A retarding enhanced graphene-poly carboxylic acid composite water reducing agent and a preparation method thereof

Abstract

This invention discloses a retarded and reinforced graphene-polycarboxylate composite water-reducing agent and its preparation method. The preparation steps are as follows: (1) preparing a hydrolysate of γ-methacryloxypropyltrimethoxysilane; (2) preparing a low-oxygen-content graphene dispersion, and adding the hydrolysate obtained in step (1) to it; reacting, drying, and obtaining functionalized graphene with polymerizable double bonds grafted on the surface; (3) heating and dissolving isopentenyl alcohol polyoxyethylene ether macromonomer and water to obtain solution 1; (4) adding solution A, solution B and solution C dropwise to solution 1; (5) keeping warm and aging, cooling to room temperature, and obtaining a retarded and reinforced graphene-polycarboxylate composite water-reducing agent. The composite water-reducing agent of this invention exhibits a controllable retarding effect. The composite water-reducing agent of this invention can more efficiently improve the compressive and flexural strength of cement-based materials. The reaction conditions are mild and no special equipment is required. It is suitable for the technical transformation and upgrading of existing polycarboxylate water-reducing agent production lines.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology and relates to a retarded and reinforced graphene-polycarboxylate composite water-reducing agent and its preparation method. Background Technology

[0002] Polycarboxylate superplasticizers are an indispensable core component in modern high-performance concrete, widely used due to their advantages such as high water reduction rate and low spread loss. However, traditional polycarboxylate superplasticizers mainly disperse cement particles through electrostatic repulsion and steric hindrance effects, which limits their ability to improve the later mechanical properties of cement-based materials.

[0003] To further improve the mechanical properties and durability of cement-based materials, researchers have attempted to combine nanomaterials with water-reducing agents. Graphene oxide (GO) has become a research hotspot due to its unique two-dimensional sheet structure and excellent mechanical properties. The surface of graphene oxide is rich in hydrophilic oxygen-containing functional groups such as carboxyl and hydroxyl groups, which can provide abundant nucleation sites for cement hydration products, accelerating the hydration reaction and often exhibiting a setting-promoting effect. However, this characteristic can lead to excessively rapid loss of concrete workability, causing inconvenience during construction. Furthermore, the oxygen-containing functional groups on graphene oxide sheets can disrupt its intrinsic sp... 2 The hybrid structure leads to a significant decrease in its theoretical modulus and strength, making it difficult to fully realize the true potential of graphene.

[0004] Currently, numerous studies and patents have been dedicated to developing graphene-polycarboxylate composite water-reducing agents, but most technical solutions have significant limitations. For example, Chinese patent CN106478895A discloses a graphene oxide composite polycarboxylate water-reducing agent. The graphene oxide prepared using the Hummer method has a large number of hydroxyl and carboxyl groups on its surface. These groups have strong associative hydrogen bonds with the water-reducing agent monomers, causing the monomers to polymerize on the graphene sheet structure, thereby increasing the interlayer spacing between the graphene oxide sheets. However, this method fails to polymerize graphene oxide into the polymer backbone of the polycarboxylate water-reducing agent; it merely encapsulates the polycarboxylate water-reducing agent in the interlayer space. This method does not fundamentally solve the dispersion stability problem of graphene oxide in the polymer matrix, and the coagulation-promoting properties of graphene oxide still exist. The patent with publication number CN112707668A attempts to modify polyol acrylates with silane coupling agents and graphene oxide, but its ultimate goal is still to prepare a shrinkage-reducing polycarboxylate superplasticizer. Moreover, the modification target is small molecule esters, and it does not involve directly grafting graphene onto the polycarboxylate backbone through chemical bonds to solve the key problems of dispersion and retarding. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a retarded and reinforced graphene-polycarboxylate composite water-reducing agent.

[0006] The second objective of this invention is to provide a method for preparing a retarded and reinforced graphene-polycarboxylate composite water-reducing agent.

[0007] The third objective of this invention is to provide an application of a retarding and reinforcing graphene-polycarboxylate composite water-reducing agent in retarding and reinforcing concrete.

[0008] The technical solution of this invention is summarized as follows: A method for preparing a retarded and reinforced graphene-polycarboxylate composite water-reducing agent includes the following steps: (1) Mix γ-methacryloxypropyltrimethoxysilane with an 80%-95% volume fraction of aqueous ethanol or isopropanol solution at a mass ratio of 1:(5-10), adjust the pH to 4-5, and let stand for 5-30 minutes to obtain a hydrolysate of γ-methacryloxypropyltrimethoxysilane. (2) Add low oxygen content graphene to water, ethanol or ethanol-water solution at a ratio of 1g: (10-100mL), stir evenly to obtain a dispersion, add hydrolysate of γ-methacryloxypropyltrimethoxysilane obtained in step (1) to the dispersion; react, dry to obtain functionalized graphene with polymerizable double bonds grafted on the surface. (3) In the reactor, add isopentenyl alcohol polyoxyethylene ether macromonomer (commercial product) and water at a mass ratio of 1: (0.8-2), heat to 55-65℃ and stir to dissolve, to obtain solution 1; (4) Add solutions A, B and C to solution 1; The A solution is: weigh acrylic acid, chain transfer agent, water and functionalized graphene grafted with polymerizable double bonds, mix well, and the mass ratio of the acrylic acid, chain transfer agent, water and functionalized graphene grafted with polymerizable double bonds to the isopentenyl alcohol polyoxyethylene ether macromonomer in step (3) is (0.10-0.15):(0.001-0.003):(0.9-2.5):(0.0005-0.02):1; Solution B is an aqueous solution of oxidant with a mass concentration of 3.5%-8%, wherein the molar amount of oxidant is 1%-3% of the total molar amount of acrylic acid and isopentenyl alcohol polyoxyethylene ether macromonomer; Solution C is a reducing agent aqueous solution with a mass concentration of 0.5%-3%, wherein the molar amount of the reducing agent is 0.4%-1% of the total molar amount of acrylic acid and isopentenyl alcohol polyoxyethylene ether macromonomer; (5) Keep warm at 55-65℃ for 1-5 hours, then cool to room temperature to obtain a slow-setting and reinforced graphene-polycarboxylate composite water-reducing agent.

[0009] Preferably, the reaction temperature in step (2) is 50-80℃ and the reaction time is 2-4 hours.

[0010] Preferably, the mass ratio of γ-methacryloyloxypropyltrimethoxysilane to low-oxygen-content graphene is (2-8):1, and the oxygen atom content of the low-oxygen-content graphene is 2wt%~6wt%.

[0011] Preferably, the chain transfer agent is mercaptopropionic acid, mercaptoacetic acid, mercaptoethanol, sodium 3-mercapto-1-propanesulfonate, or sodium hypophosphite.

[0012] Preferably, the oxidant is hydrogen peroxide, ammonium persulfate, sodium persulfate, or potassium persulfate.

[0013] Preferably, the reducing agent is vitamin C, sodium bisulfite formaldehyde, sodium bisulfite, or sodium metabisulfite.

[0014] Preferably, the steps for adding solutions A, B, and C are as follows: simultaneously add solutions B and C, completing the addition over 3-4 hours; begin adding solution A 5-15 minutes after adding solutions B and C, completing the addition of solution A over 2.5-3.5 hours.

[0015] The above preparation method produces a retarded and reinforced graphene-polycarboxylate composite water-reducing agent.

[0016] The above-mentioned retarding and reinforcing graphene-polycarboxylate composite water-reducing agent is used in the retarding and reinforcement of concrete.

[0017] Advantages of this invention: 1. This invention involves covalently modifying low-oxygen-content graphene with γ-methacryloxypropyltrimethoxysilane, introducing polymerizable double bonds onto the surface of the low-oxygen-content graphene. This functionalized graphene with polymerizable double bonds grafted onto its surface can participate as a monomer in the free radical copolymerization of polycarboxylic acids, firmly grafted onto the polymer backbone through strong chemical bonds. This method fundamentally solves the problem of graphene agglomeration, achieving its long-term, stable, and uniform dispersion in water-reducing agent systems and cement pastes.

[0018] 2. In contrast to the accelerating effect of traditional graphene oxide, the composite water-reducing agent of this invention exhibits a controllable retarding effect. The mechanism lies in the hydrophobic and chemically inert nature of the chemically grafted low-oxygen-content graphene sheets. These sheets form a dense physical barrier film on the surface of cement particles, effectively hindering the initial contact between water molecules and cement particles and the diffusion of hydration products, thereby slowing down the hydration process. This characteristic significantly prolongs the setting time of the cement paste, which is beneficial for long-distance transportation of concrete and the construction of large-volume concrete, effectively overcoming the defect of graphene oxide causing excessively rapid loss of workability.

[0019] 3. Due to the complete spline structure of low-oxygen graphene... 2 Carbon structures possess intrinsic mechanical properties far superior to those of graphene oxide. This invention utilizes chemical grafting to uniformly disperse and firmly anchor carbon within cement hydration products, fully leveraging its two-dimensional nano-reinforcing effects, such as bridging, crack deflection, and pull-out effects, thereby more efficiently enhancing the compressive and flexural strength of cement-based materials.

[0020] 4. The preparation method of this invention ingeniously combines the functionalization of graphene with the synthesis process of polycarboxylic acid, and adopts a simultaneous dropping process under a redox initiation system. The reaction conditions are mild, no special equipment is required, and it is suitable for the technical transformation and upgrading of existing polycarboxylic acid water-reducing agent production lines, and has good prospects for industrial application. Detailed Implementation

[0021] The preparation of low-oxygen-content graphene in the following embodiments is based on the method disclosed in CN115893397A, and the specific steps are as follows: (1) Graphene powder prepared by liquid phase exfoliation and peracetic acid disinfectant with a mass fraction of 0.5% were added to a high-pressure stirred reactor; the ratio of graphene powder to the above peracetic acid disinfectant was 0.5 kg / L. (2) Turn on the mechanical stirrer at 200 rpm and heat to 180°C for 8 hours; (3) After the reaction vessel is cooled to room temperature, the solid-liquid mixture in the vessel is filtered and the obtained solid is dried. This is low oxygen content graphene, which has oxygen-containing functional groups such as hydroxyl and carboxyl groups on its surface, with an oxygen content of 2wt%~6wt%, a sheet size of 0.5-5μm, and 1-10 layers.

[0022] The present invention will be further described below through specific embodiments.

[0023] Example 1 A method for preparing a retarded and reinforced graphene-polycarboxylate composite water-reducing agent includes the following steps: (1) Mix γ-methacryloxypropyltrimethoxysilane with a 90% volume fraction of aqueous ethanol solution (or a 90% volume fraction of aqueous isopropanol solution) at a mass ratio of 1:7.5, adjust the pH to 4.5 with glacial acetic acid, and let stand for 20 minutes to obtain a hydrolysate of γ-methacryloxypropyltrimethoxysilane. (2) Add low oxygen content graphene to water at a ratio of 1g: 50mL, stir evenly to obtain a dispersion, add hydrolysate of γ-methacryloxypropyltrimethoxysilane obtained in step (1) to the dispersion; react at 50℃ for 4 hours, dry to obtain functionalized graphene with polymerizable double bonds grafted on the surface. The mass ratio of γ-methacryloyloxypropyltrimethoxysilane to low-oxygen-content graphene is 5:1; the oxygen atom content of the low-oxygen-content graphene is 2wt%~6wt%. (3) In the reactor, add isopentenyl alcohol polyoxyethylene ether macromonomer and water in a mass ratio of 1:1.4, heat to 60°C and stir to dissolve, to obtain solution 1; (4) Add solutions A, B and C to solution 1; The A solution is made by mixing acrylic acid, chain transfer agent (mercaptopropionic acid), water, and functionalized graphene grafted with polymerizable double bonds. The mass ratio of the acrylic acid, chain transfer agent, water, and functionalized graphene grafted with polymerizable double bonds to the isopentenyl alcohol polyoxyethylene ether macromonomer in step (3) is 0.125:0.002:1.7:0.01:1. Solution B is an aqueous solution of an oxidant (hydrogen peroxide) with a mass concentration of 5.5%, wherein the molar amount of hydrogen peroxide is 2% of the total molar amount of acrylic acid and isopentenyl polyoxyethylene ether macromonomer; The C solution is a vitamin C aqueous solution with a mass concentration of 1.75%, wherein the molar amount of vitamin C is 0.7% of the total molar amount of acrylic acid and isopentenyl alcohol polyoxyethylene ether macromonomer; The preferred steps for adding solutions A, B, and C are as follows: simultaneously add solutions B and C, completing the addition over 3.5 hours; begin adding solution A 10 minutes after adding solutions B and C, and complete the addition of solution A over 3 hours. (5) After being kept at 60℃ for 3 hours and cooled to room temperature, a slow-setting and reinforced graphene-polycarboxylic acid composite water-reducing agent is obtained.

[0024] Example 2 A method for preparing a retarded and reinforced graphene-polycarboxylate composite water-reducing agent includes the following steps: (1) Mix γ-methacryloxypropyltrimethoxysilane with an 80% volume fraction of isopropanol aqueous solution (or an 80% volume fraction of ethanol aqueous solution) at a mass ratio of 1:10, adjust the pH to 5.0 with glacial acetic acid, and let stand for 5 minutes to obtain a hydrolysate of γ-methacryloxypropyltrimethoxysilane. (2) Add low oxygen content graphene to ethanol at a ratio of 1g: 10mL, stir evenly to obtain a dispersion, add the hydrolysate of γ-methacryloxypropyltrimethoxysilane obtained in step (1) to the dispersion, react at 65℃ for 3 hours, dry to obtain functionalized graphene with polymerizable double bonds grafted on the surface. The mass ratio of γ-methacryloyloxypropyltrimethoxysilane to low-oxygen-content graphene is 2:1; the oxygen atom content of the low-oxygen-content graphene is 2wt%~6wt%. (3) In the reactor, add isopentenyl alcohol polyoxyethylene ether macromonomer and water at a mass ratio of 1:0.8, heat to 55°C and stir to dissolve, to obtain solution 1; (4) Add solutions A, B and C to solution 1; The A solution is: acrylic acid, chain transfer agent (thioglycolic acid), water and functionalized graphene grafted with polymerizable double bonds on the surface are mixed well. The mass ratio of acrylic acid, chain transfer agent, water and functionalized graphene grafted with polymerizable double bonds to the isopentenyl alcohol polyoxyethylene ether macromonomer in step (3) is 0.10:0.003:0.9:0.0005:1. Solution B is a 3.5% (w / w) aqueous solution of ammonium persulfate, wherein the molar amount of ammonium persulfate is 3% of the total molar amount of acrylic acid and isopentenyl alcohol polyoxyethylene ether macromonomer; Solution C is a 0.5% (w / w) aqueous solution of sodium bisulfite and formaldehyde, wherein the molar amount of sodium bisulfite and formaldehyde is 0.4% of the total molar amount of acrylic acid and isopentenyl alcohol polyoxyethylene ether macromonomers. The preferred steps for adding solutions A, B, and C are as follows: simultaneously add solutions B and C, completing the addition over 3 hours; begin adding solution A 5 minutes after adding solutions B and C, completing the addition of solution A over 2.5 hours. (5) After being kept at 55℃ for 5 hours and cooled to room temperature, a slow-setting and reinforced graphene-polycarboxylic acid composite water-reducing agent is obtained.

[0025] Example 3 A method for preparing a retarded and reinforced graphene-polycarboxylate composite water-reducing agent includes the following steps: (1) Mix γ-methacryloxypropyltrimethoxysilane with a 95% volume fraction of aqueous ethanol solution (or a 95% volume fraction of aqueous isopropanol solution) at a mass ratio of 1:5, adjust the pH to 4 with glacial acetic acid, and let stand for 30 minutes to obtain a hydrolysate of γ-methacryloxypropyltrimethoxysilane. (2) At a ratio of 1g: 100mL, graphene with low oxygen content was added to an aqueous ethanol solution with a volume fraction of 50%, stirred evenly to obtain a dispersion, and the hydrolysate of γ-methacryloyloxypropyltrimethoxysilane obtained in step (1) was added to the dispersion; the reaction was carried out at 80℃ for 2 hours, and dried to obtain functionalized graphene with polymerizable double bonds grafted on the surface. The mass ratio of γ-methacryloyloxypropyltrimethoxysilane to low-oxygen-content graphene is 8:1; the oxygen atom content of the low-oxygen-content graphene is 2wt%~6wt%. (3) In the reactor, add isopentenyl alcohol polyoxyethylene ether macromonomer and water in a mass ratio of 1:2, heat to 65°C and stir to dissolve, to obtain solution 1; (4) Add solutions A, B and C to solution 1; Solution A is prepared by mixing acrylic acid, chain transfer agent (mercaptoethanol, or alternatively sodium 3-mercapto-1-propanesulfonate or sodium hypophosphite), water, and functionalized graphene grafted with polymerizable double bonds. The mass ratio of acrylic acid, chain transfer agent, water, and functionalized graphene grafted with polymerizable double bonds to the isopentenyl alcohol polyoxyethylene ether macromonomer in step (3) is 0.15:0.001:2.5:0.02:1. Solution B is an 8% potassium persulfate aqueous solution (or sodium persulfate aqueous solution), wherein the molar amount of potassium persulfate (or sodium persulfate) is 1% of the total molar amount of acrylic acid and isopentenyl alcohol polyoxyethylene ether macromonomer; The C solution is a 3% (w / w) aqueous solution of sodium bisulfite (or sodium metabisulfite), wherein the molar amount of sodium bisulfite (or sodium metabisulfite) is 1% of the total molar amount of acrylic acid and isopentenyl alcohol polyoxyethylene ether macromonomer; The preferred steps for adding solutions A, B, and C are as follows: simultaneously add solutions B and C, completing the addition over 4 hours; begin adding solution A 15 minutes after adding solutions B and C, completing the addition of solution A over 3.5 hours. (5) The mixture was kept at 65°C for 1 hour and then cooled to room temperature to obtain a slow-setting and reinforced graphene-polycarboxylic acid composite water-reducing agent.

[0026] Comparative Example 1 The preparation steps are the same as in Example 1, except that no functionalized graphene with polymerizable double bonds grafted onto the surface is added when preparing solution A.

[0027] Comparative Example 2 The low-oxygen-content graphene in Example 1 was replaced with graphene oxide (GO) with an oxygen content of 20 wt%-30 wt%, and the rest was the same as in Example 1.

[0028] Performance testing The products obtained in the above examples and comparative examples were subjected to performance tests. The water-reducing agent dosage (products prepared in Examples 1-3 and Comparative Examples 1-2) was 2% of the mass of cementitious materials in concrete (based on solid content). The tests were conducted in accordance with GB / T 50080-2016 and GB / T 50081-2019, and the results are shown in Table 1.

[0029] Table 1 Performance Test Results

[0030] As shown in Table 1: 1. Dispersion Stability: The products of Examples 1-3 of this invention all exhibited excellent stability, with no sedimentation or stratification after standing for 7 days. This proves that chemical grafting is an effective and necessary means to solve the problem of dispersion of low-oxygen graphene.

[0031] 2. Spread Loss Value: The products of Examples 1-3 of this invention exhibit a significant retarding effect, with a spread change of ≤20 mm over 2 hours, far less than that of Comparative Example 1 (50 mm) using a common water-reducing agent. The products of Examples 1-3 are completely different from the accelerating effect (55 mm) caused by the use of graphene oxide in Comparative Example 2, demonstrating the essential difference between the physical barrier retarding mechanism of low-oxygen-content graphene and the chemical nucleation accelerating mechanism of graphene oxide. This invention effectively improves the workability retention of concrete.

[0032] 3. Mechanical Properties: The product of this invention significantly improves the 28-day compressive strength of concrete (10%~30%) compared to Comparative Example 1 (benchmark) and Comparative Example 2 (slight improvement). This fully demonstrates that chemically grafted low-oxygen-content graphene can more effectively exert its nano-reinforcing effect, resulting in stronger interfacial bonding with the cement matrix and higher reinforcement and toughening efficiency.

[0033] In summary, this invention has successfully prepared a retarded and reinforced graphene-polycarboxylate composite water-reducing agent with excellent dispersion stability, unique retarding function, and significant reinforcing effect through a specific chemical grafting process. Its comprehensive performance far exceeds that of existing technologies such as graphene oxide composites, and it solves a long-standing technical contradiction in this field.

Claims

1. A preparation method of a set retarding enhanced graphene-poly carboxylic acid composite water reducing agent, characterized in that Includes the following steps: (1) Mix γ-methacryloxypropyltrimethoxysilane with an 80%-95% volume fraction of aqueous ethanol or an 80%-95% volume fraction of aqueous isopropanol at a mass ratio of 1:5-10, adjust the pH to 4-5, and let stand for 5-30 minutes to obtain γ-methacryloxypropyltrimethoxysilane hydrolysate; (2) Add low oxygen content graphene to water, ethanol or ethanol aqueous solution at a ratio of 1g:10-100mL, stir evenly to obtain a dispersion, add the hydrolysate of γ-methacryloxypropyltrimethoxysilane obtained in step (1) to the dispersion, react, dry, and obtain functional graphene with polymerizable double bonds grafted on the surface. (3) In the reactor, add isopentenyl alcohol polyoxyethylene ether macromonomer and water in a mass ratio of 1:0.8-2, heat to 55-65℃ and stir to dissolve, to obtain solution 1; (4) Add solutions A, B and C to solution 1; The A solution is: acrylic acid, chain transfer agent, water and functionalized graphene grafted with polymerizable double bonds, mixed well; the mass ratio of the acrylic acid, chain transfer agent, water and functionalized graphene grafted with polymerizable double bonds to the isopentenyl alcohol polyoxyethylene ether macromonomer in step (3) is 0.10-0.15: 0.001-0.003: 0.9-2.5: 0.0005-0.02:1; Solution B is an aqueous solution of oxidant with a mass concentration of 3.5%-8%, wherein the molar amount of oxidant is 1%-3% of the total molar amount of acrylic acid and isopentenyl polyoxyethylene ether macromonomer; The C solution is a reducing agent aqueous solution with a mass concentration of 0.5%-3%, wherein the molar amount of the reducing agent is 0.4%-1% of the total molar amount of acrylic acid and isopentenyl alcohol polyoxyethylene ether macromonomer; (5) The mixture is kept at 55-65℃ for 1-5 hours and then cooled to room temperature to obtain a slow-setting and reinforced graphene-polycarboxylate composite water-reducing agent; The mass ratio of γ-methacryloyloxypropyltrimethoxysilane to low-oxygen-content graphene is 2-8:1, and the oxygen atom content of the low-oxygen-content graphene is 2wt%~6wt%.

2. The preparation method according to claim 1, characterized in that... The reaction temperature in step (2) is 50-80℃, and the reaction time is 2-4 hours.

3. The preparation method according to claim 1, characterized in that... The chain transfer agent is mercaptopropionic acid, mercaptoacetic acid, mercaptoethanol, sodium 3-mercapto-1-propanesulfonate, or sodium hypophosphite.

4. The preparation method according to claim 1, characterized in that... The oxidant is hydrogen peroxide, ammonium persulfate, sodium persulfate, or potassium persulfate.

5. The preparation method according to claim 1, characterized in that... The reducing agent is vitamin C, sodium bisulfite formaldehyde, sodium bisulfite, or sodium metabisulfite.

6. The preparation method according to claim 1, characterized in that... The steps for adding solutions A, B, and C are as follows: simultaneously add solutions B and C, completing the addition in 3-4 hours; starting 5-15 minutes after adding solutions B and C, begin adding solution A, completing the addition of solution A in 2.5-3.5 hours.

7. A retarded and reinforced graphene-polycarboxylate composite water-reducing agent prepared by the preparation method according to any one of claims 1-6.

8. The application of the retarding and reinforcing graphene-polycarboxylate composite water-reducing agent of claim 7 in retarding and reinforcing concrete.

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