A sulfate-resistant polycarboxylate superplasticizer and a preparation method thereof

Abstract

The present application relates to the technical field of building admixtures, and particularly relates to a sulfate-resistant polycarboxylate superplasticizer and a preparation method thereof. The sulfate-resistant polycarboxylate superplasticizer is prepared by polymerization of a vinyl polyether macromonomer, an unsaturated carboxylic acid and a functional monomer in the presence of an oxidizing agent, a reducing agent and a chain transfer agent. The functional monomer has a specific molecular structure, and a new and unique structure of polycarboxylate superplasticizer is formed. The sulfate-resistant polycarboxylate superplasticizer has excellent sulfate-resistant competitive adsorption performance, and can significantly improve the fluidity and slump retention of concrete. Therefore, the sulfate-resistant polycarboxylate superplasticizer prepared by the present application has the advantages of low dosage, high water-reducing rate, small slump loss, good cement adaptability and sulfate resistance.

Description

Technical Field

[0001] This invention relates to the field of building admixtures technology, and in particular to a sulfate-resistant polycarboxylate superplasticizer and its preparation method. Background Technology

[0002] Polycarboxylate superplasticizers, due to their excellent water-reducing and dispersing properties, can maintain the fluidity of fresh concrete with a low water-cement ratio even at low dosages, making them an important component of high-strength and high-fluidity concrete admixtures. However, both theoretical research and engineering applications indicate that polycarboxylate superplasticizers are incompatible with concrete components. In some cases, polycarboxylate superplasticizers may exhibit poor dispersion and rapid slump loss in concrete. This is mainly because polycarboxylate superplasticizers cannot avoid interacting with sulfates when used in concrete engineering: on the one hand, cement and admixtures in concrete contain sulfates; on the other hand, other concrete admixtures often contain sulfates, such as expanding agents and early-strength agents.

[0003] In patent CN105713150, a strong adsorption group—phosphate group—is introduced into the block polycarboxylic acid backbone structure with a well-defined sequence distribution through reversible addition-fragmentation chain transfer polymerization. This enhances the adsorption capacity of the block polycarboxylic acid and improves its resistance to sulfate. However, this synthesis method is complex and difficult to control, making industrial production impossible. Patent CN104311761 uses reversible addition-fragmentation chain transfer polymerization to prepare a comb-shaped polyether block polyacrylic acid copolymer dispersant and applies it to the dispersion of cement systems. However, the copolymer dispersant has a simple composition, a single structure, and few adjustable factors in solution conformation, resulting in poor adaptability to cement, especially poor sulfate resistance. Therefore, how to prepare a sulfate-resistant polycarboxylic acid superplasticizer to overcome the problems of sulfate sensitivity and insufficient water-reducing effect of existing polycarboxylic acid superplasticizers is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] To address the problems of existing polycarboxylate superplasticizers being sensitive to sulfates and having insufficient water-reducing effect, this invention provides a sulfate-resistant polycarboxylate superplasticizer and its preparation method.

[0005] The present invention provides a method for preparing a sulfate-resistant polycarboxylate superplasticizer, comprising the following steps: adding functional monomers, vinyl polyether macromonomers, oxidants and solvents into a reaction vessel containing water and stirring to carry out the reaction; simultaneously adding a reducing agent aqueous solution, an unsaturated carboxylic acid aqueous solution and a chain transfer agent aqueous solution; and keeping the mixture at a constant temperature to obtain a copolymer product; and then adjusting the pH to 6-7 with a pH adjuster to obtain the sulfate-resistant polycarboxylate superplasticizer.

[0006] The mass ratio of the functional monomer to the vinyl polyether macromonomer is 2-3:8-10;

[0007] The structural formula of the functional unit is as follows:

[0008] ,

[0009] Wherein, R1 is -OCH3 or -OCH2CH=CH2, R2 is -H or -CH2CH=CH2, and R3 is -H or -CH2CH=CH2 or -CH=CH-CH3.

[0010] Based on the above scheme, further, by weight parts, the functional monomer is 20-30 parts, the vinyl polyether macromonomer is 80-100 parts, the oxidant is 1-1.5 parts, the solvent is 10-40 parts, the water is 50-100 parts, the reducing agent aqueous solution is 30.5-30.9 parts, the unsaturated carboxylic acid aqueous solution is 40-55 parts, and the chain transfer agent aqueous solution is 30.3-30.9 parts.

[0011] Based on the above scheme, the reaction temperature is further specified as 20-30℃; the holding temperature is 20-30℃ and the holding time is 1-3h; the reducing agent aqueous solution, the unsaturated carboxylic acid aqueous solution and the chain transfer agent aqueous solution are added dropwise for 3-4h.

[0012] Based on the above scheme, further, the reducing agent aqueous solution is 0.5 to 0.9 parts of reducing agent dissolved in 30 parts of water; the chain transfer agent aqueous solution is 0.3 to 0.9 parts of chain transfer agent dissolved in 30 parts of water; and the unsaturated carboxylic acid aqueous solution is 10 to 25 parts of unsaturated carboxylic acid dissolved in 30 parts of water.

[0013] Based on the above scheme, the reducing agent is further selected from one or more combinations of bisulfite, sulfite, sodium formaldehyde sulfoxylate and vitamin C.

[0014] Based on the above scheme, the chain transfer agent is further comprising one or more combinations of mercaptoethanol, mercaptoacetic acid, mercaptopropionic acid, n-dodecyl mercaptoethanol and tert-dodecyl mercaptoethanol.

[0015] Based on the above scheme, the unsaturated carboxylic acid is further defined as one or more combinations of acrylic acid, methacrylic acid, and itaconic acid.

[0016] Based on the above scheme, the molecular weight of the vinyl polyether macromonomer is further 5000-6000.

[0017] The purpose of adopting the above technical solution is that high molecular weight vinyl polyether macromonomers can form a more stable dispersion system in concrete, reduce particle aggregation, and improve water reduction effect.

[0018] Based on the above scheme, the oxidant is hydrogen peroxide, the solvent is ethanol, and the pH adjuster is sodium hydroxide.

[0019] The present invention also provides a sulfate-resistant polycarboxylate superplasticizer prepared by any of the above-described methods.

[0020] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0021] Ordinary polycarboxylate superplasticizer molecules tend to shrink and form a coiled conformation in the presence of sulfates, making adsorption on cement particles difficult and affecting the dispersion and slump retention performance of polycarboxylate superplasticizers. This invention introduces a benzene ring into the molecular structure of a sulfate-resistant polycarboxylate superplasticizer. Its closed ring structure has high rigidity, limiting the flexibility of the polycarboxylate superplasticizer molecule. Furthermore, the special structure of the functional monomer, with intramolecular hydrogen bonds, increases the molecular rigidity. The synergistic effect of the benzene ring and intramolecular hydrogen bonds makes the polycarboxylate superplasticizer molecule less prone to shrinkage and coiling in sulfate-containing concrete systems. The synergistic effect of the long polyether side chains and carboxyl groups in the vinyl polyether macromonomer further facilitates adsorption of the polycarboxylate superplasticizer onto cement particles. Therefore, the sulfate-resistant polycarboxylate superplasticizer prepared by this invention has advantages such as low dosage, high water reduction rate, small slump loss, good cement compatibility, and sulfate resistance. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This application also provides the following embodiments and comparative examples:

[0024] Example 1

[0025] 20g of 2-methoxy-4-vinylphenol, 85g of ethylene glycol monovinyl polyethylene glycol ether, 10g of ethanol, 1.0g of hydrogen peroxide, and 60g of water were added to a reaction vessel, and the temperature was controlled at 20℃. Then, vitamin C aqueous solution, acrylic acid aqueous solution, and mercaptoacetic acid aqueous solution were added dropwise at a uniform rate over a period of 3 hours. After the addition was completed, the mixture was kept at the same temperature for 1 hour. An appropriate 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 polycarboxylate superplasticizer.

[0026] The solution contains 0.5g of vitamin C dissolved in 30g of water, 0.3g of mercaptoacetic acid dissolved in 30g of water, and 10g of acrylic acid dissolved in 30g of water; the molecular weight of ethylene glycol monovinyl polyethylene glycol ether is 5000.

[0027] Example 2

[0028] Add 25g of eugenol, 90g of 4-hydroxybutylvinyl polyethylene glycol ether, 30g of ethanol, 1.3g of hydrogen peroxide, and 80g of water to a reaction vessel, and control the temperature at 25℃. Then, simultaneously and uniformly add sodium formaldehyde sulfoxylate aqueous solution, acrylic acid aqueous solution, and mercaptopropionic acid aqueous solution over a period of 3 hours. After the addition is completed, keep the temperature for 1 hour, and add an appropriate amount of water to adjust the concentration of the reaction product to obtain a 50% concentration. Adjust the pH of the reaction product to 6.0-7.0 with sodium hydroxide to obtain a sulfate-resistant polycarboxylate superplasticizer.

[0029] The aqueous solution of sodium formaldehyde sulfoxylate consists of 0.7g sodium formaldehyde sulfoxylate dissolved in 30g water, the aqueous solution of mercaptopropionic acid consists of 0.5g mercaptopropionic acid dissolved in 30g water, the aqueous solution of acrylic acid consists of 18g acrylic acid solution dissolved in 30g water, and the molecular weight of 4-hydroxybutylvinyl polyethylene glycol ether is 6000.

[0030] Example 3

[0031] 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 a reaction vessel, and the temperature was controlled at 30℃. Then, vitamin C aqueous solution, acrylic acid aqueous solution, and mercaptoacetic acid aqueous solution were added dropwise at a uniform rate over a period of 3 hours. After the addition was completed, the mixture was kept at the same temperature for 1 hour. An appropriate 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 polycarboxylate superplasticizer.

[0032] The solution contains 0.9g of vitamin C dissolved in 30g of water, 0.9g of mercaptoacetic acid dissolved in 30g of water, and 25g of acrylic acid dissolved in 30g of water; the molecular weight of ethylene glycol monovinyl polyethylene glycol ether is 6000.

[0033] Comparative Example 1

[0034] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not contain 2-methoxy-4-vinylphenol, while the other raw material components and operating steps are the same as those in Example 1.

[0035] Comparative Example 2

[0036] 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 with 2-allylphenol which does not contain intramolecular hydrogen bonds, while the other raw material components and operating steps are the same as in Example 1.

[0037] Comparative Example 3

[0038] The difference between Comparative Example 3 and Example 1 is that 20g of 2-methoxy-4-vinylphenol and 85g of ethylene glycol monovinyl polyethylene glycol ether were replaced with 10g of 2-methoxy-4-vinylphenol and 110g of ethylene glycol monovinyl polyethylene glycol ether, while the remaining raw material components and operating steps were the same as in Example 1.

[0039] Comparative Example 4

[0040] The difference between Comparative Example 4 and Example 1 is that 20g of 2-methoxy-4-vinylphenol and 85g of ethylene glycol monovinyl polyethylene glycol ether were replaced with 40g of 2-methoxy-4-vinylphenol and 70g of ethylene glycol monovinyl polyethylene glycol ether. The remaining raw material components and operating steps are the same as in Example 1.

[0041] Performance Test 1

[0042] The conformation of the polycarboxylate superplasticizer solution prepared according to this invention was determined using a Malvern Panaco Viscotek 270 dynamic and static light scattering instrument. The SO4 content in the solution was adjusted using Na2SO4. 2- The concentration of the polymer was determined under the following experimental conditions: polymer concentration: 1 mg / ml, test angle: 90°, and the solution conformation results are shown in Table 1.

[0043] Table 1. Solution conformations of different polycarboxylate superplasticizers

[0044]

[0045] As shown in Table 1, the hydrodynamic radius of the polycarboxylate superplasticizer solutions prepared in Comparative Examples 1 and 2 decreased significantly after the addition of sulfate, and the molecular structure became coiled, indicating that the conformation contracted. This is mainly because ordinary polycarboxylate superplasticizers tend to shrink and form coiled conformations in the presence of sulfate. Compared with Comparative Examples 1 and 2, the hydrodynamic radius of the sulfate-resistant polycarboxylate superplasticizer solutions prepared in Examples 1-3 decreased after the addition of sulfate, but the degree of shrinkage was significantly less than that in Comparative Examples 1 and 2. This is mainly because the present invention introduces a benzene ring into the molecular structure of the sulfate-resistant polycarboxylate superplasticizer. Its closed ring structure has high rigidity, and the presence of the ring restricts the flexibility of the polycarboxylate superplasticizer molecule. In addition, the special structure of the functional monomer, with intramolecular hydrogen bonds in the molecular structure, increases the rigidity of the molecule. The synergistic effect of the two special structures, the benzene ring and the intramolecular hydrogen bonds, makes the polycarboxylate superplasticizer molecule configuration less prone to shrinkage and less likely to form a coiled conformation in the presence of sulfate.

[0046] This invention prepares a sulfate-resistant polycarboxylate superplasticizer, wherein the functional monomer and the vinyl polyether macromonomer have an optimal ratio. In Comparative Examples 3 and 4, the ratio of key raw materials in the preparation of polycarboxylate superplasticizers exceeded the range. After adding sulfate to the polycarboxylate superplasticizer solution prepared by these examples, the hydrodynamic radius of the solution decreased significantly and the molecular structure became coiled, indicating that the conformation of the superplasticizer contracted. This indicates that the superplasticizer is prone to contraction and form a coiled conformation in the presence of sulfate.

[0047] Performance Test 2

[0048] The concrete mix performance was tested according to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The concrete mix proportion was: cement 360 kg / m³. 3 790kg / m³ of manufactured sand 3 1060 kg / m³ of gravel 3 162 kg / m³ of water 3 Adding Na2SO4 to water helps to adjust the SO4 levels in the concrete system. 2- The concentration.

[0049] The specific embodiments and comparative examples of polycarboxylate superplasticizers prepared for use in concrete are shown in Table 2 below:

[0050] Table 2. Effects of different polycarboxylate superplasticizers on concrete performance

[0051]

[0052] Table 2 shows that when the polycarboxylate superplasticizers prepared in Comparative Examples 1-4 were applied to concrete, the initial dispersion and slump retention of the concrete decreased significantly after adding sulfate to the concrete water, indicating poor adaptability to sulfate. This is mainly because the hydrodynamic radius of the polycarboxylate superplasticizers prepared in Comparative Examples 1-4 decreased significantly in the presence of sulfate in the concrete system, and their molecular structure became coiled, resulting in conformational shrinkage. This made adsorption on cement particles difficult, affecting the dispersion and slump retention of the concrete. In contrast, the sulfate-resistant polycarboxylate superplasticizers prepared in Examples 1-3, when applied to concrete, showed good initial dispersion and slump retention in concrete with different sulfate contents after adding sulfate to the concrete water. The prepared sulfate-resistant polycarboxylate superplasticizers exhibited strong adaptability to sulfate. This is mainly because the hydrodynamic radius of the sulfate-resistant polycarboxylate superplasticizers prepared in Examples 1-3 decreased less in the presence of sulfate in the concrete system, resulting in less impact on their adsorption on cement particles, and thus not affecting the dispersion and slump retention of the polycarboxylate superplasticizer.

[0053] In summary, the sulfate-resistant polycarboxylate superplasticizer prepared by this invention has advantages such as low dosage, high water reduction rate, small slump loss, good cement adaptability, and sulfate resistance.

[0054] Although this document frequently uses terms such as polycarboxylate superplasticizer, vinyl polyether macromonomer, unsaturated carboxylic acid, and functional monomer, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of this invention; interpreting them as any additional limitation would be contrary to the spirit of this invention.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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 producing a sulfate-resistant polycarboxylate water reducer, characterized by, The method comprises the following steps: The functional monomer, the vinyl polyether macromonomer, the oxidizing agent and the solvent are added into a reaction kettle containing water and stirred, and then the aqueous reducing agent solution, the aqueous unsaturated carboxylic acid solution and the aqueous chain transfer agent solution are added dropwise, and the reaction is carried out, and after heat preservation, the copolymerization product is obtained, and then the pH is adjusted to 6-7 by using the pH adjuster to obtain the sulfate-resistant polycarboxylic acid water reducer. The mass ratio of the functional monomer to the vinyl polyether macromonomer is 2-3:8-10. The functional monomer has the following structural formula: ， R1 is -OCH3, R2 is -H, and R3 is -CH=CH2. R1 is -OCH3, R2 is -H, and R3 is -CH2CH=CH2. R1 is -OCH2CH=CH2, R2 is -H, and R3 is -H.

2. The method of claim 1, wherein the method is characterized by: The functional monomer is 20-30 parts, the vinyl polyether macromonomer is 80-100 parts, the oxidizing agent is 1-1.5 parts, the solvent is 10-40 parts, water is 50-100 parts, the aqueous reducing agent solution is 30.5-30.9 parts, the aqueous unsaturated carboxylic acid solution is 40-55 parts, and the aqueous chain transfer agent solution is 30.3-30.9 parts.

3. The method of claim 1, wherein the method is characterized by: The reaction temperature is 20-30 DEG C, the heat preservation temperature is 20-30 DEG C, the heat preservation time is 1-3 h, the aqueous reducing agent solution, the aqueous unsaturated carboxylic acid solution and the aqueous chain transfer agent solution are added dropwise, and the dropwise adding time is 3-4 h.

4. The method of claim 1, wherein the method is characterized by: The aqueous reducing agent solution is prepared by dissolving 0.5-0.9 parts of the reducing agent in 30 parts of water, the aqueous chain transfer agent solution is prepared by dissolving 0.3-0.9 parts of the chain transfer agent in 30 parts of water, and the aqueous unsaturated carboxylic acid solution is prepared by dissolving 10-25 parts of the unsaturated carboxylic acid in 30 parts of water.

5. The method of claim 4, wherein the method is characterized by: The reducing agent is one or more of bisulfite, sulfite, sodium formaldehyde sulfoxylate and vitamin C.

6. The method of claim 4, wherein the method is characterized by: The chain transfer agent is one or more of mercaptoethanol, mercaptoacetic acid, mercapto propionic acid, n-dodecyl mercaptan and tert-dodecyl mercaptan.

7. The method of claim 4, wherein the method is characterized by: The unsaturated carboxylic acid is one or more of acrylic acid, methacrylic acid and itaconic acid. 8.The method for preparing the sulfate-type polycarboxylate superplasticizer 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-type polycarboxylate superplasticizer according to claim 1, characterized in that: The oxidizing agent is hydrogen peroxide, the solvent is ethanol, and the pH adjuster is sodium hydroxide.

10. A sulfate-resistant polycarboxylic acid water reducer prepared by the method according to any one of claims 1-9.

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