Polymer rheology modifier as well as preparation method and application thereof

Abstract

The invention discloses a polymer rheology modifier as well as a preparation method and application thereof, and belongs to the field of building materials. The polymer rheology modifier is prepared from an acrylic monomer A, an amide monomer B and a slow-release monomer C through free radical polymerization, and the mass ratio of the monomer A to the monomer B to the monomer C is 1: (2-5): (3-9). And the number-average molecular weight of the polymer rheology modifier is 1 to 4 million. The polymer rheology modifier provided by the invention can achieve the effects of large molecular weight and long acting time.

Description

Technical Field

[0001] The present invention relates to building materials, in particular to a polymer rheology modifier and a preparation method and application thereof. Background Art

[0002] Cement-based materials refer to engineering materials that use cement as a binder. Concrete and mortar are the most common cement-based materials. As the construction of cement-based materials tends to move toward pumping, a key technical development direction for cement-based materials is high fluidity. However, as multi-scale suspension systems, cement-based materials are prone to bleeding when in a high fluidity and low viscosity state. The use of rheology modifiers is the most effective, safe, and simple way to resolve the conflict between the fluidity and resistance to segregation and bleeding in fresh cement-based materials.

[0003] Currently, a wide variety of rheology-modifying admixtures are in use, primarily including cellulose ether-based rheology modifiers, modified starch-based rheology modifiers, and high-molecular-weight copolymer electrolyte-based rheology modifiers. When added to cementitious materials, these modifiers form numerous hydrogen bonds with water molecules in the solution phase, increasing the viscosity of the solution phase and reducing the amount of free water, thereby preventing segregation and bleeding. Furthermore, they adsorb onto the surfaces of cement particles, forming a spatial network of cement particles and modifiers, enhancing the stability of the fresh cementitious paste and thus preventing segregation and bleeding. Conventional rheology modifiers are very effective in addressing the initial segregation and bleeding of cementitious materials. However, cement undergoes a hydration process, and as hydration proceeds, the rheology modifiers adsorbed on the cement particle surfaces lose their effectiveness, leading to segregation and bleeding in the cementitious materials later in the process. This delayed bleeding phenomenon severely hinders the construction of high-flow concrete and seriously compromises the service life of the concrete. CN104744623A discloses a concrete workability regulator and its preparation method. Using 2-acrylamide-2-methylpropanesulfonic acid, an unsaturated carboxylic acid or its salt, acrylamide, and N,N-methylenebisacrylamide as comonomers, a concrete workability regulator with a weight-average molecular weight of 10,000 to 100,000 is obtained. The regulator can instantly absorb a large amount of water and slowly release it, significantly improving the workability of concrete and preventing water bleeding and segregation. However, due to its low molecular weight, the regulator's effect on improving concrete segregation and water bleeding is very limited. CN107337760A also discloses a concrete workability regulator composed of a polymer with hydroxyalkyl side chains and polyaspartic acid. It can effectively improve the segregation and water bleeding of cement-based materials, and the effect is stable and long-lasting, without rapid "failure". However, the regulator's effect on cement-based material segregation and water bleeding is short, with the longest regulation time being only about 1 hour.

[0004] While existing technologies utilize various functional comonomers to prepare polymeric rheology modifiers, these modifiers suffer from low molecular weight and short duration of action, making it difficult to address the delayed bleeding of cementitious materials after one hour. Therefore, there is an urgent need to develop a polymeric rheology modifier that can address this delayed bleeding issue in cementitious materials after one hour. This is crucial for ensuring the workability and service safety of cementitious materials. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a polymer rheology modifier with large molecular weight and long action time.

[0006] Another object of the present invention is to provide a method for preparing a polymer rheology modifier that is simple to operate and highly safe.

[0007] Another object of the present invention is to provide an application of a polymer rheology modifier in cement-based materials.

[0008] Technical solution: The polymer rheology modifier of the present invention is characterized in that the modifier is prepared from acrylic monomer A, amide monomer B, and sustained-release monomer C by free radical polymerization, and the mass ratio of monomers A, B, and C is 1:(2-5):(3-9); the general structural formula of the acrylic monomer A is

[0009]

[0010] R1 is a methyl group or a hydrogen atom;

[0011] The general structural formula of the amide monomer B is

[0012]

[0013] R2 and R3 are methyl or hydrogen atoms;

[0014] The general structural formula of the sustained-release monomer C is:

[0015]

[0016] Wherein R4 is a hydrogen atom or a methyl group.

[0017] Preferably, the number average molecular weight of the polymer rheology modifier is 1-4 million.

[0018] The preparation method of the polymer rheology modifier of the present invention comprises the following steps:

[0019] Water, acrylic monomer A, amide monomer B, and slow-release monomer C are mixed and stirred, nitrogen is introduced and the temperature is increased for the first time, an initiator aqueous solution is added dropwise, and the temperature is increased for a second time to obtain a polymer rheology modifier aqueous solution.

[0020] Preferably, the initiator is one of ammonium persulfate, potassium persulfate, and 2,2-azobis(2-methylpropylimidamide) dihydrochloride, and more preferably 2,2-azobis(2-methylpropylimidamide) dihydrochloride.

[0021] Preferably, the mass concentration of the initiator in the initiator aqueous solution is 0.50-2.00%.

[0022] Preferably, the amount of the initiator aqueous solution is 0.50-2.00 times the total mass of monomers A, B, and C.

[0023] Preferably, the polymer mass concentration of the polymer rheology modifier aqueous solution is 1.50-6.00%.

[0024] Preferably, the temperature of the first heating is 50-70° C.; the time for adding the initiator aqueous solution is 1-3 hours; the temperature of the second heating is 80-100° C., and the reaction time is 2-6 hours.

[0025] The application of the polymer rheology modifier of the present invention includes its application in cement-based materials.

[0026] Preferably, the polymer rheology modifier is added to the cement-based material (in the form of an aqueous solution of the polymer rheology modifier), and the amount added after conversion into active ingredients is 0.20-1.00 ten thousandths of the mass of the cement.

[0027] Principle of the invention: The polymer rheology modifier provided by the present invention is prepared using a slow-release comonomer, which is added to a cement-based material and initially only slowly adsorbed onto the surface of cement particles; subsequently, in a strong alkaline environment of the cement base, the slow-release monomer structural units in the polymer rheology modifier are hydrolyzed, and more carboxyl adsorption groups are gradually generated in the polymer molecular structure, thereby allowing the polymer rheology modifier to continuously and continuously adsorb onto the surface of cement particles, forming a spatial network structure of polymer-cement particles, thereby enhancing the slurry stability of the cement-based material in the later stage and exerting a long-term effect of inhibiting segregation and water exudation.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The method uses three monomers, namely, acrylic acid monomers, amide monomers, and slow-release monomers, to prepare a polymer rheology modifier. The number average molecular weight of the obtained modifier is as high as 1 to 4 million, which has a significant effect on improving the segregation and bleeding of concrete; (2) The polymer rheology modifier prepared by the method is applied to cement-based materials and can inhibit segregation and bleeding. The effective duration is as long as 2 to 5 hours, which can effectively solve the delayed bleeding problem of cement-based materials after 1 hour; (3) The present invention provides a polymer rheology modifier prepared by using a slow-release comonomer, which has a simple preparation method and high safety; (4) the polymer rheology modifier provided by the present invention can be used together with other admixtures such as water reducers, accelerators, slump retaining agents, retarders, air entraining agents, defoamers, etc., and has good compatibility; (5) compared with traditional rheology modifiers, the polymer rheology modifier provided by the present invention has no effect on the initial fluidity of cement-based materials, no adverse effect on the expansion of concrete, and will not increase the amount of water reducer used when mixing cement-based materials, and has excellent comprehensive cost performance. DETAILED DESCRIPTION

[0029] The technical solution of the present invention will be further described below in conjunction with embodiments.

[0030] Example 1

[0031] The preparation method of the polymer rheology modifier of the present invention comprises the following steps:

[0032] 27000g of water, 100g of acrylic acid, 350g of N,N-dimethylacrylamide and 880g of hydroxypropyl acrylate were added to the reactor in sequence, stirring was started, and the oxygen in the reactor was replaced with nitrogen. The temperature was raised to 60°C, and 1330g of a 1% aqueous solution of 2,2-azobis(2-methylpropylimidazole) dihydrochloride (as an initiator) was uniformly added dropwise to the reactor over 2 hours. After the addition was completed, the temperature was raised to 90°C and the reaction was continued for 4 hours to finally obtain an aqueous solution of a polymer rheology modifier.

[0033] The solid content in the aqueous solution was detected by constant weight method, and the solid content in the aqueous solution was 4.38%. The number average molecular weight of the polymer rheology modifier was measured by high performance gel permeation chromatography and was 2.8061 million.

[0034] Example 2

[0035] The similarities between this embodiment and embodiment 1 are not repeated here, and the differences are as follows:

[0036] In the reactor, the amount of water added was 58000 g, and the amount of N,N-dimethylacrylamide added was 480 g.

[0037] The solid content in the aqueous solution was detected by constant weight method, and the solid content in the aqueous solution was 2.31%. The number average molecular weight of the polymer rheology modifier was measured by high performance gel permeation chromatography and was 3.6936 million.

[0038] Example 3

[0039] The similarities between this embodiment and embodiment 1 are not repeated here, and the differences are as follows:

[0040] In the reactor, the amount of N,N-dimethylacrylamide added was 210 g.

[0041] The solid content in the aqueous solution was detected by constant weight method, and the solid content in the aqueous solution was 4.02%. The number average molecular weight of the polymer rheology modifier was measured by high performance gel permeation chromatography and was 1.8058 million.

[0042] Example 4

[0043] The similarities between this embodiment and embodiment 1 are not repeated here, and the differences are as follows:

[0044] In the reactor, 620 g of hydroxypropyl acrylate was added.

[0045] The solid content in the aqueous solution was detected by constant weight method, and the solid content in the aqueous solution was 3.51%. The number average molecular weight of the polymer rheology modifier was measured by high performance gel permeation chromatography and was 2.3017 million.

[0046] Example 5

[0047] The similarities between this embodiment and embodiment 1 are not repeated here, and the differences are as follows:

[0048] In the reactor, 310 g of hydroxypropyl acrylate was added.

[0049] The solid content in the aqueous solution was detected by constant weight method, and the solid content in the aqueous solution was 2.57%. The number average molecular weight of the polymer rheology modifier was measured by high performance gel permeation chromatography and was 1.9032 million.

[0050] Example 6

[0051] The preparation method of the polymer rheology modifier of the present invention comprises the following steps:

[0052] 27000 g of water, 100 g of methacrylic acid, 350 g of N,N-dimethylacrylamide, and 880 g of hydroxypropyl methacrylate were added to the reactor in sequence, stirring was started, and the oxygen in the reactor was removed by nitrogen displacement. The temperature was raised to 70° C., and 700 g of a 2% aqueous potassium persulfate solution was uniformly added dropwise to the reactor over 3 hours. After the addition was completed, the temperature was raised to 100° C. and the reaction was continued for 2 hours to finally obtain an aqueous solution of a polymer rheology modifier.

[0053] The solid content in the aqueous solution was detected by constant weight method, and the solid content in the aqueous solution was 4.46%. The number average molecular weight of the polymer rheology modifier was measured by high performance gel permeation chromatography and was 1.0744 million.

[0054] Example 7

[0055] The preparation method of the polymer rheology modifier of the present invention comprises the following steps:

[0056] 27,000 g of water, 100 g of acrylic acid, 300 g of N-methylacrylamide, and 750 g of hydroxypropyl methacrylate were added to the reactor in sequence. Stirring was started, and the oxygen in the reactor was removed by nitrogen displacement. The temperature was raised to 50° C., and 2,200 g of a 0.5% aqueous solution of ammonium persulfate was uniformly added dropwise to the reactor over 3 hours. After the addition was completed, the temperature was raised to 100° C., and the reaction was continued for 6 hours to finally obtain an aqueous solution of a polymer rheology modifier.

[0057] The solid content in the aqueous solution was detected by constant weight method, and the solid content in the aqueous solution was 3.75%. The number average molecular weight of the polymer rheology modifier was measured by high performance gel permeation chromatography and was 1.9678 million.

[0058] In order to intuitively reflect the experimental conditions of Examples 1-7, their main parameters are shown in Table 1.

[0059] Table 1 Main parameters of Examples 1-7

[0060]

[0061] Comparative Example 1

[0062] The similarities between this comparative example and Example 1 are not repeated here, except that:

[0063] In the reactor, the amount of N,N-dimethylacrylamide added was 0 g.

[0064] The solid content in the aqueous solution was detected by constant weight method, and the solid content in the aqueous solution was 3.25%. The number average molecular weight of the polymer rheology modifier was measured by high performance gel permeation chromatography and was 901,700.

[0065] Comparative Example 2

[0066] The similarities between this comparative example and Example 1 are not repeated here, except that:

[0067] In the reactor, the amount of N,N-dimethylacrylamide added was 650 g.

[0068] In this comparative example, when the temperature was raised to 90°C and the reaction was continued for 3 hours, a semi-gel state appeared in the reactor and the reaction was stopped. The results show that when the amount of amide monomer is too high, the polymer molecular weight is too large, the production process is difficult to control, and gelation is very likely to occur.

[0069] Comparative Example 3

[0070] The similarities between this comparative example and Example 1 are not repeated here, except that:

[0071] In the reactor, the amount of hydroxypropyl acrylate added was 0 g.

[0072] The solid content in the aqueous solution was detected by constant weight method, and the solid content in the aqueous solution was 1.46%. The number average molecular weight of the polymer rheology modifier was measured by high performance gel permeation chromatography and was 2.1058 million.

[0073] Comparative Example 4

[0074] The similarities between this comparative example and Example 1 are not repeated here, except that:

[0075] In the reactor, 1200 g of hydroxypropyl acrylate was added.

[0076] In this comparative example, during the dropwise addition of the initiator (aqueous solution of 2,2-azobis(2-methylpropylimidazole) dihydrochloride), the system released heat violently, with the temperature rising sharply to 115°C, leading to explosive boiling and reaction failure. These results indicate that when the amount of sustained-release monomer is too high, the polymerization process releases excessive heat, making the production process difficult to control and prone to production accidents such as explosive boiling.

[0077] Comparative Example 5

[0078] Commercially available hydroxypropyl methylcellulose ether (purchased from Nanjing Kunda Trading Co., Ltd.) was used as the sample for this comparative example.

[0079] The modifiers obtained in Examples 1-7 and Comparative Examples 1, 3, and 5 were subjected to performance tests, including cement paste bleeding inhibition test, concrete expansion and bleeding test.

[0080] Cement paste exudation inhibition test: The test method follows the method described in Example 2.1 of US Patent No. 8148304. 1500g of cement, 900g of water, and 0.075g (solid) rheology modifier were mixed thoroughly. 100mL of the mixture was placed in a graduated cylinder and allowed to stand for 5 minutes, 1 hour, 3 hours, and 5 hours, respectively. The height of the exuded water was measured. For all samples, the solid content in the cement paste, calculated based on the mass concentration of the aqueous solution, was 0.50 parts per ten thousand of the cement mass. Specific experimental results are shown in Table 2.

[0081] Table 2 Effect of different samples on the bleeding height of cement paste

[0082]

[0083]

[0084] Note: The “benchmark” in the table refers to the control sample without any rheology modifier, that is, the traditional cement paste.

[0085] The 5-hour bleeding characteristics of cement pastes in Table 2 indicate that the polymeric rheology modifiers prepared by this method (Examples 1-7) can maintain the bleeding height of the cement paste within 6.5 cm within 5 hours. The best example is the polymeric rheology modifier prepared in Example 2, which achieved a bleeding height of only 0.5 cm after 5 hours, a 97.4% reduction compared to the baseline. A comparison of Examples 1-3 shows that increasing the amount of amide monomers helps improve bleeding at each time point. A comparison of Examples 1, 4, and 5 shows that increasing the amount of sustained-release monomers also helps improve bleeding at each time point. Comparative Example 1 and Example 1 show that when no amide comonomer is added to the rheology modifier, the water exudation inhibition effect at each time point is significantly reduced, and the water exudation height of the cement slurry after 5 hours is 12.5 cm, which is only 35.9% lower than the baseline. The data of Comparative Examples 3, 5 and Example 1 show that when no slow-release comonomer is added to the rheology modifier, the water exudation inhibition effect after 1 hour is not significantly different from that of commercially available hydroxypropyl methylcellulose ether (Comparative Example 5), and the water exudation height of the cement slurry after 5 hours is also not significantly different from the baseline, which indicates that the slow-release monomer is a key component for exerting a long-lasting effect.

[0086] Concrete expansion and bleeding test: The concrete expansion and bleeding rate in the experiment were carried out according to the methods described in Section 3.1 and Section 5.1 of the national standard GB / T50080-2002 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The mix ratio of the test concrete was 300kg / m 3 、Sand (0-4mm) 883kg / m 3、Crushed stone (4-16mm) 957kg / m 3 , water 195kg / m 3 , slump-retaining and retarding water reducer (produced by Jiangsu Subote New Materials Co., Ltd.) 5.0kg / m 3 , rheology modifier solid 20.0g / m 3 Table 3 shows the data of initial expansion and water bleeding rate at different times.

[0087] Table 3 Effects of different samples on concrete expansion and bleeding rate

[0088]

[0089]

[0090] Note: The “benchmark” in the table refers to the control group sample without any rheology modifier, that is, the benchmark concrete that meets the GB / T50080-2002 “Standard for Test Methods for Performance of Ordinary Concrete Mixtures”.

[0091] As shown in Table 3, the initial expansion and 5-hour water bleeding rate data for concrete indicate that the polymeric rheology modifier prepared by this method has no adverse effect on the initial expansion of concrete and effectively inhibits water bleeding within 5 hours, maintaining the water bleeding rate below 6.1%. The best performing sample is the polymeric rheology modifier prepared in Example 2, with a 5-hour water bleeding rate of only 1.5%, an 85.7% reduction compared to the baseline. A comparison of Examples 1-3 shows that increasing the amount of amide monomer helps suppress the water bleeding rate at each time point; a comparison of Examples 1, 4, and 5 shows that increasing the amount of slow-release monomer also helps suppress the water bleeding rate at each time point. The data from Comparative Example 1 and Example 1 show that when no amide comonomer is added to the rheology modifier, there is essentially no effect on the initial expansion of the concrete. However, the water bleeding rate inhibition effect at each time point is significantly reduced. The water bleeding rate of the concrete after 5 hours is 8.6%, which is 18.1% lower than the baseline. The data from Comparative Examples 3 and 5 and Example 1 show that when no slow-release comonomer is added to the rheology modifier, the water bleeding rates at 3 and 5 hours are slightly higher than those of the baseline and commercially available hydroxypropyl methylcellulose ether (Comparative Example 5). This indicates that the slow-release monomer plays a key role in achieving long-term water bleeding inhibition.

Claims

1. A polymer rheology modifier, characterized in that The modifier is prepared by free radical polymerization of acrylic acid monomer A, amide monomer B, and slow-release monomer C, wherein the mass ratio of monomers A, B, and C is 1:(2-5):(3-9); the general structural formula of the acrylic acid monomer A is R1 is a methyl group or a hydrogen atom; The general structural formula of the amide monomer B is R2 and R3 are methyl or hydrogen atoms; The general structural formula of the sustained-release monomer C is: Wherein R4 is a hydrogen atom or a methyl group.

2. The polymer rheology modifier according to claim 1, characterized in that The number average molecular weight of the polymer rheology modifier is 1-4 million.

3. A method for preparing the polymer rheology modifier according to claim 1, characterized in that: The following steps are involved: Water, acrylic monomer A, amide monomer B, and slow-release monomer C are mixed and stirred, nitrogen is introduced and the temperature is increased for the first time, an initiator aqueous solution is added dropwise, and the temperature is increased for a second time to obtain a polymer rheology modifier aqueous solution.

4. The preparation method according to claim 3, characterized in that The initiator is one of ammonium persulfate, potassium persulfate and 2,2-azobis(2-methylpropylimidazole) dihydrochloride.

5. The preparation method according to claim 3, characterized in that The mass concentration of the initiator in the initiator aqueous solution is 0.50-2.00%.

6. The preparation method according to claim 3, characterized in that The amount of the initiator aqueous solution is 0.50-2.00 times the total mass of monomers A, B, and C.

7. The preparation method according to claim 3, characterized in that The polymer mass concentration of the polymer rheology modifier aqueous solution is 1.50-6.00%.

8. The preparation method according to claim 3, characterized in that The temperature of the first heating is 50-70° C.; the time for adding the initiator aqueous solution is 1-3 hours; the temperature of the second heating is 80-100° C., and the reaction time is 2-6 hours.

9. Use of the polymer rheology modifier according to claim 1 in cement-based materials.

10. The use according to claim 9, characterized in that The polymer rheology modifier is added to cement-based materials, and the amount of the added active ingredient converted into effective components is 0.20-1.00 ten thousandths of the mass of the cement.

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