A special polycarboxylic water reducing agent for gypsum board

Abstract

The application relates to the technical field of admixtures for building materials, in particular to a special polycarboxylic water reducing agent for gypsum boards, which comprises the following steps: S1, preparing a multifunctional monomer mixed solution; S2, preparing an initiation system: dissolving polyether macromonomer and a chain transfer agent in part of water, placing the water in a reactor, heating to a preset temperature and keeping constant; S3, performing a gradient copolymerization reaction: under the constant temperature condition, synchronously and slowly adding the multifunctional monomer mixed solution and an oxidant aqueous solution into the initiation system; S4, performing aging and post-treatment: after the addition is completed, keeping constant temperature aging at the preset temperature, then reducing the temperature, and neutralizing with lye until the pH value is 6-7, so that the special polycarboxylic water reducing agent is obtained. The whole process does not need toxic and harmful raw materials such as formaldehyde and naphthalene, and conforms to the green chemistry direction. The problems of demolding difficulty and production line congestion caused by retardation are solved, and the mold turnover rate and the production line efficiency are significantly improved. Under a higher water reducing rate, lower porosity (non-bubble pore) and higher compactness can be obtained.

Description

Technical Field

[0001] This application relates to the field of building material admixtures, and in particular to a special polycarboxylate superplasticizer for gypsum board. Background Technology

[0002] In the gypsum board production process, water-reducing agents are crucial for improving slurry fluidity, reducing the water-to-solid ratio, and enhancing product strength. Currently, there are two main technical approaches in the industry: 1. Traditional naphthalene-based water-reducing agents; 2. (PCE).

[0003] Traditional naphthalene-based water-reducing agents have low water reduction rates (typically <20%), use harmful substances such as formaldehyde in the production process, have poor environmental performance, and involve complex processes with high energy consumption. When ordinary polycarboxylate water-reducing agents are used directly in gypsum board production, their strong surface activity destroys the bubbles formed by the soap solution, leading to an increase in the product's density and a decrease in its thermal and sound insulation properties; moreover, they have a severe retarding effect on gypsum, resulting in a significant extension of setting time, reduced production efficiency, and even the inability to demold. Summary of the Invention

[0004] This application provides a special polycarboxylate superplasticizer for gypsum board to solve the above-mentioned problems.

[0005] In a first aspect, this application provides a special polycarboxylate superplasticizer for gypsum board, comprising:

[0006] S1. Preparation of multifunctional monomer mixture: The multifunctional monomer mixture is composed of unsaturated carboxylic acid monomers, foam-stabilizing monomers and coagulation-regulating monomers dissolved in water;

[0007] S2. Preparation of the initiation system: Dissolve the polyether macromonomer and chain transfer agent in some water, place them in a reactor, heat to the preset temperature and keep the temperature constant.

[0008] S3. Perform gradient copolymerization reaction: Under constant temperature conditions, the multifunctional monomer mixture obtained in step S1 and the aqueous oxidant solution are simultaneously and slowly added dropwise to the initiation system in step S2.

[0009] S4. Maturation and post-treatment: After the addition is complete, the mixture is kept warm and matured at the preset temperature, then cooled down and neutralized with alkali solution to a pH value of 6-7 to obtain the special polycarboxylate superplasticizer.

[0010] Beneficial effects: It solves three major challenges: high water reduction, stable foaming, and controlled setting. Water reduction rates can reach 25%-35% or more, while maintaining stable product density, thermal insulation, and soundproofing properties. Setting time can be adjusted to match production rhythm. The entire process requires no toxic or harmful raw materials such as formaldehyde or naphthalene, conforming to green chemistry principles, ensuring product safety and environmental friendliness. It solves the problems of difficult demolding and production line congestion caused by slow setting, significantly improving mold turnover and production line efficiency. At higher water reduction rates, gypsum board can achieve lower porosity (non-bubble pores) and higher density, thereby further improving physical properties such as compressive strength and water resistance. The one-step copolymerization process is simpler than naphthalene-based synthesis, with milder reaction conditions (low temperature) and lower energy consumption. Furthermore, the high water reduction rate itself can reduce gypsum usage or increase strength, resulting in cost savings.

[0011] Optionally, the foam-stabilizing functional monomer in step S1 is a (meth)acrylate containing C8-C18 alkyl groups, preferably at least one of dodecyl methacrylate and octadecyl acrylate, and the settling functional monomer is an olefinic unsaturated monomer containing phosphonic acid groups, sulfonic acid groups or amide groups; preferably at least one of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), vinylphosphonic acid, and acrylamide.

[0012] Beneficial effects: While maintaining the high water reduction rate (>25%) of PCE, it successfully solves the two major compatibility challenges of foam stabilization and retarding in gypsum systems. This ensures the low density and excellent thermal and sound insulation properties of gypsum board products, while controlling the setting time within a suitable production process range, guaranteeing production efficiency. The production process is formaldehyde-free, making it environmentally friendly; the one-step synthesis process simplifies the process, reduces energy consumption, and is suitable for large-scale production. By integrating multiple functions into one product through molecular design, it avoids compatibility issues that may arise from compounding multiple additives, making it easier to use and ensuring more stable quality control.

[0013] Optionally, the polyether macromonomer in step S2 is at least one of isopentenyl polyoxyethylene ether or methyl allyl alcohol polyoxyethylene ether, the chain transfer agent is at least one of mercaptoacetic acid, mercaptopropionic acid or mercaptoethanol, and the amount of the chain transfer agent is 0.1%-0.5% of the total mass of all monomers.

[0014] Beneficial effects: Isoprene alcohol polyoxyethylene ether or methyl allyl alcohol polyoxyethylene ether ensures a high water reduction rate of over 25%; precise chain transfer control (0.1%-0.5%) gives the product an ideal molecular weight, enabling it to have both good dispersibility and adaptability in gypsum slurries. The final polymer can effectively stabilize bubbles and precisely control setting time, perfectly solving the compatibility problem of ordinary PCE.

[0015] Optionally, the oxidant in step S3 is at least one of ammonium persulfate, potassium persulfate, or hydrogen peroxide, and the amount of the oxidant is 0.5%-2.0% of the total mass of all monomers.

[0016] Beneficial effects: With an optimized dosage of 0.5%-2.0% and a gradient dropping process, mild and stable polymerization was achieved, improving performance stability and ensuring that the resulting PCE has a suitable molecular weight, narrow molecular weight distribution, and uniform functional group distribution. This avoids safety risks such as explosive polymerization and material overflow caused by improper initiators, and the reaction time is controllable, resulting in high production efficiency.

[0017] Optionally, the molar ratio of materials used in step S1 to step S2 is:

[0018] Polyether macromonomer: Unsaturated carboxylic acid monomer: Foam stabilizing monomer: Settling regulating monomer = 1:(2.0-4.0):(0.05-0.25):(0.1-0.5).

[0019] Beneficial effects: The PCE synthesized through this precise molar ratio simultaneously achieves high water reduction rate (synergistic effect of carboxyl groups and polyethers), excellent foam stability (low proportion of hydrophobic chain interaction), and controllable setting time (precise intervention of setting-regulating groups), perfectly solving the application defects of ordinary PCEs mentioned in the background. Compared with general PCEs, this design, through a "low proportion of functional monomer embedding" strategy, maintains the core water reduction capacity while specifically enhancing its special application performance in gypsum systems.

[0020] Optionally, the preset temperature in step S2 is 58-62℃.

[0021] Beneficial effects: Ensures the synthesized PCE possesses the designed comb-like structure and functional group ratio, with a narrow molecular weight distribution. Constant medium-temperature process conditions facilitate precise control in industrial production, guaranteeing batch-to-batch stability. Suitable ripening temperature ensures complete reaction, resulting in low free monomer content in the finished product, making it environmentally friendly and stable. Reduces safety risks such as material overflow and explosive polymerization caused by high temperatures.

[0022] Optionally, the dripping time in step S3 is 2.5-3.5 hours.

[0023] Beneficial effects: Ensures the synthesized polymer has a highly reproducible comb-like structure, with effective integration of foam-stabilizing and setting-regulating functional groups. Achieves high water reduction rate, excellent protection of gypsum bubbles, and precise control of setting time, solving two major defects of ordinary PCE. Avoids production safety hazards such as burst polymerization and material overflow, and minimizes batch-to-batch variations in product quality.

[0024] Optionally, the step of dissolving the polyether macromonomer and chain transfer agent in a portion of water and placing them in a reactor specifically includes: dissolving the polyether macromonomer and chain transfer agent in deionized water and stirring them in a reactor to form a homogeneous solution;

[0025] Performing a gradient copolymerization reaction includes: under constant temperature and stirring conditions, simultaneously and slowly adding the multifunctional monomer mixture obtained in step S1 and the aqueous oxidant solution to the initiation system in step S2.

[0026] Beneficial effects: A "three-in-one" special water-reducing agent with high water reduction rate, excellent foam stabilization ability, and controllable setting regulation function was directly synthesized. This avoids the safety risks (powder spillage, gelation) associated with explosive polymerization, and ensures good production reproducibility. The resulting polymer has a narrow molecular weight distribution, uniform functional group distribution, and minimal batch-to-batch performance differences.

[0027] Optionally, the total monomer mass concentration of the multifunctional monomer mixture is 35%-45%.

[0028] Beneficial effects: Stable fluid properties ensure precise and repeatable dripping operations, avoiding pumping failures or reaction runaways caused by fluctuations in solution properties (such as sudden viscosity changes or precipitation), resulting in high production safety. This guarantees batch-to-batch stability of the final water-reducing agent product in terms of water reduction, foam stabilization, and setting regulation performance.

[0029] Optionally, the heat preservation and curing process includes stirring and heat preservation at the above-mentioned preset temperature for 1.5-2.5 hours.

[0030] Beneficial effects: Ensures that all designed functions (high water reduction, foam stabilization, precise setting regulation) are fully and stably transferred to the final product, resulting in consistent performance across batches. Completely eliminating residual monomers is a key chemical method to address the side effects of ordinary PCE in gypsum, such as "slow setting and easy foam breakage." Obtaining a "completely reacted" system avoids quality problems such as viscosity changes and gelation caused by slow post-polymerization during storage and transportation. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 A flowchart of a special polycarboxylate superplasticizer for gypsum board provided in one embodiment of this application; Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0034] Furthermore, the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article, unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship.

[0035] The embodiments of this application will now be described in further detail with reference to the accompanying drawings.

[0036] Traditional naphthalene-based water-reducing agents have low water reduction rates (typically <20%), use harmful substances such as formaldehyde in the production process, resulting in poor environmental performance, complex processes, and high energy consumption. When ordinary polycarboxylate water-reducing agents are directly used in gypsum board production, their strong surface activity destroys the bubbles formed by the soap solution, leading to an increase in the product's density and a decrease in its thermal and sound insulation properties; moreover, they have a severe retarding effect on gypsum, resulting in a significant extension of setting time, reduced production efficiency, and even the inability to demold.

[0037] Based on this, this application provides a special polycarboxylate superplasticizer for gypsum board, which is prepared by a multifunctional monomer mixture: the multifunctional monomer mixture is composed of unsaturated carboxylic acid monomers, foam-stabilizing monomers, and setting-regulating monomers dissolved in water; it inherits and optimizes the highly efficient dispersion properties of unsaturated carboxylic acid monomers, exhibiting a significant water-reducing effect on gypsum slurry, reducing the water-to-gypsum ratio, and improving the final strength of gypsum board. Initiation system preparation: the polyether macromonomer and chain transfer agent are dissolved in a portion of water, placed in a reactor, heated to a preset temperature, and kept at that temperature; gradient copolymerization reaction is performed: under constant temperature conditions, the prepared multifunctional monomer mixture and an oxidant aqueous solution are simultaneously and slowly added dropwise to the initiation system; maturation and post-treatment are carried out: after the addition is complete, the mixture is kept at the preset temperature for maturation, then cooled, and neutralized with alkali solution to a pH of 6-7 to obtain the special polycarboxylate superplasticizer. Intelligent control of the adsorption behavior of superplasticizer molecules on the surface of gypsum crystals and the hydration and crystallization process of gypsum avoids or greatly reduces the severe retarding side effects of traditional polycarboxylate superplasticizers, ensuring that the setting time meets the normal production rhythm. The entire process is an aqueous system, requiring no organic solvents, and the selected raw materials are environmentally friendly. The resulting product is a homogeneous and stable liquid, easy to store, transport, and automatically metered for industrial application.

[0038] Figure 1A flowchart of a special polycarboxylate superplasticizer for gypsum board provided in one embodiment of this application includes:

[0039] S1. Preparation of multifunctional monomer mixture: The multifunctional monomer mixture is composed of unsaturated carboxylic acid monomers, foam-stabilizing monomers and coagulation-regulating monomers dissolved in water.

[0040] S2. Preparation of the initiation system: Dissolve the polyether macromonomer and chain transfer agent in some water, place them in a reactor, heat to the preset temperature and keep the temperature constant.

[0041] S3. Perform gradient copolymerization reaction: Under constant temperature conditions, the multifunctional monomer mixture obtained in step S1 and the aqueous oxidant solution are simultaneously and slowly added dropwise to the initiation system in step S2.

[0042] S4. Curing and post-treatment: After the addition is complete, keep it warm at the preset temperature for curing, then cool it down and neutralize it with alkali solution to a pH value of 6-7 to obtain the special polycarboxylate superplasticizer.

[0043] Technical Background and Working Principle: In the gypsum board production industry, traditional naphthalene-based water-reducing agents face elimination due to their low water reduction rate and poor environmental performance. Direct application of ordinary polycarboxylate superplasticizers presents two key compatibility challenges: damage to the bubble structure leading to increased bulk density and severe delay in gypsum setting. This product utilizes polyether macromonomers to construct a "comb-like" main chain, leveraging steric hindrance to achieve highly efficient water reduction. Simultaneously, it introduces foam-stabilizing monomers, whose polymerized functional segments enhance bubble film strength, protecting the product's thermal and sound insulation properties. Furthermore, it incorporates setting-regulating monomers, which preferentially and controllably complex with calcium ions, buffering the excessive inhibition of gypsum crystal growth by the main chain, thereby precisely regulating setting time. Ultimately, this product integrates highly efficient dispersion, bubble protection, and crystal growth regulation, becoming a specialized polymer that solves industry pain points.

[0044] Technical Solution and Component Functions: This integrated synthesis process employs gradient copolymerization, a one-step copolymerization method to synthesize multiple functional components in situ into an integrated product. The specific steps include: first, premixing unsaturated carboxylic acid monomers (serving as the main chain backbone and adsorption groups), foam-stabilizing monomers (for strengthening the bubble film structure), and settling-regulating monomers (for precisely controlling the settling rate) to form a solution; then, constructing a reaction environment in the reaction system primarily composed of polyether macromonomers (providing steric hindrance and a water-reducing core) and chain transfer agents (regulating molecular weight distribution); next, copolymerizing through synchronous, slow gradient addition to ensure uniform integration of functional units into the polymer backbone; finally, after curing, cooling, and neutralization to a weakly acidic state with an alkali solution (to improve product solubility and storage stability), a stable, specialized polycarboxylate water-reducing agent is obtained. Throughout the process, each component works synergistically to fulfill its specific function under the action of the redox initiation system, collectively forming the foundation for the product's high performance. It is important to note that stirring is continuous during the cooling process.

[0045] Beneficial effects: It solves three major challenges: high water reduction, stable foaming, and controlled setting. Water reduction rates can reach 25%-35% or more, while maintaining stable product density, thermal insulation, and soundproofing properties. Setting time can be adjusted to match production rhythm. The entire process requires no toxic or harmful raw materials such as formaldehyde or naphthalene, conforming to green chemistry principles, ensuring product safety and environmental friendliness. It solves the problems of difficult demolding and production line congestion caused by slow setting, significantly improving mold turnover and production line efficiency. At higher water reduction rates, gypsum board can achieve lower porosity (non-bubble pores) and higher density, thereby further improving physical properties such as compressive strength and water resistance. The one-step copolymerization process is simpler than naphthalene-based synthesis, with milder reaction conditions (low temperature) and lower energy consumption. Furthermore, the high water reduction rate itself can reduce gypsum usage or increase strength, resulting in cost savings.

[0046] Alternative or modified implementation methods: Unsaturated carboxylic acids: Acrylic acid can be replaced with methacrylic acid, itaconic acid, etc. Foam-stabilizing functional monomers: Other types of functional surfactant monomers can be selected according to different foam-stabilizing mechanisms (such as increasing surface viscosity, forming composite films), such as fluorinated or silicon-containing olefin monomers, or block polyether monomers with different structures. Setting-regulating functional monomers: In addition to phosphate esters, monomers with strong complexing ability, such as citric acid derivative monomers and aminotrimethylene phosphonic acid (ATMP) monomers, can be tested, but the effect curve of their complexing strength on setting time needs to be accurately evaluated. Polyether macromonomers: HPEG (isoprenol polyoxyethylene ether) can be replaced with TPEG (methoxy polyethylene glycol methacrylate), VPEG (vinyl polyethylene glycol), etc. Different side chain structures will affect water-reducing performance and slump retention.

[0047] Optionally, in step S1, the foam-stabilizing monomer is a (meth)acrylate containing C8-C18 alkyl groups, preferably at least one of dodecyl methacrylate and octadecyl acrylate, and the settling-regulating monomer is an olefinic unsaturated monomer containing phosphonic acid groups, sulfonic acid groups or amide groups; preferably at least one of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), vinylphosphonic acid, and acrylamide.

[0048] Technical Background and Working Principle: The "comb-like" structure of ordinary PCE only provides dispersion force based on steric hindrance, which cannot solve the compatibility problem in gypsum systems. Therefore, (meth)acrylate monomers containing C8-C18 long-chain alkyl groups are introduced. The hydrophobic long-chain segments formed after polymerization can anchor at the bubble-liquid film interface, synergistically enhancing the mechanical strength and elasticity of the liquid film with the soap solution foam stabilizer in the system, effectively resisting the defoaming effect of the PCE backbone, thereby maintaining the porous structure of lightweight gypsum. The introduced olefinic unsaturated monomers containing phosphonic acid groups, sulfonic acid groups, or amide groups have functional groups that react with calcium ions (Ca²⁺). +They possess stronger or more competitive complexing abilities than carboxyl groups. They preferentially bind with Ca²⁺ dissolved from gypsum. + The combination forms a soluble complex, which buffers the excessive adsorption of the main chain carboxyl groups on the growth points of gypsum dihydrate crystals, thereby achieving precise control of setting time and avoiding excessive slow setting.

[0049] Technical solution and component function: The unsaturated carboxylic acid monomer that constitutes the main chain skeleton and provides adsorption groups, the bubble stabilizing functional monomer (such as dodecyl methacrylate) that enhances bubble film stability by introducing hydrophobic long chains (C8-C18), and the condensation regulating functional monomer (such as AMPS) that contains strong complexing groups to precisely control condensation time are dissolved together in water to prepare a multifunctional monomer mixture.

[0050] Beneficial effects: While maintaining the high water reduction rate (>25%) of PCE, it successfully solves the two major compatibility challenges of foam stabilization and retarding in gypsum systems. This ensures the low density and excellent thermal and sound insulation properties of gypsum board products, while controlling the setting time within a suitable production process range, guaranteeing production efficiency. The production process is formaldehyde-free, making it environmentally friendly; the one-step synthesis process simplifies the process, reduces energy consumption, and is suitable for large-scale production. By integrating multiple functions into one product through molecular design, it avoids compatibility issues that may arise from compounding multiple additives, making it easier to use and ensuring more stable quality control.

[0051] Alternative or modified implementation methods: Besides dodecyl methacrylate and octadecyl acrylate, other (meth)acrylate monomers containing C8-C18 straight-chain or branched alkyl groups can be selected based on bubble stability requirements and cost, such as octyl methacrylate (C8) and hexadecyl methacrylate (C16). Longer alkyl chains generally provide stronger bubble stability, but may have some impact on the polymer's water solubility. In addition to AMPS, vinylphosphonic acid, and acrylamide, other monomers containing strong complexing or adsorption groups can also be considered, such as phosphonic acid groups: methacryloyloxyethylphosphonic acid, which provides stronger calcium ion chelating ability; sulfonic acid groups: sodium methacrylate sulfonate, which provides excellent dispersibility and setting retardation; and polycarboxyl groups: itaconic acid and maleic acid, which adjust the inhibitory effect on crystal growth by increasing carboxyl density and configuration. In specific implementation methods, the monomer's effect on gypsum setting time, compatibility with the main system, cost, and supply stability must be comprehensively considered.

[0052] Optionally, in step S2, the polyether macromonomer is at least one of isopentenyl alcohol polyoxyethylene ether or methyl allyl alcohol polyoxyethylene ether, and the chain transfer agent is at least one of mercaptoacetic acid, mercaptopropionic acid or mercaptoethanol, and the amount of chain transfer agent is 0.1%-0.5% of the total mass of all monomers.

[0053] Technical Background and Working Principle: Developing a dedicated PCE requires addressing the dual compatibility issues of foam stabilization and controlled setting while maintaining high water reduction rates. This necessitates a meticulously designed molecular structure, possessing both a highly efficient, dispersible "comb-like" framework and the introduction of special functional groups, while ensuring a controllable polymerization process. Using isopentenyl alcohol polyoxyethylene ether (HPEG) or methyl allyl alcohol polyoxyethylene ether (TPEG) as the polyether macromonomer provides long polyethylene oxide (PEO) side chains that create a steric hindrance effect in the gypsum slurry, forming the physical basis for high water reduction. Simultaneously, by adding 0.1%-0.5% of a mercapto-based chain transfer agent, the polymer molecular weight and distribution are precisely controlled during free radical copolymerization, preventing excessively large or small molecular weights. This ensures the final product possesses a suitable molecular structure, uniform functional distribution, and stable performance, simultaneously meeting the comprehensive requirements of high water reduction, foam stabilization, and precise setting control.

[0054] Technical solution and component function: HPEG or TPEG is selected as the polyether macromonomer because it has a well-defined and moderately active allyl ether structure, customizable PEO side chain length, and mature industrial supply. It can provide the long side chain "comb teeth" required to generate steric hindrance. At the same time, chain transfer agents such as mercaptoacetic acid, which are water-soluble, efficient and produce few by-products, are added. The amount of these agents is precisely controlled within the empirically optimized range of 0.1%-0.5% of the total monomer mass to ensure that the polymer molecular weight is within the optimal application window.

[0055] Beneficial effects: Isoprene alcohol polyoxyethylene ether or methyl allyl alcohol polyoxyethylene ether ensures a high water reduction rate of over 25%; precise chain transfer control (0.1%-0.5%) gives the product an ideal molecular weight, enabling it to have both good dispersibility and adaptability in gypsum slurries. The final polymer can effectively stabilize bubbles and precisely control setting time, perfectly solving the compatibility problem of ordinary PCE.

[0056] Alternative or modified implementation methods: Based on the polymerization mechanism, other polyoxyethylene ethers with terminal polymerizable double bonds can be considered as candidates, such as: vinyl polyoxyethylene ether (VPEG): higher activity, but slightly poorer storage stability; allyl polyoxyethylene ether (APEG): lower activity, may require adjustment of the initiation system.

[0057] Optionally, in step S3, the oxidant is at least one of ammonium persulfate, potassium persulfate, or hydrogen peroxide, and the amount of oxidant used is 0.5%-2.0% of the total mass of all monomers.

[0058] Technical background and working principle: In the one-step gradient copolymerization of gypsum-specific PCE, a redox initiation system that can efficiently and stably initiate free radical polymerization at medium and low temperatures is required, and the selection and dosage of oxidant are the key control factors.

[0059] Technical Solution and Component Functions: Through synergy with the reaction core environment constructed with S1 premixed functional monomers and S2, it ensures the orderly copolymerization of multiple monomers rather than homopolymerization; its "synchronous, slow dropwise addition" method is a key process for controlling polymerization kinetics and obtaining ideal molecular structures; and ultimately provides a prerequisite for complete and stable reaction for the maturation and post-processing of S4. The selection of these oxidants is based on their advantages of suitable activity at medium and low temperatures, excellent water solubility, non-polluting decomposition products, and strong industrial applicability. Simultaneously, precisely controlling their dosage to 0.5%-2.0% of the total mass of all monomers is crucial for performance balance: dosage below this range leads to insufficient initiation, incomplete reaction, and abnormal molecular weight; dosage above this range causes excessively rapid polymerization, intense exothermic reactions, and excessively low molecular weight, thereby impairing product dispersibility, retention, and the structure of functional monomers.

[0060] Beneficial effects: With an optimized dosage of 0.5%-2.0% and a gradient dropping process, mild and stable polymerization was achieved, improving performance stability and ensuring that the resulting PCE has a suitable molecular weight, narrow molecular weight distribution, and uniform functional group distribution. This avoids safety risks such as explosive polymerization and material overflow caused by improper initiators, and the reaction time is controllable, resulting in high production efficiency.

[0061] Alternative or modified implementation methods: Other persulfates: such as sodium persulfate, whose mechanism of action is similar to potassium / ammonium persulfate. The main difference in selection lies in the different cations, which may have a slight impact on the electrolyte environment of the final product system, as well as minor differences in cost and solubility. Other water-soluble oxidants: such as organic peroxides like tert-butyl hydroperoxide, which may have higher activity in redox systems. However, they pose relatively greater storage risks, are more expensive, and their decomposition products may introduce organic impurities.

[0062] Optionally, the molar ratio of materials used in step S1 to step S2 is:

[0063] Polyether macromonomer: Unsaturated carboxylic acid monomer: Foam stabilizing monomer: Settling regulating monomer = 1:(2.0-4.0):(0.05-0.25):(0.1-0.5).

[0064] Technical Background and Working Principle: The root cause of the failure of ordinary PCE in gypsum lies in its molecular structure being optimized for a "single function"—in pursuit of extreme water reduction, its high-density carboxyl groups and strongly hydrophilic polyether side chains lead to excessive surface activity and excessive interference with gypsum crystals. A "comb-like" framework is constructed at a ratio of 1:(2.0-4.0) to ensure sufficient adsorption sites and steric hindrance to achieve a high water reduction rate while avoiding excessively long main chains that exacerbate setting delay. Foam-stabilizing functional monomers are embedded at a very low but crucial ratio of 1:0.05-0.25, utilizing their hydrophobic long chains to reinforce the bubble film and counteract the defoaming tendency of PCE itself. Finally, setting-regulating functional monomers are introduced at a ratio of 1:0.1-0.5, precisely intervening in gypsum hydration kinetics through competitive adsorption and complexation, adjusting the uncontrollable strong setting delay to within the allowable range of the process.

[0065] Technical solutions and component functions: The ratio of polyether macromonomer to unsaturated carboxylic acid 1:(2.0-4.0) strikes a balance between ensuring sufficient adsorption points to obtain basic dispersion force and preventing excessive carboxyl groups from causing molecular shrinkage or excessive retardation; the ratio of polyether macromonomer to foam stabilizer 1:(0.05-0.25) strikes a balance between providing a clear foam stabilizing effect and avoiding the impact of excessive hydrophobic chains on product solubility and bubble quality; the ratio of polyether macromonomer to settling regulator 1:(0.1-0.5) strikes a balance between effectively counteracting strong retardation and preventing new groups from causing secondary interference to hydration.

[0066] Beneficial effects: The PCE synthesized through this precise molar ratio simultaneously achieves high water reduction rate (synergistic effect of carboxyl groups and polyethers), excellent foam stability (low proportion of hydrophobic chain interaction), and controllable setting time (precise intervention of setting-regulating groups), perfectly solving the application defects of ordinary PCEs in the background. Compared with general PCEs, this design, through the "low proportion of functional monomer embedding" strategy, maintains the core water reduction capacity while specifically enhancing its special application performance in gypsum systems.

[0067] Alternative or modified implementation methods: In practical applications, adjustments can be made according to specific needs, but the adjustment logic must follow the above balance principle: The proportion of carboxylic acid monomers can be moderately increased (e.g., towards 1:4.0), but the impact on setting time and solution viscosity must be evaluated simultaneously. The proportion of foam-stabilizing monomers can be moderately increased (e.g., towards 1:0.25), but the solubility of the product and the gas-containing structure of the slurry must be rigorously tested.

[0068] Optionally, the preset temperature in step S2 is 58-62℃.

[0069] Technical Background and Working Principle: Setting the reaction temperature to 58-62℃ is the core process parameter for synthesizing specialized polycarboxylate superplasticizers. Its purpose is to precisely control the kinetics of free radical copolymerization in aqueous solutions. This provides an optimal activation window for persulfate initiators, ensuring their stable decomposition to continuously supply free radicals and avoiding explosive reactions. At this temperature, the reactivity ratios of various functional monomers (polyether macromonomers, acrylic acid, etc.) are effectively coordinated, facilitating the achievement of copolymerization compositions close to the designed feed ratio, thereby ensuring the realization of the target molecular structure. This temperature can significantly suppress side reactions (such as polyether chain scission, excessive chain transfer, or acrylic acid homopolymerization), protecting the integrity of the polymer backbone and side chains.

[0070] Technical Solution and Component Functions: In stage S2, this preset temperature activates the system, ensuring sufficient dispersion of the polyether macromonomer and preparing the initiation conditions. During the gradient addition in S3, this preset temperature ensures a stable and controllable reaction, allowing the functional monomers to be sequentially inserted. In the S4 maturation period, it promotes complete reaction and ensures stable product performance. Simultaneously, this temperature window maintains a moderate initiator decomposition rate, providing a continuous and stable free radical source for copolymerization; it keeps the polyether macromonomers moderately active, preventing side chain degradation; it makes the copolymerization behavior of carboxylic acid monomers more ideal, and ensures that a low proportion of foam-stabilizing and setting-regulating monomers can effectively integrate into the main chain without being marginalized; it also allows the chain transfer agent to effectively adjust the molecular weight, preventing the product molecular weight from being too high or too low.

[0071] Beneficial effects: Ensures the synthesized PCE possesses the designed comb-like structure and functional group ratio, with a narrow molecular weight distribution. Constant medium-temperature process conditions facilitate precise control in industrial production, guaranteeing batch-to-batch stability. Suitable ripening temperature ensures complete reaction, resulting in low free monomer content in the finished product, making it environmentally friendly and stable. Reduces safety risks such as material overflow and explosive polymerization caused by high temperatures.

[0072] Optionally, the dripping time in step S3 is 2.5-3.5 hours.

[0073] Technical Background and Working Principle: Matching the constant decomposition rate of the initiator at 58-62℃, the slow addition of materials maintains a low monomer concentration in the system, thereby avoiding local overheating, excessively wide molecular weight distribution, and uneven embedding of functional monomers caused by explosive polymerization. It forces monomers with different polymerization rates (such as highly active acrylic acid and low-dosage foam-stabilizing and setting-regulating functional monomers) to compete for reaction in an order close to the dosing ratio, thereby ensuring the uniformity of the copolymer composition and ensuring the effective integration of all designed functional groups. This dosing time is an essential process guarantee for synthesizing a special water-reducing agent with high water reduction rate, excellent foam stabilization, and precise setting-regulating functions.

[0074] Technical Solution and Component Functions: The free radicals generated by the continuous dripping of the initiator are steadily consumed, avoiding a surge in chain termination and facilitating the formation of polymers with moderate molecular weight and narrow distribution. The polyether macromonomers, as the base material, can continuously react throughout the process, steadily building a "comb-like" main chain backbone with polyether side chains. The acrylic monomers, which are slowly dripped in, maintain a low concentration throughout, and their self-polymerization tendency is effectively suppressed, thus mainly participating in copolymerization. This allows carboxyl functional groups to be uniformly embedded in the main chain, laying the foundation for water-reducing performance. For foam-stabilizing and setting-regulating functional monomers with extremely low feed amounts, this slow dripping process provides sufficient competitive reaction time, ensuring that they are not "submerged" and can be precisely inserted into the key positions of the polymer chain according to the designed ratio.

[0075] Beneficial effects: Ensures the synthesized polymer has a highly reproducible comb-like structure, with effective integration of foam-stabilizing and setting-regulating functional groups. Achieves high water reduction rate, excellent protection of gypsum bubbles, and precise control of setting time, solving two major defects of ordinary PCE. Avoids production safety hazards such as burst polymerization and material overflow, and minimizes batch-to-batch variations in product quality.

[0076] Optionally, the polyether macromonomer and chain transfer agent are dissolved in a portion of water and placed in a reactor. Specifically, this includes: dissolving the polyether macromonomer and chain transfer agent in deionized water and stirring in a reactor to form a homogeneous solution; and under constant temperature and stirring conditions, simultaneously and slowly adding the multifunctional monomer mixture obtained in step S1 and the oxidant aqueous solution to the initiation system in step S2.

[0077] Technical Background and Working Principle: The requirements for water-reducing agents in gypsum board production are a contradictory unity. On the one hand, polyether macromonomers and chain transfer agents are used as reaction substrates to pre-establish the growth starting point with polyether side chains as the backbone and establish a full-process molecular weight adjustment mechanism. On the other hand, a mixture containing carboxylic acid, foam stabilizer, and setting regulator monomers is added synchronously and slowly with the initiator solution. This ensures that trace amounts of functional monomers are accurately and uniformly embedded in the polymer backbone, effectively suppressing the self-polymerization tendency and explosive exothermic reaction of acrylic acid.

[0078] Technical Solution and Component Functions: A multifunctional monomer mixture (containing carboxylic acid monomers, foam-stabilizing monomers, and setting-regulating monomers) is added dropwise simultaneously but separately to the initiator (an aqueous solution of oxidant). This "double-drop addition" mode ensures that the concentrations of active monomers and free radicals in the reaction system are in a controlled, low dynamic equilibrium state at any given time. All added monomers (regardless of their polymerization reactivity) must compete with the limited number of free radicals in the system to participate in the reaction. This forces the polymerization reaction to proceed in proportions close to the composition of the added solution, thus ensuring that the minimal amounts of foam-stabilizing and setting-regulating monomers can achieve uniform copolymerization with a large amount of acrylic acid monomers and polyether macromonomers, precisely embedding themselves at specific positions in the polymer backbone, rather than being "submerged" or forming homopolymer lumps. Slow dropwise addition (typically 2.5-3.5 hours) ensures a stable exothermic reaction, making it easy to control the reaction temperature within a preset window of 58-62℃ through jacket cooling, providing a stable thermodynamic environment for obtaining a uniform molecular structure.

[0079] Beneficial effects: A "three-in-one" special water-reducing agent with high water reduction rate, excellent foam stabilization ability, and controllable setting regulation function was directly synthesized. This avoids the safety risks (powder spillage, gelation) associated with explosive polymerization, and ensures good production reproducibility. The resulting polymer has a narrow molecular weight distribution, uniform functional group distribution, and minimal batch-to-batch performance differences.

[0080] Alternative or modified implementation methods: The addition of polyether macromonomers can be adjusted so that most (e.g., 70-80%) of the polyether macromonomers are used as a base, with the remaining portion mixed with functional monomers and added dropwise. However, this increases the difficulty of solution preparation. The addition of functional monomers can be adjusted to staged or variable-rate dropwise addition. For example, some carboxylic acid monomers and all polyether macromonomers can be added dropwise first to construct the main chain, and then the remaining carboxylic acid monomers and functional monomers can be added dropwise later for "end-capping" or "functionalization". This allows for more precise control over the distribution of functional groups at the ends of the molecular chain or in specific segments, but the process control is extremely complex.

[0081] Optionally, the total monomer mass concentration of the multifunctional monomer mixture is 35%-45%.

[0082] Technical Background and Working Principle: To resolve the contradiction between high water reduction rate and bubble protection / setting control when ordinary PCE is applied to gypsum systems, the concentration of the multifunctional monomer mixture is set at 35%-45%. The fundamental purpose is to provide a physicochemically stable "reactant precursor solution" for subsequent "gradient copolymerization." Firstly, this concentration ensures uniform and precise mixing of unsaturated carboxylic acids, foam stabilizers, and setting regulators. More importantly, this concentration gives the mixture moderate viscosity and fluidity, allowing for precise and stable dropwise addition while also enabling rapid dispersion after entering the reaction system. This maintains a low overall monomer concentration, effectively inhibiting acrylic acid self-polymerization and ensuring uniform copolymerization of all functional monomers.

[0083] Technical Solution and Component Functions: Firstly, it provides a precise target for the feed ratio in step S1, ensuring the accuracy of the initial mixing state. By ensuring the appropriate viscosity and flowability of the mixture, it achieves precise control of the dropping rate, stable dispersion of the exothermic reaction, and a reasonable balance of the solvent environment in the S3 dropping reaction stage, creating stable conditions. This concentration range ensures that the acrylic monomer is both fully dissolved and its activity is controlled, inhibiting its self-polymerization; at the same time, it provides a compatible microenvironment for the oil-soluble foam-stabilizing monomer and the water-soluble settling monomer, preventing their precipitation and ensuring that these trace key functional components can participate in copolymerization uniformly in a constant proportion, ultimately accurately embedding into the polymer backbone to achieve the preset foam stabilization and settling functions.

[0084] Beneficial effects: Stable fluid properties ensure precise and repeatable dripping operations, avoiding pumping failures or reaction runaways caused by fluctuations in solution properties (such as sudden viscosity changes or precipitation), resulting in high production safety. This guarantees batch-to-batch stability of the final water-reducing agent product in terms of water reduction, foam stabilization, and setting regulation performance.

[0085] Alternative or modified implementation methods: While increasing or decreasing the concentration may offer certain advantages, they also carry greater risks. For example, increasing the concentration can improve production efficiency and shorten the time, but it may exceed the solubility or compatibility limits of some monomers, leading to stratification, precipitation, or a sharp increase in viscosity of the mixture during storage or addition. Furthermore, the increased mass of reactants added per unit time results in more concentrated heat release, placing extremely high demands on the temperature control capabilities (cooling efficiency) of the reaction system, and easily causing localized overheating and explosive polymerization.

[0086] Optionally, the heat preservation process includes stirring and heat preservation at the above-mentioned preset temperature for 1.5-2.5 hours.

[0087] Technical Background and Working Principle: In the S3 "gradient copolymerization" stage, monomers are added dropwise for initial polymerization to form a polymer backbone with certain water-reducing functions. However, the polymerization reaction is not completely terminated at this point, and the molecular chain structure may be in a "metastable state." To achieve the preset, stable foam stabilization and settling regulation functions, sufficient reaction time must be provided. Therefore, the maturation process works by creating a constant-temperature dynamic environment without the replenishment of new monomers, driving the reaction to complete completely. During this period, kinetically, sufficient reaction time is provided for the residual active centers, allowing them to be consumed and their molecular weight distribution to narrow; thermodynamically, it promotes conformational relaxation of the polymer chain and stable arrangement of functional groups, thus ensuring that the preset foam stabilization and settling regulation functions are ultimately "solidified" in the molecular chain, and fundamentally eliminating unstable chemical factors that lead to foam breakage and slow settling.

[0088] Technical Solution and Component Functions: Sufficient curing creates a safe and stable foundation for subsequent cooling and neutralization. If neutralization is performed before complete curing, residual active substances may cause uncontrollable subsequent reactions during storage (such as viscosity increase or gelation), affecting product stability. During the 1.5-2.5 hours of heat preservation curing, unreacted monomers (especially acrylic acid and functional monomers) are continuously consumed to extremely low levels. Free radicals further react and annihilate each other, and the polymer chains reach their final molecular weight through chain transfer and chain termination reactions. With the final fixation of the main chain structure, the spatial positions and chemical environments of these functional groups within the polymer molecule are also finalized, fully activating and stabilizing their foam-stabilizing and settling effects. This transforms a dynamic and active reaction mixture into a chemically stable final product solution where all components have reached thermodynamic equilibrium.

[0089] Beneficial effects: Ensures that all designed functions (high water reduction, foam stabilization, precise setting regulation) are fully and stably transferred to the final product, resulting in consistent performance across batches. Completely eliminating residual monomers is a key chemical method to address the side effects of ordinary PCE in gypsum, such as "slow setting and easy foam breakage." Obtaining a "completely reacted" system avoids quality problems such as viscosity changes and gelation caused by slow post-polymerization during storage and transportation.

[0090] Alternative or modified implementation methods: While shortening or extending the curing time may offer certain advantages, the risks far outweigh these advantages. For example, shortening the curing time may result in a high residual monomer content, leading to unpredictable and severe retardation and interfacial disturbances, disrupting bubble stability, and rendering specialized designs ineffective. Extending the curing time, on the other hand, directly impacts production efficiency, and under prolonged high temperatures, the polymer backbone may undergo hydrolysis, oxidation, or partial degradation (especially in the presence of residual oxidants), resulting in a decrease in molecular weight and a decline in water-reducing properties.

Claims

1. A special polycarboxylate superplasticizer for gypsum board, characterized in that, include: S1. Preparation of multifunctional monomer mixture: The multifunctional monomer mixture is composed of unsaturated carboxylic acid monomers, foam-stabilizing monomers and coagulation-regulating monomers dissolved in water; S2. Preparation of the initiation system: Dissolve the polyether macromonomer and chain transfer agent in some water, place them in a reactor, heat to the preset temperature and keep the temperature constant. S3. Perform gradient copolymerization reaction: Under constant temperature conditions, the multifunctional monomer mixture obtained in step S1 and the aqueous oxidant solution are simultaneously and slowly added dropwise to the initiation system in step S2. S4. Maturation and post-treatment: After the addition is complete, the mixture is kept warm and matured at the preset temperature, then cooled down and neutralized with alkali solution to a pH value of 6-7 to obtain the special polycarboxylate superplasticizer.

2. The special polycarboxylate superplasticizer according to claim 1, characterized in that, The foam-stabilizing functional monomer in step S1 is a (meth)acrylate containing C8-C18 alkyl groups, preferably at least one of dodecyl methacrylate and octadecyl acrylate, and the settling functional monomer is an olefinic unsaturated monomer containing phosphonic acid groups, sulfonic acid groups or amide groups; preferably at least one of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), vinylphosphonic acid, and acrylamide.

3. The special polycarboxylate superplasticizer according to claim 1, characterized in that, In step S2, the polyether macromonomer is at least one of isopentenyl alcohol polyoxyethylene ether or methyl allyl alcohol polyoxyethylene ether, the chain transfer agent is at least one of mercaptoacetic acid, mercaptopropionic acid or mercaptoethanol, and the amount of the chain transfer agent is 0.1%-0.5% of the total mass of all monomers.

4. The special polycarboxylate superplasticizer according to claim 1, characterized in that, The oxidant in step S3 is at least one of ammonium persulfate, potassium persulfate, or hydrogen peroxide, and the amount of the oxidant is 0.5%-2.0% of the total mass of all monomers.

5. The special polycarboxylate superplasticizer according to claim 1, characterized in that, The molar ratio of materials fed in step S1 and step S2 is: Polyether macromonomer: Unsaturated carboxylic acid monomer: Foam stabilizing monomer: Settling regulating monomer = 1:(2.0-4.0):(0.05-0.25):(0.1-0.5).

6. The special polycarboxylate superplasticizer according to claim 1, characterized in that, The preset temperature mentioned in step S2 is 58-62℃.

7. The special polycarboxylate superplasticizer according to claim 1, characterized in that, The dripping time in step S3 is 2.5-3.5 hours.

8. The special polycarboxylate superplasticizer according to claim 6, characterized in that, The step of dissolving the polyether macromonomer and chain transfer agent in a portion of water and placing them in a reactor specifically includes: dissolving the polyether macromonomer and chain transfer agent in deionized water and stirring them in a reactor to form a homogeneous solution; Performing a gradient copolymerization reaction includes: under constant temperature and stirring conditions, simultaneously and slowly adding the multifunctional monomer mixture obtained in step S1 and the aqueous oxidant solution to the initiation system in step S2.

9. The special polycarboxylate superplasticizer according to claim 1, characterized in that, The total monomer mass concentration of the multifunctional monomer mixture is 35%-45%.

10. The special polycarboxylate superplasticizer according to claim 1, characterized in that, The heat preservation and curing process includes stirring and heat preservation at the preset temperature for 1.5-2.5 hours.

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