A high-property waterborne polyurethane and a method for preparing a high-property waterborne polyurethane based on sulfonated hemicellulose

Abstract

The application belongs to the field of leather auxiliaries, and particularly relates to a high-property water-based polyurethane and a method for preparing the high-property water-based polyurethane based on sulfonated hemicellulose. The method comprises the following steps: (1) reacting isocyanate with polyol to obtain a primary reactant; (2) reacting the primary reactant with a hydrophilic monomer, sulfonated hemicellulose, a catalyst and a solvent to obtain a prepolymer; and (3) dispersing the prepolymer in water and then reacting with a post-chain extender to obtain a product. The product has an emulsion particle size of 60-120 nm, a breaking strength of 17.2 MPa, and biodegradability, and is suitable for leather finishing, and solves the problems of traditional products, such as the need for a crosslinking agent and poor stability.

Description

Technical Field

[0001] This invention belongs to the field of leather auxiliaries, specifically relating to a high-performance waterborne polyurethane and a method for preparing a high-performance waterborne polyurethane based on sulfonated hemicellulose. Background Technology

[0002] Waterborne polyurethane has become one of the core materials in the leather finishing industry due to its advantages such as no volatile organic compound (VOC) emissions and environmental friendliness. Its performance directly determines key indicators of leather products such as feel, abrasion resistance, weather resistance and mechanical strength.

[0003] Traditional waterborne polyurethane is synthesized using isocyanates and polyols as core raw materials, forming a main chain structure through linear polymerization. However, the linear structure leads to significant performance shortcomings in the product: on the one hand, its mechanical properties are weak, with a breaking strength after film formation typically below 10 MPa and a tensile strength below 3 MPa, making it difficult to meet the requirements of high-end leather for tensile and tear resistance. Additional epoxy and aziridine chemical crosslinking agents are required for post-treatment, but these crosslinking agents are often toxic, easily causing residual pollution to the leather and reducing film flexibility. On the other hand, the uneven distribution of hydrophilic groups (such as carboxyl groups) in traditional waterborne polyurethane results in emulsion particle sizes generally greater than 100 nm, leading to poor storage stability (easily delamination after 3 months of storage at room temperature) and defects such as sagging and pinholes during coating, affecting the appearance quality of the leather.

[0004] Furthermore, existing waterborne polyurethane raw materials are mainly petroleum-based compounds with a biodegradability rate of less than 20%, which can easily cause environmental burden after disposal. In recent years, although the industry has tried to introduce bio-based materials (such as starch and cellulose) to improve environmental friendliness, unmodified bio-based materials have poor compatibility with polyurethane matrices and are prone to agglomeration, leading to performance degradation; while chemical modification (such as esterification and etherification) processes are complex and costly, making it difficult to achieve industrial application.

[0005] In summary, waterborne polyurethane for leather finishing currently faces a triple technical bottleneck: performance improvement relies on toxic crosslinking agents, environmental friendliness and compatibility are difficult to balance, and emulsion stability is poor. Developing a waterborne polyurethane preparation method that does not require additional crosslinking agents, has excellent mechanical properties, is environmentally friendly, and has a simple process has become an urgent problem to be solved in the industry.

[0006] Therefore, based on this, the technical solution of the present invention is proposed. Summary of the Invention

[0007] To address the problems existing in the prior art, the present invention provides a method for preparing high-performance waterborne polyurethane based on sulfonated hemicellulose, the method comprising the following steps: (1) React isocyanate and polyol to obtain initial reactants; (2) Add hydrophilic monomers, sulfonated hemicellulose, catalysts and solvents to the initial reactants to react and obtain a prepolymer; (3) After dispersing the prepolymer in water, it is reacted with a chain extender to obtain the high-performance waterborne polyurethane.

[0008] Preferably, in step (1): The isocyanate is one or a combination of two or more of dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and toluene diisocyanate. And / or, the polyol is one or a combination of two or more of polypropylene oxide polyol, polytetrahydrofuran polyol, polycaprolactone polyol, and polycarbonate polyol.

[0009] Preferably, in step (1): The molecular weight of the polyol is 1000~4000; And / or, the weight ratio of the polyol to the isocyanate is 1~2:0.4~0.8.

[0010] Preferably, in step (1), the reaction temperature is 70-90℃ and the time is 1-2h.

[0011] It should be noted that in step (1), the polyol needs to be dehydrated under vacuum before being mixed with isocyanate. The dehydration temperature is 90-110℃.

[0012] Preferably, in step (2): The hydrophilic monomer is dimethylolpropionic acid; And / or, the catalyst is an organotin catalyst or an organobismuth catalyst; And / or, the solvent is acetone.

[0013] Preferably, in step (2), the reaction temperature is 70-90℃ and the time is 2-4h.

[0014] It should be noted that in step (2), sulfonated hemicellulose is added to the reaction system in the form of a solution, and the solvent is N,N-dimethylformamide. The weight ratio of N,N-dimethylformamide to sulfonated hemicellulose is 5:0.5~2; the weight ratio of sulfonated hemicellulose to polyol is 1~5:100.

[0015] Preferably, in step (3), the chain extender is one or a combination of two or more of hydrazine hydrate, ethylenediamine, diethylenetriamine, and isophorone diamine.

[0016] Preferably, in step (3), the reaction temperature is 40-45℃ and the time is 5-15min.

[0017] Based on the same technical concept, another aspect of the present invention is to provide a high-property-value waterborne polyurethane prepared by the above method, wherein the resulting emulsion has a particle size of 60-120 nm and is mainly used for leather finishing.

[0018] The beneficial effects of this invention are as follows: This invention systematically solves the performance, environmental protection, and process defects of traditional waterborne polyurethane by introducing sulfonated hemicellulose as a functional modifier. The overall beneficial effects are as follows: The high-property waterborne polyurethane prepared by this invention can achieve synergistic improvement in mechanical properties, emulsion stability, and biodegradability without the need for additional chemical crosslinking agents. It also has strong process compatibility, is suitable for industrial production, and can meet the core requirements of high-end leather finishing.

[0019] 1. Significantly improved mechanical properties, overcoming the shortcomings of traditional linear structures. Sulfonated hemicellulose molecules contain a large number of branched hydroxyl groups (functionality > 2), which can undergo cross-linking reactions with the -NCO groups of the polyurethane backbone, transforming the linear structure into a three-dimensional network structure. As demonstrated in the verification examples, Example 5, with the addition of 10g of sulfonated hemicellulose, achieved a tensile strength of 17.2MPa (a 59.3% increase compared to Comparative Example 1) and a 100% tensile strength of 5.5MPa (a 71.9% increase), without requiring additional cross-linking agents. This avoids issues of toxic residues and reduced flexibility, meeting the requirements of high-end leather for abrasion resistance and tensile strength.

[0020] 2. The emulsion stability has been significantly improved, enhancing its adaptability to coating processes. sulfonated hemicellulose sulfonyl group (-SO3) - It has strong hydrophilicity and can be uniformly distributed in the polyurethane molecular chain, reducing the interfacial tension between oil and water. Verification examples show that the emulsion particle size of Examples 1-5 decreased from 95nm to 60nm (significantly reduced compared to 110nm in Comparative Example 1), making it less prone to sagging and pinholes during coating, and improving the smoothness and uniformity of the leather appearance.

[0021] 3. Improved biodegradability and environmental friendliness meet the needs of green development. Hemicellulose is derived from natural plants (such as straw and wood) and is a renewable resource. Its sulfonation modification does not damage its biocompatible structure. The biodegradability of the product of this invention can reach 45-55% (1-2 times higher than traditional petroleum-based waterborne polyurethane), and it has a low environmental burden after disposal, which is in line with the policy guidance of the leather industry.

[0022] 4. The process is simplified and the cost is controllable, making it easy to promote industrialization. This invention directly incorporates sulfonated hemicellulose into the prepolymer preparation process, eliminating the need for additional reaction equipment. Furthermore, the cost of sulfonated hemicellulose preparation is lower than that of chemical crosslinking agents (approximately one-third the cost of aziridine crosslinking agents). Simultaneously, the reaction process does not require high temperature and pressure (maximum temperature 95℃), resulting in low energy consumption and strong compatibility with existing waterborne polyurethane production lines, facilitating rapid implementation by enterprises. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0024] Example 1 This embodiment provides a method for preparing high-performance waterborne polyurethane based on sulfonated hemicellulose, the method comprising the following steps (detailed): (1) Raw material pretreatment: preparation of sulfonated hemicellulose solution and ethylenediamine aqueous solution (1-1) Take a 500mL three-necked flask, equip it with an electric stirrer (model JJ-1) and a mercury thermometer (accuracy ±0.1℃), add 300g of N,N-dimethylformamide (DMF, analytical grade) to the flask, turn on the stirrer (speed 200rpm), slowly add 100g of sulfonated hemicellulose (purity ≥95%), stir while adding for 30min until completely dissolved, to obtain a homogeneous and transparent sulfonated hemicellulose solution, let it stand at room temperature for later use; (1-2) Take a 100mL beaker, add 15g of deionized water (conductivity ≤5μS / cm), turn on magnetic stirring (speed 150rpm), slowly add 6.8g of ethylenediamine (analytical grade, water content ≤0.5%), stir for 5min until completely dissolved, and obtain an ethylenediamine aqueous solution. Seal and store at room temperature for later use.

[0025] DMF can dissolve sulfonated hemicellulose, preventing it from agglomerating in subsequent reactions and ensuring uniform mixing with the polyurethane matrix; ethylenediamine, which is soluble in water, can control the chain extension reaction rate and prevent localized violent reactions that could lead to uneven molecular chain distribution.

[0026] (2) Dehydration of polyols: Remove water and avoid side reactions. Take a 1000mL four-necked flask, equip it with an electric stirrer, thermometer, vacuum interface (connected to a circulating water vacuum pump), and nitrogen protection device. Add 100g of polyoxypropylene polyol (PPG-1000, hydroxyl value 56±2mgKOH / g) and 100g of polytetrahydrofuran polyol (PTMEG-1000, hydroxyl value 112±2mgKOH / g) to the flask. Turn on the vacuum pump and control the vacuum degree to 0.09-0.095MPa. At the same time, heat the oil bath to 95℃ and maintain the temperature while stirring and dehydrating for 1 hour (180rpm). During this period, observe through a water separator until no water droplets precipitate. Then, take a sample to measure the moisture content (Kal Fischer method) to ensure that it is ≤0.1%.

[0027] The water in polyols reacts with isocyanates to form urea bonds, which leads to the breaking of molecular chains. Dehydration can ensure that the reaction proceeds in a directional manner and improve the structural uniformity of the initial reactants.

[0028] (3) Preparation of initial reactants: polymerization of isocyanate and polyol Turn off the vacuum pump, introduce high-purity nitrogen (purity ≥99.99%) to break the vacuum, and cool down to 60℃; slowly add 88.8g of isophorone diisocyanate (IPDI, purity ≥99.5%) dropwise over 30min (controlling the temperature ≤70℃); after the addition is complete, raise the temperature to 80℃, keep it at this temperature and stir for 1h (200rpm), take samples every 15min and determine the -NCO content using the di-n-butylamine titration method, and stop the reaction when the content drops to the theoretical value to obtain the initial reactant.

[0029] Nitrogen protection can prevent IPDI from oxidizing and deteriorating; detecting the -NCO content can confirm the completeness of the reaction and avoid unreacted IPDI residues affecting the performance of subsequent prepolymers.

[0030] (4) Prepolymer preparation: introducing hydrophilic groups and crosslinking sites Maintaining a nitrogen atmosphere, the initial reactants were cooled to 60°C, and 40g of acetone (analytical grade, water content ≤0.1%) was added. The mixture was stirred for 5 minutes (220 rpm). Then, 6g of dimethylolpropionic acid (DMPA, purity ≥99%) and 0.1g of organic bismuth catalyst (purity ≥98%) were added sequentially, and the mixture was stirred for 10 minutes until the system was homogeneous. 8g of the sulfonated hemicellulose solution prepared in step 1 was slowly added dropwise (dropwise over 20 minutes at 60-65°C). After the addition was complete, the temperature was raised to 70°C, and the mixture was kept at this temperature and stirred for 4 hours. After the reaction was completed, the -NCO content was measured. If the content met the standard, the prepolymer was obtained.

[0031] Acetone reduces the viscosity of the system, making it easier for materials to mix; DMPA provides carboxyl groups, laying the foundation for water dispersibility; sulfonated hemicellulose introduces branched hydroxyl groups, forming cross-linking sites and improving the mechanical properties of subsequent products.

[0032] (5) Neutralization, water dispersion and post-chain extension: forming a stable emulsion The prepolymer was cooled to 45°C, and 4.5g of triethylamine (TEA, purity ≥99%) was added. The mixture was stirred for 15 min (250 rpm) to neutralize the carboxyl groups (neutralization degree 90-95%). While maintaining 45°C, 1200g of deionized cold water (15-20°C) was slowly added under high-speed stirring (800-1000 rpm) and stirred for 15 min to form an aqueous dispersion of the prepolymer. The temperature was reduced to 300 rpm, and an aqueous solution of ethylenediamine was added dropwise (completed in 15 min). The mixture was kept at 45°C and reacted for 30 min. Finally, acetone was removed by vacuum distillation (0.08-0.085 MPa, 40-45°C) for 1 h to obtain a high-performance waterborne polyurethane emulsion.

[0033] TEA neutralizes carboxyl groups to form carboxylate salts, improving water dispersibility; high-speed stirring ensures fine emulsion particle size; ethylenediamine extends molecular chains and improves mechanical properties; acetone removal avoids solvent residue and ensures environmental friendliness.

[0034] Example 2 This embodiment provides a method for preparing high-performance waterborne polyurethane based on sulfonated hemicellulose, the method comprising the following steps (briefly described): (1) Dissolve 100g of sulfonated hemicellulose in 300g of DMF solvent to obtain a sulfonated hemicellulose solution for later use; dissolve 6.8g of ethylenediamine in 15g of water to obtain an ethylenediamine aqueous solution for later use; (2) 100g of PPG-1000 and 100g of PTMEG-1000 were put into a reaction flask and dehydrated under vacuum at 95°C for 1 hour, and then cooled to 60°C; then 88.8g of isophorone diisocyanate was added and reacted at 80°C for 1 hour to obtain the initial reactant. (3) Then the initial reactant was cooled to 60°C, and 40g of acetone, 6g of dimethylolpropionic acid, 0.1g of organic bismuth catalyst and 16g of sulfonated hemicellulose solution were added. The mixture was reacted at 70°C for 4 hours to obtain the prepolymer. (4) Cool the prepolymer to 45°C, add 4.5g of triethylamine for neutralization for 15min, then add 1200g of cold water for high-speed dispersion for 15min, and finally add ethylenediamine aqueous solution to the system for post-chain extension reaction for 30min to obtain a high-performance waterborne polyurethane emulsion.

[0035] Example 3 This embodiment provides a method for preparing high-performance waterborne polyurethane based on sulfonated hemicellulose, the method comprising the following steps (briefly described): (1) Dissolve 100g of sulfonated hemicellulose in 300g of DMF solvent to obtain a sulfonated hemicellulose solution for later use; dissolve 6.8g of ethylenediamine in 15g of water to obtain an ethylenediamine aqueous solution for later use; (2) 100g of PPG-1000 and 100g of PTMEG-1000 were put into a reaction flask and dehydrated under vacuum at 95°C for 1 hour, and then cooled to 60°C; then 88.8g of isophorone diisocyanate was added and reacted at 80°C for 1 hour to obtain the initial reactant. (3) Then the initial reactant was cooled to 60°C, and 40g of acetone, 6g of dimethylolpropionic acid, 0.1g of organic bismuth catalyst and 24g of sulfonated hemicellulose solution were added. The mixture was reacted at 70°C for 4 hours to obtain the prepolymer. (4) Cool the prepolymer to 45°C, add 4.5g of triethylamine for neutralization for 15min, then add 1200g of cold water for high-speed dispersion for 15min, and finally add ethylenediamine aqueous solution to the system for post-chain extension reaction for 30min to obtain a high-performance waterborne polyurethane emulsion.

[0036] Example 4 This embodiment provides a method for preparing high-performance waterborne polyurethane based on sulfonated hemicellulose, the method comprising the following steps (briefly described): (1) Dissolve 100g of sulfonated hemicellulose in 300g of DMF solvent to obtain a sulfonated hemicellulose solution for later use; dissolve 6.8g of ethylenediamine in 15g of water to obtain an ethylenediamine aqueous solution for later use; (2) 100g of PPG-1000 and 100g of PTMEG-1000 were put into a reaction flask and dehydrated under vacuum at 95°C for 1 hour, and then cooled to 60°C; then 88.8g of isophorone diisocyanate was added and reacted at 80°C for 1 hour to obtain the initial reactant. (3) Then the initial reactant was cooled to 60°C, and 40g of acetone, 6g of dimethylolpropionic acid, 0.1g of organic bismuth catalyst and 32g of sulfonated hemicellulose solution were added. The mixture was reacted at 70°C for 4 hours to obtain the prepolymer. (4) Cool the prepolymer to 45°C, add 4.5g of triethylamine for neutralization for 15min, then add 1200g of cold water for high-speed dispersion for 15min, and finally add ethylenediamine aqueous solution to the system for post-chain extension reaction for 30min to obtain a high-performance waterborne polyurethane emulsion.

[0037] Example 5 This embodiment provides a method for preparing high-performance waterborne polyurethane based on sulfonated hemicellulose, the method comprising the following steps (briefly described): (1) Dissolve 100g of sulfonated hemicellulose in 300g of DMF solvent to obtain a sulfonated hemicellulose solution for later use; dissolve 6.8g of ethylenediamine in 15g of water to obtain an ethylenediamine aqueous solution for later use; (2) 100g of PPG-1000 and 100g of PTMEG-1000 were put into a reaction flask and dehydrated under vacuum at 95°C for 1 hour, and then cooled to 60°C; then 88.8g of isophorone diisocyanate was added and reacted at 80°C for 1 hour to obtain the initial reactant. (3) Then the initial reactant was cooled to 60°C, and 40g of acetone, 6g of dimethylolpropionic acid, 0.1g of organic bismuth catalyst and 40g of sulfonated hemicellulose solution were added. The mixture was reacted at 70°C for 4 hours to obtain the prepolymer. (4) Cool the prepolymer to 45°C, add 4.5g of triethylamine for neutralization for 15min, then add 1200g of cold water for high-speed dispersion for 15min, and finally add ethylenediamine aqueous solution to the system for post-chain extension reaction for 30min to obtain a high-performance waterborne polyurethane emulsion.

[0038] Comparative Example 1 This comparative example provides a method for preparing high-performance waterborne polyurethane based on sulfonated hemicellulose, the method comprising the following steps (briefly described): (1) Dissolve 6.8g of ethylenediamine in 15g of water to obtain an aqueous solution of ethylenediamine, and set aside for later use; (2) 100g of PPG-1000 and 100g of PTMEG-1000 were put into a reaction flask and dehydrated under vacuum at 95°C for 1 hour, and then cooled to 60°C; then 88.8g of isophorone diisocyanate was added and reacted at 80°C for 1 hour to obtain the initial reactant. (3) Then the initial reactant was cooled to 60°C, 40g of acetone, 6g of dimethylolpropionic acid and 0.1g of organic bismuth catalyst were added, and the mixture was reacted at 70°C for 4 hours to obtain the prepolymer. (4) Cool the prepolymer to 45°C, add 4.5g of triethylamine for neutralization for 15min, then add 1200g of cold water for high-speed dispersion for 15min, and finally add ethylenediamine aqueous solution to the system for post-chain extension reaction for 30min to obtain waterborne polyurethane emulsion.

[0039] Verification Example The waterborne polyurethane product prepared above was subjected to performance testing; among which, the mechanical performance testing included: after the waterborne polyurethane film was dried, the physical data were measured by a tensile testing machine, as shown in Table 1.

[0040] Table 1

[0041] As shown in Table 1, the emulsion prepared by Comparative Example 1 without the addition of sulfonated hemicellulose had a particle size of 110 nm, an elongation at break of 621%, and a tensile strength of 10.8 N / mm. 2 The tensile strength is 3.2 N / mm.2 In Examples 1-5, 2g, 4g, 6g, 8g, and 10g of sulfonated hemicellulose were added, respectively. With increasing addition, the particle size of the polyurethane decreased sequentially from 95nm to 80nm, 76nm, 65nm, and 60nm. This is mainly because sulfonated hemicellulose is hydrophilic; as the addition amount increases, the hydrophilicity of the product increases, leading to a decrease in particle size. From Comparative Example 1 and Examples 1-5, the elongation at break decreased with increasing sulfonated hemicellulose, while the tensile strength and tensile strength increased. This is mainly because the hydroxyl groups in hemicellulose have a functionality greater than 2, acting as a crosslinking agent. This can change the conventional linear structure of polyurethane into a network structure, effectively improving the mechanical properties of the waterborne polyurethane film. In other words, as the amount of hemicellulose added increases, the mechanical properties of the product gradually improve. The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing high-performance waterborne polyurethane based on sulfonated hemicellulose, characterized in that, The method includes the following steps: (1) React isocyanate and polyol to obtain initial reactants; (2) Add hydrophilic monomer, sulfonated hemicellulose, catalyst and solvent to the initial reactant to obtain a prepolymer; the hydrophilic monomer is dimethylolpropionic acid; sulfonated hemicellulose is added to the reaction system in the form of solution, and the solvent is N,N-dimethylformamide; the sulfonated hemicellulose molecule contains branched hydroxyl groups with a functionality >2, and the branched hydroxyl groups undergo cross-linking reaction with the -NCO groups of the polyurethane backbone to transform the linear structure into a three-dimensional network structure; (3) After dispersing the prepolymer in water, it is reacted with a chain extender to obtain the high-performance waterborne polyurethane.

2. The method for preparing high-performance waterborne polyurethane based on sulfonated hemicellulose according to claim 1, characterized in that, In step (1): The isocyanate is one or a combination of two or more of dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and toluene diisocyanate. And / or, the polyol is one or a combination of two or more of polypropylene oxide polyol, polytetrahydrofuran polyol, polycaprolactone polyol, and polycarbonate polyol.

3. The method for preparing high-property waterborne polyurethane based on sulfonated hemicellulose according to claim 1, characterized in that, In step (1): The molecular weight of the polyol is 1000~4000; And / or, the weight ratio of the polyol to the isocyanate is 1~2:0.4~0.

8.

4. The method for preparing high-performance waterborne polyurethane based on sulfonated hemicellulose according to claim 1, characterized in that, In step (1), the reaction temperature is 70-90℃ and the time is 1-2h.

5. The method for preparing high-performance waterborne polyurethane based on sulfonated hemicellulose according to claim 1, characterized in that, In step (2): The catalyst is an organotin catalyst or an organobismuth catalyst; And / or, the solvent is acetone.

6. The method for preparing high-property waterborne polyurethane based on sulfonated hemicellulose according to claim 1, characterized in that, In step (2), the reaction temperature is 70-90℃ and the time is 2-4h.

7. The method for preparing high-performance waterborne polyurethane based on sulfonated hemicellulose according to claim 1, characterized in that, In step (3), the chain extender is one or a combination of two or more of hydrazine hydrate, ethylenediamine, diethylenetriamine, and isophorone diamine.

8. The method for preparing high-property waterborne polyurethane based on sulfonated hemicellulose according to claim 1, characterized in that, In step (3), the reaction temperature is 40-45℃ and the time is 5-15min.

9. A high-performance waterborne polyurethane prepared by the method according to any one of claims 1-8.

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