A water reducing agent and its preparation method and application

Abstract

The present invention discloses a water reducer, a preparation method and an application thereof, and relates to the technical field of building materials. The water reducer is based on the Michael addition reaction of amide with acrylate under the catalysis of phosphazene base, and obtains bidentate decapped bisacrylate (ester) structural units by adding acrylamide-polyoxyalkylene ether macromonomer copolymer to acrylate. The introduction of such units significantly improves the initial dispersion speed of the water reducer, and has a significant advantage in adaptability to high-admixture cement compared to traditional high-performance water reducers. At the same time, the time-dependent dispersion behavior of the water reducer can be flexibly adjusted by selecting whether to retain the ester group.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and in particular to a water reducing agent, a preparation method and an application thereof. Background Art

[0002] With the rapid advancement of infrastructure construction and the booming urbanization, the demand for building materials to adapt to different scenarios is becoming increasingly complex. At the same time, the binders and admixtures used in building concrete are becoming increasingly low-carbon. This places higher demands on the adaptability of the cementitious system and the tolerance to complex scenarios of water reducers. Among them, the modification of new structures and adsorption groups of water reducers has become a powerful way to improve performance and meet these new demands.

[0003] Based on the above background, there have been many patent reports on water-reducing agents with new structures. For example, patent CN202010548340.3 discloses "a method and process for preparing a hyperbranched viscosity-reducing polycarboxylic acid water-reducing agent". This technical solution reacts acrylates with allylamine or alcoholamine substances through double bond addition or Michael addition reaction to obtain an intermediate monomer, which is then further reacted with a polyhydroxyl-containing monomer to obtain a hyperbranched functional monomer. The hyperbranched functional monomer is then bonded to a TPEG macromonomer with an unsaturated carboxylic acid or an ester monomer containing a hydrophobic group through free radical polymerization to obtain a hyperbranched viscosity-reducing carboxylic acid water-reducing agent. Patent CN202211708546.3 discloses "a shrinkage-reducing polycarboxylate water-reducing agent and its preparation method", which contains shrinkage-reducing and hyperbranched monomers. It uses vinyl polyoxyethylene ether as a monomer to synthesize the polycarboxylate water-reducing agent. The high activity of its double bond is utilized to improve the conversion rate of the reaction, so that the shrinkage-reducing functional group can be well connected to the main chain of the polycarboxylate water-reducing agent through free radical copolymerization, thereby improving the shrinkage-reducing performance of the polycarboxylate water-reducing agent; at the same time, by adding low molecular weight polyoxyethylene ether, the reaction activity is reduced, so that the reaction can be carried out at room temperature, eliminating the cooling step and saving energy. Patent CN202211219211.5 discloses "a slow-setting composite water-reducing agent and its preparation method", which is prepared by controlling the polymerization of hyperbranched precursors to prepare hyperbranched water-reducing agents, and then compounding them with modifiers. The slow-setting composite water-reducing agent of this invention can effectively eliminate the sudden increase in slump and water bleeding that may occur in concrete mixtures, and can effectively eliminate the influence of slow-setting water-reducing agents on the strength of concrete, thereby improving the strength performance of concrete. Patent CN202111331083.9 discloses "a prepolymer and its derivatives, as well as their preparation methods and applications". The prepolymer can first react with enol and the like to form an ester-containing water-reducing agent active intermediate, and then hydrolyze in an alkaline environment to form a hydroxyl-containing water-reducing agent active intermediate. The prepolymer does not contain hydroxyl groups and will not self-initiate. The reaction in which it participates is easy to control and hyperbranching will not occur. Moreover, the hydroxyl content in the obtained hydroxyl-containing water-reducing agent active intermediate is not only high, but also evenly distributed in the molecular chain. The water-reducing agent made from it can form a thicker and firm water film after hydrogen bonding with water, which plays a curing role in the concrete curing process and reduces the shrinkage and cracking of the concrete.

[0004] Although the various water-reducing agents obtained in the above technical solutions have achieved good technical effects, they still have the following shortcomings: (1) Slow dispersion speed: The initial expansion of traditional polycarboxylic acid water-reducing agents (such as PCA-IV) is less than 250 mm, and the loss rate in 45 minutes exceeds 20%. For example, the hyperbranched viscosity-reducing water-reducing agent disclosed in CN202010548340.3 can reduce viscosity, but the initial dispersion speed is insufficient; (2) Poor adaptability: In high-admixture systems (such as fly ash and calcined clay), the dispersion efficiency of traditional water-reducing agents is significantly reduced. For example, the shrinkage-reducing water-reducing agent in CN202211708546.3 improves the conversion rate, but has limited adaptability to high-admixture systems; (3) Uncontrollable slump retention: It is difficult for existing technologies to adjust the slump retention time through simple processes, resulting in limited concrete construction performance. For example, the prepolymer water-reducing agent in CN202111331083.9 can reduce concrete shrinkage, but the slump retention performance is difficult to flexibly control. Therefore, there is an urgent need for a water reducer that has rapid dispersion, high adaptability and controllable slump retention properties. Summary of the Invention

[0005] Technical problem to be solved: In response to the problems existing in the use of water reducers in the background technology, the present invention provides a water reducer and its preparation method and application. By Michael addition reaction of acrylamide-polyoxyalkylene ether copolymer and acrylate, bidentate decanoid structural units (Formula 2 to Formula 4) are introduced, which significantly improves the initial dispersion speed and adaptability to complex cement systems; by adjusting the degree of ester hydrolysis, the slump retention performance can be flexibly controlled.

[0006] Technical solution: The preparation method of a water reducing agent according to the present invention comprises the following steps:

[0007] Step 1: dispersing the acrylamide-polyoxyalkylene ether macromonomer copolymer in an aprotic polar solvent to form a dispersion with a mass concentration of 20% to 45%;

[0008] Step 2: Add a phosphazene base catalyst, and dropwise add acrylic acid ester at a constant rate at 15-45°C for 1-4 hours. After the addition is complete, keep the temperature to react for 4-20 hours to obtain an addition intermediate product solution;

[0009] Step 3: Add a precipitant to precipitate the product, recover the solvent and catalyst by fractional distillation, and disperse the precipitate in water to prepare a solution with a mass concentration of 30-50%;

[0010] Step 4: adding alkali and treating at 35-60° C. for 1-8 hours to obtain the water reducing agent SP;

[0011] The molar ratio of acrylamide to polyoxyalkylene ether structural units in the acrylamide-polyoxyalkylene ether macromonomer copolymer is (1.8-6):1, and the weight-average molecular weight is 5,000-50,000 g / mol. The acrylic acid ester is an esterification product of acrylic acid and a C1-C4 alkyl 1-4 alcohol, and the amount used is 1.5-2.2 times the molar amount of the amide group in the acrylamide-polyoxyalkylene ether copolymer.

[0012] The phosphazene base catalyst is a compound of formula 1, and its usage is 3% to 10% of the total molar amount of the main chain structural units of the copolymer:

[0013] Formula 1.

[0014] The water reducing agent SP includes structural units shown in Formula 2 to Formula 4:

[0015] (1) Structural unit 1 is shown in formula 2:

[0016] Formula 2;

[0017] In formula 2: R1 and R2 are either hydrogen atoms or methyl groups, and R3 is hydrogen, sodium, potassium, or a C1-C4 saturated hydrocarbon group substituted with 1-2 hydroxyl groups;

[0018] (2) Structural unit 2 is shown in formula 3:

[0019] Formula 3;

[0020] In formula 3: R4 is hydrogen or methyl, and R2 and R3 are defined the same as in formula 1;

[0021] (3) Structural unit 3 is shown in formula 4:

[0022] Formula 4;

[0023] In formula 4: R5 is hydrogen or methyl; R6 is hydrogen or methyl, R7 is hydrogen or C1-C4 alkyl, and the molar proportion of hydrogen in R6 is 90-100%, and the rest is methyl; X is an ester group -COO-, an oxygen atom, or a C1-C4 alkoxy group or an alkyleneoxy group -ORO-, and the oxygen atom on the alkoxy group is connected to the upper right polyoxyalkylene ether segment, and the oxygen atom on the alkyleneoxy group is respectively connected to the lower left terminal residue and the upper right polyoxyalkylene ether segment; p is a number from 15 to 100;

[0024] Among them, in formula 2 to formula 4, n1, n2, and m satisfy n1+n2+m=20~80, and (n1+n2):m=

[0025] (1.8~6.0):1; at the same time, n1:n2=40~90:60~10.

[0026] Preferably, the aprotic polar solvent in step 1 is one or more of dimethyl sulfoxide, N,N-dimethylformamide, and tetrahydrofuran.

[0027] Preferably, in step 3, the precipitant is a mixed solution of C1-C4 saturated monohydric alcohol and hexane or cyclohexane, with a volume ratio of (30-70): (70-30); and its amount is 1-1.5 times the total mass of the dispersion of the reaction system.

[0028] Preferably, the base in step 4 is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, and the amount thereof is 0.3 to 1.0 times the total molar amount of the acrylate.

[0029] The invention discloses a water reducing agent, which is prepared by adopting the above preparation method.

[0030] The present invention also discloses the use of a water-reducing agent as a cement or concrete dispersant, suitable for cementitious systems with a water-cement ratio of 0.28 to 0.55. It exhibits excellent water-reducing properties and good adaptability to different types of cement. Furthermore, its slump retention performance can be controlled by using a hydroxy ester and adjusting the hydrolysis ratio. Its dosage is 0.08% to 0.25% of the total mass of the cementitious material, and its solid content is 0.08% to 0.25% of the total mass of the cementitious material. Below this value, sufficient dispersing effect is difficult to achieve; above this value, further increasing the dosage will have no significant benefit and will easily lead to undesirable phenomena such as bleeding and segregation.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The present invention introduces bidentate deciduous structural units (Formulas 2 to 4) through the Michael addition reaction of acrylamide-polyoxyalkylene ether copolymers with acrylic esters, significantly improving the initial dispersion speed and adaptability to complex cement systems. By adjusting the degree of ester hydrolysis, the slump retention performance can be flexibly controlled.

[0033] 2. The water-reducing agent prepared by this method contains bidentate deciduous coordination structural units, which, compared with traditional polycarboxylate water-reducing agents, strengthens the coordination binding effect with the mineral phase, improves the dispersion speed and adsorption stability; and the adsorption group distribution is more compact, resulting in a fast initial dispersion speed, low water bleeding rate, and improved adaptability to cement;

[0034] 3. The water reducer introduces hydroxyl esters to adjust the hydrolysis amount of the esters, thereby flexibly adjusting the dispersion behavior and slump retention characteristics of the water reducer;

[0035] 4. It shows significant adaptability advantages to complex cementitious systems (such as high-admixture cement).

[0036] The present invention also has other beneficial effects which are described in the embodiment section of the specification and will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Flow chart of the preparation method of the water reducing agent of the present invention;

[0038] Figure 2 Schematic diagram of the synthesis mechanism of the water reducer of the present invention. DETAILED DESCRIPTION

[0039] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the following Figure 1~Figure 2 The technical solutions of the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0040] In Examples 1 to 5 of the present invention, the molecular weight of the polymers was characterized using a Shimazu LC-20AD gel permeation chromatograph (GPC) with the following parameters: gel column: Shodex SB806 + 803 two chromatographic columns connected in series; washing solution: 0.1M NaNO3 solution; mobile phase speed: 1.0mL / min; injection: 20uL 0.5% aqueous solution; detector: Shodex RI-71 differential refractometer; standard: sodium polystyrene sulfonate GPC standard (Sigma-Ald rich, molecular weight 344100, 195800, 108200, 60000, 37500, 28200, 6900, 3000, 1400).

[0041] The structures of the acrylamide-methacrylic acid polyoxyalkylene ether ester copolymers and acrylates used in Examples 1 to 5 of the present invention are shown in Table 1 below.

[0042] Table 1 Chemical structural formulas of monomers involved in the synthesis process of Examples 1 to 5:

[0043] ;

[0044] .

[0045] Note: Conversion rate refers to the polymerization conversion rate of acrylamide monomer.

[0046] Example 1: 300 parts by mass of copolymer 1 were dispersed in 700 parts of DMSO, 40 ml of 0.8 M phosphazene base solution was added, and 72 parts by mass of methyl acrylate was added dropwise at a constant rate at 25°C for 2 hours. After the addition was completed, the mixture was kept warm for 12 hours to obtain an addition intermediate product solution.

[0047] The product was then precipitated by adding 1550 parts by mass of a 50% methanol-hexane (v / v) solution, and the solvent and catalyst were recovered by fractional distillation. The resulting precipitate was dispersed in water to prepare a 40% solution. 95 parts by mass of liquid caustic soda was added and the solution was treated at 45°C for 3 hours to obtain superplasticizer SP-1.

[0048] Example 2: 400 parts by mass of copolymer 2 were dispersed in 1600 parts of DMSO, 75 ml of 0.8 M phosphazene base solution was added, and 95 parts by mass of hydroxyethyl acrylate was added dropwise at a constant rate at 45°C for 4 hours. After the addition was completed, the mixture was kept warm for 20 hours to obtain an addition intermediate product solution.

[0049] The product was then precipitated by adding 2200 parts by mass of a 70% ethanol-hexane (v / v) solution, and the solvent and catalyst were recovered by fractional distillation. The resulting precipitate was dispersed in water to prepare a 30% solution. Sixty parts by mass of liquid caustic soda was added, and the solution was treated at 60°C for 3 hours to obtain superplasticizer SP-2.

[0050] Example 3: 225 parts by mass of copolymer 3 were dispersed in 275 parts of THF, 13.5 ml of 0.8 M phosphazene base solution was added, and 67 parts by mass of ethyl acrylate was added dropwise at a constant rate at 18°C for 1 hour. After the addition was completed, the mixture was kept warm for 5 hours to obtain an addition intermediate product solution.

[0051] The product was then precipitated by adding 850 parts by mass of a 40% butanol-cyclohexane (v / v) solution, and the solvent and catalyst were recovered by fractional distillation. The resulting precipitate was dispersed in water to prepare a 50% solution. 72 parts by mass of liquid caustic soda was added and the solution was treated at 35°C for 3 hours to obtain superplasticizer SP-3.

[0052] Example 4: 350 parts by mass of copolymer 4 was dispersed in 1050 parts of DMSO, 50 ml of 0.8 M phosphazene base solution was added, and 100 parts by mass of methyl methacrylate was added dropwise at a constant rate at 35°C for 1.5 hours. After the addition was completed, the mixture was kept warm for 16 hours to obtain an addition intermediate product solution.

[0053] The product was then precipitated by adding 1800 parts by mass of a 50% methanol-cyclohexane (v / v) solution, and the solvent and catalyst were recovered by fractional distillation. The resulting precipitate was dispersed in water to prepare a 35% solution. 112 parts by mass of liquid caustic soda was added, and the solution was treated at 60°C for 6 hours to obtain superplasticizer SP-4.

[0054] Example 5: 375 parts by mass of copolymer 5 were dispersed in 1125 parts of DMSO, 45 ml of 0.8 M phosphazene base solution was added, and a mixed solution of 102 parts by mass of hydroxyethyl acrylate and 34 parts by mass of hydroxypropyl acrylate was uniformly added dropwise at 35°C for 3 hours. After the addition was completed, the mixture was kept warm for 15 hours to obtain an addition intermediate product solution.

[0055] The product was then precipitated by adding 1750 parts by mass of a 50% ethanol-cyclohexane (v / v) solution, and the solvent and catalyst were recovered by fractional distillation. The resulting precipitate was dispersed in water to prepare a 45% solution. 45 parts by mass of liquid caustic soda was added and the solution was treated at 40°C for 4 hours to obtain superplasticizer SP-5.

[0056] Performance evaluation of the water reducers obtained in Examples 1 to 5 above:

[0057] First, the dispersion behavior of each Example 1 to Example 5 for various cements was characterized by mortar fluidity. The test process was based on GB / T8077-2000. 650g of cement, 1350g of standard sand, and a water-cement ratio of 0.33 were used in the test. The cements used were benchmark cement (PI42.5), two Helin cements (PO42.5 and P.II.52.5), and Onoda cement (P.II.52.5). Each cement component was quantitatively determined by XRD (internal standard, Rietveld method) (as shown in Table 2). All tests were performed at 20°C. To further confirm the effectiveness of the water reducers of each Example 1 to Example 5, a commercial polycarboxylate water reducer of type PCA-IV produced by Jiangsu Subote New Materials Co., Ltd. was used as a comparative example.

[0058] Table 2 Types and components of cement used in the evaluation tests of Examples 1 to 5:

[0059] .

[0060] The dispersion effects of the water reducers prepared in Examples 1 to 5 of the present invention and the water reducers of the comparative example on different cements are shown in Table 3 below.

[0061] Table 3 shows the dispersing efficiency of Examples 1 to 5 and the comparative example for different types of cement mortars, with a dosage of 0.12%, expressed in terms of expansion (mm):

[0062] .

[0063] As shown in Table 3, the initial water reduction of each sample from Examples 1 to 5 in each cement was significantly greater than that of the PCA-IV commercial high-performance water reducer in the comparative example, and their water loss over time was also superior. This indicates that Examples 1 to 5 achieved rapid dispersion with short stirring times while maintaining long-term water reduction efficiency. They exhibited high water reduction and good slump retention in cements with different water loss characteristics, confirming the water-reduction efficiency and cement compatibility advantages of Examples 1 to 5. Furthermore, Example 5, which is primarily modified with hydroxy esters and has a low degree of hydrolysis, exhibited properties similar to those of a slump retainer, demonstrating the advantage of the present invention in regulating the water loss characteristics of water reducers by adjusting the degree of hydrolysis.

[0064] Based on the above tests, the compatibility of the water-reducing agents of Examples 1 through 5 in cementitious systems containing different admixtures was also tested. These tests were also conducted using mortars. To eliminate the effects of pre-added admixtures, a benchmark cement was used. Pure cement slurries and mortars containing fly ash and mineral powder at 25% by weight of the cement, and calcined clay at 5%, were tested. The cement dispersion effects of Examples 1 through 5 and the comparative example were tested, and the results are shown in Table 4.

[0065] Table 4 shows the dispersing efficiency of cement mortar with admixtures of Examples 1 to 5 and the comparative example, with a water-binder ratio of 0.35 and an admixture dosage of 0.10%, expressed in terms of expansion (mm):

[0066] .

[0067] As shown in Table 4, except for the case where the performance was better than that of the control in pure cement mortar, the performance of the samples in each embodiment only decreased slightly in the fly ash-containing mortar, while the initial dispersion of the traditional polycarboxylic acid water-reducing agent PCA-IV in the fly ash-containing system with equal water-binder ratio decreased seriously; in the mineral powder-containing system, the performance of the samples in each embodiment increased more than that of the control compared with the pure cement mortar; in the calcined clay-containing system, the performance of each sample decreased significantly less than that of the control.

[0068] In summary, the results of the above application tests confirm the effectiveness of the water reducer disclosed in the present invention.

[0069] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a water reducing agent, characterized in that: The preparation method comprises the following steps: Step 1: dispersing the acrylamide-polyoxyalkylene ether macromonomer copolymer in an aprotic polar solvent to form a dispersion with a mass concentration of 20% to 45%; Step 2: Add a phosphazene base catalyst, and dropwise add acrylic acid ester at a constant rate at 15-45°C for 1-4 hours. After the addition is complete, keep the temperature to react for 4-20 hours to obtain an addition intermediate product solution; Step 3: Add a precipitant to precipitate the product, recover the solvent and catalyst by fractional distillation, and disperse the precipitate in water to prepare a solution with a mass concentration of 30-50%; Step 4: adding alkali and treating at 35-60° C. for 1-8 hours to obtain the water reducing agent SP; The molar ratio of acrylamide to polyoxyalkylene ether structural units in the acrylamide-polyoxyalkylene ether macromonomer copolymer is (1.8-6):1, and the weight-average molecular weight is 5,000-50,000 g / mol. The acrylic acid ester is an esterification product of acrylic acid and a C1-C4 alkyl 1-4 alcohol, and the amount used is 1.5-2.2 times the molar amount of the amide group in the acrylamide-polyoxyalkylene ether copolymer. The phosphazene base catalyst is a compound of formula 1, and its usage is 3% to 10% of the total molar amount of the main chain structural units of the copolymer: Formula 1; The water reducing agent SP includes structural units shown in Formula 2 to Formula 4: (1) Structural unit 1 is shown in formula 2: Formula 2; In formula 2: R1 and R2 are either hydrogen atoms or methyl groups, and R3 is hydrogen, sodium, potassium, or a C1-C4 saturated hydrocarbon group substituted with 1-2 hydroxyl groups; (2) Structural unit 2 is shown in formula 3: Formula 3; In formula 3: R4 is hydrogen or methyl, and R2 and R3 are defined the same as in formula 1; (3) Structural unit 3 is shown in formula 4: Formula 4; In formula 4: R5 is hydrogen or methyl; R6 is hydrogen or methyl, R7 is hydrogen or C1-C4 alkyl, and the molar proportion of hydrogen in R6 is 90-100%, and the rest is methyl; X is an ester group -COO-, an oxygen atom, or a C1-C4 alkoxy group or an alkyleneoxy group -ORO-, and the oxygen atom on the alkoxy group is connected to the upper right polyoxyalkylene ether segment, and the oxygen atom on the alkyleneoxy group is respectively connected to the lower left terminal residue and the upper right polyoxyalkylene ether segment; p is a number from 15 to 100; Among them, in formula 2 to formula 4, n1, n2, and m satisfy n1+n2+m=20~80, and (n1+n2):m= (1.8~6.0):1; at the same time, n1:n2=40~90:60~10.

2. The method for preparing a water reducing agent according to claim 1, wherein In step 1, the aprotic polar solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide, and tetrahydrofuran.

3. The method for preparing a water reducing agent according to claim 1, wherein In step 3, the precipitant is a mixed solution of C1-C4 saturated monohydric alcohol and hexane or cyclohexane, with a volume ratio of (30-70): (70-30); the amount used is 1-1.5 times the total mass of the dispersion of the reaction system.

4. The method for preparing a water reducing agent according to claim 1, wherein In step 4, the base is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, and its amount is 0.3 to 1.0 times the total molar amount of the acrylate.

5. A water reducing agent, characterized in that The method is as described in any one of claims 1 to 4.

6. A use of the water reducing agent according to claim 5, characterized in that: As a cement or concrete dispersant, it is suitable for cementitious systems with a water-cement ratio of 0.28~0.55, and its dosage is 0.08%~0.25% of the total mass of the adhesive.

Images