Durable acrylic acid water reducing agent and preparation method thereof

Abstract

The invention relates to the field of water reducing agents, in particular to a durable acrylic water reducing agent and a preparation method thereof.The durable acrylic water reducing agent is characterized in that a structure with a large-steric-hindrance ester group is introduced into a polyacrylic acid chain link, large-steric-hindrance monomers and small-steric-hindrance monomers are combined, the proportion of the large-steric-hindrance groups is controlled, and on the basis that water solubility is kept, the durable acrylic water reducing agent is prepared. The water-reducing rate and the slump retaining performance at a relatively high use temperature are better considered.

Description

Technical Field

[0001] The present application relates to the field of water reducers, and in particular to a durable acrylic water reducer and a preparation method thereof. Background Art

[0002] Acrylic water reducer is usually a copolymer of acrylic acid and acrylic ester. Its mechanism of action lies in its unique molecular structure and interaction with cement particles. It mainly achieves efficient dispersion through electrostatic repulsion and steric hindrance effects, thereby significantly reducing the water-cement ratio of concrete and improving fluidity.

[0003] Typically, acrylic water reducers are prepared by reacting two monomers, acrylic acid and methyl acrylate, under the action of an initiator to form a copolymer system. The copolymer 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 agent, it is found that acrylic water-reducing agent is very easy to cause slump loss. This phenomenon has been proven in many literatures. In addition, during the production process, the loss of slump varies greatly when the temperature changes. Especially at higher temperatures (such as above 30°C), the hydration reaction and the thermal motion of the water-reducing agent molecules are accelerated, resulting in unstable adsorption, which in turn causes a greater loss of slump. The above phenomenon has narrowed the applicable temperature range of acrylic water-reducing agent, resulting in limited construction conditions and affecting the durability of acrylic water-reducing agent. Summary of the Invention

[0005] The purpose of the present application is to provide an improved polyacrylic acid water reducer, which can still maintain good slump at higher temperatures and has good water-reducing performance after addition.

[0006] First, the present application relates to a durable acrylic water reducer, comprising a polyacrylic acid polymer, wherein the polyacrylic acid polymer comprises the following monomers: Monomer A: acrylic acid or alkyl-substituted acrylic acid; Monomer B is an acrylic acid diol monoester or an alkyl-substituted acrylic acid alkyl diol monoester, and has the general formula shown in Formula I:

[0007] wherein R1 is optionally a straight-chain alkane, a branched-chain alkane or hydrogen, and R2 is optionally a straight-chain alkane, a branched-chain alkane, a cycloalkane or an aromatic hydrocarbon having not less than four carbon atoms; Monomer C: methyl acrylate or alkyl-substituted methyl acrylate.

[0008] The above scheme utilizes a composite system of three monomers. As the water-reducing agent participates in the water-reduction process, it primarily forms a negative charge on the cement particle surface through carboxyl groups. Simultaneously, its long molecular chains form a solvation layer on the cement particle surface, thereby reducing agglomeration between cement particles and increasing lubrication between cement particles, thereby reducing water usage. During this process, the solvent layer absorbs more water, and as the reaction proceeds, the concrete continuously releases heat. At higher ambient temperatures, the concrete is more likely to generate higher internal temperatures. High temperatures can weaken the steric hindrance of the aforementioned structure and reduce the lubrication effect of the solvation layer, leading to a decrease in the fluidity of the system.

[0009] Therefore, in the solution of the present application, some larger group side chains are introduced into the monomers, and the ratio of the three monomers is controlled to solve the technical problem. First, monomer A can still provide good adsorption and negative charge performance. It has a basic carboxyl structure, which can provide hydrophilicity and the ability to bind to cement particles. Among the monomers with no charge at the end, monomer C is a conventional methyl ester, while monomer B first provides a large steric hindrance. Secondly, in the process of binding with cement particles, a hydroxyl group at the far end of the hydrocarbon group is formed, which maintains good particle binding ability on the basis of high steric hindrance, better exerting the steric effect. At the same time, the use of the larger steric hindrance R2 group also improves the overall lubricity and fluidity, which better takes into account the water-reducing performance of the water-reducing agent at low addition levels and the slump retention at higher temperatures.

[0010] On the basis of the above scheme, it is further preferred that the molar ratio of monomer A, monomer B and monomer C is 2-3:0.5-1:1. In this scheme, the ratio of monomer B to monomer C needs to be controlled as a whole. Excessive addition of monomer B will lead to entanglement or conjugation effect between molecular chains, which will cause loss of overall fluidity. Within the above ratio range, the water reducer can take into account various properties as a whole.

[0011] Preferably, R2 is phenyl or alkyl-substituted phenyl. Further preferably, monomer B has the following molecular formula:

[0012] Wherein, R3 is hydrogen or methyl at any position.

[0013] By adding a certain amount of B monomer to this system, a certain amount of phenyl groups is introduced. The rigidity of the benzene ring can reduce entanglement in the system. Although the benzene ring itself is highly rigid and hydrophobic, its small incorporation has little adverse effect on the adsorption performance of the system. Instead, it enhances the water reducer's coating effect on cement particles. Furthermore, the rigid benzene ring further improves the barrier properties between cement particles, resulting in better fluidity during the concrete preparation process and requiring less water. Furthermore, by introducing a phenolic hydroxyl group at the para position of the benzene ring, the distal hydroxyl group has better binding ability with cement particles, making it easier to maintain binding with cement particles later in the reaction, thereby improving slump retention at high temperatures or in the later stages of the reaction. It also coordinates the uniform distribution of carboxyl groups on the cement particle surface, further enhancing water reduction.

[0014] Preferably, the monomer A is methacrylic acid, and / or; Said R1 is methyl, and / or; The monomer C is methyl methacrylate.

[0015] Preferably, the weight average molecular weight of the polyacrylic acid polymer is 10,000 to 100,000. Further 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, and 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.

[0016] This system utilizes a compounding of two components, high and low molecular weight. Overall, the first component, polyacrylic acid, offers improved coating properties due to its smaller size, while the second component, polyacrylic acid, has a longer molecular chain, providing excellent water retention in both the early and late stages of the reaction. In the early stages of the reaction, when the water content is high, or at lower temperatures, the water reducer with a lower molecular weight exhibits greater activity, allowing for faster formation of a coating layer and solvent layer, thereby improving fluidity. In the middle and late stages of the reaction, or at higher temperatures, as the reaction proceeds, the high-molecular-weight polyacrylic acid molecules connect to the surface of the cement particles, providing enhanced water retention and a larger collision volume. This prevents the water reducer from agglomerating with the cement particles after coating. The presence of the first component, polyacrylic acid, also ensures fluidity. The combined use of these two components ensures a balance between fluidity and coating properties, resulting in the water reducer providing excellent water-reduction and slump-retention effects at all stages and temperatures.

[0017] In addition, the present application also relates to a method for preparing the above-mentioned durable acrylic water reducer, in which monomers A and C, an initiator, and a chain transfer agent are mixed in a solvent, heated for a preliminary reaction, and monomers A and C are initially polymerized; then monomer B is added and reacted to the target molecular weight, and then the pH is adjusted to neutral.

[0018] In this scheme, monomers A and C are first pre-polymerized 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, so monomer B is better dispersed in the pre-polymer system of monomers A and C and participates in the polymerization. The steric hindrance effect of monomer B makes it more inclined to graft with monomers A and C rather than self-polymerize, thereby inserting monomer B into the A and C segments, which can separate monomer B and provide a larger gap between the chain links of monomer B in the system. In addition, in the above process, since there will be certain steric hindrance problems when monomer B is directly connected, it is more inclined to connect with the oligomer formed by monomers A and C, thereby reducing the problems of poor solubility of the water reducer and decreased binding performance caused by the continuous polymerization of monomers with large steric hindrance. In addition, the B monomer is rationally distributed on the molecular chain, which better exerts the steric hindrance effect and the binding effect of cement particles. Further preferably, during the preliminary polymerization of monomer A and monomer C, the temperature is controlled at 50-80°C, the time is 10-30 minutes, and the solvent system is preferably water. Within this range, a water reducer with higher water reduction rate and slump retention performance can be obtained as a whole.

[0019] In summary, the present application provides a polyacrylic acid-based water-reducing agent system, which introduces a structure with a large 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 ratio control, the water-reducing agent provides excellent water-reducing properties while having good slump retention performance. Further, by combining the different molecular weights of the specific polyacrylic acid structure, the corresponding water-reducing properties and slump retention performance are further improved, and the water-reducing rate and slump retention performance at higher operating temperatures are better balanced. DETAILED DESCRIPTION

[0020] The solution in this application is further described through the following specific implementation methods.

[0021] In this application, the water reducer is tested using the following methods: The water reduction rate, bleeding rate, setting time difference, slump at 20°C, change in slump at 20°C after 1 hour, slump at 35°C, and change in slump at 35°C after 1 hour of testing were determined according to GB 8076-2008 Concrete Admixtures. The weight-average molecular weight was determined using a static light scattering instrument.

[0022] In the following experiments, the concrete materials used were selected in accordance with GB 8076-2008 Concrete Admixtures. The specific mix ratios were determined in accordance with Section 6.2 of the standard. The slump was controlled to be 210±10mm at 20°C, the water-reducing agent dosage was 0.25%, and the cement dosage was 360kg / m 3 , the sand rate is 45%.

[0023] In the following embodiments, a polyacrylic acid-polyacrylate system water reducer is provided. Example 1 is taken as an example. Example 1 is a polyacrylic acid water reducer with two different molecular weights, specifically comprising a first component polyacrylic acid and a second component polyacrylic acid. The first component polyacrylic acid and the second component polyacrylic acid both contain the following three monomers: Monomer A: Methacrylic acid The molecular formula of monomer B is as follows:

[0024] Monomer C: Methyl methacrylate Wherein, the preparation method of the first component polyacrylic acid is as follows: In a reactor, monomers A and C were added, along with ammonium persulfate as an initiator and mercaptopropionic acid as a chain transfer agent, using water as the solvent. The temperature was raised to 60°C and the reaction was continued for 20 minutes. Monomer B was then added and the reaction continued at this temperature until the target molecular weight was reached. The reaction was then cooled to room temperature, neutralized with sodium hydroxide to a pH of 7, and the solvent 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.

[0025] In Example 1, the total monomer concentration was controlled to be 18%, the chain transfer agent concentration was 1.1%, the initiator concentration was 1%, and the reaction time was 9 hours. After the reaction was carried out according to this step, the weight average molecular weight of the system was measured to be 14,000.

[0026] The preparation method of the second component polyacrylic acid is similar to that of the first component polyacrylic acid, with the only difference being that the mass concentration of the chain transfer agent is 0.8%, the total mass concentration of the monomers is controlled to be 22%, the reaction time is 10 h, and the weight average molecular weight measured after the reaction is 33,000.

[0027] The first component polyacrylic acid and the second component polyacrylic acid were mixed in a mass ratio of 3:1 to obtain the water reducing agent shown in Example 1.

[0028] Example 2. Based on Example 1, this example maintains the total amount of monomer B and monomer C unchanged, and adjusts the amount and type of monomer B to conduct an orthogonal experiment. The selection of monomer B and the specific experimental results are shown in Table 1.

[0029]

[0030] Through the above-mentioned experiment, it can be seen that after introducing the monomer B containing the grafting of large steric groups, good water-reducing performance can be maintained, and longer fatty chains or a certain rigid benzene ring structure are utilized as a whole, which maintains the stability of the outer solvent layer of cement particles, maintains good water-reducing performance, and compared to m-diphenol ester, p-diphenol ester is adopted to have better effect, and slump is substantially not affected at higher temperatures. Although the long-chain alkyl groups such as butyl, hexyl and cyclohexyl are selected to improve the slump-retaining performance at high temperatures to a certain extent, on the one hand, due to the excessive mobility of the long-chain alkyl group itself, it cannot provide sufficient rigidity to avoid adsorption between the system, and has the tendency to form molecular entanglements more easily, so the effect is slightly poor, but still better than embodiment 2-24. It is worth noting that the experimental group using cyclohexyl has better water-reducing performance than straight-chain alkyl group as a whole, but is weaker than phenyl as a whole, and its reason may be that cyclohexanediol is more prone to the esterification of alcoholic hydroxyl and carboxyl groups in the system and affects its attachment to cement particles and steric hindrance, thereby causing the overall water-reducing performance to be weakened to a certain extent.

[0031] As for the mix ratio, too little monomer C will lead to poor performance, which is specifically reflected in the obvious slump loss at 35°C. When the increase in monomer C leads to a decrease in monomer B, the fewer rigid segments will also make it easier for cement particles to collide with each other, and the water reduction rate will also be reduced to a certain extent.

[0032] Example 3: Based on the monomer combinations selected in Examples 1 and 2, this example increases or decreases the ratio of monomer A. The details are shown in Table 2.

[0033]

[0034] From the experiments in Table 2, it can be seen that controlling the proportion of monomer A has a significant effect on the water-reducing performance of the system. Since the increase or decrease of monomer A in the system has a significant effect on the water solubility of the water reducer and the adhesion to the cement particles, a too large proportion of monomer A will lead to a certain degree of reduction in the water reduction rate and a significant loss in slump at 35°C. However, a too low proportion will have defects similar to those of a high proportion of monomer B, with a significant increase in the overall water reduction and water bleeding rate.

[0035] Example 4: Based on Example 1, this example adjusts the molecular weights 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.

[0036]

[0037] Specifically, for polyacrylic acid molecules with different molecular weights, this can be achieved by adjusting the monomer mass concentration, reaction time, and the amount of chain transfer agent added, as follows: The total mass concentration of monomers was 16%, the mass concentration of chain transfer agent was 1.2%, and the holding time after monomer B was added was adjusted to 7.5 h, resulting in a weight average molecular weight of 7000.

[0038] The total mass concentration of monomers was 18%, the mass concentration of chain transfer agent was 1.06%, and the holding time after monomer B was added was adjusted to 9 h, resulting in a weight average molecular weight of 10,000.

[0039] The total mass concentration of monomers was 22%, the mass concentration of chain transfer agent was 0.75%, and the holding time after monomer B was added was adjusted to 10 h, resulting in a weight average molecular weight of 38,000.

[0040] The total mass concentration of monomers was 25%, the mass concentration of chain transfer agent was 0.7%, and the holding time after monomer B was added was adjusted to 12 h, resulting in a weight average molecular weight of 45,000.

[0041] The experimental results of each test group in Table 3 are shown in Table 4.

[0042]

[0043] The data in Table 4 show that the combination of two polyacrylic acids with different molecular weights further improves slump after a one-hour reaction at different temperatures, significantly enhancing fluidity during the reaction. The molecular weight of the low-molecular-weight first component, polyacrylic acid, should not exceed 15,000, otherwise the overall water reduction rate will be significantly reduced. The molecular weight of the high-molecular-weight second component, polyacrylic acid, should not exceed 40,000, otherwise its solubility will be significantly reduced, resulting in significant losses in various parameters.

[0044] Example 5. In this example, based on Example 1, the reaction process was adjusted, specifically, including the following experimental groups.

[0045] In experimental group 5-1, compared with Example 1, all materials were directly mixed and then reacted. The reaction time and reaction temperature were controlled to be consistent with those in Example 1, that is, 60° C. for 10 h 20 min.

[0046] Experimental group 5-2, based on Example 1, the prepolymerization reaction time was adjusted to 30 min.

[0047] Experimental group 5-3, based on Example 1, the prepolymerization reaction time was adjusted to 60 min.

[0048] Experimental group 5-4, based on Example 1, the prepolymerization reaction time was adjusted to 10 min.

[0049] The experiment was conducted on Example 5, and the results are shown in Table 5.

[0050]

[0051] The above experimental groups show that the prepolymerization reaction can significantly improve the water-reducing performance and high-temperature slump-retention performance of the system in this embodiment. This is likely due to the fact that the prepolymerized flexible segments help improve the binding properties between the water-reducing agent and cement particles and its dispersion in water, thereby preventing the large steric hindrance of the carboxyl group monomer B in the acrylic acid monomer from being unable to fully function. However, the degree of prepolymerization should not be too high, otherwise it will easily lead to excessive dispersion of the overall hydrophobic and hydrophilic properties of the system, resulting in a significant decrease in the overall water-reducing and water-bleeding properties.

[0052] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A durable acrylic water reducer, characterized in that: Contains a polyacrylic acid polymer, wherein the polyacrylic acid polymer comprises the following monomers: Monomer A: acrylic acid or alkyl-substituted acrylic acid; Monomer B is an acrylic acid diol monoester or an alkyl-substituted acrylic acid diol monoester, and has the general formula shown in Formula I: ； wherein R1 is optionally a straight-chain alkane, a branched-chain alkane or hydrogen, and R2 is optionally a straight-chain alkane, a branched-chain alkane, a cycloalkane or an aromatic hydrocarbon having not less than four carbon atoms; Monomer C: methyl acrylate or alkyl-substituted methyl acrylate.

2. A durable acrylic water reducer according to claim 1, characterized in that: R2 is phenyl or alkyl-substituted phenyl.

3. A durable acrylic water reducer according to claim 1, characterized in that: Monomer B has the following molecular formula: ； Wherein, R3 is hydrogen or methyl at any position.

4. A durable acrylic water reducer according to claim 1, characterized in that: The weight average molecular weight of the polyacrylic acid polymer is 10,000 to 100,000.

5. A durable acrylic water reducer according to claim 4, characterized in that: 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 10,000-14,000, the weight average molecular weight of the second component polyacrylic acid is 30,000-38,000, and the mass ratio of the first component polyacrylic acid to the second component polyacrylic acid is 1-5:

1.

6. A durable acrylic water reducer according to claim 1, characterized in that: The monomer A is methacrylic acid, and / or; Said R1 is methyl, and / or; The monomer C is methyl methacrylate.

7. A durable acrylic water reducer according to claim 1, characterized in that: The molar ratio of monomer A, monomer B and monomer C is 2-3:0.5-1:

1.

8. The method for preparing a durable acrylic water reducer according to any one of claims 1 to 7, characterized in that: In a solvent, monomer A and monomer C, an initiator, and a chain transfer agent are mixed and heated for a preliminary reaction to cause preliminary polymerization of monomer A and monomer C; then monomer B is added and reacted to the target molecular weight, and then the pH is adjusted to neutral.

9. The method for preparing a durable acrylic water reducer according to claim 8, characterized in that: During the initial polymerization of monomer A and monomer C, the temperature is controlled at 50-80° C. and the time is 10-30 minutes.

10. The method for preparing a durable acrylic water reducer according to claim 8, characterized in that: The solvent is water.

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