 is changed from 1 part to 2 parts, the water absorption rate is reduced, the contact angle is increased, and the tensile strength is improved; compared with Example 1, the amount of tannic acid in step (2) of Example 3 is changed from 1 part to 2 parts, the water absorption rate is reduced, the contact angle is increased, and the tensile strength is improved; Example 4 uses enzymatic lignin LIG-Ⅱ, and the mechanical properties are better; Example 5 uses hydrogenated castor oil, and the hydrophobicity is better; Example 6 uses enzymatic lignin LIG-Ⅱ and hydrogenated castor oil, and the mechanical properties and hydrophobicity are better; Compared with Example 1, tannic acid is not added in step (2) of Comparative Example 1, and the water absorption rate is increased. Add, the contact angle decreases, and the tensile strength decreases; compared with Example 1, Comparative Example 2 uses polypropylene glycol B (article number P103209, molecular weight 400g / mol) instead of polypropylene glycol A (article number P103208, molecular weight 2000g / mol), because the molecular weight of polypropylene glycol B is too small, resulting in poor effect, and the tensile strength decreases; compared with Example 1, Comparative Example 3 uses polytetrahydrofuran B (article number P903557, molecular weight 250g / mol) instead of polypropylene glycol A (article number P103208, molecular weight 2000g / mol), because the molecular weight of polytetrahydrofuran B is too small, resulting in poor effect, and the tensile strength decreases.

Claims

1. A method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane, characterized in that: The following steps are involved: (1) mixing lignin, polyol, castor oil and diisocyanate to carry out a first polymerization reaction to obtain a first prepolymer; (2) mixing the first prepolymer obtained in step (1) with the first chain extender and tannic acid, and performing a second polymerization reaction to obtain a second prepolymer; (3) mixing the second prepolymer obtained in step (2) with an organic metal catalyst and performing a third polymerization reaction to obtain a third prepolymer; (4) adding a neutralizing agent dropwise to the third prepolymer obtained in step (3) to carry out a neutralization reaction to obtain a fourth prepolymer; (5) adding the auxiliary agent to water and mixing evenly, then adding the fourth prepolymer obtained in step (4) and mixing evenly, and performing an emulsification reaction to obtain a polyurethane emulsion; (6) The polyurethane emulsion obtained in step (5) is mixed with the second chain extender to carry out a chain extension reaction to obtain a bio-based waterborne polyurethane with high hydrophobicity and high mechanical strength.

2. The method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane according to claim 1, wherein: The raw materials are as follows in parts by weight: 50-70 parts of lignin, 30-50 parts of polyol, 3-8 parts of castor oil, 40-60 parts of diisocyanate, 5-9 parts of a first chain extender, 1-4 parts of tannic acid, 0.05-0.3 parts of an organic metal catalyst, 4-7 parts of a neutralizer, 450-650 parts of water, 1.8-5.3 parts of an auxiliary agent, and 2-4 parts of a second chain extender.

3. The method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane according to claim 1, characterized in that: The lignin is enzymatically hydrolyzed lignin, with a residual sugar content of ≤3.0%, an ash content of ≤5.0%, a moisture content of ≤12.0%, and a phenolic hydroxyl content of ≥3.0%.

4. The method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane according to claim 1, wherein: The polyol is polypropylene glycol and / or polytetrahydrofuran, and the molecular weight of the polyol is 900-4000 g / mol.

5. The method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane according to claim 1, wherein: The castor oil is hydrogenated castor oil, with a hydroxyl value of 150 mgKOH / g and a saponification value of 178 mgKOH / g.

6. The method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane according to claim 1, wherein: The diisocyanate is selected from one or more of isophorone diisocyanate, hexamethylene diisocyanate and hydrogenated phenylmethane diisocyanate.

7. The method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane according to claim 1, characterized in that: The first chain extender is 2,2-dimethylol propionic acid and / or dimethylol butyric acid; The organometallic catalyst is an organosilver catalyst and / or an organobismuth catalyst; The neutralizing agent is triethylamine and / or triethanolamine; The second chain extender is selected from one or more of ethylenediamine, isophoronediamine or hydroxyethylethylenediamine.

8. The method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane according to claim 1, characterized in that: The auxiliary agents include defoaming agents, wetting agents and leveling agents.

9. The method for preparing a highly hydrophobic and high mechanical strength bio-based waterborne polyurethane according to claim 1, wherein: In step (1), the temperature of the first polymerization reaction is 70-90° C. and the time is 0.5-2 h; The time of the second polymerization reaction in step (2) is 0.5 to 1 hour; The temperature of the third polymerization reaction in step (3) is 80-85°C, the time is 0.8-2h, and the reaction degree is controlled to be 80-90%; The dropwise addition time of the neutralizing agent in step (4) is 5 to 15 minutes; the temperature of the neutralization reaction is 55 to 60°C, and the time is 1 to 1.5 hours; The conditions of the emulsification reaction in step (5) are: under stirring conditions, the reaction temperature is 10-20°C, and the reaction time is 0.5-1h; The chain extension reaction step in step (6) includes: slowly adding the second chain extender to the aqueous polyurethane emulsion, stirring at a speed of 1000-1500 rpm, and the chain extension reaction time is 0.5-1 h.

10. A highly hydrophobic and high mechanical strength bio-based waterborne polyurethane, characterized in that: Prepared according to the method according to any one of claims 1 to 9.

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