Sulfate-resistant polycarboxylate superplasticizer and preparation method thereof

Abstract

The invention relates to the technical field of building admixtures, in particular to a sulfate-resistant polycarboxylate superplasticizer and a preparation method thereof. The sulfate-resistant polycarboxylate superplasticizer is prepared by performing polymerization reaction on a vinyl polyether macromonomer, unsaturated carboxylic acid and a functional monomer under the condition that an oxidizing agent, a reducing agent and a chain transfer agent are added, the polycarboxylate superplasticizer with a novel unique structure is formed by utilizing a specific molecular structure of the functional monomer, and the sulfate-resistant polycarboxylate superplasticizer has excellent sulfate competitive adsorption resistance and can be used as a water reducing agent. The flowability and slump retaining performance of the concrete are obviously improved. Therefore, the sulfate-resistant polycarboxylate superplasticizer prepared by the invention has the advantages of low mixing amount, high water-reducing rate, small slump loss, good cement adaptability, sulfate resistance and the like.

Description

Technical Field

[0001] The invention relates to the technical field of building admixtures, and in particular to a sulfate-resistant polycarboxylate water-reducing agent and a preparation method thereof. Background Art

[0002] Polycarboxylate water reducer has excellent water-reducing and dispersing properties. It can keep the fresh concrete with low water-binder ratio fluid at a low dosage, so it is an important component of high-strength and high-fluidity concrete admixtures. However, theoretical research and engineering applications have shown that polycarboxylate water reducer is incompatible with concrete components. In some cases, polycarboxylate water reducer will have poor dispersion effect and rapid concrete slump loss. This is mainly because polycarboxylate water reducer cannot avoid the effect of sulfate when used in concrete engineering: on the one hand, cement and admixtures in concrete contain sulfate; on the other hand, other concrete admixtures often contain sulfate, such as expansion agent, early strength agent, etc.

[0003] In patent CN105713150, a strong adsorption group-phosphate group is introduced into the main chain structure of block polycarboxylic acid with clear sequence structure distribution through reversible addition-fragmentation chain transfer polymerization, so that the adsorption capacity of block polycarboxylic acid is stronger, thereby improving its resistance to sulfate. The synthesis method is complex and difficult to control, and it is impossible to achieve industrial production. Patent CN104311761 adopts reversible addition-fragmentation chain transfer polymerization to prepare a comb-shaped polyether block polyacrylic acid copolymer dispersant and apply it to the dispersion of cement system, but the copolymer dispersant has a simple composition, a single structure, and few adjustable factors of solution conformation, so it has poor adaptability to cement, especially poor sulfate resistance. Therefore, how to prepare a sulfate-resistant polycarboxylate water-reducing agent to overcome the problem that the existing polycarboxylate water-reducing agent is sensitive to sulfate and has insufficient water-reducing effect is a technical problem that technicians in this field need to solve urgently. Summary of the invention

[0004] In order to solve the problem that the existing polycarboxylate water reducer is sensitive to sulfate and has insufficient water reducing effect, the present invention provides a sulfate-resistant polycarboxylate water reducer and a preparation method thereof.

[0005] The invention provides a method for preparing a sulfate-resistant polycarboxylate water-reducing agent, comprising the following steps: adding a functional monomer, a vinyl polyether macromonomer, an oxidant and a solvent into a reaction kettle filled with water, stirring and reacting, adding a reducing agent aqueous solution, an unsaturated carboxylic acid aqueous solution and a chain transfer agent aqueous solution at the same time, keeping the temperature to obtain a copolymer product, and then adjusting the pH to 6-7 with a pH regulator to obtain the sulfate-resistant polycarboxylate water-reducing agent; The mass ratio of the functional monomer to the vinyl polyether macromonomer is 2-3:8-10; Wherein, the functional monomer structural formula is: , Among them, R 1 OCH 3 or -OCH 2 CH=CH 2 , R 2 -H or -CH 2 CH=CH 2 , R 3 -H or -CH 2 CH=CH 2 or -CH=CH-CH 3 .

[0006] On the basis of the above scheme, further, by weight, the functional monomer is 20 to 30 parts, the vinyl polyether macromonomer is 80 to 100 parts, the oxidant is 1 to 1.5 parts, the solvent is 10 to 40 parts, the water is 50 to 100 parts, the reducing agent aqueous solution is 30.5 to 30.9 parts, the unsaturated carboxylic acid aqueous solution is 40 to 55 parts and the chain transfer agent aqueous solution is 30.3 to 30.9 parts.

[0007] On the basis of the above scheme, further, the reaction temperature is 20-30°C; the insulation temperature is 20-30°C, and the insulation time is 1-3h; the reducing agent aqueous solution, unsaturated carboxylic acid aqueous solution and chain transfer agent aqueous solution are added dropwise for 3-4h.

[0008] On the basis of the above scheme, further, the reducing agent aqueous solution is 0.5-0.9 parts of reducing agent dissolved in 30 parts of water; the chain transfer agent aqueous solution is 0.3-0.9 parts of chain transfer agent dissolved in 30 parts of water; the unsaturated carboxylic acid aqueous solution is 10-25 parts of unsaturated carboxylic acid dissolved in 30 parts of water.

[0009] On the basis of the above scheme, further, the reducing agent is one or more combinations of bisulfite, sulfite, sodium formaldehyde sulfoxylate and vitamin C.

[0010] On the basis of the above scheme, further, the chain transfer agent is one or more combinations of mercaptoethanol, thioglycolic acid, mercaptopropionic acid, n-dodecyl mercaptan and tert-dodecyl mercaptan.

[0011] On the basis of the above scheme, further, the unsaturated carboxylic acid is one or more combinations of acrylic acid, methacrylic acid and itaconic acid.

[0012] On the basis of the above scheme, further, the molecular weight of the vinyl polyether macromonomer is 5000-6000.

[0013] The purpose of adopting the above technical scheme is that the high molecular weight vinyl polyether macromonomer can form a more stable dispersion system in concrete, reduce particle aggregation, and improve the water reduction effect.

[0014] On the basis of the above scheme, further, the oxidant is hydrogen peroxide, the solvent is ethanol, and the pH adjuster is sodium hydroxide.

[0015] The present invention also provides a sulfate-resistant polycarboxylate water-reducing agent prepared by any of the above methods for preparing the sulfate-resistant polycarboxylate water-reducing agent.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: Ordinary polycarboxylate water-reducing agent molecules are easy to shrink and form a curled conformation in the presence of sulfate, which makes it difficult to adsorb on cement particles, affecting the dispersion and slump-retaining performance of polycarboxylate water-reducing agent. The present invention introduces a benzene ring into the molecular structure of the sulfate-resistant polycarboxylate water-reducing agent, and its closed cyclic structure has high rigidity. The presence of the ring limits the flexibility of the polycarboxylate water-reducing agent molecule. In addition, the special structure of the functional monomer has intramolecular hydrogen bonds in the molecular structure, which increases the rigidity of the molecule. The two special structures of the benzene ring and the intramolecular hydrogen bonds act synergistically, making the polycarboxylate water-reducing agent molecular configuration difficult to shrink and difficult to form a curled conformation in the concrete system where sulfate exists, and then the longer polyether side chains and carboxyl groups in the synergistic vinyl polyether macromonomers make the polycarboxylate water-reducing agent easier to adsorb on cement particles. Therefore, the sulfate-resistant polycarboxylate water-reducing agent prepared by the present invention has the advantages of low dosage, high water reduction rate, small slump loss, good cement adaptability, and sulfate resistance. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] The present application also provides the following embodiments and comparative examples: Example 1 20g of 2-methoxy-4-vinylphenol, 85g of ethylene glycol monovinyl polyglycol ether, 10g of ethanol, 1.0g of hydrogen peroxide and 60g of water were added to the reactor, the temperature was controlled at 20°C, and then vitamin C aqueous solution, acrylic acid aqueous solution and thioglycolic acid aqueous solution were added dropwise at a uniform speed for 3h. After the addition was completed, the temperature was kept for 1h, and a suitable amount of water was added to adjust the concentration of the reaction product to 50%. The pH of the reaction product was adjusted to 6.0-7.0 with sodium hydroxide to obtain a sulfate-resistant polycarboxylic acid water reducer; Among them, the vitamin C aqueous solution is 0.5g of vitamin C dissolved in 30g of water, the thioglycolic acid aqueous solution is 0.3g of thioglycolic acid dissolved in 30g of water, and the acrylic acid aqueous solution is 10g of acrylic acid dissolved in 30g of water; the molecular weight of ethylene glycol monovinyl polyethylene glycol ether is 5000.

[0019] Example 2 25g of eugenol, 90g of 4-hydroxybutyl vinyl polyglycol ether, 30g of ethanol, 1.3g of hydrogen peroxide and 80g of water were added to the reactor, the temperature was controlled at 25°C, and then sodium formaldehyde sulfoxylate aqueous solution, acrylic acid aqueous solution and mercaptopropionic acid aqueous solution were added dropwise at a uniform speed for 3h. After the addition was completed, the temperature was kept for 1h, and a suitable amount of water was added to adjust the concentration of the reaction product to 50%. The pH of the reaction product was adjusted to 6.0-7.0 with sodium hydroxide to obtain a sulfate-resistant polycarboxylic acid water reducer; Among them, the sodium formaldehyde sulfoxylate aqueous solution is 0.7g sodium formaldehyde sulfoxylate dissolved in 30g water, the mercaptopropionic acid aqueous solution is 0.5g mercaptopropionic acid dissolved in 30g water, and the acrylic acid aqueous solution is 18g acrylic acid solution dissolved in 30g water; the molecular weight of 4-hydroxybutyl vinyl polyethylene glycol ether is 6000.

[0020] Example 3 30g of 2-(allyloxy)phenol, 100g of ethylene glycol monovinyl polyethylene glycol ether, 40g of ethanol, 1.5g of hydrogen peroxide and 70g of water were added to the reactor, the temperature was controlled at 30°C, and then the vitamin C aqueous solution, acrylic acid aqueous solution and thioglycolic acid aqueous solution were added dropwise at a uniform speed for 3h. After the addition was completed, the temperature was kept for 1h, and a suitable amount of water was added to adjust the concentration of the reaction product to 50%. The pH of the reaction product was adjusted to 6.0-7.0 with sodium hydroxide to obtain a sulfate-resistant polycarboxylic acid water reducer; Among them, the vitamin C aqueous solution is 0.9g of vitamin C dissolved in 30g of water, the thioglycolic acid aqueous solution is 0.9g of thioglycolic acid dissolved in 30g of water, and the acrylic acid aqueous solution is 25g of acrylic acid dissolved in 30g of water; the molecular weight of ethylene glycol monovinyl polyethylene glycol ether is 6000.

[0021] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that: Comparative Example 1 does not add 2-methoxy-4-vinylphenol, and the remaining raw material components and operating steps are the same as those of Example 1.

[0022] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, 2-methoxy-4-vinylphenol containing intramolecular hydrogen bonds in Example 1 is replaced by 2-allylphenol without intramolecular hydrogen bonds, and the remaining raw material components and operating steps are the same as those in Example 1.

[0023] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that 20 g of 2-methoxy-4-vinylphenol and 85 g of ethylene glycol monovinyl polyethylene glycol ether are replaced by 10 g of 2-methoxy-4-vinylphenol and 110 g of ethylene glycol monovinyl polyethylene glycol ether, and the remaining raw material components and operating steps are the same as those in Example 1.

[0024] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that 20 g of 2-methoxy-4-vinylphenol and 85 g of ethylene glycol monovinyl polyethylene glycol ether are replaced by 40 g of 2-methoxy-4-vinylphenol and 70 g of ethylene glycol monovinyl polyethylene glycol ether, and the remaining raw material components and operating steps are the same as those in Example 1.

[0025] Performance Test 1 The conformation of the polycarboxylate water-reducing agent solution prepared by the present invention was measured using a Malvern Panalytical Viscotek 270 dynamic and static light scattering instrument. 2 SO 4 Adjust the SO in the solution 4 2- The experimental conditions are as follows: polymer concentration: 1 mg / ml, test angle: 90°, and the solution conformation results are shown in Table 1.

[0026] Table 1 Solution conformations of different polycarboxylate superplasticizers

[0027] As can be seen from Table 1, after adding sulfate to the polycarboxylate water-reducing agent solutions prepared in Comparative Examples 1 and 2, their hydrodynamic radius is significantly reduced, and the molecular structure is in a curled state, indicating that their conformation has shrunk, which is mainly due to the fact that the ordinary polycarboxylate water-reducing agent is easy to shrink and form a curled conformation in the presence of sulfate; compared with Comparative Examples 1 and 2, after adding sulfate to the sulfate-resistant polycarboxylate water-reducing agent solutions prepared in Examples 1 to 3, their hydrodynamic radius becomes smaller, but the degree of reduction is significantly less than that of Comparative Examples 1 and 2, which is mainly due to the introduction of benzene rings into the molecular structure of the sulfate-resistant polycarboxylate water-reducing agent in the present invention, and its closed ring structure has high rigidity. The presence of the ring limits the flexibility of the polycarboxylate water-reducing agent molecule. In addition, the special structure of the functional monomer has intramolecular hydrogen bonds in the molecular structure, which increases the rigidity of the molecule. The two special structures of the benzene ring and the intramolecular hydrogen bonds work synergistically, making it difficult for the polycarboxylate water-reducing agent molecular configuration to shrink and form a curled conformation in the solution in the presence of sulfate.

[0028] The present invention prepares sulfate-resistant polycarboxylate water-reducing agent, wherein the functional monomer and the vinyl polyether macromonomer have an optimal ratio. When the polycarboxylate water-reducing agent is prepared in Comparative Examples 3 and 4, the ratio of key raw materials exceeds the range. After sulfate is added to the prepared polycarboxylate water-reducing agent solution, its hydrodynamic radius is significantly reduced, and the molecular structure is in a curled state, indicating that its conformation is shrunk, indicating that it is easy to shrink and form a curled conformation in the presence of sulfate.

[0029] Performance Test 2 The concrete mixture performance test was carried out in accordance with GB / T 50080-2016 "Standard for Test Methods for Performance of Ordinary Concrete Mixtures". The concrete mix ratio is: cement 360kg / m 3 、Mechanical sand 790kg / m 3 、Stone 1060kg / m 3 、Water 162kg / m 3 , add Na 2 SO 4 , using Na 2 SO 4 Adjusting SO in concrete system 4 2- concentration.

[0030] The performance of the polycarboxylate water-reducing agent prepared in the specific examples and comparative examples when applied to concrete is shown in Table 2 below: Table 2 Effects of different polycarboxylate water reducers on concrete properties

[0031] As can be seen from Table 2, the polycarboxylate water-reducing agents prepared in Comparative Examples 1 to 4 are applied to concrete. After sulfate is added to the concrete water, the initial dispersion performance and slump retention of the concrete are significantly reduced, showing that they are not adaptable to sulfate. This is mainly because the polycarboxylate water-reducing agents prepared in Comparative Examples 1 to 4 have a significantly reduced hydrodynamic radius in the concrete system where sulfate exists, and the molecular structure is in a curled state. Its conformation shrinks, making it difficult to adsorb on cement particles, affecting the dispersion and slump retention of concrete. The sulfate-resistant polycarboxylate water-reducing agents prepared in Examples 1 to 3 are used for concrete. After sulfate is added to the concrete water, concretes with different sulfate contents have good initial dispersion and slump retention. The prepared sulfate-resistant polycarboxylate water-reducing agents show strong adaptability to sulfate. This is mainly because the sulfate-resistant polycarboxylate water-reducing agents prepared in Examples 1 to 3 have a smaller degree of reduction in hydrodynamic radius in the concrete system where sulfate exists, which has a smaller effect on its adsorption on cement particles, and thus does not affect the dispersion and slump retention of the polycarboxylate water-reducing agents.

[0032] In summary, the sulfate-resistant polycarboxylate water-reducing agent prepared by the present invention has the advantages of low dosage, high water reduction rate, small slump loss, good cement adaptability, and sulfate resistance.

[0033] Although the terms such as polycarboxylate water-reducing agent, vinyl polyether macromonomer, unsaturated carboxylic acid and functional monomer are used more frequently in this article, the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a sulfate-resistant polycarboxylate water-reducing agent, characterized in that: The following steps are involved: The functional monomer, vinyl polyether macromonomer, oxidant and solvent are added to a reaction kettle filled with water and stirred, and a reducing agent aqueous solution, an unsaturated carboxylic acid aqueous solution and a chain transfer agent aqueous solution are added to react, and a copolymer product is obtained after heat preservation, and then the pH is adjusted to 6-7 with a pH regulator to obtain a sulfate-resistant polycarboxylate water-reducing agent; The mass ratio of the functional monomer to the vinyl polyether macromonomer is 2-3:8-10; Wherein, the functional monomer structural formula is: ， Among them, R1 is -OCH3 or -OCH2CH=CH2, R2 is -H or -CH2CH=CH2, and R3 is -H or -CH2CH=CH2 or -CH=CH-CH3.

2. The method for preparing the sulfate-resistant polycarboxylate water-reducing agent according to claim 1, characterized in that: In parts by weight, the functional monomer is 20 to 30 parts, the vinyl polyether macromonomer is 80 to 100 parts, the oxidant is 1 to 1.5 parts, the solvent is 10 to 40 parts, the water is 50 to 100 parts, the reducing agent aqueous solution is 30.5 to 30.9 parts, the unsaturated carboxylic acid aqueous solution is 40 to 55 parts and the chain transfer agent aqueous solution is 30.3 to 30.9 parts.

3. The method for preparing the sulfate-resistant polycarboxylate water-reducing agent according to claim 1, characterized in that: The reaction temperature is 20-30° C.; the insulation temperature is 20-30° C., and the insulation time is 1-3 hours; the reducing agent aqueous solution, the unsaturated carboxylic acid aqueous solution and the chain transfer agent aqueous solution are added dropwise for 3-4 hours.

4. The method for preparing the sulfate-resistant polycarboxylate water-reducing agent according to claim 1, characterized in that: The reducing agent aqueous solution is 0.5-0.9 parts of reducing agent dissolved in 30 parts of water; the chain transfer agent aqueous solution is 0.3-0.9 parts of chain transfer agent dissolved in 30 parts of water; the unsaturated carboxylic acid aqueous solution is 10-25 parts of unsaturated carboxylic acid dissolved in 30 parts of water.

5. The method for preparing the sulfate-resistant polycarboxylate water-reducing agent according to claim 4, characterized in that: The reducing agent is one or more combinations of bisulfite, sulfite, sodium formaldehyde sulfoxylate and vitamin C.

6. The method for preparing the sulfate-resistant polycarboxylate water-reducing agent according to claim 4, characterized in that: The chain transfer agent is one or more combinations of mercaptoethanol, thioglycolic acid, mercaptopropionic acid, n-dodecyl mercaptan and tert-dodecyl mercaptan.

7. The method for preparing the sulfate-resistant polycarboxylate water-reducing agent according to claim 4, characterized in that: The unsaturated carboxylic acid is one or more combinations of acrylic acid, methacrylic acid and itaconic acid.

8. The method for preparing the sulfate-resistant polycarboxylate water-reducing agent according to claim 1, characterized in that: The molecular weight of the vinyl polyether macromonomer is 5000-6000.

9. The method for preparing the sulfate-resistant polycarboxylate water-reducing agent according to claim 1, characterized in that: The oxidant is hydrogen peroxide, the solvent is ethanol, and the pH adjuster is sodium hydroxide.

10. A sulfate-resistant polycarboxylate water-reducing agent prepared according to the method for preparing a sulfate-resistant polycarboxylate water-reducing agent according to any one of claims 1 to 9.

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