A gypsum water-reducing agent with low fluidity loss over time, its preparation method and application

Abstract

This invention pertains to building material admixtures, specifically relating to a gypsum water-reducing agent, its preparation method, and its application. The preparation method of the gypsum water-reducing agent involves a free radical polymerization reaction of ethylene glycol monovinyl polyoxyethylene ether macromonomer, 4,4,4-trifluorobutenoic acid, and an esterified macromonomer in the presence of a chain transfer agent. The esterified macromonomer is the esterification product of methoxy polyethylene glycol and 1-butene-2,3,4-tricarboxylic acid. The resulting free radical polymerization product is the gypsum water-reducing agent. The gypsum water-reducing agent obtained using the method provided by this invention exhibits minimal loss of fluidity over time, demonstrating significant promise for industrial application.

Description

Technical Field

[0001] This invention pertains to building material admixtures, specifically relating to a gypsum water-reducing agent with minimal loss of fluidity over time, its preparation method, and its application. Background Technology

[0002] Gypsum building materials are recognized worldwide and widely used in developed countries as green and environmentally friendly building materials. With the vigorous promotion of environmental protection measures such as solid waste utilization, gypsum building materials can effectively utilize solid waste during use. However, the strength of building gypsum is generally low. One important reason is that the actual mixing water consumption is far greater than its theoretical hydration water requirement, leading to increased porosity and decreased strength in the hardened body. Simply using gypsum retarders can slow down the setting of gypsum, but it will further reduce the strength of gypsum. Using ordinary concrete water-reducing agents has problems such as large loss of fluidity and easy deterioration of water-reducing agents during storage. Therefore, reducing the water-to-gypsum hydration ratio, improving the hydration rheology of gypsum, enhancing the strength of the hardened body, and improving the anti-corrosion performance of water-reducing agents are of great significance for the application of building gypsum.

[0003] Currently, commercially available high-performance gypsum water-reducing agents mainly include lignin sulfonate derivatives, naphthalene sulfonate formaldehyde condensates, sulfonated melamine derivatives, and polycarboxylate derivatives. Among these, lignin sulfonate derivatives are used relatively infrequently. Naphthalene sulfonate formaldehyde condensates, sulfonated melamine derivatives, and polycarboxylate derivatives generally suffer from poor applicability, low water reduction rates, high air content, insignificant reinforcing effects, severe retardation of setting, and reduced strength. Therefore, the development of specialized gypsum water-reducing agents plays a crucial role in the development of gypsum building materials.

[0004] CN112358578A discloses a polycarboxylate gypsum water-reducing agent, its preparation method, and its application. The raw materials for its preparation include polyoxyethylene ether, acrylic acid, methacrylic acid, sodium methacrylate sulfonate, 2-acrylamide-2-methylpropanesulfonic acid, initiator, pH adjuster, deionized water, nano-sized inorganic particles, and optional molecular weight adjuster. This method uses polycarboxylate early-strength monomers to improve strength, but this can easily lead to excessive loss of gypsum-based fluidity and deterioration of the water-reducing agent if stored for too long.

[0005] After hardening, building gypsum evaporates a large amount of water, leaving many pores. The presence of these pores reduces the strength of the gypsum, and the rapid hydration rate of the gypsum leads to a significant loss of fluidity. Adding concrete polycarboxylate superplasticizer as a surfactant can change the interfacial structure and electrochemical properties of gypsum particles through adsorption, and exert a dispersing effect through the double-layer repulsion effect and steric hindrance effect. However, because the hydration rate of gypsum is too fast, the concrete superplasticizer cannot effectively improve the problem of excessive fluidity loss in gypsum-based materials. Summary of the Invention

[0006] One of the objectives of this invention is to overcome the problem of excessive fluidity loss over time in existing gypsum water-reducing agents, and to provide a method for preparing a gypsum water-reducing agent with minimal fluidity loss over time.

[0007] The second objective of this invention is to provide a gypsum water-reducing agent prepared by the above method.

[0008] The third objective of this invention is to provide the application of the above-mentioned gypsum water-reducing agent in the construction field.

[0009] After in-depth research, the inventors of this invention discovered that a gypsum water-reducing agent prepared by simultaneously using ethylene glycol monovinyl polyoxyethylene ether macromonomer, 4,4,4-trifluorobutenoic acid, acrylic acid, and esterified macromonomer (the esterification reaction product of methoxy polyethylene glycol and 1-butene-2,3,4-tricarboxylic acid) as polymerizing monomers can significantly reduce fluidity loss. The reason for this is speculated to be that the main cause of gypsum fluidity loss is the gypsum hydration rate. Ordinary gypsum polycarboxylic acid water-reducing agent molecules act on the surface of gypsum particles, and through electrostatic repulsion and steric hindrance, the gypsum gains fluidity. However, the rapid hydration rate of gypsum results in the rapidly generated gypsum hydration products encapsulating ordinary gypsum water-reducing agent molecules, significantly reducing the number of water-reducing agent molecules and leading to a rapid loss of gypsum fluidity. In contrast, the gypsum water-reducing agent obtained by simultaneously using ethylene glycol monovinyl polyoxyethylene ether macromonomer, acrylic acid, 4,4,4-trifluorobutenoic acid, and esterified macromonomer as polymerizing monomers, on the one hand, reduces fluidity loss during use due to the 4,4,4-trifluorobutenoic acid macromonomer. The synergistic effect of trifluorobutenoic acid, acrylic acid, and 1-butene-2,3,4-tricarboxylic acid allows for slow hydrolysis under alkaline conditions, releasing more water-reducing agent molecules. This helps alleviate the fluidity loss in gypsum caused by the rapid loss of water-reducing agent molecules, reducing fluidity loss over time. Furthermore, the use of ethylene glycol monovinyl polyoxyethylene ether, a macromonomer with a specific structure, reduces the spatial resistance of the polyether side chain's movement, allowing for freer movement, a larger range of motion, and increased degrees of freedom. This improves the encapsulation and entanglement of the polyether side chains, resulting in less fluidity loss in gypsum over time. In addition, the high adsorption rate and good dispersion effect of the fluorine groups in 4,4,4-trifluorobutenoic acid, when introduced into gypsum water-reducing agents, helps improve gypsum fluidity and compensate for fluidity loss. Based on these findings, this invention was completed.

[0010] Specifically, the preparation method of the gypsum water-reducing agent provided by the present invention includes a free radical polymerization reaction of ethylene glycol monovinyl polyoxyethylene ether macromonomer, 4,4,4-trifluorobutenoic acid, acrylic acid and esterified macromonomer in the presence of a chain transfer agent. The esterified macromonomer is the esterification reaction product of methoxy polyethylene glycol and 1-butene-2,3,4-tricarboxylic acid. The resulting free radical polymerization product is the gypsum water-reducing agent.

[0011] The present invention also provides a gypsum water-reducing agent prepared by the above method.

[0012] Furthermore, the present invention also provides the application of the gypsum water-reducing agent in the construction field.

[0013] The gypsum water-reducing agent obtained by the method provided by this invention has minimal loss of fluidity over time and is highly promising for industrial application.

[0014] In a preferred embodiment, the free radical polymerization reaction uses a redox initiator, which is composed of an oxidant and a reducing agent. The reducing agent contains at least sodium formaldehyde bisulfite. In this case, the corrosion resistance of the gypsum water-reducing agent can be improved while achieving a smaller flow loss over time, thus broadening its application prospects. Detailed Implementation

[0015] The preparation method of the gypsum water-reducing agent provided by the present invention includes a free radical polymerization reaction of ethylene glycol monovinyl polyoxyethylene ether macromonomer, 4,4,4-trifluorobutenoic acid, acrylic acid and esterified macromonomer in the presence of a chain transfer agent. The esterified macromonomer is the esterification reaction product of methoxy polyethylene glycol and 1-butene-2,3,4-tricarboxylic acid. The resulting free radical polymerization product is the gypsum water-reducing agent.

[0016] This invention does not particularly limit the type of initiator used in the free radical polymerization reaction, and it can be at least one selected from azo initiators, peroxide initiators, and redox initiators. Specific examples of azo initiators include, but are not limited to, at least one of: dimethyl azobisisobutyrate, azobisisobutyramidine hydrochloride, azodicarbonamide, azobisisopropylimidazoline hydrochloride, azoisobutylcyanoformamide, azodicyclohexylformonitrile, azobiscyanopentanoic acid, azobisisopropylimidazoline, azobisisobutyronitrile, azobisisovalerate, and azobisisoheptanenitrile. Specific examples of peroxide initiators include, but are not limited to, at least one of: hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, benzoyl peroxide, and benzoyl tert-butyl peroxide. Specific examples of redox initiators include, but are not limited to, at least one of: sulfate-sulfite, persulfate-thiourea, persulfate-organic salt, and ammonium persulfate-aliphatic amine. The sulfate-sulfite can be selected from at least one of sodium sulfate-sodium sulfite, potassium sulfate-potassium sulfite, and ammonium sulfate-ammonium sulfite. The persulfate-thiourea can be selected from at least one of sodium persulfate-thiourea, potassium persulfate-thiourea, and ammonium persulfate-thiourea. The persulfate-organic salt can be selected from at least one of sodium persulfate-potassium acetate, potassium persulfate-potassium acetate, and ammonium persulfate-ammonium acetate. The ammonium persulfate-aliphatic amine can be ammonium persulfate-N,N-tetramethylethylenediamine and / or ammonium persulfate-diethylamine.

[0017] In a preferred embodiment, the free radical polymerization reaction employs a redox initiator composed of an oxidant and a reducing agent. The reducing agent contains at least sodium formaldehyde bisulfite, which also improves the anti-corrosion properties of the gypsum water-reducing agent. Furthermore, the oxidant is preferably hydrogen peroxide.

[0018] In a preferred embodiment, the free radical polymerization reaction is carried out according to the following steps:

[0019] S1. Dissolve the ethylene glycol monovinyl polyoxyethylene ether macromonomer in water to obtain solution A; dissolve 4,4,4-trifluorobutenoic acid, acrylic acid, and esterified macromonomer in water to obtain solution B; dissolve the reducing agent and chain transfer agent in water to obtain solution C; dissolve the oxidizing agent in water to obtain solution D.

[0020] S2. Under stirring conditions, solutions B, C, and D are simultaneously added dropwise to solution A. After the addition is complete, the reaction is stirred continuously. Then, the pH value of the system is adjusted to 6.5-7.5 to obtain the gypsum water-reducing agent mother liquor.

[0021] In a preferred embodiment, the mass ratio of ethylene glycol monovinyl polyoxyethylene ether macromonomer to water in the preparation of solution A is (40-45):(45-50). The amount of ethylene glycol monovinyl polyoxyethylene ether macromonomer used can be 40-45 parts by weight, such as 40, 42, 44, 45 parts by weight or any value between them; the amount of water used can be 45-50 parts by weight, such as 45, 47, 48, 50 parts by weight or any value between them.

[0022] In a preferred embodiment, the mass ratio of 4,4,4-trifluorobutenoic acid, acrylic acid, esterified macromonomer and water in the preparation of solution B is (0.5-1)(2-3):(1-2):(0.9-1). The amount of 4,4,4-trifluorobutenoic acid can be 0.5-1 parts by weight, such as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 parts by weight or any value between them; the amount of acrylic acid can be 2-3 parts by weight, such as 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3 parts by weight or any value between them; the amount of esterified macromonomer can be 1-2 parts by weight, such as 1, 1.2, 1.4, 1.6, 1.8, 2 parts by weight or any value between them; the amount of water can be 0.9-1 parts by weight, such as 0.9, 0.92, 0.94, 0.96, 0.98, 1 part by weight or any value between them.

[0023] In a preferred embodiment, the mass ratio of reducing agent, chain transfer agent, and water in the preparation of solution C is (0.05-0.1):(0.15-0.2):(3-5). The amount of reducing agent can be 0.05-0.1 parts by weight, such as 0.05, 0.06, 0.08, 0.1 parts by weight, or any value between them; the amount of chain transfer agent can be 0.15-0.2 parts by weight, such as 0.15, 0.16, 0.17, 0.18, 0.19, 0.2 parts by weight, or any value between them; and the amount of water can be 3-5 parts by weight, such as 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5 parts by weight, or any value between them.

[0024] In a preferred embodiment, the mass ratio of oxidant to water in the preparation of solution D is (0.2-0.3):(2-3). The amount of oxidant can be 0.2-0.3 parts by weight, such as 0.2, 0.22, 0.24, 0.26, 0.28, 0.3 parts by weight or any value between them; the amount of water can be 2-3 parts by weight, such as 2, 2.2, 2.4, 2.6, 2.8, 3 parts by weight or any value between them.

[0025] In a preferred embodiment, the mass ratio of solution A, solution B, solution C and solution D is (85-95):(4.9-7):(3.2-5.3):(2.2-3.3). The amount of solution A can be 85-95 parts by weight, such as 85, 87, 89, 91, 93, 95 parts by weight or any value between them; the amount of solution B can be 4.9-7 parts by weight, such as 4.9, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.8, 7 parts by weight or any value between them; the amount of solution C can be 3.2-5.3 parts by weight, such as 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.1, 5.3 parts by weight or any value between them; the amount of solution D can be 2.2-3.3 parts by weight, such as 2.2, 2.5, 2.8, 3, 3.1, 3.3 parts by weight or any value between them.

[0026] In a preferred embodiment, the dripping conditions include a temperature of 5-15°C, such as 5°C, 8°C, 10°C, 12°C, 15°C or any value between them; and a time of 40-50 min, such as 40 min, 42 min, 45 min, 48 min, 50 min or any value between them.

[0027] In a preferred embodiment, the conditions for the stirring reaction include a temperature of 20-25°C, such as 20°C, 21°C, 22°C, 23°C, 24°C, 25°C or any value between them; and a time of 50-60 min, such as 50 min, 52 min, 55 min, 58 min, 60 min or any value between them.

[0028] In this invention, the ethylene glycol monovinyl polyoxyethylene ether macromonomer (CH2CHOCH2CH2O(CH2CH2O)) n H) By modifying the molecular structure, the unsaturated double bonds in the molecular structure can be directly connected to an oxygen atom to form a CO bond molecular structure. This change in molecular structure can shift the electron cloud distribution of the double bonds, thereby improving the charge environment of the unsaturated double bonds. This makes the double bonds in the macromonomer much more reactive than those in ordinary macromonomers, and more conducive to free radical polymerization. Furthermore, the specific structure of the ethylene glycol monovinyl polyoxyethylene ether macromonomer can reduce the steric hindrance of the polyether side chain, allowing for freer movement and a larger range of motion. This increased freedom of movement enhances the encapsulation and entanglement of the polyether side chains, ultimately resulting in less flowability loss over time in the gypsum water-reducing agent. Additionally, the number average molecular weight of the ethylene glycol monovinyl polyoxyethylene ether macromonomer is preferably 3000-5000, such as 3000, 3200, 3500, 3800, 4000, 4200, 4500, 4800, 5000, or any value between them.

[0029] In a preferred embodiment, the esterified macromonomer is prepared by the following method: under an inert gas atmosphere, methoxy polyethylene glycol, 1-butene-2,3,4-tricarboxylic acid, a catalyst, and a polymerization inhibitor are mixed uniformly, and then the resulting mixture is subjected to an esterification reaction. The mass ratio of the methoxy polyethylene glycol to 1-butene-2,3,4-tricarboxylic acid is preferably (4-6):1, such as 4:1, 4.5:1, 5:1, 5.5:1, 6:1, or any value between them. The number average molecular weight of the methoxy polyethylene glycol is preferably 2000-3000, such as 2000, 2200, 2400, 2600, 2800, 3000, or any value between them. The mass ratio of the catalyst to 1-butene-2,3,4-tricarboxylic acid is preferably (0.1-0.3):1, such as 0.1:1, 0.2:1, 0.3:1, or any value between them. The catalyst may be, for example, concentrated sulfuric acid. The preferred mass ratio of the polymerization inhibitor to 1-butene-2,3,4-tricarboxylic acid is (0.001-0.1):1, such as 0.001:1, 0.005:1, 0.01:1, 0.02:1, 0.04:1, 0.06:1, 0.08:1, 0.1:1, or any value between them. The polymerization inhibitor may be, for example, hydroquinone and / or phenothiazine. The esterification reaction conditions may include a temperature of 160-200°C, such as 160°C, 170°C, 180°C, 190°C, 200°C, or any value between them; and a time of 1-10 h, such as 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, or any value between them.

[0030] In a preferred embodiment, specific examples of the chain transfer agent include, but are not limited to, at least one of mercaptopropionic acid, mercaptoacetic acid, and mercaptoethanol.

[0031] The present invention also provides a gypsum water-reducing agent prepared by the above method.

[0032] Furthermore, the present invention also provides the application of the gypsum water-reducing agent in the construction field.

[0033] The present invention will be described in detail below through embodiments.

[0034] Preparation Example 1

[0035] Under nitrogen protection, 260 parts by weight of methoxy polyethylene glycol (MPEG-2400), 10 parts by weight of concentrated sulfuric acid, 50 parts by weight of 1-butene-2,3,4-tricarboxylic acid, 0.4 parts by weight of hydroquinone and 0.05 parts by weight of phenothiazine were mixed evenly, and then heated to 180°C and held for 4 hours to obtain the esterified macromonomer.

[0036] Preparation Example 2

[0037] Under nitrogen protection, 260 parts by weight of methoxy polyethylene glycol (MPEG-2000), 2.6 parts by weight of concentrated sulfuric acid, 65 parts by weight of 1-butene-2,3,4-tricarboxylic acid, and 0.45 parts by weight of hydroquinone were mixed evenly, and then heated to 200°C and held for 1 hour to obtain the esterified macromonomer.

[0038] Preparation Example 3

[0039] Under nitrogen protection, 260 parts by weight of methoxy polyethylene glycol (MPEG-3000), 13 parts by weight of concentrated sulfuric acid, 43 parts by weight of 1-butene-2,3,4-tricarboxylic acid and 0.45 parts by weight of phenothiazine were mixed evenly, and then the mixture was heated to 160°C and held for 10 hours to obtain the esterified macromonomer.

[0040] Example 1

[0041] S1. Mix 40 parts by weight of ethylene glycol monovinyl polyoxyethylene ether with a number average molecular weight of 5000 and 47 parts by weight of water at 30°C until homogeneous, then cool to 15°C to obtain solution A; mix 0.5 parts by weight of 4,4,4-trifluorobutenoic acid, 2.5 parts by weight of acrylic acid, 2 parts by weight of esterified macromonomer (prepared from Preparation Example 1) and 1 part by weight of water until homogeneous to obtain solution B; mix 0.07 parts by weight of sodium formaldehyde sulfoxylate, 0.15 parts by weight of chain transfer agent and 3 parts by weight of water until homogeneous to obtain solution C; mix 0.2 parts by weight of hydrogen peroxide and 2 parts by weight of water until homogeneous to obtain solution D;

[0042] S2. Add solutions B, C and D dropwise to solution A at 5℃ simultaneously, with the addition time controlled to be completed in 40 minutes. Then stir the reaction at 20℃ for 60 minutes. After the reaction is completed, adjust the pH value to 7.0 to obtain the gypsum water-reducing agent, denoted as LZ-KZJ1.

[0043] Example 2

[0044] S1. Mix 45 parts by weight of ethylene glycol monovinyl polyoxyethylene ether with a number average molecular weight of 3000 and 50 parts by weight of water at 30°C until homogeneous, then cool to 15°C to obtain solution A; mix 1 part by weight of 4,4,4-trifluorobutenoic acid, 3 parts by weight of acrylic acid, 1 part by weight of esterified macromonomer (prepared from Preparation Example 2) and 0.9 parts by weight of water until homogeneous to obtain solution B; mix 0.05 parts by weight of sodium formaldehyde sulfoxylate, 0.15 parts by weight of chain transfer agent and 3 parts by weight of water until homogeneous to obtain solution C; mix 0.3 parts by weight of hydrogen peroxide and 3 parts by weight of water until homogeneous to obtain solution D;

[0045] S2. Add solutions B, C and D dropwise to solution A at 15℃ simultaneously, with the addition time controlled to be completed in 50 minutes. Then stir the reaction at 25℃ for 40 minutes. After the reaction is completed, adjust the pH value to 7.0 to obtain the gypsum water-reducing agent, denoted as LZ-KZJ2.

[0046] Example 3

[0047] S1. Mix 40 parts by weight of ethylene glycol monovinyl polyoxyethylene ether with a number average molecular weight of 5000 and 47 parts by weight of water at 30°C until homogeneous, then cool to 15°C to obtain solution A; mix 0.7 parts by weight of 4,4,4-trifluorobutenoic acid, 2.3 parts by weight of acrylic acid, 1 part by weight of esterified macromonomer (prepared from Preparation Example 3) and 0.9 parts by weight of water until homogeneous to obtain solution B; mix 0.1 parts by weight of sodium formaldehyde sulfoxylate, 0.2 parts by weight of chain transfer agent and 5 parts by weight of water until homogeneous to obtain solution C; mix 0.2 parts by weight of hydrogen peroxide and 2 parts by weight of water until homogeneous to obtain solution D;

[0048] S2. Add solutions B, C and D dropwise to solution A at 10℃ simultaneously, with the addition time controlled to be completed in 50 minutes. Then stir the reaction at 22℃ for 55 minutes. After the reaction is completed, adjust the pH value to 7.0 to obtain the gypsum water-reducing agent, denoted as LZ-KZJ3.

[0049] Example 4

[0050] S1. Mix 45 parts by weight of ethylene glycol monovinyl polyoxyethylene ether with a number average molecular weight of 4000 and 48 parts by weight of water at 30°C until homogeneous, then cool to 10°C to obtain solution A; mix 0.8 parts by weight of 4,4,4-trifluorobutenoic acid, 2.7 parts by weight of acrylic acid, 1 part by weight of esterified macromonomer (prepared from Preparation Example 1) and 0.9 parts by weight of water until homogeneous to obtain solution B; mix 0.1 parts by weight of sodium formaldehyde sulfoxylate, 0.15 parts by weight of chain transfer agent and 3 parts by weight of water until homogeneous to obtain solution C; mix 0.2 parts by weight of hydrogen peroxide and 2 parts by weight of water until homogeneous to obtain solution D;

[0051] S2. Add solutions B, C and D dropwise to solution A at 8℃ simultaneously, with the addition time controlled to be completed in 50 minutes. Then stir the reaction at 23℃ for 60 minutes. After the reaction is completed, adjust the pH value to 7.0 to obtain the gypsum water-reducing agent, denoted as LZ-KZJ4.

[0052] Example 5

[0053] S1. Mix 40 parts by weight of ethylene glycol monovinyl polyoxyethylene ether with a number average molecular weight of 3000 and 47 parts by weight of water at 30°C until homogeneous, then cool to 15°C to obtain solution A; mix 1 part by weight of 4,4,4-trifluorobutenoic acid, 3 parts by weight of acrylic acid, 2 parts by weight of esterified macromonomer (prepared from Preparation Example 2) and 1 part by weight of water until homogeneous to obtain solution B; mix 0.05 parts by weight of sodium formaldehyde bisulfite, 0.18 parts by weight of chain transfer agent and 4 parts by weight of water until homogeneous to obtain solution C; mix 0.3 parts by weight of hydrogen peroxide and 2 parts by weight of water until homogeneous to obtain solution D;

[0054] S2. Add solutions B, C and D dropwise to solution A at 9℃ simultaneously, with the addition time controlled to be completed in 50 minutes. Then stir the reaction at 24℃ for 58 minutes. After the reaction is completed, adjust the pH value to 7.0 to obtain the gypsum water-reducing agent, denoted as LZ-KZJ5.

[0055] Example 6

[0056] S1. Mix 42 parts by weight of ethylene glycol monovinyl polyoxyethylene ether with a number average molecular weight of 4000 and 49 parts by weight of water at 30°C until homogeneous, then cool to 5°C to obtain solution A; mix 0.6 parts by weight of 4,4,4-trifluorobutenoic acid, 2.9 parts by weight of acrylic acid, 2 parts by weight of esterified macromonomer (prepared from Preparation Example 3) and 0.9 parts by weight of water until homogeneous to obtain solution B; mix 0.05 parts by weight of sodium formaldehyde bisulfite, 0.2 parts by weight of chain transfer agent and 3 parts by weight of water until homogeneous to obtain solution C; mix 0.3 parts by weight of hydrogen peroxide and 3 parts by weight of water until homogeneous to obtain solution D;

[0057] S2. Add solutions B, C and D dropwise to solution A at 12℃ simultaneously, with the addition time controlled to be completed in 50 minutes. Then stir the reaction at 21℃ for 59 minutes. After the reaction is completed, adjust the pH value to 7.0 to obtain the gypsum water-reducing agent, denoted as LZ-KZJ6.

[0058] Example 7

[0059] The gypsum water-reducing agent was prepared according to the method of Example 3, except that sodium formaldehyde sulfoxylate was replaced with the same amount of vitamin C by weight, and the resulting gypsum water-reducing agent was designated as LZ-KZJ7.

[0060] Comparative Example 1

[0061] The gypsum water-reducing agent was prepared according to the method of Example 4, except that no esterified macromonomer was added, and the other conditions were the same as in Example 4, to obtain the reference gypsum water-reducing agent, denoted as DLZ-KZJ1.

[0062] Comparative Example 2

[0063] The gypsum water-reducing agent was prepared according to the method of Example 1, except that ethylene glycol monovinyl polyoxyethylene ether was replaced by the same amount of 4-hydroxybutyl vinyl polyoxyethylene ether (number average molecular weight of 5000) by weight. The other conditions were the same as in Example 1, and a reference gypsum water-reducing agent was obtained, denoted as DLZ-KZJ2.

[0064] Comparative Example 3

[0065] The gypsum water-reducing agent was prepared according to the method of Comparative Example 2, except that no esterified macromonomer was added, and the other conditions were the same as those of Comparative Example 2, to obtain the reference gypsum water-reducing agent, denoted as DLZ-KZJ3.

[0066] Comparative Example 4

[0067] The gypsum water-reducing agent was prepared according to the method of Example 1, except that 4,4,4-trifluorobutenoic acid was replaced by the same amount of acrylic acid by weight, and the other conditions were the same as in Example 1, to obtain the reference gypsum water-reducing agent, denoted as DLZ-KZJ4.

[0068] Comparative Example 5

[0069] PC-3000 gypsum water-reducing agent, purchased from Suzhou Xingbang Chemical Co., Ltd., was used and dissolved to a mass concentration of 40%, designated as DLZ-KZJ5.

[0070] Test case

[0071] Mix 50 parts by weight of hemihydrate gypsum, 35 parts by weight of cement (Hongshi P·O52.5), 12 parts by weight of manufactured sand, 0.1 parts by weight of defoamer D609, 0.1 parts by weight of sodium lignosulfonate retarder, and 0.2 parts by weight of potassium tartrate evenly. Then add the corresponding amounts of gypsum water-reducing agent LZ-KZJ1~LZ-KZJ7 and reference gypsum water-reducing agent DLZ-KZJ1~DLZ-KZJ5 and stir evenly to obtain gypsum-based mortar.

[0072] (1) Flowability of gypsum mortar: The flowability of gypsum mortar was tested according to JC / T 1023-2007 "Gypsum-based self-leveling mortar". The test results are detailed in Table 1.

[0073] (2) Corrosion resistance: The gypsum water-reducing agents obtained in the above examples and the reference gypsum water-reducing agent obtained in the comparative example were stored in an open environment at 50°C, and the experimental phenomena were observed during the storage process. The test results are detailed in Table 2.

[0074] Table 1

[0075]

[0076] As shown in Table 1 above, the gypsum water-reducing agent obtained using the method provided by this invention exhibits minimal loss of fluidity over time. A comparison between Example 1 and Comparative Example 2 reveals that diethylene glycol monovinyl ether polyether is more effective than 4-hydroxybutyl vinyl polyoxyethylene ether in reducing fluidity loss over time. A comparison between Example 4 and Comparative Examples 1, 2, and 3 shows that the use of ester macromonomers is beneficial in reducing fluidity loss over time.

[0077] Table 2

[0078]

[0079]

[0080] As shown in Table 2 above, when the free radical polymerization reaction is carried out using a redox initiator and the reducing agent contains sodium formaldehyde bisulfite, the resulting gypsum water-reducing agent has better anti-corrosion properties and a broader application prospect.

[0081] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for preparing a gypsum water-reducing agent, characterized in that, This method involves a free radical polymerization reaction of ethylene glycol monovinyl polyoxyethylene ether macromonomer, 4,4,4-trifluorobutenoic acid, acrylic acid, and esterified macromonomer in the presence of a chain transfer agent. The esterified macromonomer is the esterification product of methoxy polyethylene glycol and 1-butene-2,3,4-tricarboxylic acid. The resulting free radical polymerization product is the gypsum water-reducing agent.

2. The method for preparing the gypsum water-reducing agent according to claim 1, characterized in that, The free radical polymerization reaction uses a redox initiator, which is composed of an oxidant and a reducing agent, and the reducing agent contains at least sodium formaldehyde bisulfite.

3. The method for preparing the gypsum water-reducing agent according to claim 2, characterized in that, The free radical polymerization reaction is carried out according to the following steps: S1. Dissolve the ethylene glycol monovinyl polyoxyethylene ether macromonomer in water to obtain solution A; dissolve 4,4,4-trifluorobutenoic acid, acrylic acid, and esterified macromonomer in water to obtain solution B; dissolve the reducing agent and chain transfer agent in water to obtain solution C; dissolve the oxidizing agent in water to obtain solution D. S2. Under stirring conditions, solutions B, C, and D are simultaneously added dropwise to solution A. After the addition is complete, the reaction is stirred continuously. Then, the pH value of the system is adjusted to 6.5-7.5 to obtain the gypsum water-reducing agent mother liquor.

4. The method for preparing the gypsum water-reducing agent according to claim 3, characterized in that, In the preparation of solution A, the mass ratio of ethylene glycol monovinyl polyoxyethylene ether macromonomer to water is (40-45):(45-50).

5. The method for preparing the gypsum water-reducing agent according to claim 3, characterized in that, In the preparation of solution B, the mass ratio of 4,4,4-trifluorobutenoic acid, acrylic acid, esterified macromonomer and water is (0.5-1):(2-3):(1-2):(0.9-1).

6. The method for preparing the gypsum water-reducing agent according to claim 3, characterized in that, In the preparation of solution C, the mass ratio of reducing agent, chain transfer agent and water is (0.05-0.1):(0.15-0.2):(3-5).

7. The method for preparing the gypsum water-reducing agent according to claim 3, characterized in that, The mass ratio of oxidant to water in the preparation of solution D is (0.2-0.3):(2-3).

8. The method for preparing the gypsum water-reducing agent according to claim 3, characterized in that, The mass ratio of solutions A, B, C, and D is (85-95):(4.9-7):(3.2-5.3):(2.2-3.3).

9. The method for preparing the gypsum water-reducing agent according to claim 3, characterized in that, The conditions for the dropwise addition include a temperature of 5-15℃ and a time of 40-50 min; the conditions for the stirring reaction include a temperature of 20-25℃ and a time of 50-60 min.

10. The method for preparing the gypsum water-reducing agent according to any one of claims 1-9, characterized in that, The number average molecular weight of the ethylene glycol monovinyl polyoxyethylene ether macromonomer is 3000-5000.

11. The method for preparing the gypsum water-reducing agent according to any one of claims 1-9, characterized in that, The esterified macromonomer was prepared by the following method: under inert gas protection, methoxy polyethylene glycol, 1-butene-2,3,4-tricarboxylic acid, catalyst and polymerization inhibitor were mixed evenly, and then the resulting mixture was subjected to an esterification reaction.

12. The method for preparing the gypsum water-reducing agent according to claim 11, characterized in that, The mass ratio of the methoxy polyethylene glycol to 1-butene-2,3,4-tricarboxylic acid is (4-6):

1.

13. The method for preparing the gypsum water-reducing agent according to claim 11, characterized in that, The number average molecular weight of the methoxy polyethylene glycol is 2000-3000.

14. The method for preparing the gypsum water-reducing agent according to claim 11, characterized in that, The esterification reaction conditions include a temperature of 160-200℃ and a time of 1-10h.

15. The method for preparing the gypsum water-reducing agent according to any one of claims 1-9, characterized in that, The chain transfer agent is selected from at least one of mercaptopropionic acid, mercaptoacetic acid, and mercaptoethanol.

16. A gypsum water-reducing agent prepared by the method according to any one of claims 1-15.

17. The application of the gypsum water-reducing agent according to claim 16 in the construction field.

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