Modified polycarboxylic acid water-reducing agent and preparation method therefor

Abstract

The present application relates to the technical field of water-reducing agents, and in particular to a modified polycar-boxylic acid water-reducing agent and a preparation method therefor. The preparation method for the modified polycarboxylic acid water-reducing agent provided by the present application comprises: (1) adding water into a reaction vessel, heating to 70-90C, adding poly(ethylene glycol) methyl ether methacrylate and methacrylic acid, and introducing nitrogen for protection; dropwise adding an initiator within 1 h; continuously stirring and carrying out copoly merization reaction for 1-4 h to obtain a polycarboxylic acid water-re ducing agent initial product; and (2) adding copper bromide, isobutyric acid and dimethy1 adipate into the reaction vessel, continuously reacting for 20-50 min, and then adding a regulator to regulate the pH value to 8-9.5, thereby obtaining the modified polycarboxylic acid water-reducing agent. The water reducing agent provided by the present application has excellent water reducing effect and slump retaining properties.

Description

A modified polycarboxylate water reducer and preparation method thereof

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 12, 2023, with application number 202311701139.4 and invention name “A modified polycarboxylic acid water-reducing agent and its preparation method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the technical field of water reducers, and specifically relates to a modified polycarboxylic acid water reducer and a preparation method thereof. Background Art

[0003] Concrete is a crucial building material in modern construction, primarily composed of cement, active admixtures, coarse aggregate, fine aggregate, and water. During construction, to maintain adequate workability and performance, concrete's fluidity must be enhanced or maintained. Increasing water usage can lead to excessive micropores in the hardened cement, severely impacting the physical, mechanical, and durability properties of the hardened concrete. A water reducer is a concrete admixture that reduces mixing water usage while maintaining a relatively constant slump. This reduction in mixing water significantly improves the strength and durability of concrete, thereby enhancing its overall performance.

[0004] Polycarboxylate superplasticizers have been widely used in concrete, becoming a mainstream product in the concrete water-reducing agent market. The main chain of the polycarboxylate superplasticizer molecule firmly adsorbs to the surface of cement particles, effectively preventing hydration and improving their plasticity. The side chains surround the cement particles, acting as both steric hindrance and electrostatic repulsion. This differs from the electrostatic repulsion dispersion mechanism of traditional superplasticizers, resulting in superior dispersion and water-reducing effects, ultimately improving the overall performance of concrete products. Because the molecular structure of polycarboxylate superplasticizers is easily modifiable, effective molecular structures can be designed based on the cement dispersion mechanism, such as the number of main chain repeating units, side chain length, and density. This designability of the molecular structure and properties of polycarboxylate superplasticizers is of great significance for further improving the serialization and functionalization of water-reducing agents.

[0005] At present, polycarboxylic acid water reducers have played an important role in reducing the amount of water used in concrete mixing. However, their effect on concrete slump retention is relatively poor, that is, the slump loss of mixed concrete is large after a period of time, which requires further research and improvement.

[0006] Summary of the Invention

[0007] The present application addresses the problem that polycarboxylic acid water reducers have poor slump retention, and provides a modified polycarboxylic acid water reducer and a preparation method thereof, wherein the water reducer has excellent water-reducing effect and excellent slump retention.

[0008] A method for preparing a modified polycarboxylate water-reducing agent comprises the following steps:

[0009] (1) Add water to a reaction vessel, raise the temperature to 70°C to 90°C, add polyethylene glycol methyl ether methacrylate and methacrylic acid, and introduce nitrogen protection; add the initiator dropwise within 1 hour; continue stirring to carry out copolymerization reaction for 1 hour to 4 hours to obtain a preliminary product of polycarboxylate water reducer;

[0010] (2) Add copper bromide, dodecyl alcohol ester and dimethyl adipate to a reaction vessel, continue the reaction for 20 minutes to 50 minutes, then add a regulator to adjust the pH to 8 to 9.5 to obtain a modified polycarboxylate water reducer.

[0011] Furthermore, the weight ratio of polyethylene glycol methyl ether methacrylate to methacrylic acid in step (1) is 1:0.1-0.3.

[0012] Furthermore, the initiator in step (1) is sodium persulfate, potassium persulfate or ammonium persulfate, and the amount of the initiator is 0.5% to 2% of the total weight of polyethylene glycol methyl ether methacrylate and methacrylic acid.

[0013] Furthermore, the copper bromide in step (2) is 0.02% to 0.07% of the total weight of polyethylene glycol methyl ether methacrylate and methacrylic acid.

[0014] Furthermore, the dodecyl alcohol ester in step (2) is 2% to 8% of the total weight of polyethylene glycol methyl ether methacrylate and methacrylic acid.

[0015] Furthermore, the dimethyl adipate in step (2) is 2% to 8% of the total weight of polyethylene glycol methyl ether methacrylate and methacrylic acid.

[0016] Furthermore, the regulator in step (2) is one of potassium hydroxide, sodium hydroxide, sodium carbonate and potassium carbonate, and is added in the form of an aqueous solution thereof.

[0017] In the above method, an appropriate amount of water is added, and the total solid content of the modified polycarboxylate water-reducing agent obtained by the reaction is 15% to 30% by weight.

[0018] A modified polycarboxylic acid water-reducing agent is prepared by the above method.

[0019] Beneficial technical effects of this application: During the preparation process of a polycarboxylate water-reducing agent, this application utilizes dodecyl alcohol ester and dimethyl adipate to synergistically modify the initial product of the water-reducing agent, resulting in a modified polycarboxylate water-reducing agent that not only exhibits excellent water-reducing properties but also exhibits excellent slump retention. Concrete mixtures using this modified polycarboxylate water-reducing agent exhibit lower 1-hour loss in expansion and 1-hour loss in slump than concrete using unmodified water-reducing agent. This demonstrates that the modified polycarboxylate water-reducing agent obtained by this method can maintain excellent fluidity and workability in concrete over a period of time, extending the transportation and handling time of concrete, and facilitating long-distance transportation and use of concrete.

[0020] Implementation Method

[0021] The present application is further described below with reference to specific embodiments, but this should not be construed as limiting the present application.

[0022] Example 1

[0023] The preparation method of a modified polycarboxylic acid water reducer of this embodiment includes the following preparation steps:

[0024] (1) Add 5000 parts of water to a reaction vessel, heat to 90°C, add 1000 parts of polyethylene glycol methyl ether methacrylate and 200 parts of methacrylic acid, and introduce nitrogen protection; add 12 parts of initiator dropwise within 1 hour; continue stirring to carry out copolymerization reaction for 3 hours to obtain a preliminary product of polycarboxylate water reducer.

[0025] (2) 0.84 parts of copper bromide, 72 parts of dodecyl alcohol ester and 96 parts of dimethyl adipate were added to a reaction vessel, and the reaction was continued for 20 minutes. Then, a regulator was added to adjust the pH to 9.0 to obtain a modified polycarboxylate water reducer.

[0026] Example 2

[0027] The preparation method of a modified polycarboxylic acid water reducer of this embodiment includes the following preparation steps:

[0028] (1) Add 5000 parts of water to a reaction vessel, heat to 75° C., add 1000 parts of polyethylene glycol methyl ether methacrylate and 100 parts of methacrylic acid, and introduce nitrogen protection; add 5.5 parts of initiator dropwise within 1 hour; continue stirring to carry out copolymerization reaction for 4 hours to obtain a preliminary product of polycarboxylate water reducer;

[0029] (2) 0.44 parts of copper bromide, 22 parts of dodecyl alcohol ester and 66 parts of dimethyl adipate were added to a reaction vessel, and the reaction was continued for 40 minutes. Then, a regulator was added to adjust the pH to 8.0 to obtain a modified polycarboxylate water reducer.

[0030] Example 3

[0031] The preparation method of a modified polycarboxylic acid water reducer of this embodiment includes the following preparation steps:

[0032] (1) Add 5000 parts of water to a reaction vessel, heat to 80°C, add 1000 parts of polyethylene glycol methyl ether methacrylate and 300 parts of methacrylic acid, and introduce nitrogen protection; add 26 parts of initiator dropwise within 1 hour; continue stirring to carry out copolymerization reaction for 1 hour to obtain a preliminary product of polycarboxylate water reducer;

[0033] (2) 0.65 parts of copper bromide, 104 parts of dodecyl alcohol ester and 52 parts of dimethyl adipate were added to a reaction vessel, and the reaction was continued for 30 minutes. Then, a regulator was added to adjust the pH to 9.5 to obtain a modified polycarboxylate water reducer.

[0034] Example 4

[0035] The preparation method of a modified polycarboxylic acid water reducer of this embodiment includes the following preparation steps:

[0036] (1) Add 5000 parts of water to a reaction vessel, heat to 70°C, add 1000 parts of polyethylene glycol methyl ether methacrylate and 200 parts of methacrylic acid, and introduce nitrogen protection; add 18 parts of initiator dropwise within 1 hour; continue stirring to carry out copolymerization reaction for 2 hours to obtain a preliminary product of polycarboxylate water reducer;

[0037] (2) 0.24 parts of copper bromide, 48 parts of dodecyl alcohol ester and 24 parts of dimethyl adipate were added to a reaction vessel, and the reaction was continued for 50 minutes. Then, a regulator was added to adjust the pH to 8.4 to obtain a modified polycarboxylate water reducer.

[0038] Comparative Example 1 was compared with Example 1, but without the modification in step (2), and included the following preparation steps:

[0039] (1) Add 5000 parts of water to a reaction vessel, heat to 90°C, add 1000 parts of polyethylene glycol methyl ether methacrylate and 200 parts of methacrylic acid, and introduce nitrogen protection; add 12 parts of initiator dropwise within 1 hour; continue stirring to carry out copolymerization reaction for 3 hours to obtain a preliminary product of polycarboxylate water reducer.

[0040] Comparative Example 2 is compared with Example 1, in which no dodecyl alcohol ester is added in step (2), and comprises the following preparation steps:

[0041] (1) Add 5000 parts of water to a reaction vessel, heat to 90° C., add 1000 parts of polyethylene glycol methyl ether methacrylate and 200 parts of methacrylic acid, and introduce nitrogen protection; add 12 parts of initiator dropwise within 1 hour; continue stirring to carry out copolymerization reaction for 3 hours to obtain a preliminary product of polycarboxylate water reducer;

[0042] (2) 0.84 parts of copper bromide and 96 parts of dimethyl adipate were added to a reaction vessel, and the reaction was continued for 20 minutes. Then, a regulator was added to adjust the pH to 9.0 to obtain a modified polycarboxylate water reducer.

[0043] Comparative Example 3 is compared with Example 1: dimethyl adipate is not added in step (2), and the following preparation steps are included:

[0044] (1) Add 5000 parts of water to a reaction vessel, heat to 90° C., add 1000 parts of polyethylene glycol methyl ether methacrylate and 200 parts of methacrylic acid, and introduce nitrogen protection; add 12 parts of initiator dropwise within 1 hour; continue stirring to carry out copolymerization reaction for 3 hours to obtain a preliminary product of polycarboxylate water reducer;

[0045] (2) 0.84 parts of copper bromide and 72 parts of dodecyl alcohol ester were added to a reaction vessel, and the reaction was continued for 20 minutes. Then, a regulator was added to adjust the pH to 9.0 to obtain a modified polycarboxylate water reducer.

[0046] Comparative performance tests were conducted using the water-reducing agents obtained in the above examples and comparative examples. The cement used was 42.5# ordinary Portland cement, and the test concrete grade was C30. The water reduction rate was determined according to GB 8076-2008, "Concrete Admixtures," and the time-dependent loss of expansion and slump was determined according to GB / T 50080-2016, "Standard for Test Methods of Ordinary Concrete Mixtures." The comparative test results are shown in Table 1.

[0047] Table 1 Performance comparison test of water reducer

[0048] From the test results in Table 1, it can be seen that: (1) the water reduction rate of the water-reducing agent of the embodiment is 33% to 37%, which is significantly higher than the water reduction rate of the comparative example, indicating that the water-reducing effect of the water-reducing agent modified by the method of the present application is significantly improved; (2) the loss of expansion over time (64 mm to 82 mm) and the loss of slump over time (12 mm to 20 mm) of the water-reducing agent of the embodiment are significantly lower than those of the comparative example, indicating that the modified water-reducing agent obtained by the method of the present application can maintain excellent fluidity and workability of concrete for a period of time, can extend the transportation time and operation time of concrete, and is conducive to the long-distance transportation and use of concrete.

[0049] The water reducer of Comparative Example 1, which was not modified with either dodecyl alcohol ester or dimethyl adipate, had the lowest water reduction rate and the highest 1-hour loss in expansion and 1-hour loss in slump. The water reducers of Comparative Example 2 (modified with dimethyl adipate alone) and Comparative Example 3 (modified with dodecyl alcohol ester alone), while somewhat improved in performance compared to the water reducer of Comparative Example 1, still fell far short of the performance of the water reducer of the Examples. This suggests that dodecyl alcohol ester and dimethyl adipate have a synergistic effect on the performance of the retarder.

[0050] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a modified polycarboxylate water-reducing agent, characterized in that: The following steps are involved: (1) adding water to a reaction vessel, raising the temperature to 70°C to 90°C, adding polyethylene glycol methyl ether methacrylate and methacrylic acid, and introducing nitrogen protection; adding an initiator dropwise within 1 hour; continuing to stir and perform copolymerization for 1 hour to 4 hours to obtain a preliminary product of a polycarboxylate water reducer; (2) Add copper bromide, dodecanol ester and dimethyl adipate to the reaction container, continue the reaction for 20 min to 50 min, then add a pH adjuster to adjust the pH to 8 to 9.5 to obtain a modified polycarboxylate water reducer.

2. The method for preparing a modified polycarboxylate water-reducing agent according to claim 1, characterized in that: The weight ratio of polyethylene glycol methyl ether methacrylate to methacrylic acid in the step (1) is 1:0.1-0.

3.

3. A method for preparing a modified polycarboxylate water-reducing agent according to claim 1 or 2, characterized in that: The initiator in step (1) is sodium persulfate, potassium persulfate or ammonium persulfate, and the amount of the initiator used is 0.5% to 2% of the total weight of polyethylene glycol methyl ether methacrylate and methacrylic acid.

4. The method for preparing a modified polycarboxylate water-reducing agent according to claim 1 or 2, characterized in that: The copper bromide in the step (2) is 0.02% to 0.07% of the total weight of the polyethylene glycol methyl ether methacrylate and methacrylic acid.

5. The method for preparing a modified polycarboxylate water-reducing agent according to claim 1 or 2, characterized in that: The dodecanol ester in step (2) is 2% to 8% of the total weight of polyethylene glycol methyl ether methacrylate and methacrylic acid.

6. The method for preparing a modified polycarboxylate water-reducing agent according to claim 1 or 2, characterized in that: The dimethyl adipate in step (2) is 2% to 8% of the total weight of polyethylene glycol methyl ether methacrylate and methacrylic acid.

7. The method for preparing a modified polycarboxylate water-reducing agent according to claim 1, characterized in that: The regulator in step (2) is one of potassium hydroxide, sodium hydroxide, sodium carbonate and potassium carbonate, and is added in the form of a pH regulator aqueous solution.

8. A modified polycarboxylate water reducer, characterized in that: It is prepared by the method according to any one of claims 1 to 7.

9. The modified polycarboxylate water-reducing agent according to claim 8, characterized in that: The total solid content of the modified polycarboxylate water reducer is 15% to 30% by weight.