Polycarboxylate-type water reducing agent as well as preparation method and application thereof

Abstract

The preparation method comprises the following steps: firstly, carrying out a ring-opening esterification reaction on an acrylic acid monomer and alkylene oxide under the action of a catalyst to synthesize carboxylic acid monomers with different hydrophilic-lipophile values (HLB values); the polycarboxylate-type water reducing agents with different HLB (Hydrophile-Lipophile Balance) values are synthesized by a three-drop-adding water-phase free radical polymerization method. Compared with the prior art, the polycarboxylic acid water reducer and the preparation method thereof have the characteristics of simple synthesis process and excellent slump loss resistance and workability improvement performance.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete admixtures, in particular to a polycarboxylic acid-based water reducer and a preparation method and application thereof. Background Art

[0002] Polycarboxylate superplasticizers are the third generation of concrete water reducers. Their molecular structure is comb-shaped, with carboxylate adsorption groups as the main chain and polyether side chains of a certain molecular weight. They also have two mechanisms of action: steric hindrance and electrostatic interaction (Shui Liangliang et al., Research Progress on the Action Mechanism of Polycarboxylate Superplasticizers [J], Journal of Building Materials, 2020, 23(1): 64-69+76). Compared to high-efficiency water reducers with linear molecular structures and primarily electrostatic interaction, polycarboxylate superplasticizers have performance advantages such as lower dosage, higher water reduction rate, and better fluidity retention. They are the most widely used type of water reducer in the concrete water reducer market.

[0003] Polycarboxylic acid-based water reducers are synthesized from acrylic monomers, polyether macromonomers, etc. through free radical polymerization. Acrylic monomers and polyether macromonomers account for the largest proportion of raw materials by mass and are also the focus and hotspot of basic theoretical research and industrialization research (Lei et al., 40 years of PCE superplasticizers-History, current state-of-the-art and an outlook[J], Cement and Concrete Research, 2022, 157:106826).

[0004] Polyether macromonomers account for over 85% of the raw material mass of polycarboxylate superplasticizers and are the most widely used raw material in polycarboxylate superplasticizers. Polyether macromonomers are generally synthesized by ring-opening polymerization of unsaturated alcohols containing double bonds with ethylene oxide. By varying the type of unsaturated alcohol, polyether macromonomers with varying double bond polymerization reactivity can be prepared, including allyl polyethylene glycol ether (APEG), methylallyl polyethylene glycol ether (HPEG), 3-isopentenyl polyethylene glycol ether (TPEG or IPEG), vinyl polyethylene glycol ether (VPEG), and vinyloxybutyl polyethylene glycol ether (VBPEG). Furthermore, the introduction of hydrophobic structural units into polyether macromonomers can adjust the HLB value of polycarboxylate superplasticizers, significantly impacting their performance.Plank et al. (Influence of the HLB value of polycarboxylate superplasticizers on the flow behavior of mortar and concrete[J], Cement and Concrete Research, 2014, 60: 45-50) showed that the HLB of polycarboxylate superplasticizers has an important influence on the rheological properties of mixed concrete; Ran et al. (Effect of the Different Hydrophobic Groups of Polycarboxylate Superplasticizers on the Properties in Cement Mortars[J], Polymer Composites, 2017, 38(9): 1783-1791) showed that the polycarboxylate superplasticizers synthesized using polyether macromonomers synthesized from unsaturated alcohols with long alkyl carbon chains and ethylene oxide had reduced initial water-reducing performance and improved slump retention performance; Fan et al. (Synthesis and performance of polycarboxylate superplasticisers with different propylene oxide contents[J], Advances in Cement Research, 2019, 31(5): 205-213,), the introduction of hydrophobic PO structural units into polycarboxylate water-reducing agents can reduce the shear viscosity of cement paste and improve the slump retention performance of water-reducing agents; Qian et al. (Synthesis, characterization and working mechanism of a novel polycarboxylate superplasticizer for concrete possessing reduced viscosity [J], Construction and Building Materials, 2018, 169: 452-461) showed that the introduction of hydrophobic PO structural units into polyether macromonomers can reduce the surface tension of polycarboxylate water-reducing agents, which is beneficial to the wetting of the cement particle surface and the introduction of a large number of tiny bubbles, thereby reducing the slip resistance between cement particles.

[0005] The above research results indicate that adjusting the molecular structure and HLB value of polyether macromonomers can improve the solution conformation, adsorption properties, adsorption layer thickness, and surface tension of polycarboxylate superplasticizers, thereby influencing their application properties such as water reduction, slump retention, workability, and viscosity reduction. However, adjustments to the molecular structure and HLB value of polyether macromonomers primarily affect the performance of polycarboxylate superplasticizers through the side chains formed by the polyether macromonomers. Research on the effects of adjustments to the main chain molecular structure and HLB value of polycarboxylate superplasticizers on these properties is lacking.

[0006] Acrylic monomers are the second-largest raw material by mass in polycarboxylic acid-based water-reducers. Examples of monomers reported in literature and patents include acrylic acid, methacrylic acid, itaconic acid, maleic anhydride, hydroxyethyl acrylate, and hydroxypropyl acrylate. Since the synthesis of polycarboxylic acid-based water-reducers involves a free radical copolymerization reaction between acrylic monomers and polyether macromonomers, the matching of the polymerization activities between the double bonds is crucial, directly impacting monomer conversion during polymerization and product performance. Adjusting the backbone molecular structure and HLB of polycarboxylic acid-based water-reducers through adjustments to material ratios and process parameters, such as the acid-ether ratio, addition method, catalyst, reaction temperature, and addition time, is not a viable approach. Consequently, acrylic acid, hydroxyethyl acrylate, and hydroxypropyl acrylate remain the most commonly used acrylic monomers in the current synthesis of polycarboxylic acid-based water-reducers.

[0007] Therefore, there is an urgent need for a preparation method of a polycarboxylic acid-based water reducer to solve the problem that the main chain molecular structure and HLB value of the polycarboxylic acid-based water reducer are difficult to flexibly adjust. Summary of the Invention

[0008] The purpose of the present invention is to provide a polycarboxylic acid water reducer, a preparation method thereof, and an application thereof in order to solve the above-mentioned problems. The present invention addresses the problem that the main chain molecular structure and HLB value of the polycarboxylic acid water reducer are difficult to flexibly adjust. First, a carboxylic acid monomer having a different molecular structure and HLB value but the same double bond polymerization activity as the original acrylic acid monomer is synthesized. Then, the carboxylic acid monomer and acrylic acid are used as the main raw materials to synthesize the polycarboxylic acid water reducer in a redox system. This improves the application performance of the polycarboxylic acid water reducer, and the preparation method is simple and easy to master.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] The present invention relates to a polycarboxylic acid-based water reducer, its preparation method, and application. First, an acrylic acid monomer and an alkylene oxide undergo a ring-opening esterification reaction in the presence of a catalyst to synthesize carboxylic acid monomers with different hydrophilicity and lipophilicity values (HLB values). Using the carboxylic acid monomers and polyether macromonomers as raw materials, a three-drop aqueous phase free radical polymerization method is used to synthesize the polycarboxylic acid-based water reducers with different HLB values. Compared with the prior art, the polycarboxylic acid-based water reducer and its preparation method of the present invention have the advantages of a simple synthesis process, excellent collapse-preserving properties, and improved workability.

[0011] The first object of the present invention is to provide a method for preparing a polycarboxylate water reducer, the method comprising the following steps:

[0012] (1) Synthesis of carboxylic acid monomer: Using acrylic acid monomer and alkylene oxide as raw materials, a ring-opening polymerization reaction occurs under the action of a catalyst to obtain a carboxylic acid monomer;

[0013] (2) Synthesis of polycarboxylic acid water reducer: Water, oxidant, acidifying agent and polyether macromonomer are used as base material, carboxylic acid monomer, reducing agent and chain transfer agent are added to the base material respectively, and the polycarboxylic acid water reducer is obtained by reaction.

[0014] Furthermore, the carboxylic acid monomer is synthesized by a ring-opening reaction of an excess of acrylic acid monomer and alkylene oxide, and the reaction process is shown in the following formula (B).

[0015]

[0016] Furthermore, the alkylene oxide includes one or more of styrene oxide (phenyl ethylene oxide), cyclohexene oxide, glycidol, butyl ethylene oxide, isopropyl glycidyl ether, butyl glycidyl ether, phenyl glycidyl ether, benzyl glycidyl ether, glycidyl furfuryl ether, octyl glycidyl ether, and trimethyl glycidyl ammonium chloride.

[0017] Furthermore, the acrylic acid monomer is one or more of acrylic acid, methacrylic acid, itaconic acid and maleic acid. The molecular structure of the acrylic acid monomer is shown in the following formula (C).

[0018]

[0019] Furthermore, the acrylic monomer is one or more of acrylic acid, methacrylic acid, itaconic acid and maleic acid.

[0020] Furthermore, the catalyst is a tertiary amine catalyst.

[0021] Furthermore, the catalyst includes one or more of triethylamine, N,N-dimethylethanolamine, triethanolamine, triisopropanolamine, monoethanoldiisopropanolamine, and diethanolmonoisopropanolamine. The tertiary amine catalyst is complexed with the acrylic acid monomer to form a salt to form a catalytically active species, thereby enhancing the ring-opening polymerization activity of the acrylic acid monomer towards alkylene oxide.

[0022] Furthermore, in step (1), the mass ratio of acrylic monomer, catalyst and alkylene oxide is 1:(0.0001-0.001):(0.01-0.1).

[0023] Furthermore, in step (1), the ring-opening polymerization reaction uses acrylic monomer and catalyst as primer, and alkylene oxide is added dropwise into the primer to react. After the addition is completed, the reaction is continued for a certain period of time while keeping warm to obtain a polycarboxylic acid-based water reducer.

[0024] Furthermore, in step (1), the reaction pressure is normal pressure and the reaction temperature is 20-50°C;

[0025] Furthermore, in step (1), the alkylene oxide is added dropwise for 1.0-3.0 hours, and after the addition of the alkylene oxide is completed, the heat preservation reaction time is 1.0 hour.

[0026] Furthermore, the acidifying agent is one or more of acetic acid, polyacrylic acid (50%) (abbreviated as PAA), hydrolyzed polymaleic anhydride (50%) (abbreviated as PMAn), concentrated sulfuric acid (98%), and phosphoric acid (85%).

[0027] Furthermore, the oxidant is one or more of hydrogen peroxide (H2O2, mass fraction 27.5%), sodium persulfate, and ammonium persulfate.

[0028] Preferably, hydrogen peroxide (27.5%) is used as the oxidizing agent.

[0029] Furthermore, the polyether macromonomer includes one or more of methallyl polyethylene glycol ether, 3-isopentenyl polyethylene glycol ether, ethylene glycol monovinyl polyethylene glycol ether and vinyloxybutyl polyethylene glycol ether.

[0030] Further preferably, the polyether macromonomer includes one or more of commercially available methyl allyl polyethylene glycol ether (HPEG2400), 3-isopentenyl polyethylene glycol ether (TPEG2400), ethylene glycol monovinyl polyethylene glycol ether (EPEG3000) and vinyloxybutyl polyethylene glycol ether (VPEG3000).

[0031] Furthermore, the molecular formula of the polyether macromonomer is shown in the following formula (A):

[0032]

[0033] Wherein, m is a positive integer.

[0034] Furthermore, the reducing agent is one or more of vitamin C, bleaching agent, E51, etc.

[0035] More preferably, vitamin C (abbreviated as Vc) is used as the reducing agent.

[0036] Furthermore, the chain transfer agent is one or more of mercaptoethanol, thioglycolic acid, mercaptopropanol, mercaptopropionic acid, etc.

[0037] Furthermore, the amount of the oxidant is 0.5%-1.0% of the mass of the polyether macromonomer.

[0038] Furthermore, the amount of the acidifying agent is 0.05%-0.1% of the mass of the polyether macromonomer.

[0039] Furthermore, the amount of the carboxylic acid monomer is 5%-15% of the mass of the polyether macromonomer.

[0040] Furthermore, the amount of the reducing agent is 0.1%-0.3% of the mass of the polyether macromonomer.

[0041] Furthermore, the amount of the chain transfer agent is 0.2%-0.6% of the mass of the polyether macromonomer.

[0042] More preferably, mercaptoethanol, which is used in small amounts and has a low price, is selected as the chain transfer agent.

[0043] Furthermore, step (2) specifically includes the following process:

[0044] Water, an oxidizing agent, an acidifying agent and a polyether macromonomer are used as a base material, a carboxylic acid monomer is used as a dropping liquid A, a reducing agent is prepared into an aqueous solution as a dropping liquid B, and a chain transfer agent is prepared into an aqueous solution as a dropping liquid C. Under certain temperature and time conditions, the dropping liquids A, B and C are continuously added dropwise to the base material for reaction. After the addition is completed, the temperature is kept constant and the reaction is continued for a certain time to obtain a polycarboxylic acid-based water reducer.

[0045] Furthermore, the reducing agent is diluted with water to 50 wt % as the dropwise addition liquid B.

[0046] Furthermore, the chain transfer agent is diluted with water to 50 wt % as the dropwise addition liquid C.

[0047] Furthermore, in step (2), the reaction pressure is normal pressure, the initial dropwise addition temperature is 15-25°C, and the maximum temperature during the dropwise addition and insulation process is ≤40°C; the dropwise addition time of the dropwise addition liquid A is 1.0-3.0h, and the dropwise addition time of the dropwise addition liquid B and the dropwise addition liquid C is extended by 0.2-0.5h than that of the dropwise addition liquid A. After the dropwise addition is completed, the reaction is continued for 1.0h by insulation.

[0048] Furthermore, step (2) specifically includes the following process:

[0049] The reaction conditions are normal pressure. First, the polyether macromonomer is diluted with water to a solid content of 60 wt%. Then, an acidifying agent is added and stirred thoroughly until completely dissolved (stirring for 0.1-0.2 hours). Then, an oxidizing agent is added and stirring is continued for 0.1-0.2 hours to obtain a base material. After the base material is prepared, three dropwise additions, namely, dropwise addition liquid A, dropwise addition liquid B, and dropwise addition liquid C, are added dropwise simultaneously while stirring. The addition time of dropwise addition liquid A is set to 1.0-3.0 hours, and the addition time of dropwise addition liquids B and C is extended by 0.2-0.5 hours compared to dropwise addition liquid A. After the addition is completed, the temperature is maintained for 1.0 hours.

[0050] The second purpose of this embodiment is to provide a polycarboxylic acid-based water reducer, which is prepared by the above preparation method, wherein the monomer conversion rate of the polyether macromonomer is ≥90%, the weight average molecular weight of the polycarboxylic acid-based water reducer is 20,000-800,000, and the molecular weight distribution is ≤2.0.

[0051] The third purpose of this embodiment is to provide an application of the polycarboxylic acid water reducer prepared by the above preparation method, wherein the polycarboxylic acid water reducer is used as a concrete admixture.

[0052] Furthermore, the polycarboxylate water reducer has higher initial expansion and slump of concrete, shorter outflow time, and better workability improvement performance.

[0053] Compared with the prior art, the beneficial effects of the present invention are embodied in the following aspects:

[0054] 1) The present invention provides a polycarboxylic acid-based water reducer, a preparation method thereof, and an application thereof. Based on existing acrylic acid monomers, a hydrophobic group or a quaternary ammonium salt group is introduced through a ring-opening reaction of acrylic acid monomers with alkylene oxides, thereby adjusting the HLB value (hydrophile-lipophile balance) and molecular structure of the main chain of the polycarboxylic acid-based water reducer. The polycarboxylic acid-based water reducer has the characteristics of strong adjustability of the main chain molecular structure, simple synthesis method, and good economic efficiency.

[0055] 2) The present invention provides a polycarboxylic acid-based water reducer, a preparation method, and an application thereof. Acrylic acid monomers react with alkylene oxide to generate an esterification product, namely a carboxylic acid monomer. This solves the problem that traditional acrylic acid monomers have few types and little variation in molecular structure. It also avoids the traditional esterification reaction process with its long reaction time, high reaction temperature, and the need for a water agent.

[0056] 3) The present invention provides a polycarboxylic acid-based water reducer, a preparation method, and an application thereof. A low-temperature, high-efficiency synthesis process for acrylic acid and alkylene oxide is developed. Tertiary amine substances are used as catalysts to form amine salts as catalyst active species by complexing with carboxylic acid groups, thereby improving the efficiency of the ring-opening reaction of carboxylic acid groups on alkylene oxides. Thirdly, by optimizing the material ratio of acrylic acid monomers to alkylene oxides, some acrylic acid monomers are esterified and modified, thereby ensuring the selectivity and yield of monoester products in carboxylic acid monomers. Fourthly, the carboxylic acid monomers generated by the reaction contain hydroxyl groups, which can improve the water solubility of the esterified products to a certain extent.

[0057] 4) The present invention provides a polycarboxylic acid water reducer, its preparation method, and application, which not only maintains the double bond polymerization activity of acrylic monomers, but also increases the application of acrylic monomers with different molecular structures in the polymerization reaction of polycarboxylic acid water reducers, thereby improving the solution conformation, adsorption performance, bubble structure, and surface tension of the polycarboxylic acid water reducer, thereby affecting the application properties of the water reducer, such as water reduction, slump retention, workability, and viscosity reduction.

[0058] 5) The present invention provides a polycarboxylic acid-based water reducer, a preparation method thereof, and an application thereof. Introducing an acidifying agent during the polymerization process of the polycarboxylic acid-based water reducer has the effect of enhancing the double bond polymerization activity of the polyether macromonomer, especially for reaction conditions with a low acid-ether molar ratio, and can significantly improve the monomer conversion rate of the polyether macromonomer and the application performance of the final prepared product. DETAILED DESCRIPTION

[0059] The present invention is described in detail below with reference to specific embodiments, but is by no means intended to limit the present invention. Any features, such as preparation methods, materials, structures, or composition ratios, that are not explicitly described in this technical solution are considered to be common technical features disclosed in the prior art.

[0060] These embodiments are merely illustrative and are not intended to limit the scope of the present invention. Based on the disclosure herein, those skilled in the art will be able to modify the chemical reagents, processes, and reaction equipment within the scope of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be within the scope of protection of the present invention.

[0061] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0062] In the present embodiment, the reaction of acrylic acid monomers with alkylene oxides was confirmed by acid-base titration. The alkylene oxide conversion was calculated by comparing the standard alkali solution consumption before and after the addition of the alkylene oxide. The weight-average molecular weight, molecular weight distribution (PDI), and monomer conversion of the low-molecular-weight polycarboxylic acid and early-strength water-reducing admixture were determined using a Wyatt Technology Corporation gel permeation chromatography instrument (mobile phase: 0.1 mol / L aqueous NaNO₃ solution; mobile phase speed: 1 ml / min; injection volume: 20 μl; sample preparation concentration: 0.5% (g sample / g mobile phase); detector: Shodex RI-71 differential refractive index detector; standard: polyethylene glycol GPC standard (Sigma-Aldrich, molecular weights: 1,010,000, 478,000, 263,000, 118,000, 44,700, 18,600, 6,690, 1960, 628, 232).

[0063] Example

[0064] The examples provide a polycarboxylate-based water reducer and a method for preparing the same. The examples are divided into two parts: the synthesis of the carboxylate monomer and the preparation of the polycarboxylate-based water reducer. Parts in the examples are specifically parts by mass; the amounts of other materials added are converted to parts by mass.

[0065] (1) Preparation of carboxylic acid monomer

[0066] The molecular structures and code details of acrylic monomers and alkylene oxides are shown in Table 1.

[0067] Table 1 Molecular structures and codes of acrylic monomers or alkylene oxides

[0068]

[0069] The carboxylic acid monomer is synthesized by ring-opening polymerization using acrylic acid monomer and alkylene oxide as raw materials in the presence of a tertiary amine catalyst. The material ratio and process conditions for the synthesis of the carboxylic acid monomer are shown in Table 2.

[0070] Table 2 Material ratio table and process conditions of carboxylic acid monomer (unit: mass parts)

[0071]

[0072]

[0073] Carboxylic acid monomer synthesis steps: According to the raw material ratios in Table 2, weigh the acrylic monomer and catalyst into a reactor, stir thoroughly until completely dissolved, and control the temperature to the set temperature. Weigh the alkylene oxide as the dropwise addition liquid, set the addition time, and control the reaction temperature to the set temperature during the addition. After the addition is completed, continue the reaction at this temperature for 1.0 hour to obtain the carboxylic acid monomers, which are named SD-1 to SD-7 in order.

[0074] The reaction degree of the carboxylic acid monomer is calculated based on the alkylene oxide conversion rate. The acid-base titration method is used to calculate the consumption of standard alkali solution (0.01 mol / L) before and after the reaction and convert it into the alkylene oxide conversion rate.

[0075] Table 3 Acid-base titration test of carboxylic acid monomers

[0076]

[0077]

[0078] (2) Synthesis of polycarboxylic acid water reducer

[0079] The material ratio for the synthesis of polycarboxylic acid water reducer is shown in Table 4.

[0080] Table 4 Material ratios for the synthesis of polycarboxylic acid water reducers (unit: parts by mass)

[0081]

[0082] The process parameter settings for the synthesis of polycarboxylic acid-based water reducer are shown in Table 5.

[0083] Table 5 Process parameters for the synthesis of polycarboxylate water reducers

[0084]

[0085]

[0086] The synthesis steps of the polycarboxylic acid-based water reducer are as follows: according to the amounts in the material ratio table 4, the polyether macromonomer is weighed and added to the reaction device and diluted with water to 60% solid content; the acidifying agent is weighed and added to the reaction device, and stirred for 0.1h until fully dissolved; and H2O2 is weighed.

[0087] (27.5%) was added to the reaction apparatus and stirred for 0.1 h until fully mixed. The temperature of the reaction system was controlled to the set value in Table 5.

[0088] Weigh the corresponding carboxylic acid monomer SD and dilute it with water to 80% solids to form Dropping Solution A. Weigh the reducing agent Vc and dilute it with water to 5% solids to form Dropping Solution B. Weigh the chain transfer agent mercaptoethanol and dilute it with water to 50% solids to form Dropping Solution C. Set the addition times for Dropping Solution A, Dropping Solution B, and Dropping Solution C according to the process parameters in Table 5. During the additions, maintain the reaction temperature at the values specified in Table 5. After the additions are complete, continue the reaction at this temperature for 1.0 h. Then, dilute the mixture with water to 40% solids to obtain the finished polycarboxylic acid-based water-reducing agent.

[0089] The polycarboxylate water reducer in the examples was tested using GPC. The test results are shown in Table 6.

[0090] Table 6 GPC test of polycarboxylate water reducer

[0091]

[0092] Comparative Example 1

[0093] This comparative example provides a method for preparing a polycarboxylic acid-based water reducer, comprising the following steps:

[0094] Weigh 100g of HPEG2400 polyether monomer and dilute with water to 60% solids. Add 0.06 parts of acetic acid, an acidifying agent, and stir for 0.1h until fully dissolved. Then, add 0.7 parts of 27.5% H2O2 and stir for 0.1h until thoroughly mixed. Weigh 9.0 parts of acrylic acid and dilute with water to 80% solids as Dropping Solution A; weigh 0.25 parts of reducing agent Vc and dilute with water to 5% solids as Dropping Solution B; weigh 0.56 parts of chain transfer agent mercaptopropionic acid and dilute with water to 50% solids as Dropping Solution C.

[0095] The starting temperature was set at 10°C, and the addition time of the droplets A, B, and C was set at 2.5h, 3.0h, and 3.0h, respectively. The temperature was not controlled during the addition process, and the reaction system temperature reached a maximum of 45.2°C. After the addition was completed, the reaction was kept warm for 1.0h, and water was added to dilute it to 40% solid content to obtain the finished polycarboxylic acid water reducer. GPC test showed that M n =17446,M w =31054, PDI=1.78, monomer conversion rate 82.35%.

[0096] In Comparative Example 1, acrylic acid was not modified by reacting with alkylene oxide; the initial dropwise addition temperature was low, and the maximum reaction temperature exceeded the limit. The monomer conversion rate in Comparative Example 1 was lower than that in the Examples.

[0097] Comparative Example 2

[0098] This comparative example provides a method for preparing a polycarboxylic acid-based water reducer, comprising the following steps:

[0099] Weigh 12.0 parts of maleic acid, add 0.006 parts of triethanolamine as a catalyst, weigh 0.6 parts of glycidol, and add the alkylene oxide dropwise at 35°C and normal pressure for 1.0 hour. After the addition is complete, continue the reaction at this temperature for 1.0 hour to obtain the carboxylic acid monomer SD-8.

[0100] Weigh 100g of TPEG2400 polyether monomer and dilute it with water to 60% solids. Add 0.07 parts of 85% phosphoric acid (acidifying agent) and stir for 0.1h until fully dissolved. Then, add 1.5 parts of 27.5% H2O2 and stir for 0.1h until thoroughly mixed. Weigh 12.35 parts of SD-8 and dilute it with water to 80wt% as Dropping Solution A. Weigh 0.35 parts of reducing agent Vc and dilute it with water to 5% as Dropping Solution B. Weigh 0.1 parts of chain transfer agent mercaptoethanol and dilute it with water to 50wt% as Dropping Solution C.

[0101] The starting temperature was set at 40°C, and the addition time of the droplets A, B, and C was set at 2.0h, 2.5h, and 2.5h, respectively. The temperature of the reaction system was controlled to be ≤60°C during the addition. After the addition was completed, the reaction was kept warm for 1.0h, and water was added to dilute the mixture to 40% solid content to obtain the finished product of the polycarboxylic acid water reducer. According to GPC test, M n =21446,M w =41176, PDI=1.97, monomer conversion rate 74.83%.

[0102] In Comparative Example 2, only maleic acid was used to react with alkylene oxide, the amount of hydrogen peroxide used exceeded the standard, the initial set temperature was 40°C, and the maximum temperature was ≤60°C; the amount of mercaptoethanol used was relatively low. The monomer conversion rate in Comparative Example 2 was lower than that in the examples.

[0103] Comparative Example 3

[0104] This comparative example provides a method for preparing a polycarboxylic acid-based water reducer, comprising the following steps:

[0105] Weigh 12.0 parts of acrylic acid and 8.0 parts of itaconic acid, add 0.006 parts of triethanolamine as a catalyst, and weigh 5.0 parts of cyclohexane. Add the cyclohexane dropwise at 85°C and atmospheric pressure for 1.0 hour. After the addition is complete, continue the reaction at this temperature for 1.0 hour to obtain carboxylic acid monomer SD-9.

[0106] Weigh 100g of EPEG2400 polyether monomer and dilute with water to 60% solids. Then, add 0.75 parts of 27.5% H2O2 and stir for 0.1h until thoroughly mixed. Weigh 20.35 parts of SD-9 and dilute with water to 80wt% as Dropping Solution A. Weigh 0.25 parts of reducing agent Vc and dilute with water to 5% as Dropping Solution B. Weigh 0.45 parts of chain transfer agent mercaptoethanol and dilute with water to 50wt% as Dropping Solution C.

[0107] The starting temperature was set at 5°C, and the addition time of the droplets A, B, and C was set at 0.9h, 1.0h, and 1.0h, respectively. The temperature of the reaction system was controlled to be ≤20°C during the addition. After the addition was completed, the reaction was kept warm for 1.0h, and water was added to dilute the mixture to 40% solid content to obtain the finished product of the polycarboxylic acid water reducer. GPC test showed that M n =23794,M w =39736, PDI=1.67, monomer conversion rate 85.83%.

[0108] In Comparative Example 3, the amount of cyclohexene oxide exceeded the standard, the amount of SD-9 exceeded the standard, the initial setting temperature was 5° C., and the maximum temperature was ≤20° C. The monomer conversion rate of Comparative Example 3 was lower than that of the examples.

[0109] Application Example 1

[0110] The fluidity test of cement paste was conducted in accordance with GB / T8077-2023, "Test Method for Homogeneity of Concrete Admixtures." The water-reducing agent was diluted to a 10% solids content. Conch PO 42.5 cement was used with a water-cement ratio of 0.29 and an admixture dosage of 0.10% of the cement content. The fluidity of the cement paste was measured on a flat glass plate. The viscosity of the cement paste was measured in accordance with GB / T10274-2008, "Viscosity Measurement Method." Commercially available polycarboxylate-based water-reducers PCE-1 and PCE-2 were used as comparison samples. The test results for the cement paste are shown in Table 7.

[0111] Table 7 Cement paste fluidity test

[0112]

[0113]

[0114] The data in the table show that the polycarboxylate superplasticizer prepared using the preparation method of the present invention exhibits slightly better initial water-reducing performance than commercially available and comparative example samples, but exhibits a significant advantage in slump retention. Furthermore, in a rotational viscosity test of the initial neat slurry, the polycarboxylate superplasticizer of the present invention demonstrates a significant reduction in neat slurry viscosity.

[0115] Application Example 2

[0116] The performance of the polycarboxylic acid water-reducing agent of the present invention was tested using a concrete test. The test was conducted with reference to the provisions of the national standard GB / T 8076-2008 "Concrete Admixtures". The cement used was Conch PO 42.5 cement, the fly ash was secondary ash; the sand was medium sand with a fineness modulus Mx=2.6, and the sand had a moisture content of 5%; the gravel was continuously graded crushed stone with a particle size of 5 to 20 mm, and the gravel had a moisture content of 2%. The dosage of the water-reducing agent (solid content 10%) was 1.3%. The bulk density of C30 strength grade concrete is 2316Kg / m 3 The raw material proportions of concrete test are shown in Table 8.

[0117] Table 8 Concrete raw material ratio

[0118]

[0119] The concrete test data of polycarboxylate water reducer are shown in Table 9.

[0120] Table 9 Concrete test of polycarboxylate water reducer

[0121]

[0122]

[0123] The data in the table show that the polycarboxylate water-reducing agent prepared using the preparation method of the present invention exhibits slightly better initial concrete expansion and slump than those of Comparative Examples 1-3 and commercially available samples. Furthermore, an inverted slump bucket test revealed that the polycarboxylate water-reducing agent prepared using the preparation method of the present invention exhibits a shorter outflow time and a significantly shorter time to reach 500 mm expansion than those of Comparative Examples 1-3 and commercially available samples. This demonstrates that the polycarboxylate water-reducing agent prepared using the preparation method of the present invention exhibits superior workability-improving properties.

[0124] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a polycarboxylic acid water reducer, characterized in that: The preparation method comprises the following steps: (1) Using acrylic acid monomer and alkylene oxide as raw materials, a ring-opening polymerization reaction occurs under the action of a catalyst to obtain a carboxylic acid monomer; (2) Using water, an oxidizing agent, an acidifying agent, and a polyether macromonomer as a base material, a carboxylic acid monomer, a reducing agent, and a chain transfer agent are added to the base material respectively to react to obtain a polycarboxylic acid-based water reducer.

2. A polycarboxylic acid water reducer according to claim 1, characterized in that: The acrylic acid monomer is one or more of acrylic acid, methacrylic acid, itaconic acid and maleic acid; The alkylene oxide includes one or more of styrene oxide, cyclohexene oxide, glycidol, butyl ethylene oxide, isopropyl glycidyl ether, butyl glycidyl ether, phenyl glycidyl ether, benzyl glycidyl ether, glycidyl furfuryl ether, octyl glycidyl ether, and trimethyl glycidyl ammonium chloride; The acrylic acid monomer is one or more of acrylic acid, methacrylic acid, itaconic acid and maleic acid; The catalyst is a tertiary amine catalyst.

3. A polycarboxylic acid water reducer according to claim 2, characterized in that: The catalyst includes one or more of triethylamine, N,N-dimethylethanolamine, triethanolamine, triisopropanolamine, monoethanoldiisopropanolamine and diethanolmonoisopropanolamine.

4. A polycarboxylic acid water reducer according to claim 1, characterized in that: In step (1), the mass ratio of acrylic monomer, catalyst, and alkylene oxide is 1:(0.0001-0.001):(0.01-0.1); In step (1), the reaction pressure is normal pressure and the reaction temperature is 20-50°C; In step (1), the ring-opening polymerization reaction uses acrylic acid monomer and catalyst as the primer, and the alkylene oxide is added dropwise into the primer to react. After the addition is completed, the reaction is continued for a certain period of time while keeping the temperature to obtain a polycarboxylic acid-based water reducer; In step (1), the alkylene oxide is added dropwise for 1.0-3.0 hours. After the addition of the alkylene oxide is completed, the heat preservation reaction time is 1.0 hour.

5. A polycarboxylic acid water reducer according to claim 1, characterized in that: The acidifying agent is one or more of acetic acid, polyacrylic acid, hydrolyzed polymaleic anhydride, concentrated sulfuric acid, and phosphoric acid; The oxidant is one or more of hydrogen peroxide, sodium persulfate, and ammonium persulfate; The polyether macromonomer includes one or more of methallyl polyethylene glycol ether, 3-isopentenyl polyethylene glycol ether, ethylene glycol monovinyl polyethylene glycol ether and vinyloxybutyl polyethylene glycol ether; The reducing agent is one or more of vitamin C, Diaobaikuai, and E51; The chain transfer agent is one or more of mercaptoethanol, thioglycolic acid, mercaptopropanol, and mercaptopropionic acid.

6. A polycarboxylic acid water reducer according to claim 1, characterized in that: The amount of the oxidant is 0.5%-1.0% of the mass of the polyether macromonomer; The amount of the acidifying agent is 0.05%-0.1% of the mass of the polyether macromonomer; The amount of the carboxylic acid monomer is 5%-15% of the mass of the polyether macromonomer; The amount of the reducing agent is 0.1%-0.3% of the mass of the polyether macromonomer; The amount of the chain transfer agent is 0.2%-0.6% of the mass of the polyether macromonomer.

7. The polycarboxylic acid water reducer according to claim 1, characterized in that: Step (2) specifically includes the following process: Water, an oxidizing agent, an acidifying agent and a polyether macromonomer are used as a base material, a carboxylic acid monomer is used as a dropping liquid A, a reducing agent is prepared into an aqueous solution as a dropping liquid B, and a chain transfer agent is prepared into an aqueous solution as a dropping liquid C. Under certain temperature and time conditions, the dropping liquids A, B and C are continuously added dropwise to the base material for reaction. After the addition is completed, the temperature is kept constant and the reaction is continued for a certain time to obtain a polycarboxylic acid-based water reducer.

8. A polycarboxylic acid water reducer according to claim 7, characterized in that: The reducing agent is diluted with water to 50 wt % as dropwise addition liquid B; The chain transfer agent is diluted with water to 50 wt % as dropwise addition liquid C; In step (2), the reaction pressure is normal pressure, the initial dropwise addition temperature is 15-25°C, and the maximum temperature during the dropwise addition and insulation process is ≤40°C; The dropping time of the dropwise addition liquid A is 1.0-3.0 h, and the dropping time of the dropwise addition liquid B and the dropwise addition liquid C is extended by 0.2-0.5 h compared with the dropwise addition liquid A. After the dropwise addition is completed, the reaction is continued by keeping warm for 1.0 h.

9. A polycarboxylate water reducer prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The monomer conversion rate of the polyether macromonomer is ≥90%, the weight average molecular weight of the polycarboxylic acid water reducer is 20,000-800,000, and the molecular weight distribution is ≤2.

0.

10. An application of a polycarboxylate water reducer prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The polycarboxylate water reducer is used as a concrete admixture.

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