A thickening and water-retaining agent with a cross-linked structure and its preparation method

Abstract

This invention relates to a thickening and water-retaining agent with a cross-linked structure and its preparation method. By weight, it comprises: 10 parts of unsaturated acid monomer; 5-30 parts of acrylamide; 1-5 parts of unsaturated amide monomer; 5-10 parts of unsaturated sulfonate monomer; 0.1-1 part of cross-linking agent; 0.5-2 parts of oxidant; 0.5-6 parts of polymerizable reducing agent; and water. The thickening and water-retaining agent with a cross-linked structure prepared by this invention, during the hydration process of cement, continuously adds cross-linking structure through the hydrolysis effect of amide groups, and continuously and slowly releases free water to replenish the free water consumed during hydration. This meets the flowability requirements of concrete after hydration, solving the problems of existing thickening and water-retaining agents that cannot simultaneously meet the initial and post-hydration thickening and water-retaining properties and flowability requirements of concrete, and also addressing the issue of storage stability.

Description

Technical Field

[0001] This invention relates to the field of concrete admixtures, specifically to a thickening and water-retaining agent with a cross-linked structure and its preparation method. Background Technology

[0002] The main function of concrete thickeners and water-retaining agents is to effectively increase the viscosity of the liquid phase of the system by changing the physical properties of concrete, thereby enhancing the interaction between particles, avoiding problems such as segregation and bleeding, and achieving high stability of high-flow concrete. They are an indispensable component of concrete admixtures.

[0003] The most commonly used thickeners on the market are cellulose-based and polypropylene-based. Cellulose-based products are mainly solid and have excellent thickening and water-retaining effects at low dosages. However, cellulose-based products have problems such as slow dissolution, poor compatibility with water-reducing agents, and the tendency for the prepared solution to spoil, which can negatively affect the initial and long-term fluidity, setting time, and strength of concrete, thus limiting their application. Polypropylene-based products have better compatibility with water-reducing agents, and their molecular structure is highly designable, which has attracted widespread attention and development.

[0004] Patent CN114014995A describes the preparation of a cross-linked polyether-based concrete water-retaining agent using allyl polyoxyethylene ether, polyvinyl alcohol, unsaturated amide monomers, unsaturated carboxylic acid monomers, unsaturated cationic monomers, and a cross-linking agent.

[0005] CN114685733A uses a self-made monomer with a water-retaining group to prepare a comb-shaped thickening and water-retaining agent with a linear water-retaining side chain, wherein the water-retaining group is a polyethyleneimine segment and an acrylamide unit.

[0006] There are many types of polypropylene thickeners and water-retaining agents, but the molecular weight and performance of these products vary greatly. They often fail to meet the requirements of both initial and post-loss thickening and water-retaining properties and flowability of concrete, and they also have storage stability issues. Summary of the Invention

[0007] Therefore, it is necessary to provide a thickening and water-retaining agent with a cross-linked structure that satisfies the initial and long-term water retention and flow properties of concrete, as well as its storage stability, and its preparation method, which is of great significance to the working stability of concrete.

[0008] To achieve the above objectives, the present invention provides a technical solution:

[0009] A thickening and water-retaining agent with a cross-linked structure, wherein the raw materials for preparation, by weight, include:

[0010]

[0011] The crosslinking agent includes at least one of N,N'-methylenebisacrylamide, N,N'-vinylbisacrylamide, and N,N'-(1,2-dihydroxyethylene)diacrylamide.

[0012] Preferably, the polymerizable reducing agent has the following structural formula:

[0013]

[0014] Wherein, R1 is H or CH3;

[0015] R² is (CH²)x, 1 ≤ x ≤ 4.

[0016] Preferably, the unsaturated acid monomer includes acrylic acid or methacrylic acid.

[0017] Preferably, the structural formula of the unsaturated amide monomer is as follows:

[0018]

[0019] Wherein, R3 is H or CH3;

[0020] R4 can be H, OH, Cl, B(OH)2, NO2, SO3 or SO2NH2;

[0021] R5 can be H, OH, Cl, B(OH)2, NO2, SO3 or SO2NH.

[0022] Preferably, the unsaturated sulfonate monomer comprises 2-acrylamide-2-methylpropanesulfonic acid.

[0023] Preferably, the unsaturated acid includes at least one of acrylic acid and methacrylic acid.

[0024] Preferably, the oxidant includes at least one of potassium persulfate and ammonium persulfate.

[0025] This invention provides a method for preparing a thickening and water-retaining agent with a cross-linked structure, comprising the following steps:

[0026] The unsaturated acid monomer is divided into two parts, and one part of the unsaturated acid monomer, the polymerizable reducing agent and water are mixed to form solution A;

[0027] Prepare solution B by mixing the oxidant with water;

[0028] Another portion of unsaturated acid monomers, acrylamide, unsaturated amide monomers, unsaturated sulfonate monomers, crosslinking monomers and water are mixed to prepare a base material;

[0029] An alkaline solution is added to the substrate to adjust its pH to 7.0–8.0, and then solution A and solution B are added dropwise to the substrate to initiate the reaction.

[0030] The initial reaction temperature is 30-45℃, and the dropwise addition time of solution A and solution B is 1-2 hours. After the dropwise addition is completed, the reaction is kept at the temperature for 1-3 hours to obtain a thickening and water-retaining agent with a cross-linked structure at a mass concentration of 15wt%-20wt%.

[0031] The beneficial effects of this invention are:

[0032] This invention uses an oxidant and a polymerizable reducing agent to form a redox initiation system, and introduces a crosslinking agent. The polymerizable reducing agent can form a high molecular weight polymer by free radical initiating monomer polymerization under the action of the oxidant, and can also participate in polymerization as a monomer. The tertiary amines on the side groups of the high molecular weight polymer can react with the oxidant to continue to form free radicals to initiate the polymerization of monomers, forming a polymer with a higher molecular weight crosslinked structure (i.e., a thickening and water-retaining agent with a crosslinked structure).

[0033] The thickening and water-retaining agent with a cross-linked structure prepared by this invention continuously adds cross-linked structure through the hydrolysis effect of amide groups during the hydration process of cement, and continuously and slowly releases free water to replenish the free water consumed during the hydration process, thereby meeting the flowability requirements of the thickening and water-retaining agent for concrete over time.

[0034] The thickening and water-retaining agent with a cross-linked structure prepared by this invention has a simple process, is stable in storage, and meets the initial and long-term water retention and flow properties of concrete. Detailed Implementation

[0035] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0036] In the embodiments, unless otherwise specified, the experimental methods used are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0037] A thickening and water-retaining agent with a cross-linked structure, wherein the raw materials for preparation, by weight, include:

[0038]

[0039] The crosslinking agent includes at least one of N,N'-methylenebisacrylamide, N,N'-vinylbisacrylamide, and N,N'-(1,2-dihydroxyethylene)diacrylamide.

[0040] In one embodiment, the polymerizable reducing agent has the following structural formula:

[0041]

[0042] Wherein, R1 is H or CH3;

[0043] R² is (CH²)x, 1 ≤ x ≤ 4.

[0044] In one embodiment, the polymerizable reducing agent is N,N-dimethylaminopropylacrylamide, N-(dimethylaminopropyl)methacrylamide, or N-(dimethylaminoethyl)methacrylamide.

[0045] In one embodiment, the unsaturated acid monomer includes acrylic acid or methacrylic acid.

[0046] In one embodiment, the unsaturated amide monomer has the following structural formula:

[0047]

[0048] Wherein, R3 is H or CH3;

[0049] R4 can be H, OH, Cl, B(OH)2, NO2, SO3 or SO2NH2;

[0050] R5 can be H, OH, Cl, B(OH)2, NO2, SO3 or SO2NH.

[0051] This invention introduces rigid phenyl groups through copolymerization of phenyl-containing unsaturated amide monomers, making the structure of the high molecular weight cross-linked thickener and water-retaining agent more flexible. Furthermore, the thickener and water-retaining agent with a cross-linked structure prepared by this invention continuously adds cross-linked structure during the hydration process of cement through the hydrolysis effect of amide groups, and continuously and slowly releases free water to replenish the free water consumed during the hydration process, thus meeting the fluidity requirements of the thickener and water-retaining agent for concrete over time.

[0052] The cross-linked thickening and water-retaining agent prepared by this invention has a simple process, is stable in storage, and meets the initial and long-term water retention and flow properties of concrete.

[0053] All monomers involved in the polymerization have water-retaining groups such as amide or carboxyl groups. That is, under low dosage conditions, they can achieve the effects of water locking, water retention, and thickening by hydrogen bonding between the water-retaining groups and water.

[0054] In one embodiment, the unsaturated amide monomer is at least one selected from N-phenylacrylamide, N-p-hydroxyphenylacrylamide, N-[4-(sulfonyl)phenyl]acrylamide, N-[4-(sulfonamide)phenyl]acrylamide, 3-methylacrylamidophenylboronic acid, 3-acrylamidophenylboronic acid, and N-(4-nitrophenyl)acrylamide.

[0055] In one embodiment, the unsaturated sulfonate monomer comprises 2-acrylamide-2-methylpropanesulfonic acid.

[0056] In one embodiment, the oxidant includes at least one of potassium persulfate and ammonium persulfate.

[0057] This invention provides a method for preparing a thickening and water-retaining agent with a cross-linked structure, comprising the following steps:

[0058] The unsaturated acid monomer is divided into two parts, and one part of the unsaturated acid monomer, the polymerizable reducing agent and water are mixed to form solution A;

[0059] Prepare solution B by mixing the oxidant with water;

[0060] Another portion of unsaturated acid monomers, acrylamide, unsaturated amide monomers, unsaturated sulfonate monomers, crosslinking monomers and water are mixed to prepare a base material;

[0061] An alkaline solution is added to the substrate to adjust its pH to 7.0–8.0, and then solution A and solution B are added dropwise to the substrate to initiate the reaction.

[0062] The initial reaction temperature is 30-45℃, and the dropwise addition time of solution A and solution B is 1-2 hours. After the dropwise addition is completed, the reaction is kept at the temperature for 1-3 hours to obtain a thickening and water-retaining agent with a cross-linked structure at a mass concentration of 15wt%-20wt%.

[0063] Example 1

[0064] (1) Mix 5 parts acrylic acid, 3 parts N-p-hydroxyphenylacrylamide, 15 parts acrylamide, 5 parts 2-acrylamide-2-methylpropanesulfonic acid with an aqueous solution to prepare a base material. Add sodium hydroxide solution to the base material and adjust the pH value of the base solution to 7.0-8.0.

[0065] (2) Prepare solution A by mixing the remaining 5 parts of acrylic acid, 3 parts of N,N-dimethylaminopropylacrylamide, and 0.5 parts of N,N'-methylenebisacrylamide with water;

[0066] (3) Prepare solution B by mixing potassium persulfate with water;

[0067] (4) The initial reaction temperature is 40℃, the dropwise addition time of solution A and solution B is 1.5h, and after the dropwise addition is completed, the solution is kept at a constant temperature for 2h to obtain a thickening and water-retaining agent 1 with a cross-linked structure at a mass concentration of 15wt%.

[0068] The experimental procedures for Examples 2-4 and Comparative Examples 1-2 were the same as those for Example 1, except that the raw material ratios for Examples 2-4 and Comparative Examples 1-2 were changed. The raw material ratios for the examples are shown in Table 1, and the raw material ratios for the comparative examples are shown in Table 2. In these examples, monomer A is an unsaturated acid monomer, monomer B is an unsaturated amide monomer, and monomer C is an unsaturated sulfonate monomer.

[0069] Table 1. Raw material ratio table for the embodiment

[0070]

[0071] Table 2 Comparative Example Raw Material Ratio Table

[0072]

[0073]

[0074] To effectively verify the effect of the thickening and water-retaining agent, this invention tested and verified the concrete by reducing the amount of cementitious material by 30 kg and the sand ratio by 2-4% in a representative C30 mix ratio, so that the initial spread of the concrete was 500 mm to 650 mm, and the concrete should have obvious stone leakage or stone accumulation in the initial state, and obvious water bleeding or grout bleeding after the initial stage or after standing for a period of time.

[0075] Concrete mix proportion: Cement 330kg / m³ 3 780kg / m³ of sand 3 Stone 1040kg / m 3 175 kg / m³ of water 3 .

[0076] The admixture formula is: standard polycarboxylate superplasticizer: slump retainer: retarder: water = 800:200:100:3900.

[0077] The concrete test results are shown in Table 3.

[0078] Table 3. Concrete performance test results

[0079]

[0080] As shown in Table 3, Comparative Example 1, which has a branched structure but no cross-linked structure, has comparable performance to the examples except for a slightly higher dosage, indicating that the cross-linked structure performs better. Comparative Example 2, which has neither cross-linked nor branched structures, has a higher dosage, poorer workability, and poorer thickening, water retention, and storage stability.

[0081] The cross-linked thickening and water-retaining agents prepared in Examples 1-4 have a lower dosage and better thickening and water-retaining effects on concrete at 0h and 1.5h, with little impact on fluidity.

[0082] After storing the samples of Comparative Example 2 and Example 1 for 8 months, the performance of Example 1 did not decrease, while the thickening and water retention properties of the sample of Comparative Example 2 decreased, indicating poor stability. This shows that the cross-linking structure helps to improve the stability of the product.

[0083] It should be noted that the specific parameters or reagents in the above embodiments are specific or preferred embodiments under the concept of the present invention, and not limitations thereof; those skilled in the art can make adaptive adjustments within the concept and protection scope of the present invention.

Claims

1. A thickening water-retaining agent having a crosslinked structure, characterized by comprising a water-soluble polymer having a plurality of hydrophilic groups and a crosslinking agent. The raw materials are prepared by weight parts, including: an unsaturated acid monomer 10 parts; acrylamide 5-30 parts; an unsaturated amide monomer 1-5 parts; an unsaturated sulfonate monomer 5-10 parts; a crosslinking agent 0.1-1 parts; an oxidizing agent 0.5-2 parts; a polymerizable reducing agent 0.5-6 parts; and water; wherein the crosslinking agent includes at least one of N,N'-methylenebisacrylamide, N,N'-vinylbisacrylamide and N,N'-(1,2-dihydroxyethylene)bisacrylamide; the polymerizable reducing agent has the following structural formula: ； wherein R1 is H or CH3; R2 is (CH2)x, 1≤x≤4; the unsaturated amide monomer has the following structural formula: ； wherein R3 is H or CH3; R4 is H, OH, Cl, B(OH)2, NO2 or SO2NH2; R5is H, OH, Cl, B(OH)2, NO2, SO3H or SO2NH 2； the unsaturated acid monomer includes acrylic acid or methacrylic acid.

2. The thickening water retaining agent according to claim 1, characterized by The unsaturated sulfonate monomer includes 2-acrylamido-2-methylpropane sulfonic acid.

3. The thickening water retaining agent according to claim 1, characterized by, The oxidizing agent includes at least one of potassium persulfate and ammonium persulfate.

4. A method for producing the thickening water-retaining agent having a crosslinked structure according to any one of claims 1 to 3, characterized by, The method includes the steps of: dividing the unsaturated acid monomer into two parts, and preparing a solution A by mixing one part of the unsaturated acid monomer, the polymerizable reducing agent, the crosslinking agent and water; preparing a solution B by mixing the oxidizing agent and water; mixing the other part of the unsaturated acid monomer, acrylamide, the unsaturated amide monomer, the unsaturated sulfonate monomer and water to prepare a base material; adding a base solution to the base material to adjust the pH value of the base material to 7.0-8.0, and adding the solution A and the solution B dropwise to the base material to start the reaction; the initial reaction temperature is 30-45℃, the dropping time of the solution A and the solution B is 1h-2h, after the dropping is completed, the reaction is kept for 1-3h, and a thickening water-retaining agent with a crosslinking structure having a mass concentration of 15wt%-20wt% is obtained.

Images