Polymer graft modified graphene oxide as well as preparation method and application thereof

Abstract

The invention discloses polymer graft modified graphene oxide as well as a preparation method and application thereof, and belongs to the field of building materials. The polymer grafted modified graphene oxide comprises graphene oxide and a polymer grafted on the surface of the graphene oxide through an ester bond, and the grafting mass ratio of the graphene oxide to the polymer is 1: (0.15-0.75). The preparation method of the polymer grafted modified graphene oxide comprises the following steps: firstly, carrying out esterification reaction on hydroxyl on the surface of graphene oxide and a reversible addition-fragmentation chain transfer polymerization (RAFT) chain transfer agent to generate GO of which the surface is grafted with the RAFT chain transfer agent; and adding a methacrylic acid monomer and an initiator, and carrying out RAFT polymerization on the surface of the GO to obtain a target product. The polymer grafting modified graphene oxide provided by the invention can achieve the effects of high polymer grafting ratio and capability of improving the fluidity of cement paste.

Description

Technical Field

[0001] The present invention relates to building materials, in particular to polymer-grafted modified graphene oxide and a preparation method and application thereof. Background Art

[0002] Cement concrete is the most widely used and most versatile basic material in the world today, playing a vital role in the process of industrialization and urbanization. However, defects such as low tensile strength, poor toughness, and easy cracking of traditional concrete affect its safety and durability. Improving the mechanical properties, volume stability, and durability of concrete has important theoretical value and practical application significance for improving its safe use and service life. Using nanotechnology to regulate the microstructure and aggregation state of cement hydration products to enhance the mechanical properties, volume stability, and durability of concrete is an important approach. Adding nanomaterials (such as nano-silica, nano-calcium carbonate, carbon nanotubes, and graphene) to cement-based materials can accelerate cement hydration, induce the formation of hydration products, reduce the porosity of cement-based materials, and increase density, thereby improving the mechanical and impermeability properties of cement concrete.

[0003] Graphene oxide (GO) nanosheets possess an extremely large specific surface area and excellent mechanical and flexibility properties. Their surface contains numerous reactive groups (hydroxyl, carboxyl, and epoxy groups), making them hydrophilic and capable of dispersing in water to form nanodispersions, making them easily composited with cement-based materials. Compared to zero-dimensional nanoparticles and one-dimensional nanotubes, GO nanosheets offer greater advantages in improving the mechanical, rheological, and permeability properties of cement matrices due to their two-dimensional interfacial interactions with the cement matrix. Furthermore, the numerous oxygen-containing reactive groups on the GO surface provide excellent reaction sites for subsequent chemical modification. Therefore, GO exhibits promising application prospects in improving the strength, toughness, permeability, and durability of cement-based materials.

[0004] Existing research has shown that the addition of small amounts of GO can significantly improve the mechanical properties of cement-based materials (compressive, flexural, tensile, and splitting strength). However, above a certain dosage, the strengthening and toughening effects decrease due to poor dispersion of GO in the cement matrix. Some researchers have confirmed that GO disperses poorly in high-alkali, high-salt cement pastes, forming aggregates and preventing the full realization of its strengthening and toughening effects.

[0005] In order to improve the dispersibility and stability of GO in alkaline cement paste, researchers modified the surface of GO with polymers and added it to cement-based materials. For example, GO physically modified with polyvinyl alcohol was added to cement-based materials to greatly increase the compressive and flexural strength of cement-based materials (Constr.Build.Mater., 2020, 258: 119647 (1-10)). GO was physically modified with polycarboxylic acid copolymers, which had a higher strengthening and toughening effect on cement-based materials than conventional GO (Constr.Build.Mater., 2018, 190: 150-163). CN118164706A discloses a high-performance concrete defoaming material based on graphene oxide, its preparation method and application. Block polyether is grafted on the surface of GO, and the modified GO material obtained is more easily attached to the surface of the bubble liquid film, specifically exerting defoaming performance, so that the concrete has higher hardening strength and durability. CN118164705A discloses a highly foam-stable and highly durable material, preparation method, and application suitable for high-altitude, low-pressure conditions. Not only is a block polyether grafted onto the GO surface, but the polyether ends are also ionized, enabling it to significantly stabilize the air content of concrete under harsh geographical conditions of high altitude and low pressure, thereby improving the durability of the concrete.

[0006] Existing technologies modify the surface of GO through physical modification or chemical grafting. Although it can improve the dispersibility of GO in cement paste to a certain extent, there are certain defects. The physical modification method has limited effect. The dispersibility and compatibility of GO in cement concrete cannot meet the requirements of high-performance cement concrete. The block polyether chemical grafting modification has a cumbersome synthesis process and uses a large amount of liquefied hydrocarbon hazardous chemicals. At the same time, a large number of side reactions occur in the solution phase, resulting in a low grafting density on the GO surface. Therefore, developing a controllable, high-grafting density GO surface grafting modification method and applying it to the preparation of modified GO is of great significance to improving the performance regulation of GO in cement concrete. Summary of the Invention

[0007] Purpose of the invention: The purpose of the present invention is to provide a polymer-grafted modified graphene oxide with a high polymer grafting ratio and the ability to improve the fluidity of cement paste.

[0008] Another object of the present invention is to provide a method for preparing polymer-grafted modified graphene oxide that is simple to operate and highly safe.

[0009] Another object of the present invention is to provide an application of polymer-grafted modified graphene oxide in cement mortar.

[0010] Technical solution: The polymer grafted modified graphene oxide described in the present invention includes graphene oxide and a polymer grafted on the surface of the graphene oxide through an ester bond, and the grafting mass ratio of the graphene oxide to the polymer is 1:(0.15-0.75).

[0011] The method for preparing polymer-grafted modified graphene oxide of the present invention comprises the following steps:

[0012] (1) GO is dispersed in an organic solvent, 2-(dodecylthiocarbonylthio)-2-methylpropionic acid, 4-dimethylaminopyridine and tricyclohexylcarbodiimide are added, the temperature is raised for reaction, centrifuged, washed and dried to obtain RAFT chain transfer agent-grafted GO;

[0013] (2) Dispersing the sample obtained in step (1) in an organic solvent, adding a polymerization monomer and an initiator, heating the mixture under nitrogen conditions, centrifuging, washing, and freeze-drying to obtain the target product.

[0014] Preferably, the GO surface oxidation degree in step (1) is 25.00-30.00%; the concentration of GO in the organic solvent is 5-50 g / L; the reaction temperature is 60-80° C., and the reaction time is 10-20 h.

[0015] Preferably, the amount of 2-(dodecylthiocarbonylthio)-2-methylpropionic acid in step (1) is 5.00-20.00% of the mass of GO; the molar ratio of 2-(dodecylthiocarbonylthio)-2-methylpropionic acid, 4-dimethylaminopyridine and tricyclohexylcarbodiimide is 1:(0.05-0.15):(1.20-1.50).

[0016] Preferably, the organic solvent in step (1) and step (2) is the same, which is one of N,N-dimethylformamide, toluene and xylene.

[0017] Preferably, the concentration of the RAFT chain transfer agent grafted GO in the organic solvent in step (2) is 5.00-50.00 g / L.

[0018] Preferably, the polymerization monomer in step (2) is one of methacrylic acid, methyl methacrylate, and ethyl methacrylate; and the amount of the polymerization monomer is 10.00-45.00% of the mass of the RAFT chain transfer agent grafted GO.

[0019] Preferably, the initiator in step (2) is an azo initiator, more preferably azobisisobutyl cyanide; the amount of the initiator used is 0.10-0.30% of the mass of the polymerization monomer.

[0020] Preferably, the reaction temperature in step (2) is 80-100° C., and the reaction time is 10-20 h.

[0021] The application of the polymer grafted modified graphene oxide described in the present invention includes the application of polymer grafted modified GO in cement-based materials.

[0022] Preferably, the amount of the polymer grafted modified GO in the cement-based material is 0.05-0.20% of the mass of the cement.

[0023] Principle of the invention: Reversible addition-fragmentation chain transfer (RAFT) polymerization is used to graft polymers onto the surface of GO. By designing and regulating the molecular chain structure of the grafted polymer, the polymer-grafted GO sheets are well dispersed and adsorbed in the cement paste, promoting cement hydration. The resulting hydration product is dense and uniform, improving the flexural and compressive strength of the cement-based material. Furthermore, due to the steric hindrance of the polymer chains adsorbed on the modified GO on the surface of the cement particles, the addition and adsorption of the polymer-grafted GO promotes the dispersion of cement particles, thus improving the fluidity of the cement-based material.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The method adopts the RAFT polymerization method to graft a polymethacrylic acid polymer with strong adsorption onto the surface of GO, so as to obtain a modified GO material with a high polymer grafting ratio, and the grafting mass fraction can reach up to about 75%; (2) The polymer grafted modified GO provided by the present invention is added to the cement mortar, which can effectively improve the fluidity of the cement paste, up to 20.4%, and promote the uniform dispersion of cement particles; (3) The polymer grafted modified GO provided by the present invention is added to the cement paste, which can greatly improve the compressive strength and flexural strength of the cement mortar, up to 13.3% and 98.1% respectively, and has excellent strengthening and toughening effects; compared with unmodified GO, the polymer grafted modified GO provided by the present invention is added to the cement mortar, which increases the compressive strength and flexural strength of the cement mortar by 8.0% and 59.6% respectively, and the flexural-compression ratio is increased by 48.0%. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be further described below in conjunction with embodiments.

[0026] The GO used in the present invention is prepared by improving the Hummers method. The main method steps are referenced to document 1 (Lv Xiang. Preparation and polymer modification of graphene. Wuhan University of Technology, 2011) and document 2 (Gong Shuishui, Determination of the content of carboxyl functional groups in graphene oxide by infrared spectroscopy. China Testing, 2016, 42 (4), 38-44), and graphene with different oxidation degrees, that is, GO with different hydroxyl contents, is prepared by changing the amount of potassium permanganate. In addition, the hydroxyl density on the GO surface is determined according to the peak area ratio of hydroxyl C-OH using infrared spectroscopy and X-ray photoelectron spectroscopy, and the test method is referenced to document 3 (Wei Gang. Determination of the surface oxidation degree of graphene oxide by infrared spectroscopy. Spectroscopy and Spectral Analysis, 2020, 40 (6), 1722-1727). The homemade GO used in the present invention has a sheet diameter of 5-20 μm and a specific surface area of ​​300-350 m 2 / g, and the surface oxidation degree is 26.52%.

[0027] All other chemical reagents used in the examples of the present invention were of analytical grade and purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0028] Example 1

[0029] The method for preparing polymer-grafted modified graphene oxide of the present invention comprises the following steps:

[0030] (1) 2.50 g of GO (surface oxidation degree 26.52%) was dispersed in 100 mL of N,N-dimethylformamide by ultrasonication to form a uniform suspension. 0.38 g of 2-(dodecylthiocarbonylthio)-2-methylpropionic acid, 0.013 g of 4-dimethylaminopyridine, and 0.29 g of tricyclohexylcarbodiimide were added to the suspension. The mixture was stirred at 70 °C for 15 h, centrifuged and washed until the supernatant was colorless, vacuum dried, and weighed to obtain 2.85 g of RAFT chain transfer agent-grafted GO. The obtained sample was named RAFT-GO.

[0031] (2) 2.85 g of RAFT-GO obtained in step (1) was ultrasonically dispersed in 100 mL of N,N-dimethylformamide, 0.95 g of methacrylic acid and 0.0019 g of azobisisobutyl cyanide were added, and nitrogen was continuously bubbled through the mixture. The mixture was stirred and reacted at 90°C for 15 hours, centrifuged and washed until the supernatant was colorless, and freeze-dried to obtain 3.72 g of polymer-grafted modified graphene oxide A, which was the target product.

[0032] Thermogravimetric analysis of the target product showed that the mass ratio of GO to the grafted polymer in the polymer-grafted modified graphene oxide of the present invention was 1:0.49.

[0033] Example 2

[0034] The method for preparing polymer-grafted modified graphene oxide of the present invention comprises the following steps:

[0035] (1) 2.50 g of GO (surface oxidation degree 26.52%) was dispersed in 100 mL of N,N-dimethylformamide by ultrasonication to form a uniform suspension. 0.15 g of 2-(dodecylthiocarbonylthio)-2-methylpropionic acid, 0.0075 g of 4-dimethylaminopyridine, and 0.12 g of tricyclohexylcarbodiimide were added to the suspension. The mixture was stirred at 80 °C for 15 h, centrifuged and washed until the supernatant was colorless, vacuum dried, and weighed to obtain 2.62 g of RAFT chain transfer agent-grafted graphene oxide. The obtained sample was named RAFT-GO.

[0036] (2) 2.62 g of RAFT-GO obtained in step (1) was ultrasonically dispersed in 100 mL of N,N-dimethylformamide, 0.29 g of methacrylic acid and 0.0009 g of azobisisobutylcyanide were added, and nitrogen was continuously bubbled through the mixture. The mixture was stirred and reacted at 100 ° C for 15 hours, centrifuged and washed until the supernatant was colorless, and freeze-dried to obtain 2.88 g of polymer-grafted modified graphene oxide B, which was the target product.

[0037] Thermogravimetric analysis of the target product showed that the mass ratio of GO to the grafted polymer in the polymer-grafted modified graphene oxide of the present invention was 1:0.16.

[0038] Example 3

[0039] The method for preparing polymer-grafted modified graphene oxide of the present invention comprises the following steps:

[0040] (1) 2.50 g of GO (surface oxidation degree 26.52%) was dispersed in 100 mL of N,N-dimethylformamide by ultrasonication to form a uniform suspension. 0.48 g of 2-(dodecylthiocarbonylthio)-2-methylpropionic acid, 0.0096 g of 4-dimethylaminopyridine, and 0.33 g of tricyclohexylcarbodiimide were added to the suspension. The mixture was stirred at 60 °C for 20 h, centrifuged and washed until the supernatant was colorless, vacuum dried, and weighed to obtain 2.92 g of RAFT chain transfer agent-grafted graphene oxide. The obtained sample was named RAFT-GO.

[0041] (2) 2.92 g of RAFT-GO obtained in step (1) was ultrasonically dispersed in 100 mL of N,N-dimethylformamide, 1.31 g of methacrylic acid and 0.0015 g of azobisisobutylcyanide were added, and nitrogen was continuously bubbled through the mixture. The mixture was stirred and reacted at 80°C for 20 hours, centrifuged and washed until the supernatant was colorless, and freeze-dried to obtain 4.19 g of polymer-grafted modified graphene oxide C, the target product.

[0042] Thermogravimetric analysis of the target product showed that the mass ratio of GO to the grafted polymer in the polymer-grafted modified graphene oxide of the present invention was 1:0.71.

[0043] Example 4

[0044] The method for preparing polymer-grafted modified graphene oxide of the present invention comprises the following steps:

[0045] (1) 0.52 g of GO (surface oxidation degree 26.52%) was dispersed in 100 mL of toluene by ultrasonication to form a uniform suspension. 0.078 g of 2-(dodecylthiothiocarbonylthio)-2-methylpropionic acid, 0.0039 g of 4-dimethylaminopyridine, and 0.066 g of tricyclohexylcarbodiimide were added to the suspension. The mixture was stirred at 70 °C for 20 h, centrifuged and washed until the supernatant was colorless, vacuum dried, and weighed to obtain 0.58 g of RAFT chain transfer agent-grafted graphene oxide. The obtained sample was named RAFT-GO.

[0046] (2) 0.58 g of RAFT-GO obtained in step (1) was ultrasonically dispersed in 100 mL of toluene, 0.20 g of methyl methacrylate and 0.0004 g of azobisisobutylcyanide were added, and nitrogen was continuously bubbled through the mixture. The mixture was stirred and reacted at 80° C. for 20 hours, centrifuged and washed until the supernatant was colorless, and freeze-dried to obtain 0.75 g of polymer-grafted modified graphene oxide D, the target product.

[0047] Thermogravimetric analysis of the target product showed that the mass ratio of GO to the grafted polymer in the polymer-grafted modified graphene oxide of the present invention was 1:0.48.

[0048] Example 5

[0049] The method for preparing polymer-grafted modified graphene oxide of the present invention comprises the following steps:

[0050] (1) 0.52 g of GO (surface oxidation degree 26.52%) was ultrasonically dispersed in 100 mL of xylene to form a uniform suspension. 0.078 g of 2-(dodecylthiothiocarbonylthio)-2-methylpropionic acid, 0.0039 g of 4-dimethylaminopyridine, and 0.066 g of tricyclohexylcarbodiimide were added to the suspension. The mixture was stirred at 70 °C for 20 h, centrifuged and washed until the supernatant was colorless, vacuum dried, and weighed to obtain 0.57 g of RAFT chain transfer agent-grafted graphene oxide. The obtained sample was named RAFT-GO.

[0051] (2) 0.57 g of RAFT-GO obtained in step (1) was ultrasonically dispersed in 100 mL of xylene, 0.20 g of ethyl methacrylate and 0.0004 g of azobisisobutyl cyanide were added, and nitrogen was continuously bubbled through the mixture. The mixture was stirred and reacted at 90° C. for 20 hours, centrifuged and washed until the supernatant was colorless, and freeze-dried to obtain 0.73 g of polymer-grafted modified graphene oxide E, which was the target product.

[0052] Thermogravimetric analysis of the target product showed that the mass ratio of GO to the grafted polymer in the polymer-grafted modified graphene oxide of the present invention was 1:0.45.

[0053] Example 6

[0054] The method for preparing polymer-grafted modified graphene oxide of the present invention comprises the following steps:

[0055] (1) 4.80 g of GO (surface oxidation degree 26.52%) was dispersed in 100 mL of N,N-dimethylformamide by ultrasonication to form a uniform suspension. 0.25 g of 2-(dodecylthiothiocarbonylthio)-2-methylpropionic acid, 0.012 g of 4-dimethylaminopyridine, and 0.21 g of tricyclohexylcarbodiimide were added to the suspension. The mixture was stirred at 70 °C for 15 h, centrifuged and washed until the supernatant was colorless, vacuum dried, and weighed to obtain 5.00 g of RAFT chain transfer agent-grafted graphene oxide. The obtained sample was named RAFT-GO.

[0056] (2) 5.00 g of RAFT-GO obtained in step (1) was ultrasonically dispersed in 100 mL of N,N-dimethylformamide, 0.50 g of methacrylic acid and 0.0010 g of azobisisobutylcyanide were added, and nitrogen was continuously bubbled through the mixture. The mixture was stirred and reacted at 90 ° C for 15 hours, centrifuged and washed until the supernatant was colorless, and freeze-dried to obtain 5.44 g of polymer-grafted modified graphene oxide F, which was the target product.

[0057] Thermogravimetric analysis of the target product showed that the mass ratio of GO to the grafted polymer in the polymer-grafted modified graphene oxide of the present invention was 1:0.16.

[0058] Example 7

[0059] The method for preparing polymer-grafted modified graphene oxide of the present invention comprises the following steps:

[0060] (1) 2.50 g of GO (surface oxidation degree 26.52%) was dispersed in 100 mL of N,N-dimethylformamide by ultrasonication to form a uniform suspension. 0.19 g of 2-(dodecylthiocarbonylthio)-2-methylpropionic acid, 0.0095 g of 4-dimethylaminopyridine, and 0.16 g of tricyclohexylcarbodiimide were added to the suspension. The mixture was stirred at 70 °C for 15 h, centrifuged and washed until the supernatant was colorless, vacuum dried, and weighed to obtain 2.67 g of RAFT chain transfer agent-grafted graphene oxide. The obtained sample was named RAFT-GO.

[0061] (2) 2.67 g of RAFT-GO obtained in step (1) was ultrasonically dispersed in 100 mL of N,N-dimethylformamide, 0.95 g of methacrylic acid and 0.0019 g of azobisisobutylcyanide were added, and nitrogen was continuously bubbled through the mixture. The mixture was stirred and reacted at 90°C for 15 hours, centrifuged and washed until the supernatant was colorless, and freeze-dried to obtain 3.55 g of polymer-grafted modified graphene oxide G, which was the target product.

[0062] Thermogravimetric analysis of the target product showed that the mass ratio of GO to the grafted polymer in the polymer-grafted modified graphene oxide of the present invention was 1:0.46.

[0063] Example 8

[0064] The method for preparing polymer-grafted modified graphene oxide of the present invention comprises the following steps:

[0065] (1) 2.50 g of GO (surface oxidation degree 26.52%) was dispersed in 100 mL of N,N-dimethylformamide by ultrasonication to form a uniform suspension. 0.18 g of 2-(dodecylthiothiocarbonylthio)-2-methylpropionic acid, 0.0095 g of 4-dimethylaminopyridine, and 0.16 g of tricyclohexylcarbodiimide were added to the suspension. The mixture was stirred at 70 °C for 15 h, centrifuged and washed until the supernatant was colorless, vacuum dried, and weighed to obtain 2.66 g of RAFT chain transfer agent-grafted graphene oxide. The obtained sample was named RAFT-GO.

[0066] (2) 2.66 g of RAFT-GO obtained in step (1) was ultrasonically dispersed in 100 mL of N,N-dimethylformamide, 1.17 g of methacrylic acid and 0.0019 g of azobisisobutylcyanide were added, and nitrogen was continuously bubbled through the mixture. The mixture was stirred and reacted at 90°C for 15 hours, centrifuged and washed until the supernatant was colorless, and freeze-dried to obtain 3.75 g of polymer-grafted modified graphene oxide H, the target product.

[0067] Thermogravimetric analysis of the target product showed that the mass ratio of GO to the grafted polymer in the polymer-grafted modified graphene oxide of the present invention was 1:0.51.

[0068] In order to intuitively reflect the experimental conditions of Examples 1-8, their main parameters are shown in Table 1.

[0069] Table 1 Main parameters of sample AF

[0070]

[0071] Comparative Example 1

[0072] 2.50 g of GO (surface oxidation degree 26.52%) was ultrasonically dispersed in 100 mL of N,N-dimethylformamide to form a homogeneous suspension. To this suspension were added 0.38 g of 2-(dodecylthiothiocarbonylthio)-2-methylpropionic acid, 0.013 g of 4-dimethylaminopyridine, and 0.29 g of tricyclohexylcarbodiimide. The mixture was stirred at 70°C for 15 hours. The supernatant was then centrifuged and washed until colorless, dried under vacuum, and weighed to yield 2.85 g of RAFT chain transfer agent-grafted graphene oxide, designated sample S1. Thermogravimetric analysis of sample S1 revealed a mass ratio of GO to grafted polymer of 1:0.14.

[0073] Comparative Example 2

[0074] 2.50 g of GO (surface oxidation degree 26.52%) was ultrasonically dispersed in 100 mL of N,N-dimethylformamide. 0.95 g of methacrylic acid and 0.0019 g of azobisisobutylcyanide were added. Nitrogen was continuously bubbled through the solution, and the mixture was stirred at 90°C for 15 hours. The mixture was then centrifuged, washed, and freeze-dried until the supernatant became colorless. This yielded 3.05 g of modified graphene oxide, designated S2. Thermogravimetric analysis of sample S2 revealed a mass ratio of GO to grafted polymer of 1:0.23.

[0075] Comparative Example 3

[0076] The GO prepared by the improved Hummers method was used as sample S3 of comparative example 3 without any treatment.

[0077] Performance tests were conducted on samples AF and S1-S3, including the effects of the samples on the fluidity of cement paste and the effects of the samples on the compressive and flexural strength of cement mortar after being added to the cement mortar.

[0078] Cement paste fluidity test: The test was conducted in accordance with the relevant provisions of GB / T 8077-2000, "Test Method for Homogeneity of Concrete Admixtures." Samples AF and S1-S3 were tested for cement paste fluidity. The cement used was 300g of Jiangnan Onoda P·II52.5 cement, with a mixing amount of 87g of water. The polycarboxylate superplasticizer used was provided by Jiangsu Subote New Materials Co., Ltd., at a dosage of 0.10% of the cement mass. The sample to be tested was pre-dispersed in water to prepare a suspension with a mass concentration of 1%. The suspension was then added to the cement paste according to the "solid content" in Table 2, divided by 1%. The test results are shown in Table 2.

[0079] Cement Mortar Strength Test: The test was conducted in accordance with the relevant provisions of GB / T 17671-1999, "Test Method for Cement Mortar Strength (ISO Method)." The test samples were concreted and tested for compressive and flexural strength. The cement used was 450g of Konan Onoda P.II 52.5 cement; 1350g of standard sand; and 135g of mixing water. The polycarboxylate superplasticizer used was provided by Jiangsu Subote New Materials Co., Ltd., at a dosage of 0.16% of the cement mass. The test sample was pre-dispersed in water to prepare a 1% suspension. The suspension was then added to the cement mortar, calculated by dividing the "solid content" in Table 3 by 1%. Compressive and flexural strength tests were conducted in accordance with the test methods in GB / T 17671-1999, "Test Method for Cement Mortar Strength (ISO Method)." The test blocks were placed in a standard curing room and then tested after 28 days of curing. The test results are shown in Table 3.

[0080] Table 2 Effect of different samples on cement paste fluidity

[0081]

[0082]

[0083] Note: The "baseline" in the table refers to the control group sample without any modified or unmodified graphene sample, that is, traditional hydraulic concrete; "solid content" refers to the amount of sample converted into its effective content (generally called solid content) in cement (expressed as mass fraction), solid content = sample content × solid content.

[0084] From the cement paste fluidity data in Table 2, it can be seen that the polymer grafted modified GO (i.e., samples AF) prepared by RAFT grafting polymerization can improve the fluidity of cement paste. This is mainly because after the polymer is grafted onto the GO surface, the polymer grafted modified GO can be efficiently adsorbed to the surface of cement particles, thereby playing a certain dispersing role. And the data in Table 2 can draw a conclusion that when the dosage of polymer grafted modified GO is in the range of 0.05-0.20%, the higher the dosage, the better the effect of improving the fluidity of cement paste. The higher the proportion of polymer in the polymer grafted modified GO, the better the effect of improving the fluidity of cement paste (the polymer proportion in samples B, A, and C increases in turn). The longer the polymer chain in the polymer grafted modified GO, the better the effect of improving the fluidity of cement paste (the polymer chain length in samples A, G, and H increases in turn). Samples S1 and S2 used as reference for comparison slightly reduced the fluidity of the cement paste, while the addition of unmodified graphene oxide S3 significantly reduced the fluidity of the cement paste. This was mainly due to the ultrafine powder characteristics of the unmodified GO, which made the dispersion of the cement paste more difficult.

[0085] Table 3 Effect of different samples on cement mortar strength

[0086]

[0087] Note: The "baseline" in the table refers to the control group sample without any modified or unmodified graphene sample, that is, traditional hydraulic concrete; "solid content" refers to the amount of sample converted into its effective content (generally called solid content) in cement (expressed as mass fraction), solid content = sample content × solid content.

[0088] From the cement mortar strength data in Table 3, it can be seen that polymer-grafted modified GO prepared by RAFT graft polymerization can improve the compressive and flexural strength of cement mortar. The best one is sample A prepared in Example 1. Compared with the benchmark sample, at a solid content of 0.2%, the compressive strength increased by 13.3%, the flexural strength increased by 98.1%, and the flexural-compression ratio increased by more than 70%, showing excellent strengthening and toughening effects. At the same time, the data in Table 3 can be concluded that when the content of polymer-grafted modified GO is in the range of 0.05-0.20%, the higher the content, the better the strengthening and toughening effect on cement mortar. As the polymer ratio in polymer-grafted modified GO increases, the strengthening and toughening effect on cement mortar shows a trend of first increasing and then decreasing (the polymer ratio in samples B, A, and C increases in turn). The longer the polymer chain in polymer-grafted modified GO, the worse the strengthening and toughening effect on cement mortar (the polymer chain length in samples A, G, and H increases in turn). The modified graphene oxides S1, S2 and unmodified graphene oxide used as reference for comparison also have the effect of strengthening and toughening, but the improvement in the fold-to-compression ratio is small, and the effect is only 70-90% of the performance effect of the polymer grafted modified graphene oxide.

Claims

1. A polymer grafted modified graphene oxide, characterized in that: The invention comprises graphene oxide and a polymer grafted on the surface of the graphene oxide through an ester bond, wherein the grafting mass ratio of the graphene oxide to the polymer is 1:(0.15-0.75).

2. A method for preparing polymer-grafted modified graphene oxide according to claim 1, characterized in that: The following steps are involved: (1) GO is dispersed in an organic solvent, 2-(dodecylthiocarbonylthio)-2-methylpropionic acid, 4-dimethylaminopyridine and tricyclohexylcarbodiimide are added, the temperature is raised for reaction, centrifugation, washing and drying are performed to obtain RAFT chain transfer agent-grafted graphene oxide; (2) Dispersing the sample obtained in step (1) in an organic solvent, adding a polymerization monomer and an initiator, heating the mixture under nitrogen conditions, centrifuging, washing, and freeze-drying to obtain the target product.

3. The preparation method according to claim 2, characterized in that The GO surface oxidation degree described in step (1) is 25.00-30.00%; the concentration of GO in the organic solvent is 5-50 g / L; the reaction temperature is 60-80° C., and the reaction time is 10-20 h.

4. The preparation method according to claim 2, characterized in that The amount of 2-(dodecylthiocarbonylthio)-2-methylpropionic acid used in step (1) is 5.00-20.00% of the mass of GO; the molar ratio of 2-(dodecylthiocarbonylthio)-2-methylpropionic acid, 4-dimethylaminopyridine and tricyclohexylcarbodiimide is 1:(0.05-0.15):(1.20-1.50).

5. The preparation method according to claim 2, characterized in that The organic solvent in step (1) and step (2) is the same, which is one of N,N-dimethylformamide, toluene and xylene.

6. The preparation method according to claim 2, characterized in that The concentration of the RAFT chain transfer agent grafted graphene oxide in the organic solvent in step (2) is 5.00-50.00 g / L.

7. The preparation method according to claim 2, characterized in that The polymerization monomer in step (2) is one of methacrylic acid, methyl methacrylate, and ethyl methacrylate; the amount of the polymerization monomer is 10.00-45.00% of the mass of the RAFT chain transfer agent grafted graphene oxide.

8. The preparation method according to claim 2, characterized in that The initiator in step (2) is an azo initiator; the amount of the initiator used is 0.10-0.30% of the mass of the polymerization monomer.

9. Use of the polymer grafted modified graphene oxide according to claim 1 in cement-based materials.

10. The use according to claim 9, characterized in that The content of the polymer grafted modified graphene oxide in the cement-based material is 0.05-0.20% of the mass of the cement.

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