A pyrrolidone-grafted lignin carboxylate, its preparation method and application

Abstract

The invention discloses a preparation method and application of pyrrolidone-grafted lignin carboxylate. By mass fraction, the formula is as follows: 20-40 parts of lignin, 5-20 parts of alkali, 10-20 parts of epoxy group-containing vinyl monomer, 5-20 parts of carboxyl group-containing vinyl monomer, 10-30 parts of N-vinylpyrrolidone, 0.2-1.5 parts of initiator, and 90-240 parts of deionized water. In this method, a precursor containing pyrrolidone and carboxylic acid groups is first prepared, and then in an alkaline medium, the epoxy group of the precursor undergoes a nucleophilic substitution reaction with the hydroxyl group in the lignin molecule to graft the precursor onto the lignin molecule, thereby obtaining pyrrolidone-grafted lignin carboxylate. The pyrrolidone-grafted lignin carboxylate prepared by the present invention contains 0.5-2.0 mmol / g of pyrrolidone groups and 1.8-3.0 mmol / g of carboxyl groups, and can be used as an efficient dispersant in the field of aqueous ceramic pigment slurries.

Description

Technical Field

[0001] The present invention belongs to the field of natural polymer materials, and particularly relates to a pyrrolidone-grafted lignin carboxylate, a preparation method thereof and an application thereof. Background Art

[0002] In the modern ceramic surface decoration industry, oil-based ceramic inks using esters, hydrocarbons, etc. as solvents are mainly used. Since the volatilization of organic solvents in such ceramic inks seriously harms the ecological environment and human health, it restricts the sustainable development of the ceramic surface decoration industry. Moreover, the ink has a large thixotropy, is thick and viscous, and has poor leveling property. After the ink is transferred to the printing substrate, it spreads, presenting a "flowering" phenomenon; the oil-based ceramic ink also has the disadvantages of high viscosity and easy clogging of the inkjet printing nozzles. Therefore, considering various reasons such as the environment, cost, and sales, the transformation of ceramic inks from an organic-based system to an aqueous-based system is a major trend in future development. Therefore, it is particularly important to develop water-based ceramic inks, including the development of aqueous dispersants with functions of assisting grinding and dispersing particles.

[0003] In recent years, there have been many reports on the research of aqueous dispersants for ceramic pigments. Patent CN107686844A, an aqueous polymer ceramic pigment grinding and dispersing agent and a preparation method and application thereof, discloses a preparation method of a dispersant effective for ceramic pigments (such as praseodymium yellow). This method copolymerizes acrylic acid, itaconic acid and monomer molecules (glycerol monomethacrylate or D-glucosamide ethyl methacrylate) to obtain a ceramic pigment dispersant. Research shows that this dispersant has a good dispersion stability effect on praseodymium yellow pigment. After grinding, the particle size of praseodymium yellow pigment is between 600 and 800 nm, and the sedimentation rate remains at about 10% after fifteen days. Patent CN112457717A, an aqueous ceramic ink for inkjet printing and a preparation method and application thereof, prepares a ceramic pigment dispersant polymerized from methyl methacrylate, methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and glycerol monomethacrylate as monomers. After adding a dispersant, a wetting agent, an anti-settling agent, a resin, etc. to the pigment and then performing ultrafine grinding on the ceramic pigment, the pigment D 90The range is 854 - 954 nm. This aqueous ceramic pigment meets the requirements of inkjet printing, can decorate the surface of ceramic plates, and has a good color display effect after decoration. North, Shannon M., Armes, Steven P.. Aqueous one-pot synthesis of well-defined zwitterionic diblock copolymers by RAFT polymerization: an efficient and environmentally-friendly route to a useful dispersant for aqueous pigments[J]. Green chemistry, 2021, 23(3): 1248 - 1258. A diblock zwitterionic polymer PMAA-PDMA was synthesized by RAFT one-pot method using methacrylic acid (MAA) and 2-(dimethylamino)ethyl methacrylate (DMA). It was proven to be an effective dispersant for iron oxide yellow pigments. After ultrafine grinding, the pigment particle size was below 400 nm, meeting the requirements of inkjet printing.

[0004] The dispersants used in the above aqueous ceramic pigment slurries also have the following problems: 1. The grinding efficiency is relatively low, and it is difficult for D 90 to be less than 200 nm after grinding; 2. The stability is poor, the particle size is easy to grow, and stratification and hard precipitation are likely to occur during storage at room temperature and hot storage, affecting the use; 3. There is no suitable high-efficiency dispersant, resulting in the current ceramic pigment slurry industry still being an oily system, and there is an urgent need for an aqueous ceramic pigment slurry system that can be industrially produced.

[0005] The application of lignin as a dispersant has a long history. Patent CN104745009A, a pigment dispersant combination containing lignin and its preparation method, discloses a preparation method of a pigment dispersant containing lignin. In this method, lignin is first reacted with 2-bromo-isobutyryl bromide and alkyl polyethylene glycol ether acrylate to obtain a dispersant, and then polyethylene glycol monoalkyl ether is reacted with 2-bromo-isobutyryl bromide and sodium azide to obtain a reaction solution, which is then reacted with alkynyl-containing lignin to obtain another dispersant. The two dispersants are compounded and a small amount of wetting agent, defoaming agent, antibacterial agent, etc. are added for the grinding of ceramic pigments, effectively reducing the pigment particle size, and the pigment shows good dispersion stability and coloring power. Patent CN111607036A, a lignin-modified polycarboxylate dispersant and its preparation method and application, first reacts polyoxyethylene propylene ether and epichlorohydrin with lignin to obtain a lignin-based polyether monomer, and then reacts the lignin-based polyether monomer with an unsaturated carboxylic acid or its derivative or a lipophilic comonomer to obtain a lignin-modified polycarboxylate dispersant. Applying it to the pesticide field enhances the binding force between the adjuvant and the pesticide and improves the stability of the preparation.

[0006] The above shows that lignin has been well applied in the nano-dispersion system. And under the background of the increasingly depleted petroleum resources, biomass resources with rich reserves have also attracted the attention of all parties due to their renewable and biodegradable characteristics. However, untreated lignin cannot be directly used as a water-based dispersant, so it is necessary to conduct directional modification on lignin to improve its adsorption and hydrophilicity. The addition of hydrophilic groups makes lignin easily soluble in water, providing the possibility for the preparation of water-based dispersants. The adsorption group, as an anchoring group, adsorbs on the surface of the particles to be dispersed, and prevents the agglomeration between particles through steric hindrance, electrostatic repulsion and other effects.

[0007] The present invention develops a new functional lignin dispersant and its synthesis process. A precursor is obtained by copolymerizing an epoxy-group-containing vinyl monomer, a carboxyl-group-containing vinyl monomer and an N-vinylpyrrolidone monomer, and then the precursor is reacted with a lignin solution under high-temperature alkaline conditions to obtain pyrrolidone-grafted lignin carboxylate. After being applied to the grinding of inorganic ceramic pigments, the particle size of the color paste is reduced to below 200 nm, and there is no obvious stratification and precipitation phenomenon in the color paste after one week of heat storage, and the color paste has good heat storage stability. Summary of the Invention

[0008] The object of the present invention is to overcome the disadvantages and deficiencies of the prior art, and to provide a pyrrolidone-grafted lignin carboxylate, which has good grinding aid effect and dispersion stability on ceramic pigment particles, and enables the prepared aqueous ceramic ink to be applied to the inkjet printing and ceramic surface decoration industries. The present invention improves the hydrophilicity of lignin and its adsorption performance on inorganic pigment particles by modifying lignin, so as to make it an efficient dispersant for preparing aqueous ceramic pigment slurries. Specifically, an epoxy group-containing vinyl monomer, a carboxyl group-containing vinyl monomer and an N-vinylpyrrolidone monomer are first copolymerized to obtain a precursor, and then the precursor undergoes a nucleophilic substitution reaction with the hydroxyl group in the lignin molecule under alkaline conditions to obtain the pyrrolidone-grafted lignin carboxylate.

[0009] Another object of the present invention is to provide a preparation method of the above pyrrolidone-grafted lignin carboxylate.

[0010] Still another object of the present invention is to provide the application of the above pyrrolidone-grafted lignin carboxylate.

[0011] A preparation method of a pyrrolidone-grafted lignin carboxylate includes the following steps:

[0012] (1) By mass, 10-20 parts of an epoxy group-containing vinyl monomer, 5-20 parts of a carboxyl group-containing vinyl monomer, 10-30 parts of N-vinylpyrrolidone and 30-120 parts of water are mixed evenly to obtain a solution, and then 0.2-1.5 parts of an initiator are added dropwise to the solution, and a precursor is obtained by reaction;

[0013] (2) By mass, 20-40 parts of lignin and 60-120 parts of water are mixed evenly, heated and 5-20 parts of an alkali are added and stirred for reaction to obtain an aqueous lignin solution, and then the precursor obtained in step (1) is added and mixed evenly, and after reaction, it is cooled to obtain the pyrrolidone-grafted lignin carboxylate.

[0014] The epoxy group-containing vinyl monomer in step (1) is at least one of glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, and 1,2-epoxy-5-ethylene.

[0015] The carboxyl group-containing vinyl monomer in step (1) is at least one of itaconic acid, acrylic acid, maleic acid, and methacrylic acid.

[0016] The initiator in step (1) is at least one of ammonium persulfate, potassium persulfate, azobisisobutyronitrile, azobisisoheptonitrile, and dimethyl azobisisobutyrate.

[0017] The dropwise addition in step (1) is completed within 30-60 minutes; preferably 30 minutes.

[0018] The dropping in step (1) is carried out under a protective atmosphere; preferably, it is carried out under the protection of a nitrogen atmosphere.

[0019] The conditions for the reaction in step (1) are to react at 50-80 °C for 0.5-2 hours; preferably, react at 60 °C for 2 h.

[0020] The lignin in step (2) is at least one of alkali lignin, enzymatically hydrolyzed lignin, high boiling alcohol lignin, and lignin sulfonate.

[0021] The alkali in step (2) is at least one of sodium hydroxide and potassium hydroxide.

[0022] The conditions for heating in step (2) are to heat to 70-90 °C.

[0023] The conditions for the reaction in step (2) are to react at 70-90 °C for 2-5 hours.

[0024] Preferably, the preparation method further includes the following steps:

[0025] (3) Add anhydrous ethanol to the product solution and stir evenly, then filter to remove the precipitated liquid; then continue to add deionized water to dissolve the solid precipitate, add anhydrous ethanol again and stir evenly, and filter to remove the precipitated liquid. Operate like this 3 times, and the purified pyrrolidone-grafted lignin carboxylate product can be obtained.

[0026] A pyrrolidone-grafted lignin carboxylate is prepared by the above method.

[0027] In the pyrrolidone-grafted lignin carboxylate, the content of pyrrolidone groups is 0.5-2.0 mmol / g.

[0028] Application of the above pyrrolidone-grafted lignin carboxylate in the preparation of a dispersant.

[0029] Application of the above pyrrolidone-grafted lignin carboxylate in the field of preparing an aqueous ceramic pigment color paste as a dispersant.

[0030] The present invention has the following advantages and effects compared with the prior art:

[0031] 1. At present, an oily system is adopted in the field of ceramic pigment color pastes, which has the disadvantages of easy sedimentation, easy color variation, environmental pollution after burning, and high cost; the aqueous ceramic pigment color paste system is generally unstable, and existing dispersants cannot meet the performance requirements of aqueous ceramic pigment color pastes. The present invention synthesizes a functional lignin dispersant, introducing pyrrolidone groups with complexing and adsorption functions into the lignin molecule, greatly improving the adsorption strength on the surface of inorganic pigments. It realizes the production of aqueous nano-pigment color pastes by a grinding process with inorganic pigments as raw materials in an aqueous medium.

[0032] 2. The pyrrolidone-grafted lignin carboxylate of the present invention has a pyrrolidone as an adsorption group, which can undergo a high-intensity complexation adsorption with the surface of inorganic pigment particles. Thus, the molecules of the dispersant are anchored on the surface of the pigment particles and do not desorb during the collision of high-frequency Brownian motion; the anionic carboxyl group of the dispersant brings negative charges to the surface of the pigment particles, so that the particles do not agglomerate and settle during the collision. In addition, the three-dimensional structure of lignin has a large steric hindrance to prevent the agglomeration of pigment particles.

[0033] 3. The pyrrolidone-grafted lignin carboxylate of the present invention can be used as a dispersant to prepare nano-pigment color pastes through a grinding process in an aqueous medium. The prepared nano-pigment color pastes have good grinding efficiency and thermal storage stability, and the minimum D 90 particle size is lower than 150 nm, and after thermal storage at 60 °C for 7 days, the D 90 particle size is lower than 200 nm, without water separation and precipitation, and the comprehensive performance meets the performance requirements of nano-ceramic pigment color pastes.

[0034] 4. The present invention uses lignin as the main raw material, and the prepared dispersant has environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the infrared spectrum diagram of the pyrrolidone-grafted lignin carboxylate D1 obtained in Example 1.

[0036] Figure 2 It is the zeta potential of the pyrrolidone-grafted lignin carboxylates D1, D2, and D3 obtained in Example 1, Example 2, and Example 3.

[0037] Figure 3 It is the scanning electron microscope diagram of the color paste obtained after grinding without adding a dispersant and adding the color paste obtained after grinding in Example 1.

[0038] Figure 4 It is the particle size distribution of the color paste obtained after grinding without adding a dispersant and adding the color paste obtained after grinding in Example 1, Example 2, and Example 3.

[0039] Figure 5 It is the viscosity of the color paste obtained after grinding without adding a dispersant and adding the color paste obtained after grinding in Example 1, Example 2, and Example 3.

[0040] Figure 6 It is the thermal storage stability of the color paste obtained after grinding by adding Example 1, Example 2, and Example 3.

[0041] Figure 7 It is the zeta potential of the aqueous solution of Example 1, the color paste without adding a dispersant, and the color paste obtained after grinding by adding Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0042] The present invention will be further described in detail below in conjunction with embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0043] If the specific test conditions are not specified in the following implementation examples, they are usually in accordance with conventional test conditions or the test conditions recommended by the reagent company. The materials, reagents, etc. used, unless otherwise specified, are all reagents and materials obtained from commercial channels.

[0044] Example 1

[0045] (1) Add 10.0 g of allyl glycidyl ether, 13.0 g of itaconic acid, 11.0 g of N-vinylpyrrolidone and 51.0 g of deionized water to a four-necked flask, stir evenly to obtain a mixed solution, and dropwise add 0.3 g of initiator ammonium persulfate to the solution under nitrogen protection. The addition is completed in 30 min. After the addition of the initiator is completed, the reaction is carried out at a constant temperature of 60 °C for 2 hours to obtain a precursor.

[0046] (2) Add 25.0 g of alkali lignin and 60.0 g of deionized water to a four-necked flask, then heat up to 70 °C, add 10.0 g of sodium hydroxide, stir and dissolve evenly to obtain an aqueous lignin solution. Then add the precursor solution prepared in step (1), stir and mix evenly, and react at 90 °C for 2.5 hours to obtain pyrrolidone-grafted lignin carboxylate. Add anhydrous ethanol to the product solution, stir evenly, and filter to remove the precipitated liquid; then continue to add deionized water to dissolve the solid precipitate, add anhydrous ethanol again, stir evenly, and filter to remove the precipitated liquid. Operate like this 3 times to obtain a purified pyrrolidone-grafted lignin carboxylate product.

[0047] The pyrrolidone-grafted lignin carboxylate obtained in Example 1 of this example is named D1. The content of pyrrolidone groups in D1 is 0.67 mmol / g, and the carboxyl content is 2.42 mmol / g.

[0048] Example 2

[0049] (1) Add 14.0 g of glycidyl methacrylate, 20.0 g of itaconic acid, 19.0 g of N-vinylpyrrolidone and 90.0 g of deionized water to a four-necked flask, stir evenly to obtain a mixed solution, and dropwise add 0.4 g of initiator ammonium persulfate to the solution under nitrogen protection. The addition is completed in 30 min. After the addition of the initiator is completed, the reaction is carried out at a constant temperature of 70 °C for 2 hours to obtain a precursor.

[0050] (2) Add 33.0 g of alkali lignin and 81.0 g of deionized water into a four-necked flask, then heat up to 80 °C, add 14.0 g of sodium hydroxide, stir and dissolve evenly to obtain an aqueous lignin solution. Then add the precursor solution prepared in step (1), stir and mix evenly, and react at 70 °C for 5 hours to obtain pyrrolidone-grafted lignin carboxylate. Add anhydrous ethanol to the product solution and stir evenly, filter to remove the precipitated liquid; then continue to add deionized water to dissolve the solid precipitate, add anhydrous ethanol again and stir evenly, filter to remove the precipitated liquid. Operate like this 3 times to obtain the purified pyrrolidone-grafted lignin carboxylate product.

[0051] The pyrrolidone-grafted lignin carboxylate obtained in Example 2 of this example is named D2. The content of pyrrolidone groups in D2 is 1.23 mmol / g, and the carboxyl content is 2.93 mmol / g.

[0052] Example 3

[0053] (1) Add 16.0 g of allyl glycidyl ether, 5.0 g of itaconic acid, 26.0 g of N-vinyl pyrrolidone and 72.0 g of deionized water into a four-necked flask, stir evenly to obtain a mixed solution, and dropwise add 0.5 g of initiator azobisisobutyronitrile into the solution under nitrogen protection. The dropping is completed in 40 min. After the initiator is dropped, carry out a constant-temperature reaction at 80 °C for 1 hour to prepare a precursor.

[0054] (2) Add 28.0 g of alkali lignin and 90.0 g of deionized water into a four-necked flask, then heat up to 90 °C, add 7.0 g of sodium hydroxide, stir and dissolve evenly to obtain an aqueous lignin solution. Then add the precursor prepared in step (1), stir and mix evenly, and react at 85 °C for 3 hours. To obtain pyrrolidone-grafted lignin carboxylate. Add anhydrous ethanol to the product solution and stir evenly, filter to remove the precipitated liquid; then continue to add deionized water to dissolve the solid precipitate, add anhydrous ethanol again and stir evenly, filter to remove the precipitated liquid. Operate like this 3 times to obtain the purified pyrrolidone-grafted lignin carboxylate product.

[0055] The pyrrolidone-grafted lignin carboxylate obtained in Example 3 of this example is named D3. The content of pyrrolidone groups in D3 is 1.87 mmol / g, and the carboxyl content is 1.95 mmol / g.

[0056] Example 4

[0057] (1) Add 10.0 g of allyl glycidyl ether, 8.6 g of methacrylic acid, 10.0 g of N-vinyl pyrrolidone, and 45.0 g of deionized water to a four-necked flask, stir evenly to obtain a mixed solution, and dropwise add 0.2 g of initiator ammonium persulfate to the mixed solution under nitrogen protection. The addition is completed in 30 min. After the addition of the initiator is completed, carry out a constant-temperature reaction at 50 °C for 0.5 h to obtain a precursor.

[0058] (2) Add 30.0 g of alkali lignin and 90.0 g of deionized water to a four-necked flask, then heat up to 90 °C, add 14.0 g of potassium hydroxide, stir and dissolve evenly to obtain an aqueous lignin solution. Then add the precursor prepared in step (1), stir and mix evenly, and react at 90 °C for 3.5 h. That is, pyrrolidone-grafted lignin carboxylate is obtained. Add anhydrous ethanol to the product solution, stir evenly, and filter to remove the precipitate; then continue to add deionized water to dissolve the solid precipitate, add anhydrous ethanol again, stir evenly, and filter to remove the precipitate. Operate like this 3 times to obtain a purified pyrrolidone-grafted lignin carboxylate product.

[0059] In this Example 4, the content of pyrrolidone groups in the pyrrolidone-grafted lignin carboxylate is 0.5 mmol / g, and the carboxyl content is 2.03 mmol / g.

[0060] Example 5

[0061] (1) Add 17.5 g of allyl glycidyl ether, 15.0 g of methacrylic acid, 30.0 g of N-vinyl pyrrolidone, and 60.0 g of deionized water to a four-necked flask, stir evenly to obtain a mixed solution, and dropwise add 0.5 g of initiator dimethyl 2,2'-azobis(2-methylpropionate) to the mixed solution under nitrogen protection. The addition is completed in 30 min. After the addition of the initiator is completed, carry out a constant-temperature reaction at 70 °C for 0.8 h to obtain a precursor.

[0062] (2) Add 40.0 g of enzymatically hydrolyzed lignin and 120.0 g of deionized water to a four-necked flask, then heat up to 80 °C, add 15.0 g of potassium hydroxide, stir and dissolve evenly to obtain an aqueous lignin solution. Then add the precursor solution prepared in step (1), stir and mix evenly, and react at 80 °C for 2 h. That is, pyrrolidone-grafted lignin carboxylate is obtained. Add anhydrous ethanol to the product solution, stir evenly, and filter to remove the precipitate; then continue to add deionized water to dissolve the solid precipitate, add anhydrous ethanol again, stir evenly, and filter to remove the precipitate. Operate like this 3 times to obtain a purified pyrrolidone-grafted lignin carboxylate product.

[0063] In this example, the content of pyrrolidone groups in the pyrrolidone-grafted lignin carboxylate is 2.00 mmol / g, and the carboxyl content is 2.17 mmol / g.

[0064] Example 6

[0065] (1) 11.5 g of glycidyl methacrylate, 13.0 g of acrylic acid, 14.0 g of N-vinylpyrrolidone and 51.2 g of deionized water were added to a four-necked flask, stirred evenly to obtain a mixed solution, and 0.4 g of initiator azobisisobutyronitrile was added dropwise to the mixed solution under nitrogen protection. The addition was completed in 30 min. After the addition of the initiator was completed, the reaction was carried out at a constant temperature of 80 °C for 0.5 h to obtain a precursor.

[0066] (2) 40.0 g of alkali lignin and 120.0 g of deionized water were added to a four-necked flask, then the temperature was raised to 70 °C, 11.0 g of potassium hydroxide was added, and the mixture was stirred and dissolved evenly to obtain an aqueous lignin solution. Then the precursor solution prepared in step (1) was added, stirred and mixed evenly, and the reaction was carried out at 90 °C for 5 h. Thus, pyrrolidone-grafted lignin carboxylate was obtained. Anhydrous ethanol was added to the product solution and stirred evenly, and the precipitated liquid was filtered off; then deionized water was added to the solid precipitate to dissolve it, and anhydrous ethanol was added again and stirred evenly, and the precipitated liquid was filtered off. This operation was carried out 3 times to obtain a purified pyrrolidone-grafted lignin carboxylate product.

[0067] In this example, the content of pyrrolidone groups in the pyrrolidone-grafted lignin carboxylate was 0.76 mmol / g, and the carboxyl content was 1.95 mmol / g.

[0068] Example 7

[0069] (1) 11.0 g of glycidyl acrylate, 11.6 g of maleic acid, 15.0 g of N-vinylpyrrolidone and 73.7 g of deionized water were added to a four-necked flask, stirred evenly to obtain a mixed solution, and 1.0 g of initiator potassium persulfate was added dropwise to the mixed solution under nitrogen protection. The addition was completed in 60 min. After the addition of the initiator was completed, the reaction was carried out at a constant temperature of 50 °C for 2 h to obtain a precursor.

[0070] (2) 20.0 g of lignosulfonate and 60.0 g of deionized water were added to a four-necked flask, then the temperature was raised to 70 °C, 10.0 g of sodium hydroxide was added, and the mixture was stirred and dissolved evenly to obtain an aqueous lignin solution. The precursor solution prepared in step (1) was added, stirred and mixed evenly, and the reaction was carried out at 70 °C for 2 h to obtain pyrrolidone-grafted lignin carboxylate. Anhydrous ethanol was added to the product solution and stirred evenly, and the precipitated liquid was filtered off; then deionized water was added to the solid precipitate to dissolve it, and anhydrous ethanol was added again and stirred evenly, and the precipitated liquid was filtered off. This operation was carried out 3 times to obtain a purified pyrrolidone-grafted lignin carboxylate product.

[0071] In this example, the content of pyrrolidone groups in the pyrrolidone-grafted lignin carboxylate was 0.87 mmol / g, and the carboxyl content was 1.80 mmol / g.

[0072] Example 8

[0073] (1) Add 20.0 g of allyl glycidyl ether, 5.0 g of acrylic acid, 26.5 g of N-vinylpyrrolidone, and 120.0 g of deionized water to a four-necked flask, stir evenly to obtain a mixed solution, and dropwise add 1.5 g of initiator ammonium persulfate to the mixed solution under nitrogen protection. The dropping is completed in 60 min. After the initiator is added dropwise, carry out a constant-temperature reaction at 80 °C for 1 hour to obtain a precursor.

[0074] (2) Add 30.0 g of sodium lignosulfonate and 90.0 g of deionized water to a four-necked flask, then heat up to 70 °C, add 5.0 g of sodium hydroxide, stir and dissolve evenly to obtain an aqueous lignin solution. Then add the precursor solution prepared in step (1), stir and mix evenly, and react at 70 °C for 3 hours to obtain pyrrolidone-grafted lignin carboxylate. Add anhydrous ethanol to the product solution, stir evenly, and filter to remove the precipitated liquid; then continue to dissolve the solid precipitate in deionized water, add anhydrous ethanol again, stir evenly, and filter to remove the precipitated liquid. Perform such operations 3 times to obtain a purified pyrrolidone-grafted lignin carboxylate product.

[0075] In this example, the content of pyrrolidone groups in pyrrolidone-grafted lignin carboxylate is 1.75 mmol / g, and the carboxyl content is 2.06 mmol / g.

[0076] Example 9

[0077] (1) Add 17.0 g of 1,2-epoxy-5-ethylene, 8.6 g of methacrylic acid, 30.0 g of N-vinylpyrrolidone, and 75.0 g of deionized water to a four-necked flask, stir evenly to obtain a mixed solution, and dropwise add 0.5 g of initiator ammonium persulfate to the mixed solution under nitrogen protection. The dropping is completed in 30 min. After the initiator is added dropwise, carry out a constant-temperature reaction at 50 °C for 2 hours to obtain a precursor.

[0078] (2) Add 40.0 g of alkali lignin and 120.0 g of deionized water to a four-necked flask, then heat up to 90 °C, add 7.0 g of potassium hydroxide, stir and dissolve evenly to obtain an aqueous lignin solution. Then add the precursor solution prepared in step (1), stir and mix evenly, and react at 90 °C for 2.5 hours to obtain pyrrolidone-grafted lignin carboxylate. Add anhydrous ethanol to the product solution, stir evenly, and filter to remove the precipitated liquid; then continue to dissolve the solid precipitate in deionized water, add anhydrous ethanol again, stir evenly, and filter to remove the precipitated liquid. Perform such operations 3 times to obtain a purified pyrrolidone-grafted lignin carboxylate product.

[0079] In this example, the content of pyrrolidone groups in pyrrolidone-grafted lignin carboxylate is 1.97 mmol / g, and the carboxyl content is 1.80 mmol / g.

[0080] Example 10

[0081] (1) Add 15.0 g of 1,2-epoxy-5-ethylene, 20.0 g of methacrylic acid, 10.0 g of N-vinylpyrrolidone, and 75.0 g of deionized water into a four-necked flask, stir evenly to obtain a mixed solution, and dropwise add 1.5 g of initiator ammonium persulfate to the mixed solution under nitrogen protection. The addition is completed in 60 min. After the addition of the initiator is completed, the reaction is carried out at a constant temperature of 80 °C for 2 hours to obtain a precursor.

[0082] (2) Add 30.0 g of high-boiling alcohol lignin and 90.0 g of deionized water into a four-necked flask, then heat up to 80 °C, add 11.5 g of potassium hydroxide, stir and dissolve evenly to obtain an aqueous lignin solution. Then add the precursor solution prepared in step (1), stir and mix evenly, and react at 80 °C for 4 hours to obtain pyrrolidone-grafted lignin carboxylate. Add anhydrous ethanol to the product solution, stir evenly, and filter to remove the precipitate; then continue to add deionized water to dissolve the solid precipitate, add anhydrous ethanol again, stir evenly, and filter to remove the precipitate. Operate like this 3 times to obtain the purified pyrrolidone-grafted lignin carboxylate product.

[0083] In this example, the content of pyrrolidone groups in pyrrolidone-grafted lignin carboxylate is 0.68 mmol / g, and the carboxyl content is 2.19 mmol / g.

[0084] Example 11

[0085] (1) Add 18.5 g of allyl glycidyl ether, 19.0 g of itaconic acid, 15.0 g of N-vinylpyrrolidone, and 30.0 g of deionized water into a four-necked flask, stir evenly to obtain a mixed solution, and dropwise add 1.0 g of initiator dimethyl 2,2'-azobis(2-methylpropionate) to the mixed solution under nitrogen protection. The addition is completed in 60 min. After the addition of the initiator is completed, the reaction is carried out at a constant temperature of 60 °C for 1.5 hours to obtain a precursor.

[0086] (2) Add 30.0 g of high-boiling alcohol lignin and 60.0 g of deionized water into a four-necked flask, then heat up to 80 °C, add 20.0 g of potassium hydroxide, stir and dissolve evenly to obtain an aqueous lignin solution. Then add the precursor solution prepared in step (1), stir and mix evenly, and react at 80 °C for 2 hours to obtain pyrrolidone-grafted lignin carboxylate. Add anhydrous ethanol to the product solution, stir evenly, and filter to remove the precipitate; then continue to dissolve the solid precipitate in deionized water, add anhydrous ethanol again, stir evenly, and filter to remove the precipitate. Operate like this 3 times to obtain the purified pyrrolidone-grafted lignin carboxylate product.

[0087] In this example, the content of pyrrolidone groups in pyrrolidone-grafted lignin carboxylate is 0.87 mmol / g, and the carboxyl content is 3.00 mmol / g.

[0088] Example 12

[0089] (1) Add 12.0 g of allyl glycidyl ether, 20.0 g of maleic acid, 22.0 g of N-vinyl pyrrolidone and 120.0 g of deionized water into a four-necked flask, stir evenly to obtain a mixed solution, and dropwise add 0.6 g of initiator azodiisooctanenitrile to the mixed solution under nitrogen protection, and complete the dropping in 30 min. After the initiator is added dropwise, carry out a constant-temperature reaction at 80 °C for 0.5 hour to obtain a precursor.

[0090] (2) Add 40.0 g of enzymatically hydrolyzed lignin and 120.0 g of deionized water into a four-necked flask, then heat up to 70 °C, add 17.0 g of sodium hydroxide, stir and dissolve evenly to obtain an aqueous lignin solution. Then add the precursor solution prepared in step (1), stir and mix evenly, and react at 70 °C for 5 hours to obtain pyrrolidone-grafted lignin carboxylate. Add anhydrous ethanol to the product solution, stir evenly, and filter to remove the precipitate; then continue to dissolve the solid precipitate in deionized water, add anhydrous ethanol again, stir evenly, and filter to remove the precipitate. Operate like this 3 times to obtain the purified pyrrolidone-grafted lignin carboxylate product.

[0091] In this example, the content of pyrrolidone groups in pyrrolidone-grafted lignin carboxylate is 1.54 mmol / g, and the carboxyl content is 2.42 mmol / g.

[0092] Perform infrared spectrum analysis on the purified product D1 obtained from the reaction in Example 1, and use alkali lignin (AL) as a control at the same time. The results are as Figure 1 shown. It can be seen from Figure 1 that the peak at 3431 cm -1 is attributed to the stretching vibration of O-H and N-H, and the infrared at 1572 cm -1 , 1408 cm -1The characteristic peak attributed to the carboxylate group has an obvious peak shape and masks the characteristic peak of N-vinylpyrrolidone at around 1670 cm -1 proving the existence of the carboxylate group; the stretching vibration of the ether bond in allyl glycidyl ether is at 1123 cm -1 ; the stretching vibration of the aromatic ether is at 1275 cm -1 , proving that the carboxyl group and pyrrolidone group are successfully grafted onto the lignin molecule

[0093] Taking alkali lignin (AL) as a control, the nitrogen (N) element content of D1, D2, and D3 was determined by elemental analysis, and the content of pyrrolidone groups in D1, D2, and D3 was calculated based on the N content; at the same time, the carboxyl group content of D1, D2, and D3 was determined by automatic potentiometric titration, and the results are shown in Table 1.

[0094] Table 1 Titration results

[0095]

[0096] From the data in Table 1, the N element content in AL is 0.10%; through the calculation of the N element content, the contents of pyrrolidone groups in D1, D2, and D3 are 0.67, 1.23, and 1.87 mmol / g, respectively.

[0097] The zeta potential of the prepared D1, D2, and D3 was tested, and the results are as Figure 2 shown. It can be Figure 2 seen that the absolute value of the zeta potential is D2 > D1 > D3, which is consistent with the order of their carboxyl group content from more to less (the carboxyl group contents in D1, D2, and D3 are 2.42, 2.93, and 1.95 mmol / g, respectively). And between pH = 5 - 10, the absolute value of the zeta potential of D1, D2, and D3 is greater than 30 mv (30 mv is the minimum absolute value of the zeta potential for colloidal particles to stably exist in an aqueous medium), indicating that the colloidal particles of D1, D2, and D3 can stably exist in an aqueous medium.

[0098] Four commonly used ceramic pigments, cobalt blue (original particle size of 4.0 μm), cadmium red (original particle size of 1.8 μm), titanium chromium brown (original particle size of 0.9 μm), and copper chromium black (original particle size of 1.9 μm), were selected as the research objects. Using D1, D2, and D3 as dispersants, nano-ceramic pigment slurries with a solid content of 20 wt.% were prepared by water-based grinding method. The addition amount of the dispersant was 10 wt.% of the slurry. And lignosulfonate, a commonly used dispersant in the field, was used as the dispersant to prepare the slurry under the same conditions as the control group. A planetary ball mill (Changsha Miqi Instrument Equipment Co., Ltd., YXQM-2L) was used to grind the nano-slurry at a speed of 400 rpm for 4 h; zirconia beads with a diameter of 0.3 mm were used as the grinding material, and the mass ratio of the beads to the slurry was 3:1. The particle sizes of the prepared nano-slurries are shown in Table 2.

[0099] Table 2 shows the D of the 4 slurries ground with dispersants D1, D2, D3 and lignosulfonate 90 Particle size.

[0100] Table 2 Test results of particle size after grinding

[0101]

[0102]

[0103] As can be seen from Table 2, after grinding with dispersants D1, D2, and D3 for 4 hours, the D of the four pigment particles 90 Particle size decreased to less than 150 nm, far better than the grinding effect of lignosulfonate. It shows that the synthesized dispersant has good grinding aid effect, can greatly improve the grinding efficiency and the dispersant has good versatility for common inorganic ceramic pigments.

[0104] Taking cobalt blue pigment as an example, the particle size and distribution of the original cobalt blue particles and the cobalt blue particles after adding D1 were compared by scanning electron microscopy, as Figure 3 shown. From Figure 3 it can be seen that the cobalt blue particles without dispersant exist in the form of large aggregates in the medium. The particle size of the pigment particles after adding the dispersant and grinding is significantly reduced, and they can maintain a uniformly dispersed state in the medium.

[0105] Taking cobalt blue pigment as an example, the particle size distribution tests were carried out on the cobalt blue slurry ground without dispersant and the slurries ground with D1, D2, and D3 dispersants used. The results are as Figure 4 shown. From Figure 4 it can be seen that after adding the dispersant, the D 90 Particle size of the pigment particles is significantly reduced, and the particle size distribution of the slurry becomes narrower and the particle size distribution is more uniform, which meets the requirements of the particle size distribution of ceramic inks for inkjet printing.

[0106] The rheological properties of cobalt blue pastes without dispersant and those prepared with dispersants D1, D2, and D3 were tested, and the results are as follows. Figure 5 As can be seen, Figure 5 adding dispersants can effectively reduce the apparent viscosity of cobalt blue pastes, and the pastes change from having obvious pseudoplastic characteristics to being close to those of Newtonian fluids.

[0107] The thermal storage stability of cobalt blue nano-pastes prepared with dispersants D1, D2, and D3 was studied, and the results are as follows. Figure 6 As can be seen, Figure 6 after 7 days of thermal storage in an oven at 60 °C, the D 90 particle size of the pastes prepared with D2 and D3 is less than 200 nm, and the D 90 particle size of the paste prepared with D1 is below 150 nm. The increase in the particle size of the pastes is less than 15%, and it still belongs to the particle size range of colloids. Therefore, Brownian motion in the pastes is still the dominant motion of the particles, so the stability of the pastes is good. In summary, the dispersants prepared in the examples of the present invention can be used to produce waterborne inorganic pigment nano-pastes with good thermal storage stability.

[0108] After diluting cobalt blue pastes without dispersant and those prepared with dispersants D1, D2, and D3 in an aqueous medium, their zeta potentials were measured, and the results are as follows. Figure 7 As can be seen, Figure 7 the zeta potential of the paste without dispersant is about -10 mV, which is much lower than the potential required for particles to remain stable in an aqueous solution. The lowest zeta potential of the cobalt blue paste prepared with dispersant D1 can reach -52.8 mV. According to the DLVO theory, the greater the absolute value of the surface zeta potential of particles in a particle dispersion system, the greater the electrostatic repulsive force between particles, and the more stable the system. Therefore, after adding dispersants, the pastes have higher electrostatic repulsive potential energy and better stability.

[0109] When the pyrrolidone-grafted lignin carboxylate prepared in the present invention is used as a dispersant in the grinding of cobalt blue, cadmium red, titanium chromium brown, and copper chromium black waterborne inorganic pigment pastes, the D 90 particle size of the pastes all decreases to below 150 nm within 4 hours. This shows that the prepared dispersant has the characteristics of high grinding efficiency and good versatility for inorganic ceramic pigments. Taking the cobalt blue paste as an example, rheological property tests and zeta potential characterization were carried out. The results show that pyrrolidone-grafted lignin carboxylate as a dispersant can not only effectively reduce the viscosity of the paste, but also increase the zeta potential of nano-particles in the paste, inhibit the agglomeration of nano-particles, and the stability of the paste is good. The results of the thermal storage stability experiment show that the D 90The particle size is less than 200 nm, and there is no water separation or precipitation phenomenon. The comprehensive performance meets the requirements of water-based nano-ceramic pigment pastes. The nano-ceramic pigment pastes prepared with the dispersant in the present invention can maintain dispersion stability for a long time and have the potential for industrial application.

[0110] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of pyrrolidone-grafted lignin carboxylate, characterized in that It includes the following steps: (1) By mass parts, mix 10 - 20 parts of epoxy group-containing vinyl monomers, 5 - 20 parts of carboxyl group-containing vinyl monomers, 10 - 30 parts of N-vinylpyrrolidone and 30 - 120 parts of water to obtain a solution, and then dropwise add 0.2 - 1.5 parts of an initiator to the solution, and react to obtain a precursor; (2) By mass parts, mix 20 - 40 parts of lignin and 60 - 120 parts of water, heat and add 5 - 20 parts of an alkali and stir to react to obtain an aqueous lignin solution, then add the precursor obtained in step (1), mix well, cool after reaction, and obtain pyrrolidone-grafted lignin carboxylate; The epoxy group-containing vinyl monomer described in step (1) is at least one of glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether; The carboxyl group-containing vinyl monomer described in step (1) is at least one of itaconic acid, acrylic acid, maleic acid, methacrylic acid.

2. The preparation method according to claim 1, wherein: The initiator described in step (1) is at least one of ammonium persulfate, potassium persulfate, azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate.

3. The preparation method according to claim 1, wherein: The dropwise addition described in step (1) is completed within 30 - 60 min; The dropwise addition described in step (1) is carried out under a protective atmosphere; The reaction conditions in step (1) are to react at 50 - 80 °C for 0.5 - 2 hours.

4. The preparation method according to claim 1, wherein: The lignin described in step (2) is at least one of alkali lignin, enzymatically hydrolyzed lignin, high boiling alcohol lignin, lignin sulfonate.

5. The preparation method according to claim 1, wherein: The alkali described in step (2) is at least one of sodium hydroxide, potassium hydroxide; The heating conditions in step (2) are to heat to 70 - 90 °C; The reaction conditions in step (2) are to react at 70 - 90 °C for 2 - 5 hours.

6. Pyrrolidone-grafted lignin carboxylate prepared by the preparation method according to any one of claims 1 - 5.

7. Use of the pyrrolidone-grafted lignin carboxylate according to claim 6 in the preparation of a dispersant.

8. Use of the pyrrolidone-grafted lignin carboxylate according to claim 6 in the field of preparing an aqueous ceramic pigment slurry as a dispersant.

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