Lignin-based waterborne polyurethane, and preparation method and application thereof

Abstract

The present application discloses a lignin-based waterborne polyurethane, which is prepared from a system consisting of 50-80 parts of bio-based polytrimethylene ether glycol, 15-30 parts of 1,5-pentane diisocyanate, 1-20 parts of enzymatic hydrolysis lignin, 0.1-2 parts of a catalyst, 3-8 parts of a hydrophilic chain extender and 2.3-6.1 parts of a neutralizing agent, and a second organic solvent for dissolving the enzymatic hydrolysis lignin, the mass ratio of the second organic solvent to the enzymatic hydrolysis lignin being (5-9):(0.5-4). The lignin-based waterborne polyurethane has the advantages of simple preparation method, high bio-based content, good emulsion stability, good tensile strength, flexibility and heat resistance after curing and film forming, and can be used to prepare printing coatings without adding color paste, and the fabric treated by the printing coatings has bright color and soft hand feeling.

Description

Technical Field

[0001] This invention belongs to the field of waterborne polyurethane materials technology, specifically relating to lignin-based waterborne polyurethane, its preparation method, and its application. Background Technology

[0002] With increasing global awareness of environmental protection, countries are imposing increasingly stringent restrictions on volatile organic compound (VOC) emissions. Waterborne polyurethane coatings, due to their advantages such as solvent-free evaporation, low odor, non-flammability, good flexibility, and strong adhesion, are gradually becoming an environmentally friendly alternative to traditional solvent-based polyurethane coatings. However, the raw materials for traditional waterborne polyurethane coatings are mostly derived from petrochemical products. These raw materials are not only toxic and corrosive but also non-renewable, and their application is limited as petroleum resources dwindle.

[0003] Lignin is an abundant aromatic compound in nature. Due to the presence of various functional groups, including aliphatic and aromatic hydroxyl groups, lignin has the potential to be used in bio-based polyurethanes. Enzymatic hydrolysis of lignin is a novel type of lignin obtained through microbial enzymatic hydrolysis. Compared with traditional alkali lignin and sulfate lignin, enzymatic hydrolyzed lignin has a variety of active groups and better reactivity, which can be utilized to develop environmentally friendly and high-performance waterborne polyurethane materials. Summary of the Invention

[0004] The first objective of this invention is to provide a lignin-based waterborne polyurethane to solve at least one of the aforementioned technical problems.

[0005] A second objective of this invention is to provide a method for preparing lignin-based waterborne polyurethane to solve at least one of the aforementioned technical problems.

[0006] A third objective of the present invention is to provide an application of lignin-based waterborne polyurethane to solve at least one of the aforementioned technical problems.

[0007] According to a first aspect of the invention, a lignin-based aqueous polyurethane is provided, which is prepared from a system of raw materials in parts by weight: 50-80 parts of bio-based polyether diol, 15-30 parts of 1,5-pentanediisocyanate (PDI), 1-20 parts of enzymatically hydrolyzed lignin (EL), 0.1-2 parts of catalyst, 3-8 parts of hydrophilic chain extender and 2.3-6.1 parts of neutralizer, and a second organic solvent for dissolving the enzymatically hydrolyzed lignin, wherein the mass ratio of the second organic solvent to the enzymatically hydrolyzed lignin is (5-9):(0.5-4).

[0008] In some embodiments, the bio-based polyether diol may be bio-based polytrimethylene ether diol (PO3G).

[0009] The lignin-based waterborne polyurethane of the present invention uses bio-based materials such as bio-based polyether diol, 1,5-pentanediisocyanate and enzymatically hydrolyzed lignin as raw materials, reducing the use of non-renewable petroleum-based materials, making it green and environmentally friendly. The lignin-based waterborne polyurethane has good emulsion stability and good thermal stability, tensile strength and flexibility after curing into a film.

[0010] In some embodiments, the number average molecular weight of the bio-based polyether diol can be 500 to 2700.

[0011] In some embodiments, the number-average molecular weight of the bio-based polyether diol can be 1000.

[0012] In some embodiments, the number-average molecular weight of enzymatically hydrolyzed lignin can be 1000 to 6000.

[0013] In some embodiments, the number-average molecular weight of enzymatically hydrolyzed lignin can be 1300.

[0014] In some embodiments, the hydrophilic chain extender may be selected from at least one of 2,2-dimethylolpropionic acid and 2,2-dimethylolbutyric acid.

[0015] In some embodiments, the catalyst may be a bismuth catalyst. Specifically, the bismuth catalyst may be selected from at least one of organobismuth, bismuth neodecanoate, and bismuth isooctanoate.

[0016] In some embodiments, the neutralizing agent may be selected from at least one of triethylamine, triethanolamine, sodium hydroxide, ammonia, and N-methyldiethanolamine.

[0017] According to a second aspect of the present invention, a method for preparing lignin-based waterborne polyurethane is provided, the method comprising the following steps:

[0018] S1. React bio-based polyether diol and 1,5-pentanediisocyanate at 80-90°C for 2-4 hours, then add the first mixture, hydrophilic chain extender and catalyst, and react at 70-80°C for 4-6 hours. Add the first organic solvent to obtain lignin-based waterborne polyurethane prepolymer.

[0019] S2. Cool the lignin-based waterborne polyurethane prepolymer to a temperature below 50°C, add a neutralizing agent and react for 10-20 minutes, add water to carry out an emulsification reaction, and remove the first organic solvent under vacuum at 40-50°C to obtain the product.

[0020] The first mixture is obtained by enzymatically hydrolyzing lignin and dissolving it in a second organic solvent.

[0021] The method for preparing lignin-based waterborne polyurethane of the present invention introduces enzymatic hydrolysis of lignin into the waterborne polyurethane system, resulting in a high bio-based content in the waterborne polyurethane emulsion. The preparation method is simple and low in cost.

[0022] In some embodiments, the first organic solvent may be selected from at least one of acetone and butanone.

[0023] In some embodiments, the second organic solvent may be selected from at least one of N,N-diethylformamide (DEF) and γ-valerol (GVL). Specifically, the reaction system is difficult to form a film without the addition of EL, but is difficult to dissolve when EL is introduced; therefore, a second organic solvent is used to dissolve the enzymatically hydrolyzed lignin. The selected second organic solvent is a green, environmentally friendly, and low-toxic organic solvent, which can not only dissolve the enzymatically hydrolyzed lignin, but also be used in the production of dyeing and printing industries where highly toxic organic solvents are prohibited.

[0024] In some embodiments, the mass ratio of enzymatically hydrolyzed lignin to the second organic solvent can be (0.5-4):(5-9).

[0025] In some embodiments, the mass ratio of enzymatically hydrolyzed lignin to the second organic solvent can be (0.5-2):(5-9).

[0026] In some embodiments, in step S2, the emulsification reaction can be carried out by stirring at a speed of 800-900 r / min for 0.8-1.5 hours.

[0027] According to a third aspect of the invention, the application of lignin-based waterborne polyurethane in printing coatings is provided.

[0028] The lignin-based waterborne polyurethane of the present invention can be formulated into a printing coating. The entire process does not require the addition of traditional petroleum-based color paste. The printing coating is applied to the surface of the fabric by mechanical or manual methods. The fabric treated with the printing coating has bright colors, no obvious fading after heat treatment, high resilience, and a soft hand feel.

[0029] In some embodiments, the printing coating comprises, by weight, the following components: 170-190 parts of lignin-based waterborne polyurethane, 0.5-1.5 parts of defoamer, 0.5-1.5 parts of pH adjuster, 1.4-1.8 parts of nonionic emulsifier, 8-12 parts of humectant, 2-4 parts of thickener, and 1.5-2.5 parts of crosslinking agent.

[0030] The beneficial effects of this invention are as follows:

[0031] (1) The lignin-based waterborne polyurethane of the present invention introduces enzymatic hydrolysis of lignin into the reaction system of waterborne polyurethane, which can not only modify waterborne polyurethane to obtain waterborne polyurethane with good emulsion stability, but also has good thermal stability, tensile strength and flexibility after curing into film, and improve flame retardancy. At the same time, the natural pigments in lignin can be used as natural dyes for coating printing, which helps to alleviate the high energy consumption and high pollution problems caused by the large-scale use of industrial color pastes in the printing and dyeing industry.

[0032] (2) The preparation method of lignin-based waterborne polyurethane of the present invention is simple and low in cost;

[0033] (3) The lignin-based waterborne polyurethane of the present invention can be used to prepare printing coatings. Fabrics treated with printing coatings have bright colors, soft hand feel, and high resilience. Attached Figure Description

[0034] Figure 1 Infrared spectra of the lignin-based waterborne polyurethane prepared by enzymatic hydrolysis of lignin in this invention, the lignin-based waterborne polyurethane prepared in Examples 1-3, and the waterborne polyurethane prepared in Comparative Example 1.

[0035] Figure 2 The stress-strain curves are of the cured films of lignin-based waterborne polyurethane prepared in Examples 1-3 of the present invention and waterborne polyurethane prepared in Comparative Example 1.

[0036] Figure 3 The particle size distribution diagrams are shown for the lignin-based waterborne polyurethanes prepared in Examples 1-3 of this invention and the waterborne polyurethanes prepared in Comparative Example 1.

[0037] Figure 4 The XRD curves are of the cured films of the lignin-based waterborne polyurethane prepared in Examples 1-3 of the present invention and the waterborne polyurethane prepared in Comparative Example 1.

[0038] Figure 5 The TGA curves are of the cured films of the lignin-based waterborne polyurethane prepared in Examples 1-3 of this invention and the waterborne polyurethane prepared in Comparative Example 1.

[0039] Figure 6 The curing curves of the lignin-based waterborne polyurethane prepared in Examples 1-3 of this invention and the waterborne polyurethane prepared in Comparative Example 1 are shown.

[0040] Figure 7 (A) is a photograph of the printing coating applied to white cotton fabric in Application Example 2 of the present invention; Figure 7 (B) is a photograph of the printing coating applied to white cotton fabric in Application Example 3 of the present invention. Figure 7 (C) is a photograph of the printing coating applied to white cotton fabric in Application Example 4 of the present invention;

[0041] Figure 8 (A) is a photograph of the printing coating of the present invention, Example 2, applied to a swimsuit fabric; Figure 8 (B) is a photograph of the printing coating of the present invention, Example 3, applied to a swimsuit fabric. Figure 8 (C) is a photograph of the printing coating of the present invention, Example 4, applied to a swimsuit fabric. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials and reagents involved in the following embodiments are all commercially available.

[0043] The enzymatically hydrolyzed lignin used in the following examples was purchased from Xinyuan Biotechnology Co., Ltd., with a purity of over 90%, a phenolic hydroxyl content of 8% to 16%, and a number-average molecular weight of 1300.

[0044] Example 1

[0045] This embodiment provides a method for preparing lignin-based waterborne polyurethane, including the following steps:

[0046] Add 50g of PO3G (number average molecular weight of 1000) and 18g of PDI to a 1000mL three-necked flask, and react at 85℃ for 3h. Then add the first mixture obtained by dissolving 1.7g of enzymatically hydrolyzed lignin in 15g of GVL, 3g of DMPA and 0.2g of organic bismuth catalyst 8108, and react at 75℃ for 5h. Then add 20g of acetone to adjust the viscosity of the system to obtain the prepolymer.

[0047] The prepolymer was cooled to below 50°C, and 2.3g of TEA was added for neutralization reaction for 15 minutes. Then, 100g of deionized water was added for emulsification for 1 hour. Finally, acetone was removed under vacuum at 45°C to obtain the final product. The calculated bio-based content of the lignin-based waterborne polyurethane is 88.69%.

[0048] Example 2

[0049] This embodiment provides a method for preparing lignin-based waterborne polyurethane. The difference from Example 1 is that the mass of enzymatically hydrolyzed lignin in this embodiment is 3.45 g. Calculations show that the bio-based content of the lignin-based waterborne polyurethane is 88.96%.

[0050] Example 3

[0051] This embodiment provides a method for preparing lignin-based waterborne polyurethane. The difference from Example 1 is that the mass of enzymatically hydrolyzed lignin in this embodiment is 5.3 g. Calculations show that the bio-based content of the lignin-based waterborne polyurethane is 89.23%.

[0052] Example 4

[0053] This embodiment provides a method for preparing lignin-based waterborne polyurethane. The difference from Example 1 is that the mass of enzymatically hydrolyzed lignin in this embodiment is 7.2 g. Calculations show that the bio-based content of the lignin-based waterborne polyurethane is 89.49%.

[0054] Example 5

[0055] This embodiment provides a method for preparing lignin-based waterborne polyurethane. The difference from Example 1 is that the mass of enzymatically hydrolyzed lignin in this embodiment is 9.2 g. Calculations show that the bio-based content of the lignin-based waterborne polyurethane is 89.75%.

[0056] Example 6

[0057] This embodiment provides a method for preparing lignin-based waterborne polyurethane. The difference from Example 1 is that the mass of enzymatically hydrolyzed lignin in this embodiment is 11.4 g. Calculations show that the bio-based content of the lignin-based waterborne polyurethane is 90.02%.

[0058] Comparative Example 1

[0059] This comparative example provides a method for preparing waterborne polyurethane, comprising the following steps:

[0060] Add 50g of PO3G (number average molecular weight of 1000) and 18g of PDI to a 1000mL three-necked flask and react at 85℃ for 3h. Then add 3g of DMPA and 0.2g of organic bismuth catalyst 8108 to the reaction system and react at 75℃ for 5h. Finally, add 20g of acetone to the reaction system to adjust the viscosity of the system and obtain the prepolymer.

[0061] The prepolymer was cooled to below 50°C, neutralized with 2.3g of TEA for 15 minutes, then emulsified with 100g of deionized water for 1 hour. Acetone was removed under vacuum to obtain the final product. The calculated bio-based content of the waterborne polyurethane was 88.42%.

[0062] Application Example 1

[0063] This application example provides a printing coating comprising, by weight, the following components: 180 parts lignin-based waterborne polyurethane, 0.5 to 1.5 parts defoamer, 1 part pH adjuster, 1.6 parts nonionic emulsifier, 10 parts humectant, 2 to 4 parts thickener, and 2 parts crosslinking agent.

[0064] Application Example 2

[0065] This application example provides a printing coating comprising, by weight, the following components: 180 parts of lignin-based waterborne polyurethane prepared in Example 1, 1 part of silicone defoamer HY310, 1 part of pH adjuster diethanolamine, 1.6 parts of nonionic emulsifier AEO-9, 10 parts of humectant propylene glycol, 3 parts of thickener TT 935, and 2 parts of crosslinking agent aziridine.

[0066] Application Example 3

[0067] This application example provides a printing coating comprising, by weight, the following components: 180 parts of lignin-based waterborne polyurethane prepared in Example 2, 1 part of silicone defoamer HY310, 1 part of pH adjuster diethanolamine, 1.6 parts of nonionic emulsifier AEO-9, 10 parts of humectant propylene glycol, 3 parts of thickener TT 935, and 2 parts of crosslinking agent aziridine.

[0068] Application Example 4

[0069] This application example provides a printing coating comprising, by weight, the following components: 180 parts of lignin-based waterborne polyurethane prepared in Example 3, 1 part of silicone defoamer HY310, 1 part of pH adjuster diethanolamine, 1.6 parts of nonionic emulsifier AEO-9, 10 parts of humectant propylene glycol, 3 parts of thickener TT 935, and 2 parts of crosslinking agent aziridine.

[0070] Experimental Example 1

[0071] In this experiment, Fourier transform infrared spectroscopy was used to characterize the structure of the lignin-based waterborne polyurethanes of Examples 1-3, the waterborne polyurethane of Comparative Example 1, and the enzymatically hydrolyzed lignin (EL) used in the embodiments of this invention. The transmission medium was a 25mm × 4mm potassium bromide window, and the scanning range was 4000–500 cm⁻¹. -1 .

[0072] Figure 1 The infrared spectral results are shown for EL, the lignin-based waterborne polyurethane prepared in Examples 1-3, and the waterborne polyurethane prepared in Comparative Example 1. Figure 1 It can be seen that the products of Examples 1-3 and Comparative Example 1 are at 2270 cm⁻¹ -1 No characteristic absorption peak for isocyanate groups (-N=C=O) was observed at 1720 cm⁻¹, indicating that the isocyanate groups of PDI reacted completely with the hydroxyl groups of PO₃G. -1 Nearby (1713cm) -1 The absorption peak observed is attributed to the stretching vibration of C=O in the carbonyl group, a result of hydrogen bonding and dipole-dipole interactions. At 2930 cm⁻¹... -1 and 1369cm -1 The nearby spectral bands correspond to the CH antisymmetric stretching and bending vibrations of -CH3, respectively. At 2864 cm⁻¹ -1 The nearby absorption peaks are attributed to the symmetric stretching vibrations of the methylene (-CH2-) group. Compared to the infrared spectrum of the product of Comparative Example 1, the infrared spectra of the lignin-based waterborne polyurethanes of Examples 1-3 are at 3337 cm⁻¹. -1 The absorption band widens at 1713 cm⁻¹, and at 1713 cm⁻¹... -1 1037cm -1The increased intensity of the characteristic peak at 3340 cm⁻¹ indicates that EL has been successfully introduced into the waterborne polyurethane system. The above data demonstrate the successful synthesis of lignin-based waterborne polyurethane. Comparing the infrared spectra of the products from Examples 1-3, it was found that with increasing EL content, the absorption peak at 3340 cm⁻¹... -1 Nearby (3337cm) -1 The signal band gradually widens, and the intensity of the merged peaks increases with the increase of EL content.

[0073] Experimental Example 2

[0074] This experiment tested the tensile properties of the cured films of lignin-based waterborne polyurethane (EL-WPU) prepared in Examples 1-3 and the waterborne polyurethane prepared in Comparative Example 1.

[0075] Preparation of cured film: Weigh the lignin-based waterborne polyurethane prepared in Examples 1-3 and the waterborne polyurethane prepared in Comparative Example 1 respectively and place them in petri dishes. Dry them at room temperature for 8 hours and then place them in an electric thermostatic drying oven at 60°C for 12 hours.

[0076] The tensile properties of the cured film were tested using an electronic universal testing machine according to GB / T 1040.2-2006. The crosshead speed was set to 20 mm / min, and the sample size was 40.0 mm × 10.0 mm × 0.5 mm (length × width × thickness). The tensile property test results are shown in Table 1 and... Figure 2 As shown.

[0077] Table 1 Tensile strength test of lignin-based waterborne polyurethane cured film

[0078] sample Tensile strength (MPa) Elongation at break (%) Comparative Example 1 0.56 405.69 Example 1 2 816.87 Example 2 3.62 1412.89 Example 3 3.26 2230.22

[0079] As shown in Table 1, the tensile strength and elongation at break significantly increased when enzymatically hydrolyzed lignin (EL) was added to the waterborne polyurethane. This is likely because EL contains a large number of rigid benzene ring structures. When EL reacts with other raw materials, the EL-WPU molecular chains are tightly cross-linked, and EL, as a hard segment, enters the polymer molecular chains, forming a complex network structure, thereby increasing the mechanical properties of the cured film. Simultaneously, EL can act as a filler, filling the gaps between polymer molecular chains, thus increasing the physical bond density of the polymer. Furthermore, hydroxyl-rich EL and the waterborne polyurethane dispersion can form hydrogen bonds, enhancing their compatibility and establishing stable interfacial interactions. Therefore, adding EL can improve the mechanical properties of the waterborne polyurethane cured film. Comparing the tensile strength test results of the cured films in Examples 1-3, it was found that as the EL content in EL-WPU increased, the tensile strength of the cured film first increased and then decreased, while the elongation at break increased. The reason why the tensile strength of the lignin-based waterborne polyurethane cured film in Example 3 is lower than that in Example 2 is that excessive EL exists in the emulsion system as a filler, increasing the gaps between molecular chains. The reason why the elongation at break increases with the increase of EL content is that, on the one hand, the low molecular weight components in EL can act as plasticizers, reducing the interaction forces between polymer molecular chains in the matrix material, making the chain segments easier to slide, thereby improving the flexibility and elongation at break of the material; on the other hand, the addition of EL will affect the entanglement and movement tendency of EL-WPU molecular chains, making them more conducive to the plastic deformation of waterborne polyurethane, thereby increasing the elongation at break.

[0080] Experimental Example 3

[0081] This experiment tested the particle size of the lignin-based waterborne polyurethanes prepared in Examples 1-3 and the waterborne polyurethane prepared in Comparative Example 1.

[0082] The aqueous polyurethane emulsion was diluted 100 times with distilled water, and the particle size distribution and zeta potential of the dispersion were analyzed using a laser particle size analyzer.

[0083] Figure 3 This is a graph showing the particle size distribution results of the waterborne polyurethane emulsion. Figure 3 It can be seen that when enzymatically hydrolyzed lignin (EL) is added to the waterborne polyurethane emulsion, the particle size of the lignin-based waterborne polyurethane increases significantly. As the amount of EL added increases, the particle size of the lignin-based waterborne polyurethane gradually increases, because the EL structure contains a rigid benzene ring structure. Excessive EL addition can cause particle aggregation and entanglement, leading to an increase in emulsion particle size and particle size distribution width.

[0084] Table 2 Zeta potential of waterborne polyurethane emulsions

[0085] sample Zeta potential (mV) Comparative Example 1 30.2 Example 1 34.8 Example 2 35.6 Example 3 40.3

[0086] Table 2 shows the Zeta potential test results of different waterborne polyurethane emulsions. As can be seen from Table 2, the Zeta potentials of the lignin-based waterborne polyurethanes in Examples 1-3 are all greater than 30, indicating that the prepared lignin-based waterborne polyurethanes have good storage stability. Furthermore, the Zeta potentials of the lignin-based waterborne polyurethanes in Examples 1-3 are all greater than the Zeta potential of the waterborne polyurethane in Comparative Example 1, and the Zeta potential increases with increasing EL addition, indicating that the introduction of EL effectively improves the emulsion stability of the waterborne polyurethane.

[0087] Test Example 4

[0088] In this experiment, XRD tests were performed on the cured films of the lignin-based waterborne polyurethane (EL-WPU) prepared in Examples 1-3 and the waterborne polyurethane emulsion prepared in Comparative Example 1.

[0089] The crystallinity of the cured film was analyzed using a Bruker D2 advanced instrument (Bruker, Ettlingen). The tube voltage was maintained at 30 kV and the tube current at 10 mA. The scanning angle was 5°–60°, and the step size was 0.02°.

[0090] Figure 4 The XRD curve of the cured film of the waterborne polyurethane emulsion is shown below. Figure 4 It can be seen that within the range of 2θ from 5° to 60°, the XRD curves of the various waterborne polyurethane cured films show similar trends, with a diffuse diffraction peak appearing near 2θ = 20°. The peak intensity of the cured film of the waterborne polyurethane emulsion in Comparative Example 1 is the highest. As the amount of EL added increases, the peak intensity of the waterborne polyurethane cured film gradually decreases, indicating that the addition of EL reduces the crystallinity of the waterborne polyurethane cured film. This may be because EL and the waterborne polyurethane dispersion form hydrogen bonds, increasing the inhibitory effect of hard segments on the crystallization of soft segments. This suggests that the lignin-based waterborne polyurethane cured film of the present invention may have good flexibility.

[0091] Experimental Example 5

[0092] This experiment tested the thermal stability of the cured films of the lignin-based waterborne polyurethane (EL-WPU) prepared in Examples 1-3 and the waterborne polyurethane emulsion prepared in Comparative Example 1.

[0093] Thermal stability was tested using a thermal analyzer with a nitrogen flow rate of 20 mL / min, a heating rate of 10 °C / min, and a test temperature range of 25 °C to 800 °C.

[0094] The thermal decomposition curves of all waterborne polyurethane cured films are similar and can be divided into three stages. In the first stage, the mass loss of the film is between 40-250℃, possibly due to the evaporation of a small amount of residual moisture and residual catalysts and solvents. In the second stage, between 250-380℃, the pyrolysis of the hard segments of polyurethane includes the breaking of chemical bonds such as urethane esters. In the third stage, after 380-500℃, the mass loss of the film is due to the further thermal degradation of the soft segments, such as polyols and EL. Table 3 shows the thermal decomposition data of waterborne polyurethane emulsion cured films.

[0095] Table 3 Thermal decomposition data of waterborne polyurethane cured films

[0096] sample <![CDATA[T 10％ (℃)]]> <![CDATA[T 50％ (℃)]]> <![CDATA[T max (1st / 2nd)(℃)]]> Comparative Example 1 317.5 383.5 258.33 / 396.66 Example 1 325 400.66 216.4 / 416.83 Example 2 324.66 398.83 265 / 408.5 Example 3 326.66 400.33 261.5 / 411.83

[0097] As can be seen from Table 3, the maximum thermal decomposition temperature (T) of the EL-WPU cured film is... max The temperature first increased and then decreased with the increase of EL addition, indicating that adding an appropriate amount of EL to the polymer can effectively improve thermal stability and slow down the pyrolysis process. The maximum thermal decomposition temperature of Examples 2 and 3 was lower than that of Example 1. This may be because the benzene ring structure contained in EL crosslinks with the molecular chain, thereby forming a complex crosslinked structure in the polymer, which acts as a thermal barrier for the molecular chain, thus delaying the pyrolysis process of EL-WPU.

[0098] Figure 5 TGA curves of cured films from different waterborne polyurethane emulsions. Figure 6 The DTG curves of cured films from different waterborne polyurethane emulsions are obtained from... Figure 5 It can be seen that the residual carbon content increases with the increase of EL addition, from Figure 6 It can be seen that the thermal decomposition temperature of the EL-WPU curing film in Examples 1 to 3 is higher than that of the waterborne polyurethane emulsion curing film in Comparative Example 1, indicating that the addition of EL can effectively improve the heat resistance of the polymer.

[0099] Experimental Example 6

[0100] In this experimental example, the printing pigments obtained by mixing the components in Examples 2 to 4 were used to perform hand screen printing (3 cuts × 3 passes) on white cotton fabric and swimsuit fabric measuring 25cm × 25cm. The printed white cotton fabric and swimsuit fabric were then placed in a superheater at 135°C and dried for 2 minutes.

[0101] The elasticity of the overheated white cotton fabric and swimsuit fabric was tested by touch. The fabric was stretched from the high-elasticity direction, and the cracks on the surface were observed. The elasticity was divided into 5 levels based on the cracks. Level 1: Initially, it takes a lot of force to pull, but then it suddenly becomes easier. The cracks are wide and long and very obvious, and the original fabric color can be seen. Level 2: Initially, it takes a lot of force to pull, but then it suddenly becomes easier. The cracks are obvious but thinner than Level 1. There are obvious cracks. Level 3: Initially, it takes little force to pull, but then the pulling force gradually decreases. The cracks become shorter and fewer, and there are obvious gaps. Level 4: Initially, it takes little force to pull, but then the pulling force decreases less significantly. The cracks are not very obvious, and there are some gaps. Level 5: Initially, it takes little force to pull, but then the pulling force remains the same. There are no cracks, but there are a few dot-like gaps.

[0102] Figure 7 A photograph of a piece of white cotton fabric with printing pigments applied. Figure 8 The image shows a swimsuit fabric coated with printing pigments, and the color changes were observed. It was found that the fabric treated with the printing pigments exhibited vibrant colors and showed no significant fading after heat treatment, indicating that the printing pigments have good thermal stability and can be printed onto fabrics. Furthermore, sizing tests of the printing pigments revealed that the addition of EL improved the dispersibility and leveling properties of the printing paste. Figure 7 and Figure 8 It can also be seen that the printing paste has good fluidity and can evenly cover the fabric surface.

[0103] Upon touch, the fabric treated with the printing coating was found to be soft. Elasticity tests showed that the fabrics treated with the printing coatings in Examples 2-4 had an elasticity level of 5, while the fabrics treated with the printing coatings in Table 4 using the same method had an elasticity level of 2. This indicates that the fabrics treated with the printing coatings containing enzymatically hydrolyzed lignin have high resilience.

[0104] Table 4 Printing Coating Formula

[0105] raw material weight Waterborne polyurethane prepared in Comparative Example 1 180 copies HY310 1 copy diethanolamine 1 copy AEO-9 1.6 copies Propylene glycol 10 copies TT935 3 copies Azpropirine 2 copies

[0106] In summary, compared with the prior art, the beneficial effects of this technical solution are as follows:

[0107] (1) A lignin-based waterborne polyurethane with high bio-based content was prepared by introducing enzymatic hydrolysis of lignin into the waterborne polyurethane system. The preparation method is simple, green and environmentally friendly, and low in cost.

[0108] (2) Without the addition of EL, the system is difficult to form a film. After adding EL, the enzymatic hydrolysis of lignin can be used as a film-forming aid for waterborne polyurethane, solving the technical problem of difficult film formation when PO3G and PDI are used to prepare waterborne polyurethane. In addition, the addition of EL improves the pigment dispersion and leveling properties. It has natural pigments that can be used as pigments for printing coatings. The preparation of printing coatings does not require the addition of color paste, thereby alleviating the environmental pollution and wastewater discharge problems caused by the large-scale use of dyes in the printing and dyeing industry.

[0109] (3) The lignin-based waterborne polyurethane of the present invention has good tensile strength, flexibility and heat resistance after curing into a film. The printing coating made from lignin-based waterborne polyurethane is applied to the fabric and has bright color. The fabric does not fade significantly after overheating. It has high resilience and soft hand feel.

[0110] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A lignin-based waterborne polyurethane, characterized in that, The system is prepared from the following raw materials in parts by weight: 50-80 parts of bio-based polytrimethylene ether glycol, 15-30 parts of 1,5-pentanediisocyanate, 1-20 parts of enzymatically hydrolyzed lignin, 0.1-2 parts of catalyst, 3-8 parts of hydrophilic chain extender, and 2.3-6.1 parts of neutralizer, and a second organic solvent for dissolving the enzymatically hydrolyzed lignin, wherein the mass ratio of the second organic solvent to the enzymatically hydrolyzed lignin is (5-9):(0.5-4); the second organic solvent is selected from at least one of N,N-diethylformamide and γ-valerolactone.

2. The lignin-based waterborne polyurethane according to claim 1, characterized in that, The number-average molecular weight of the bio-based polytrimethylene ether glycol is 500-2700, and the number-average molecular weight of the enzymatically hydrolyzed lignin is 1000-6000.

3. The lignin-based waterborne polyurethane according to claim 1, characterized in that, The catalyst is selected from at least one of organic bismuth, bismuth neodecanoate, and bismuth isooctanoate; the hydrophilic chain extender is selected from at least one of 2,2-dimethylolpropionic acid and 2,2-dimethylolbutyric acid.

4. The lignin-based waterborne polyurethane according to claim 1, characterized in that, The neutralizing agent is selected from at least one of triethylamine, triethanolamine, sodium hydroxide, ammonia, and N-methyldiethanolamine.

5. The method for preparing lignin-based waterborne polyurethane according to any one of claims 1 to 4, characterized in that, The preparation method includes the following steps: S1. Bio-based polytrimethylene ether glycol and 1,5-pentanediisocyanate are reacted at 80~90℃, then the first mixture, hydrophilic chain extender and catalyst are added, and the reaction is carried out at 70~80℃. The first organic solvent is added to obtain lignin-based waterborne polyurethane prepolymer. S2. Cool the lignin-based waterborne polyurethane prepolymer to a temperature below 50°C, add a neutralizing agent to react, add water to carry out an emulsification reaction, and remove the first organic solvent under vacuum at 40~50°C to obtain the product. The first mixture is prepared by dissolving the enzymatically hydrolyzed lignin in a second organic solvent.

6. The preparation method according to claim 5, characterized in that, The first organic solvent is selected from at least one of acetone and butanone.

7. The preparation method according to claim 5, characterized in that, In step S2, the emulsification reaction is carried out by stirring at a speed of 800~900 r / min.

8. The application of lignin-based waterborne polyurethane according to any one of claims 1 to 4 in printing coatings.

9. The application according to claim 8, characterized in that, By weight, the printing coating comprises the following components: 170-190 parts lignin-based waterborne polyurethane, 0.5-1.5 parts defoamer, 0.5-1.5 parts pH adjuster, 1.4-1.8 parts nonionic emulsifier, 8-12 parts humectant, 2-4 parts thickener and 1.5-2.5 parts crosslinking agent.

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