A durable acrylic water-reducing agent and its preparation method

Abstract

This application relates to the field of water-reducing agents, and in particular to a durable acrylic water-reducing agent and its preparation method. The agent introduces a structure with sterically hindered ester groups into the polyacrylic acid chain. By combining sterically hindered and sterically hindered monomers and controlling the proportion of sterically hindered groups, the agent can better balance water reduction rate and slump retention performance at higher service temperatures while maintaining water solubility.

Description

Technical Field

[0001] This application relates to the field of water-reducing agents, and in particular to a durable acrylic water-reducing agent and its preparation method. Background Technology

[0002] Acrylic water-reducing agents are usually copolymers of acrylic acid and acrylate. Their mechanism of action lies in their unique molecular structure and interaction with cement particles. They achieve efficient dispersion mainly through electrostatic repulsion and steric hindrance effects, thereby significantly reducing the water-cement ratio of concrete and improving its fluidity.

[0003] Typically, acrylic water-reducing agents are formed by the reaction of two monomers, acrylic acid and methyl acrylate, under the action of an initiator to form a copolymer system. It usually has a number average molecular weight of 2000 to 5000, and its side chains can be modified by grafting molecular chains such as polyethylene glycol ether.

[0004] In the use of acrylic water-reducing agents, it has been found that acrylic water-reducing agents easily cause slump loss. This phenomenon has been proven by many documents. Moreover, during the production process, the loss of slump varies greatly with temperature changes, especially at higher temperatures (such as above 30°C). This accelerates the hydration reaction and the thermal motion of water-reducing agent molecules, leading to unstable adsorption and thus causing greater slump loss. The above phenomena narrow the applicable temperature range of acrylic water-reducing agents, resulting in limited construction conditions and affecting the durability of acrylic water-reducing agents. Summary of the Invention

[0005] The purpose of this application is to provide an improved polyacrylic acid water-reducing agent that can maintain good slump at high temperatures and has good water-reducing properties after being added.

[0006] First, this application relates to a durable acrylic water-reducing agent comprising a polyacrylic polymer, wherein the polyacrylic polymer comprises the following monomers:

[0007] Monomer A: Acrylic acid or alkyl-substituted acrylic acid;

[0008] Monomer B is a glycol monoester or an alkyl-substituted alkyl glycol monoester, having the general formula shown in Formula I:

[0009]

[0010] R1 can be selected from straight-chain alkanes, branched alkanes or hydrogen, and R2 can be selected from straight-chain alkanes, branched alkanes, cycloalkanes or aromatic hydrocarbons with not less than four carbons.

[0011] Monomer C: Methyl acrylate or alkyl-substituted methyl acrylate.

[0012] The above scheme employs a composite system of three monomers. During the water-reducing process, the carboxyl groups primarily form a negative charge on the surface of cement particles, while the long molecular chains create a solubilization layer. This reduces particle agglomeration and increases lubrication, thus reducing water usage. However, because the solubilization layer adsorbs more water, the concrete continuously releases heat during the reaction. At higher ambient temperatures, this internal temperature is more likely to rise, leading to weakened steric hindrance, reduced lubrication of the solubilization layer, and consequently decreased system fluidity.

[0013] Therefore, in this application, side chains with larger functional groups are introduced into the monomers, and the technical problem is solved by controlling the proportions of the three monomers. First, monomer A still provides good adsorption and negative charge properties. It has a basic carboxyl structure, which provides hydrophilicity and the ability to bind with cement particles. Among the uncharged monomers at the ends, monomer C is a conventional methyl ester, while monomer B first provides greater steric hindrance. Secondly, during the binding process with cement particles, it forms hydroxyl groups at the distal end of the hydrocarbon group, maintaining good particle binding ability on the basis of high steric hindrance, thus better exerting the steric hindrance effect. At the same time, the use of the more sterically hindrance R2 group also improves the overall lubricity and fluidity, which better balances the water-reducing performance of the water-reducing agent at low addition levels and the slump retention at higher temperatures.

[0014] Based on the above scheme, a further preferred option is that the molar ratio of monomer A, monomer B and monomer C is 2-3:0.5-1:1. In this scheme, the overall ratio of monomer B and monomer C needs to be controlled. If too much monomer B is added, it will cause the molecular chains to easily entangle or have a conjugation effect, which will result in a loss of overall fluidity. Within the above ratio range, the water-reducing agent can take into account various properties.

[0015] Preferably, R2 is a phenyl or alkyl-substituted phenyl group. More preferably, monomer B has the following molecular formula:

[0016]

[0017] R3 can be a hydrogen or methyl group at any position.

[0018] Adding a certain amount of monomer B to this system introduces a certain amount of phenyl groups. The rigidity of the benzene ring reduces entanglement in the system. Although the benzene ring itself is rigid and hydrophobic, its addition in small amounts has virtually no adverse effect on the adsorption performance of the system. On the contrary, it improves the coating effect of the water-reducing agent on cement particles. Simultaneously, the rigid benzene ring further enhances the barrier properties between cement particles, resulting in better flowability of the concrete during preparation and requiring less water. Building upon this, a phenolic hydroxyl group is introduced at the para-position of the benzene ring. The distal hydroxyl group has a better ability to bind with cement particles, making it easier to maintain its binding performance with cement particles in the later stages of the reaction. This improves slump retention at high temperatures or in the later stages of the reaction, while also coordinating the uniform distribution of carboxyl groups on the surface of cement particles, which is beneficial for further improving water-reducing properties.

[0019] Preferably, monomer A is methacrylic acid, and / or;

[0020] R1 is methyl, and / or;

[0021] The monomer C is methyl methacrylate.

[0022] Preferably, the weight-average molecular weight of the polyacrylic acid polymer is 10,000 to 100,000. More preferably, the polyacrylic acid polymer comprises a first component polyacrylic acid and a second component polyacrylic acid, wherein the weight-average molecular weight of the first component polyacrylic acid is 10,000 to 14,000, the weight-average molecular weight of the second component polyacrylic acid is 30,000 to 38,000, and the mass ratio of the first component polyacrylic acid to the second component polyacrylic acid is 1 to 5:1.

[0023] This system employs a two-component formulation with varying molecular weights. The first component, polyacrylic acid, with its smaller size, provides better coating performance, while the second component, polyacrylic acid, with its longer molecular chains, offers excellent water retention in both the early and later stages of the reaction. Specifically, in the early stages of the reaction when water content is high, or at lower temperatures, the lower molecular weight water-reducing agent exhibits better activity, forming the coating and solvent layers more quickly to improve fluidity. In the middle and later stages of the reaction, or at higher temperatures, as the reaction progresses, the high molecular weight polyacrylic acid molecules connect to the surface of cement particles, providing even greater water retention and a larger collision volume. This prevents the water-reducing agent from agglomerating with the cement particles. Simultaneously, the presence of the first component, polyacrylic acid, ensures fluidity. The combined use of both components ensures a balance between fluidity and coating properties, resulting in excellent water-reducing and slump-preserving effects at all stages and temperatures.

[0024] In addition, this application also relates to a method for preparing the above-mentioned durable acrylic water-reducing agent, wherein monomer A and monomer C, an initiator and a chain transfer agent are mixed in a solvent and heated to undergo a preliminary reaction, so that monomer A and monomer C undergo preliminary polymerization; then monomer B is added and the reaction is carried out to the target molecular weight, and then the pH is adjusted to neutral.

[0025] In this scheme, monomers A and C are first prepolymerized to form an oligomer system of monomers A and C. Then, monomer B is added. The overall amount of monomer B added is relatively small. Monomer B is better dispersed and participates in polymerization in the prepolymer system of monomers A and C. The steric hindrance effect of monomer B makes it more inclined to graft with monomers A and C rather than self-polymerize, thus allowing monomer B to be interspersed in the A and C segments, which can space monomer B and make the chain segments of monomer B have a larger spacing in the system. In the above process, since there is a certain steric hindrance problem when monomer B is directly connected, it is more inclined to be connected with the oligomers formed by monomers A and C. This reduces the problems of poor solubility and decreased bonding performance of water-reducing agent caused by continuous polymerization of monomers with large steric hindrance. It also makes monomer B rationally distributed on the molecular chain, better exerting the steric hindrance effect and the bonding effect of cement particles. In a further preferred embodiment, during the initial polymerization of monomers A and C, the temperature is controlled at 50–80°C and the time is controlled at 10–30 min. The solvent system is preferably water. Within this range, a water-reducing agent with higher water reduction rate and slump retention performance can be obtained overall.

[0026] In summary, this application provides a polyacrylic acid-based water-reducing agent system, which introduces a structure with a sterically hindered ester group into the polyacrylic acid chain segment and introduces a hydroxyl group into the terminal chain segment of the ester group. Combined with other monomers and proportional control, this water-reducing agent provides superior water-reducing properties while also exhibiting good slump retention. Furthermore, by coordinating different molecular weights of this specific polyacrylic acid structure, the corresponding water-reducing and slump retention properties are further enhanced, better balancing water reduction rate and slump retention performance at higher service temperatures. Detailed Implementation

[0027] The solution in this application will be further described through the following specific implementation methods.

[0028] In this application, the water-reducing agent is tested using the following methods:

[0029] The water reduction rate, bleeding rate, setting time difference, slump at 20℃, slump change at 20℃ for 1 hour, slump at 35℃, and slump change at 35℃ for 1 hour were determined according to GB 8076-2008 Concrete Admixtures. The weight-average molecular weight was determined using a static light scattering instrument.

[0030] In the following experiments, the concrete materials used were selected in accordance with GB 8076-2008 Concrete Admixtures, and the specific mix proportions were determined according to Section 6.2 of the standard. The water content was controlled so that the slump at 20℃ was 210±10mm, the water-reducing agent dosage was 0.25%, and the cement dosage was 360kg / m³. 3 The sand content is 45%.

[0031] In the following embodiments, a water-reducing agent based on a polyacrylic acid-polyacrylate system is provided. Taking Example 1 as an example, Example 1 is a water-reducing agent with two different molecular weights of polyacrylic acid, specifically comprising a first component of polyacrylic acid and a second component of polyacrylic acid. Both the first component of polyacrylic acid and the second component of polyacrylic acid contain the following three monomers:

[0032] Monomer A: Methacrylic acid

[0033] The molecular formula of monomer B is as follows:

[0034]

[0035] Monomer C: Methyl methacrylate

[0036] The preparation method of the first component, polyacrylic acid, is as follows:

[0037] In a reaction vessel, using water as a solvent, monomers A and C, ammonium persulfate as an initiator, and mercaptopropionic acid as a chain transfer agent were added. The mixture was heated to 60°C and reacted for 20 minutes. Subsequently, monomer B was added, and the reaction was continued at the target molecular weight. The mixture was then cooled to room temperature, neutralized with sodium hydroxide to pH=7, and the solvent was removed to obtain the first component, polyacrylic acid. During this process, the molar ratio of monomers A, B, and C was controlled at 2.5:1:1.

[0038] In Example 1, the total monomer concentration was controlled at 18%, the chain transfer agent concentration at 1.1%, the initiator concentration at 1%, and the reaction time was 9 hours. After reacting according to these steps, the weight-average molecular weight of the system was determined to be 14,000.

[0039] The preparation method of the second component, polyacrylic acid, is the same as that of the first component, polyacrylic acid, except that the mass concentration of its chain transfer agent is 0.8%, the total mass concentration of monomer is controlled at 22%, the reaction time is 10h, and the weight average molecular weight is 33000 after the reaction.

[0040] The first component, polyacrylic acid, and the second component, polyacrylic acid, were mixed at a mass ratio of 3:1 to obtain the water-reducing agent as shown in Example 1.

[0041] Example 2: Based on Example 1, this example maintains the total amount of monomers B and C unchanged, but adjusts the amount and type of monomer B used in an orthogonal experiment. The selection of monomer B and the specific experimental results are shown in Table 1.

[0042]

[0043] The above experiments show that introducing monomer B, which contains sterically hindered groups, maintains good water-reducing performance. The overall use of longer aliphatic chains or a relatively rigid benzene ring structure maintains the stability of the solvent layer outside the cement particles, thus preserving good water-reducing performance. Compared to resorcinol ester, parasorcinol ester has a better effect, with minimal impact on slump at higher temperatures. While using long-chain alkyl groups such as butyl, hexyl, and cyclohexyl can improve slump retention at high temperatures to some extent, their high reactivity prevents sufficient rigidity to avoid adsorption between systems and makes them more prone to molecular entanglement, resulting in slightly inferior performance, though still better than in Examples 2-24. It is noteworthy that the experimental group using cyclohexyl groups generally exhibits better water-reducing performance than straight-chain alkyl groups, but is weaker than phenyl groups. This may be because cyclohexanediol is more prone to esterification of hydroxyl and carboxyl groups in the system, affecting its adhesion to cement particles and causing steric hindrance, thus weakening the overall water-reducing performance.

[0044] Regarding the mix proportions, insufficient use of monomer C will result in poor performance, specifically manifested in significant slump loss at 35℃. When the amount of monomer C increases, resulting in a decrease in monomer B, fewer rigid segments will also lead to easier collisions between cement particles, and the water reduction rate will also decrease to some extent.

[0045] Example 3: This example is based on the monomer combinations selected in Examples 1 and 2, with adjustments made to the ratio of monomer A. See Table 2 for details.

[0046]

[0047] The experiments in Table 2 show that controlling the proportion of monomer A has a significant impact on the water-reducing performance of the system. Since the increase or decrease of monomer A in the system has a significant impact on the water solubility of the water-reducing agent and its adhesion to cement particles, an excessively high proportion will lead to a certain degree of reduction in water reduction rate and a significant loss in slump at 35℃. On the other hand, an excessively low proportion will have the same defects as an excessively high proportion of monomer B, with a significant increase in overall water reduction performance and a significant increase in bleeding rate.

[0048] Example 4: Based on Example 1, this example adjusts the molecular weight of the first component polyacrylic acid and the second component polyacrylic acid, and tries different ratios for each molecular weight combination. The specific ratios are shown in Table 3.

[0049]

[0050] Specifically, different molecular weights of polyacrylic acid molecules can be achieved by adjusting the monomer concentration, reaction time, and chain transfer agent dosage, as follows:

[0051] The total mass concentration of monomers was 16%, the mass concentration of chain transfer agent was 1.2%, and the incubation time after adding monomer B was adjusted to 7.5 h, resulting in a weight-average molecular weight of 7000.

[0052] The total mass concentration of monomers was 18%, the mass concentration of chain transfer agent was 1.06%, and the incubation time after adding monomer B was adjusted to 9 hours, resulting in a weight-average molecular weight of 10,000.

[0053] The total mass concentration of monomers was 22%, the mass concentration of chain transfer agent was 0.75%, and the incubation time after adding monomer B was adjusted to 10 h, resulting in a weight-average molecular weight of 38,000.

[0054] With a total monomer concentration of 25% and a chain transfer agent concentration of 0.7%, and after adding monomer B, the incubation time was adjusted to 12 hours, resulting in a weight-average molecular weight of 45,000.

[0055] The experimental results of each experimental group in Table 3 are shown in Table 4.

[0056]

[0057] The data in Table 4 show that using a blend of two polyacrylic acids with different molecular weights further improved the slump after 1 hour of reaction at different temperatures, demonstrating a significant improvement in fluidity during the reaction. The molecular weight of the lower molecular weight first component, polyacrylic acid, should not exceed 15,000; otherwise, the overall water reduction rate will decrease significantly. Conversely, the molecular weight of the higher molecular weight second component, polyacrylic acid, should not exceed 40,000; otherwise, its solubility will decrease significantly, leading to a noticeable loss in all parameters.

[0058] Example 5: In this example, the reaction process was adjusted based on Example 1. Specifically, the following experimental group was included.

[0059] Experimental group 5-1, compared to Example 1, directly mixed all materials and carried out the reaction. The reaction time and reaction temperature were controlled in the same way as in Example 1, that is, 60℃ for 10h20min.

[0060] Experimental group 5-2, based on Example 1, had the prepolymerization reaction time adjusted to 30 min.

[0061] In Experiment 5-3, the prepolymerization reaction time was adjusted to 60 min based on Example 1.

[0062] In experimental group 5-4, the prepolymerization reaction time was adjusted to 10 min based on Example 1.

[0063] Experiments were conducted on Example 5, and the results are shown in Table 5.

[0064]

[0065] The above experimental results show that the prepolymerization reaction can significantly improve the water-reducing performance and high-temperature slump retention of the system in this embodiment. This is likely because the flexible segments of the prepolymer help improve the bonding performance between the water-reducing agent and cement particles, as well as its dispersion performance in water, avoiding the large steric hindrance segments on the carboxyl group monomer B of the acrylic acid monomer, which prevent it from fully exerting its function. However, the degree of prepolymerization should not be too high, otherwise it may lead to excessive dispersion of the overall hydrophobic and hydrophilic properties of the system, resulting in a significant decrease in both overall water-reducing performance and bleeding resistance.

[0066] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A durable acrylic water-reducing agent, characterized in that, The invention comprises a polyacrylic acid polymer, wherein the polyacrylic acid polymer comprises a first component polyacrylic acid and a second component polyacrylic acid, the first component polyacrylic acid having a weight-average molecular weight of 10,000 to 14,000, the second component polyacrylic acid having a weight-average molecular weight of 30,000 to 38,000, and the mass ratio of the first component polyacrylic acid to the second component polyacrylic acid being 1 to 5:1; both the first component polyacrylic acid and the second component polyacrylic acid contain the following monomers: Monomer A: Acrylic acid or alkyl-substituted acrylic acid; Monomer B is a glycol monoester or an alkyl-substituted glycol monoester, having the general formula shown in Formula I: ； I Wherein, R1 is a straight-chain alkane, a branched-chain alkane, or hydrogen, and R2 is a straight-chain alkane, a branched-chain alkane, a cycloalkane, or an aromatic hydrocarbon with not less than four carbons. Monomer C: Methyl acrylate or alkyl-substituted methyl acrylate; The molar ratio of monomer A, monomer B and monomer C is 2-3:0.5-1:1; The preparation method of the polyacrylic acid polymer is as follows: In a solvent, monomers A and C, an initiator, and a chain transfer agent are mixed and heated to initiate a preliminary reaction, causing monomers A and C to undergo preliminary polymerization. Then, monomer B is added, and the reaction proceeds to the target molecular weight. The pH is then adjusted to neutral.

2. The durable acrylic water-reducing agent according to claim 1, characterized in that, R2 is a phenyl or alkyl-substituted phenyl group.

3. The durable acrylic water-reducing agent according to claim 1, characterized in that, Monomer B has the following molecular formula: ； R3 is either hydrogen or methyl.

4. The durable acrylic water-reducing agent according to claim 1, characterized in that, The monomer A is methacrylic acid, and / or; R1 is methyl, and / or; The monomer C is methyl methacrylate.

5. A method for preparing a durable acrylic water-reducing agent according to any one of claims 1 to 4, characterized in that, In a solvent, monomers A and C, an initiator, and a chain transfer agent are mixed and heated to initiate a preliminary reaction, causing monomers A and C to undergo preliminary polymerization. Then, monomer B is added, and the reaction proceeds to the target molecular weight. The pH is then adjusted to neutral.

6. The method for preparing a durable acrylic water-reducing agent according to claim 5, characterized in that, During the initial polymerization of monomers A and C, the temperature is controlled at 50–80℃ and the time is controlled at 10–30 min.

7. The method for preparing a durable acrylic water-reducing agent according to claim 5, characterized in that, The solvent is water.

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