Powder polycarboxylic acid water reducer

Abstract

The invention relates to the field of building materials, and discloses a powdery polycarboxylate superplasticizer, which is composed of the following components by mass: 80-90 parts of isopentenol polyoxyethylene ether; 8-12 parts of acrylic acid; 0.3 to 0.5 part of an oxidizing agent A; 0.1 to 0.15 part of an oxidizing agent B; 0.35 to 0.45 part of a molecular weight regulator; 0.15 to 0.2 part of a reducing agent A; 0.04 to 0.06 part of a reducing agent B; 1.8 to 2.2 parts of a neutralization solution; and 0.8 to 1.0 part of deionized water. The problems that in the prior art, water aqua transportation and packaging cost is high, raw material storage requirements are high, use is inconvenient, and the purity of produced retaining slump is not enough due to inaccurate raw material adding are solved, the flowing powder prepared through the special drying technology is green, free of pollution, free of hazardous chemicals, high in yield and suitable for industrial production. And the requirements of long-distance transportation and overseas export volume are further met.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and specifically relates to a powdered polycarboxylate water reducer. Background Art

[0002] The powdered polycarboxylate water reducer is a special admixture for concrete synthesized by a new technology. Its use greatly saves the costs of enterprises and endows concrete with excellent properties, and has been accepted by many concrete suppliers as an indispensable part. The main components of the powdered polycarboxylate water reducer are the same as those of the liquid polycarboxylate water reducer. Based on the unchanged liquid properties, it is made into a flowing powder by a special drying technology. It is mainly used in cement sculpture process components, dry-mixed mortar, high-strength mortar, self-leveling floor, tile adhesive, joint filler, gypsum products, colored wear-resistant concrete floor joint filler, grouting material, non-shrinkage grouting material, mechanical grouting material, refractory floor mortar, self-leveling mortar, dry-mixed concrete for joint filler, gypsum ceramic statue products, waterproof mortar, repair mortar, thermal insulation mortar, cement-based building premixed mortar, cement-based floor mortar, grouting agent (material), gypsum admixture, etc. It is also applicable to ordinary concrete, high-fluidity concrete, self-leveling concrete, etc. Its comprehensive indicators are excellent, green and pollution-free, and it is a high-performance environmental protection product.

[0003] At present, the traditional powdered polycarboxylate faces the problems of water reduction rate loss and material loss caused by the drying process, resulting in increased production costs, energy consumption and environmental pollution of the powdered polycarboxylate, and it is difficult to meet the current environmental protection requirements. At the same time, the current powder-forming process is single, mainly spray drying, with high water content, difficult to dry, and a protective agent silicon dioxide needs to be added during the powder-forming process, which has a great impact on the water reduction rate, with a loss rate of 10 - 20%, low recovery rate, and large dust pollution. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention provides a powdered polycarboxylate water reducer, which solves the problems of water reduction rate loss and material loss caused by the drying process in the prior art, performance degradation caused by the need to add silicon dioxide protective agent in spray drying, increased energy consumption caused by high water content, serious dust pollution during the powder-forming process and low recovery rate.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A powdered polycarboxylate water reducer is composed of the following components in parts by mass:

[0006] 80 - 90 parts of isopentenyl alcohol polyoxyethylene ether;

[0007] 8 - 12 parts of acrylic acid;

[0008] 0.3 - 0.5 part of oxidant A;

[0009] 0.1 - 0.15 part of oxidant B;

[0010] Molecular weight regulator: 0.35 - 0.45 parts;

[0011] Reducing agent A: 0.15 - 0.2 parts;

[0012] Reducing agent B: 0.04 - 0.06 parts;

[0013] Neutralizing solution: 1.8 - 2.2 parts;

[0014] Deionized water: 0.8 - 1.0 parts.

[0015] This powdered polycarboxylate superplasticizer uses isopentenyl alcohol polyoxyethylene ether (80 - 90 parts) as the main chain macromonomer. 40 - 80 ethylene oxide chain links in its molecular structure are connected by ether bonds, forming a steric hindrance structure with long side chains during the polymerization process. The long side chains form an amphiphilic molecular configuration with the carboxylic acid groups of acrylic acid (8 - 12 parts) through free radical copolymerization. Among them, the carboxyl groups of acrylic acid dissociate in the alkaline concrete environment to generate electrostatic repulsion, while the polyoxyethylene ether chains adsorb cement particles through hydrogen bond action to achieve dispersion control.

[0016] Oxidizing agent A (0.3 - 0.5 parts) selects benzoyl peroxide, whose decomposition temperature (70 - 80 °C) matches the initial temperature of the reaction system, and initiates the active sites of the macromonomer by generating benzoyloxy radicals; oxidizing agent B (0.1 - 0.15 parts) uses ammonium persulfate, which decomposes to generate sulfate radicals in the medium temperature stage (75 - 85 °C), forming a gradient initiation system with oxidizing agent A. The synergistic effect of the two free radicals breaks through the half-life limit of traditional single initiators.

[0017] The molecular weight regulator (0.35 - 0.45 parts) uses mercaptopropionic acid. Its mercapto group (-SH) precisely controls the polymer molecular weight in the range of 20,000 - 35,000 g / mol through chain transfer reactions. The staged addition strategy of mercaptopropionic acid (70% initial addition + 30% dropwise addition for supplementation) achieves narrow distribution control with a molecular weight distribution index (PDI) ≤ 1.8.

[0018] Reducing agent A (0.15 - 0.2 parts) is vitamin C, which forms a complex with Fe during the pre-dissolution stage at 25 - 35 °C to accelerate the activation of the oxidizing agent; reducing agent B (0.04 - 0.06 parts) uses sodium hypophosphite. Its P - H bond preferentially reacts with the decomposition by-product HSO4 of ammonium persulfate at high temperature (> 80 °C) to eliminate the inhibition effect of sulfate radicals on the polymerization reaction. The neutralizing solution (1.8 - 2.2 parts) uses 50% sodium hydroxide aqueous solution, and the pH value is adjusted in two stages to complete the gradient adjustment from 2.5 to 6.5 - 7.5. The first neutralization of 60 - 70% of the carboxylic acid groups maintains the reaction activity during the polymerization stage, and the second neutralization ensures storage stability. 3+ , - - ​​

[0019] Deionized water (0.8 - 1.0 parts) is used as a reaction medium to control the solid content of the system within the range of 85 - 90%. The monomer diffusion rate is adjusted through the solvation effect, and its conductivity ≤ 5 μS / cm avoids the interference of impurity ions on the free radical reaction.

[0020] Preferably, the molecular weight of the isopentenyl polyoxyethylene ether is 2400 - 4000 g / mol, and the ethylene oxide addition number is 40 - 80.

[0021] Analysis of isopentenyl polyoxyethylene ether:

[0022] In the molecular structure of this macromonomer, 40 - 80 ethylene oxide linkages are connected through ether bonds to form a steric hindrance structure with a long side chain. This structure forms an amphiphilic molecular configuration with the carboxylic acid groups of acrylic acid through free radical copolymerization during the polymerization process. During the polymerization reaction, the polyoxyethylene ether chain adsorbs cement particles through hydrogen bonding. This mechanism of action can effectively disperse cement particles and achieve the control of cement dispersion. At the same time, due to the strong hydrophilicity of the polyoxyethylene ether chain, they can undergo electrolytic dissociation in an alkaline environment, releasing negatively charged oxide groups and generating electrostatic repulsion. This electrostatic repulsion forms a steric hindrance effect between cement particles, further enhancing the dispersibility of cement particles, avoiding particle agglomeration, and maintaining the fluidity and stability of concrete.

[0023] Specifically, the range of ethylene oxide addition number (40 - 80) and the control of molecular weight (2400 - 4000 g / mol) directly affect the length and spatial structure of the molecular chain. A longer molecular chain can provide a stronger steric hindrance effect, effectively preventing the contact and coagulation between cement particles, and improving the dispersion performance and fluidity of the polymer. In addition, the appropriate control of molecular weight helps to achieve better storage stability and active control during the reaction process, avoiding performance instability caused by overly long or short molecules.

[0024] Steric hindrance and dispersion control: Isopentenyl polyoxyethylene ether interacts with the surface of cement particles through its long molecular chain and polar groups of polyoxyethylene, forming hydrogen bonds and electrostatic repulsion, thus playing a role in dispersing cement particles and maintaining the fluidity and stability of the cement paste.

[0025] Effect of electrostatic repulsion: In an alkaline concrete environment, the carboxylic acid groups of acrylic acid generate negative charges through dissociation, further enhancing the electrostatic repulsion, thereby inhibiting the aggregation of cement particles.

[0026] Function of amphiphilic molecular configuration: The amphiphilic molecular structure of polyoxyethylene ether chain and acrylic acid ensures that the water reducing agent can play a dual role of being hydrophilic and hydrophobic in the cement mixture, thus optimizing the dispersion effect of cement.

[0027] Preferably, the oxidant A is benzoyl peroxide and the oxidant B is ammonium persulfate.

[0028] Analysis of benzoyl peroxide (oxidant A):

[0029] Benzoyl peroxide is a commonly used radical initiator that can initiate polymerization by decomposing to generate benzoyl radicals (C6H5CO·). In the polymerization reaction, benzoyl peroxide first decomposes under heat or light conditions, releasing benzoyl radicals. Benzoyl radicals have strong reactivity and can react with the double bonds in the monomers to initiate polymerization. Its mechanism can be divided into the following steps:

[0030] Decomposition to generate radicals: Benzoyl peroxide decomposes under heating or light to generate benzoyl radicals (C6H5CO·).

[0031] Radical-initiated polymerization: Benzoyl radicals react with the double bonds in the monomers (acrylic acid or styrene) to initiate polymerization and form a polymer chain.

[0032] Extension of the polymer chain: Radicals continuously react with monomers to extend the polymer chain and finally form a polymer.

[0033] The advantage of this oxidant is its relatively low decomposition temperature, which enables it to effectively initiate polymerization at room temperature and has good thermal stability, contributing to an efficient polymerization process.

[0034] Analysis of ammonium persulfate (oxidant B):

[0035] Ammonium persulfate (APS) is also a commonly used radical initiator, especially widely used in aqueous phase polymerization. It initiates polymerization by releasing sulfate radicals (SO4·). Ammonium persulfate is easily decomposed in aqueous solution to generate highly oxidizing sulfate radicals, which can effectively initiate polymerization. Its mechanism can be divided into the following steps:

[0036] Decomposition of ammonium persulfate: Ammonium persulfate decomposes in aqueous solution, releasing two sulfate radicals (SO4·).

[0037] Radical-initiated polymerization: Sulfate radicals (SO4·) react with the double bonds in the monomers (acrylic acid) to generate new radicals, thereby initiating polymerization.

[0038] Extension of the polymerization chain: Sulfate radicals continuously participate in the reaction, extending the polymerization chain and ultimately forming a polymer.

[0039] The advantage of ammonium persulfate lies in its strong oxidizing property and high decomposition rate, making it particularly suitable for use in aqueous-phase polymerization. Meanwhile, its decomposition temperature is relatively high, enabling it to have better reactivity under high-temperature conditions.

[0040] When benzoyl peroxide and ammonium persulfate are used simultaneously, they can complement each other, providing different reaction conditions and types of free radicals. Benzoyl peroxide can efficiently initiate polymerization at low temperatures, while ammonium persulfate has better reactivity under high-temperature conditions. Therefore, the combination of the two can optimize the initiation and continuation of the polymerization reaction, controlling the rate of the polymerization reaction and the molecular weight of the product.

[0041] Combined initiation: Benzoyl peroxide initiates polymerization at a relatively low temperature, while ammonium persulfate plays a role at a relatively high temperature, enabling the polymerization process to proceed smoothly over a wider temperature range.

[0042] Complementary types of free radicals: Benzoyl peroxide generates benzoyl free radicals, while ammonium persulfate generates sulfate free radicals. These two types of free radicals have different reactivities, which can help achieve a more uniform polymerization reaction.

[0043] Enhanced polymerization efficiency: The combined use of the two can improve the efficiency of the polymerization reaction and better control the molecular weight and distribution of the polymer.

[0044] Preferably, the molecular weight regulator is mercaptopropionic acid.

[0045] Mercaptopropionic acid contains a highly reactive mercapto group (-SH) in its molecule. In the free radical polymerization reaction, the mercapto group of mercaptopropionic acid can undergo a chain transfer reaction with the active polymerization free radicals (benzoyl free radicals or sulfate free radicals). The chain transfer reaction proceeds through the following steps:

[0046] Free radical attacks mercaptopropionic acid: In the polymerization reaction, the generated free radicals (benzoyl free radicals or sulfate free radicals) react with the mercapto group (-SH) in mercaptopropionic acid to form a new free radical (R-SH).

[0047] Chain transfer reaction: This newly generated free radical reacts with the growing monomer in the polymerization chain, "transferring" the original active polymerization chain to the mercaptopropionic acid molecule. Through this chain transfer reaction, the growth of the active polymerization chain is terminated, and at the same time, a new free radical is generated, which can continue to initiate the polymerization reaction.

[0048] Controlling the molecular weight of the polymer: By controlling the amount of mercaptopropionic acid and the reaction conditions, the frequency of chain transfer can be adjusted. A higher chain transfer frequency leads to shorter polymer chains and ultimately a lower molecular weight; while a lower chain transfer frequency elongates the polymer chains and ultimately results in a higher molecular weight.

[0049] Preferably, the reducing agent A is vitamin C and the reducing agent B is sodium hypophosphite.

[0050] As a common reducing agent, vitamin C is widely used in chemical synthesis, especially in reactions that require the reduction of metal ions or oxides. In this system, vitamin C mainly plays a role in reducing metal ions or participating in the electron transfer process in the reaction through its strong reducibility.

[0051] Reduction reaction mechanism: Vitamin C can provide electrons in aqueous solution and be converted into dehydroascorbic acid (dehydrovitamin C). Specifically, vitamin C provides electrons to the oxidant in the reaction through its 2,3-dihydroxy structure, thereby reducing the oxidant.

[0052] Vitamin C can provide electrons through the following reaction:

[0053] C6H8O6 → C6H6O6 + 2H + + 2e -

[0054] In this process, vitamin C reduces the target substance by losing two electrons (oxidation).

[0055] Redox cycle: As a reducing agent, vitamin C can effectively participate in the reaction and achieve a redox cycle. The reducibility of vitamin C enables it to reduce metal ions, oxidants, or other compounds that need to be reduced in the reaction, thereby promoting the target chemical reaction in the reaction.

[0056] Synergistic effect: Vitamin C has strong hydrophilicity, so when it reacts in the aqueous phase, it can effectively react with substances in other solvents, provide more reducing electrons, and enhance the efficiency of the reaction.

[0057] Sodium hypophosphite (NaH2PO2) is a common reducing agent, usually used in reduction reactions, especially for the reduction of certain metal ions or oxides. It has strong reducibility and can stably release electrons at low temperatures.

[0058] Reduction reaction mechanism: The reducibility of sodium hypophosphite comes from its phosphite ion (H2PO2 - ). During the reduction process, the phosphite ion in sodium hypophosphite participates in the reaction by providing electrons, reducing the metal ions or other oxides in the oxidized state to a lower oxidation state. In the reaction, sodium hypophosphite can act as an electron donor to reduce the reactants.

[0059] The reduction reaction of sodium hypophosphite can be expressed as:

[0060] H2PO2 - + 2e - → H2PO3 -

[0061] In this reaction, sodium hypophosphite reduces H2PO2 - to H2PO3 - .

[0062] Synergistic effect: Sodium hypophosphite has a strong reducing ability and can complement each other when used together with other reducing agents (such as vitamin C). In the reaction, sodium hypophosphite can promote a stronger reduction reaction through a stronger reduction effect, thereby improving the reaction efficiency.

[0063] Temperature sensitivity of the reaction: Sodium hypophosphite is usually sensitive to temperature and can effectively provide reducing ability even at relatively low temperatures. Therefore, when the reaction conditions are appropriate, its reducing ability can be better exerted, especially when used in combination with other reducing agents, it can effectively control the rate of the reduction reaction.

[0064] Preferably, the neutralizing solution is an aqueous sodium hydroxide solution with a mass concentration of 45 - 55%.

[0065] Strong basic property:

[0066] The sodium hydroxide solution is very strongly basic. After sodium hydroxide dissolves in water, it completely ionizes to form hydroxide ions (OH - ). These hydroxide ions are strongly basic and can quickly react with acidic substances to form water and the corresponding salts. By controlling the concentration of the sodium hydroxide solution, the acid-base balance of the reaction system can be precisely adjusted.

[0067] The ionization reaction of sodium hydroxide in water can be expressed as:

[0068] NaOH → Na + + OH -

[0069] The hydroxide ions (OH - ) play a neutralizing role in the reaction. When acidic substances appear in the system, the OH - ions will react with the acidic substances (H + ions or the hydrogen ions of the acid) to undergo a neutralization reaction to form water.

[0070] pH control during the neutralization process:

[0071] The concentration of the aqueous sodium hydroxide solution is between 45% and 55%, indicating that it has a relatively high sodium hydroxide concentration. Therefore, such a concentration can provide a large amount of hydroxide ions in a relatively short time for quickly neutralizing the acidic substances generated in the reaction. By controlling the addition amount of the neutralizing solution, the pH value of the reaction system can be precisely adjusted to ensure that the reaction proceeds under ideal acid-base conditions.

[0072] If there are more acidic substances in the reaction system, the stronger sodium hydroxide solution will quickly react with the acidic substances to prevent the reaction environment from being too acidic and affecting the progress of the reaction; if there are fewer acidic substances in the reaction system, an appropriate amount of aqueous sodium hydroxide solution can ensure that the pH value will not be too low, thus protecting other components in the reaction process from being affected by the overly acidic environment.

[0073] Efficiency and stability of the neutralization reaction:

[0074] In a sodium hydroxide solution with a mass concentration of 45% - 55%, the concentration of hydroxide ions is relatively high, which means it can effectively neutralize a large amount of acidic substances in a short time. Due to the relatively fast reaction rate between sodium hydroxide and acidic substances, such a concentration can also effectively increase the reaction rate, thereby improving the efficiency of the entire reaction process.

[0075] In addition, the high-concentration aqueous sodium hydroxide solution can also help stabilize the reaction conditions, play a buffering role in the reaction, prevent drastic fluctuations in pH, and thus improve the controllability and repeatability of the reaction.

[0076] A preparation process of a powdered polycarboxylate water reducer, characterized by including the following steps:

[0077] a) Heat the isopentenyl alcohol polyoxyethylene ether to 65 - 85 °C and keep it at a constant temperature;

[0078] The isopentenyl alcohol polyoxyethylene ether will increase the collision frequency between molecules under the high-temperature condition after heating, thus accelerating its reaction with acrylic acid molecules or other polymerization monomers. This temperature range can provide a suitable environment for the subsequent polymerization reaction, making the reaction process neither too slow nor at risk of excessive degradation due to high temperature.

[0079] b) Prepare a pre-solution: Mix deionized water, reducing agent A, molecular weight regulator, and a part of acrylic acid;

[0080] Deionized water, as a solvent, can help dissolve other components, enabling the reducing agent A and the molecular weight regulator to be uniformly dispersed in the aqueous solution. The role of the reducing agent A is to participate in the reduction process in the reaction, affect the generation rate and stability of free radicals in the polymerization reaction, control the growth rate of the polymer chain, and thus regulate the molecular weight of the polymer. The molecular weight regulator controls the molecular weight of the final polymer by regulating the growth rate of the polymer chain during the polymerization process.

[0081] c) Add the remaining acrylic acid, reducing agent B, and oxidizing agent A / B to the reaction system of step a in sequence;

[0082] Under the action of reducing agent B and oxidizing agent A / B, an oxidation-reduction reaction occurs, generating free radicals. Free radicals are the active species of the polymerization reaction, and they can attack acrylic acid molecules to initiate the polymerization reaction. The oxidation-reduction reaction mechanism is as follows:

[0083] Reducing agent B and oxidizing agent A / B react to generate free radicals;

[0084] The free radicals initiate the polymerization process by undergoing an addition reaction with acrylic acid monomers;

[0085] The generated free radicals continue to attack the unreacted acrylic acid molecules, resulting in the extension of the polymer chain.

[0086] d) Dropwise add the pre-solution and maintain the reaction temperature at 70 - 85 °C for a dropping time of 3 - 4 hours;

[0087] By slowly dropwise adding the pre-solution, excessive monomer aggregation in the solution can be avoided, thereby maintaining the stability of the reaction. As the dropping progresses, the monomers in the reaction system continuously participate in the polymerization reaction to form polymer chains, and the polymerization process maintains an appropriate rate at a temperature of 70 - 85 °C. The control of the dropping time helps to stabilize the temperature and avoid excessive free radical generation caused by too fast a reaction, thereby improving the quality of the polymer.

[0088] e) After constant temperature curing for 3.5 - 4.5 hours, add a neutralizing solution to adjust the pH value;

[0089] The curing process helps the further cross-linking and stabilization of the polymer chains, making the final polymer have good properties. The addition of the neutralizing solution mainly adjusts the pH of the reaction system to prevent adverse effects on the stability and properties of the product caused by excessive acidity or alkalinity. The neutralization reaction usually neutralizes the excess hydroxide ions or hydrogen ions in the solution by adding a weak acid or base, thereby stabilizing the pH of the system.

[0090] f) After cooling, crush to a moisture content of ≤2%;

[0091] The cooling process causes the polymer molecules to gradually solidify, reducing the fluidity of the reaction system. The crushing operation breaks the solidified polymer into fine powder by mechanical force, making it more suitable for subsequent use. By controlling the cooling and crushing conditions, ensure that the moisture content of the final powder is lower than 2%, guaranteeing the stability and long-term storage of the product.

[0092] Preferably, in step a, the heating rate is 2 - 3 °C / min, and the stirring speed during the constant temperature stage is 80 - 120 rpm.

[0093] The heating rate is 2 - 3 °C / min:

[0094] Controlling the heating rate at a slow rate of 2 - 3 °C / min helps to steadily increase the temperature of the reaction system, avoiding too rapid reactions or side reactions caused by a sudden increase in temperature. The slow heating allows more time for the reactants to preheat and reach the optimal reaction temperature. This gradual heating can ensure that the activity of the isopentenyl alcohol polyoxyethylene ether molecules gradually increases, but will not cause adverse side reactions at too high a temperature due to rapid heating. In this way, the reaction rate can be effectively controlled, and more stable conditions can be provided for the subsequent reaction process.

[0095] The stirring speed during the constant temperature stage is 80 - 120 rpm:

[0096] The stirring speed during the constant temperature stage is in the range of 80 - 120 rpm. The main purpose is to keep the reactants in the system evenly dispersed, ensure uniform temperature distribution, and avoid the formation of local overheating or cold spots. At the same time, an appropriate stirring rate helps to promote the collision frequency between reactant molecules, thereby improving the efficiency of the polymerization reaction. In the polymerization reaction, especially when involving a liquid reaction system, the stirring speed has a significant impact on the uniformity and reaction rate of the reaction. If the stirring is too fast, it will cause excessive agitation of the material and the generation of bubbles; if the stirring is too slow, the reactants will be uneven, affecting the polymerization efficiency. Therefore, a stirring rate of 80 - 120 rpm can maintain good uniformity during the reaction process while avoiding the above problems.

[0097] Preferably, the addition interval time between oxidant A and oxidant B in step c is 3 - 7 minutes.

[0098] Addition of oxidant A and the initial reaction stage:

[0099] Oxidant A usually serves as the main oxidation source in the reaction, and its addition can rapidly increase the oxidation ability in the reaction system. In the initial stage of adding oxidant A, it will promote electron transfer or radical generation in the reaction system, which provides activated conditions for subsequent reactions. If oxidant B is added too early, it will cause the reaction to be too fast, local overheating, or excessive oxidation. Therefore, setting a certain interval time can ensure that the oxidation effect of oxidant A first plays its role and enables the active substances generated in the system to gradually combine with the reactants.

[0100] Addition of oxidant B and regulation of the reaction process:

[0101] Within 3 to 7 minutes after the addition of oxidant A, the oxidation reaction stabilizes to a certain extent and begins to proceed. At this time, the contact between oxidant A and the reactants has been initially established, and the oxidation reaction enters a relatively stable stage. Adding oxidant B at this time can promote the reaction process and enhance the oxidation degree of the product by further increasing the oxidation intensity. The existence of the interval ensures that the effects of the two oxidants do not interfere with each other, and through staged addition, the reaction can be better controlled, thus avoiding the reaction runaway caused by adding oxidant B prematurely.

[0102] Preferably, in step e, the neutralizing solution is added in two portions. The first portion is 60 - 70% of the total amount, and the remaining amount is added after pH detection to adjust the pH value of the system to 6.5 - 7.5.

[0103] Function of the first addition of the neutralizing solution:

[0104] The first addition of 60 - 70% of the neutralizing solution mainly serves to quickly adjust the acidity and alkalinity. At this stage, the pH value of the system is usually acidic or alkaline. Adding the initial neutralizing solution can quickly neutralize the acidic or alkaline substances in the reaction, changing the acidity and alkalinity of the reaction system. Since the neutralization reaction is an exothermic reaction, adding the neutralizing solution too quickly will cause local overheating. Therefore, by adding it in portions, this problem can be avoided, ensuring the stability of the reaction system.

[0105] Relationship between the addition of the remaining neutralizing solution and pH detection:

[0106] The addition of the remaining amount of the neutralizing solution depends on the real-time detection result of the pH value. This step ensures that the acidity and alkalinity of the system are adjusted to between 6.5 and 7.5 through precise pH control. Too high or too low pH value will affect the reaction balance or the stability of the catalyst, and even lead to incomplete reactions or side reactions. Therefore, by supplementing the remaining neutralizing solution after pH detection, the pH value of the system can be more precisely controlled, thus ensuring the stability of the reaction effect and product quality.

[0107] The present invention provides a powdered polycarboxylate water reducer. It has the following beneficial effects:

[0108] 1. Compared with the liquid polycarboxylate water-reducing agent mother liquor, the production system of 98% polycarboxylate water-reducing agent / slump-retention agent bulk synthetic powder completely solves the problems in the prior art, such as high transportation and packaging costs of water-based agents, high requirements for raw material storage, inconvenient use, and inaccurate raw material addition, resulting in insufficient slump retention purity in the production. Comparing according to the transportation cost of liquid water-reducing agents, it is 0.7 yuan per ton per kilometer for liquid. Calculated according to 300 kilometers, the transportation cost of 50% water-reducing agent is 210 yuan per ton. While the solid content of the powder water-reducing agent is 100%, under the same dosage, 50% of the transportation cost can be saved. On the basis of unchanged liquid performance, it is made into a flowing powder by a special drying technology, which is green and pollution-free, does not contain hazardous chemicals, and has a high output, further solving the needs of long-distance transportation and overseas exports.

[0109] 2. The present invention solves the problems of water-reducing rate loss and material loss caused by the drying process faced by powdered polycarboxylate in the market, reduces the production cost of polycarboxylate powder, saves energy, reduces environmental pollution, meets the current environmental protection requirements, and is energy-saving and pollution-free. It further solves the problem that the current powder-forming process in the market is single, mainly spray drying, with high water content, difficult to dry, and a protective agent silicon dioxide needs to be added during the powder-forming process, which has a great impact on the water-reducing rate, with a loss rate of about 20%, low recovery rate, and large dust pollution.

[0110] 3. The present invention solves the problem that the loss rate of polycarboxylate powder in the market reaches about 20%. The loss rate of the present invention is less than 1%, and the process is simple and convenient.

[0111] 4. The powdered polycarboxylate water-reducing agent of the present invention has a high water-reducing rate, excellent fluidity, obvious improvement in early and late strengths, good solubility, wide applicability, improves the shrinkage and creep properties of concrete, has little influence on the hydration performance, stable performance, low requirements for mechanical equipment, and improves the current situation of high production cost and large financial pressure of the spray drying system used in the market. BRIEF DESCRIPTION OF THE DRAWINGS

[0112] Figure 1 It is a schematic flow chart of the method of the present invention;

[0113] Figure 2 It is a product diagram of the powdered polycarboxylate water-reducing agent of the present invention;

[0114] Figure 3 It is a preparation flow chart of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0115] Next, in combination with the accompanying drawings of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0116] Example 1:

[0117]

[0118]

[0119] Example 2:

[0120]

[0121]

[0122] Example 3:

[0123]

[0124] By comparing the powder of polycarboxylate superplasticizer prepared with different acid-ether ratios in the above examples with the spray-dried finished product, the comparative test results are as follows:

[0125]

[0126] The action principle of polycarboxylate superplasticizer is that the anionic group carboxyl COOH on the main chain - is adsorbed on the surface of cement hydration products. The polyethylene glycol group (-CH2-CH2-O-)n on the side chain has a hydrophobic effect and produces a steric hindrance effect, so that the cement paste produces a dispersion effect. The water-reducing effect is the result of the dual action of the main chain adsorption ability and the side chain steric hindrance effect. The molecular structure parameters of ordinary polycarboxylate superplasticizer (PCE) are mainly the side chain density, side chain length and the length of the polymer main chain. For different examples, the acid-ether ratio is adjusted, that is, the molar ratio of small monomer to large monomer (a:b) - the acid-ether ratio. Based on the same oxidant and reductant, by comparing different acid-ether ratios on the water reduction rate, retention, compressive strength, moisture content, and compressive strength, it is found that Example 1 has better comprehensive performance. Example 3 has a higher acid-ether ratio, which is directly reflected in a higher water reduction rate, but the retention time is slightly worse.

[0127] By comparison, it is obtained that the powder polycarboxylate superplasticizer in Example 1 has a high water reduction rate, good retention, excellent fluidity, obvious improvement in early and late strength, good solubility, wide applicability, can improve the shrinkage and creep performance of concrete, has little influence on the hydration performance, and has stable performance.

[0128] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A powdered polycarboxylate superplasticizer, characterized in that, It is composed of components with the following mass parts ratio: 80 - 90 parts of isopentenol polyoxyethylene ether; 8 - 12 parts of acrylic acid; 0.3 - 0.5 part of oxidant A; 0.1 - 0.15 part of oxidant B; 0.35 - 0.45 part of molecular weight regulator; 0.15 - 0.2 part of reducing agent A; 0.04 - 0.06 part of reducing agent B; 1.8 - 2.2 parts of neutralizing solution; 0.8 - 1.0 part of deionized water.

2. The powdered polycarboxylate water reducer according to claim 1, wherein, The molecular weight of the isopentenol polyoxyethylene ether is 2400 - 4000 g / mol, and the ethylene oxide addition number is 40 - 80.

3. The powdered polycarboxylate water reducer according to claim 1, characterized in that, The oxidant A is benzoyl peroxide, and the oxidant B is ammonium persulfate.

4. A powdered polycarboxylate water reducer according to claim 1, characterized in that The molecular weight regulator is mercaptopropionic acid.

5. A powdered polycarboxylate superplasticizer according to claim 1, characterized in that, The reducing agent A is vitamin C, and the reducing agent B is sodium hypophosphite.

6. The powdered polycarboxylate water reducer according to claim 1, characterized in that, The neutralizing solution is an aqueous sodium hydroxide solution with a mass concentration of 45 - 55%.

7. A preparation process of the powdered polycarboxylate superplasticizer according to any one of claims 1-6, characterized in that, It includes the following steps: a) Heat the isopentenol polyoxyethylene ether to 65 - 85 °C and keep it at a constant temperature; b) Prepare a pre - solution: Mix deionized water, reducing agent A, molecular weight regulator and part of acrylic acid; c) Sequentially add the remaining acrylic acid, reducing agent B and oxidant A / B to the reaction system in step a; d) Dropwise add the pre - solution and maintain the reaction temperature at 70 - 85 °C, and the dropping time is 3 - 4 hours; e) Keep it at a constant temperature and age for 3.5 - 4.5 hours, then add the neutralizing solution to adjust the pH value; f) After cooling, crush it to a moisture content of ≤2%.

8. The preparation process according to claim 7, characterized in that, In step a, the heating rate is 2 - 3 °C / min, and the stirring speed during the constant - temperature stage is 80 - 120 rpm.

9. The preparation process according to claim 7, characterized in that, In step c, the addition interval time between oxidant A and oxidant B is 3 - 7 minutes.

10. The preparation process according to claim 7, characterized in that, In step e, the neutralizing solution is added in two times. The first time, 60 - 70% of the total amount is added, and the remaining amount is added to the system to make the pH value 6.5 - 7.5 after pH detection.

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