Preparation method of organic-inorganic sol-gel and application of organic-inorganic sol-gel in fiber modification

Abstract

The invention belongs to the technical field of composite materials, and particularly relates to a preparation method of organic-inorganic sol-gel and application of the organic-inorganic sol-gel in fiber modification. The preparation method of the organic-inorganic sol-gel provided by the invention comprises the following steps: (1) carrying out hydrolysis reaction on tetraethoxysilane, and then adding a coupling agent to carry out condensation reaction, so as to obtain a siloxane (Si-O-Si) network; and (2) adding waterborne polyurethane into the siloxane (Si-O-Si) network obtained in the step (1), and carrying out a cross-linking reaction. The organic-inorganic sol-gel prepared by the preparation method disclosed by the invention realizes tight crosslinking of organic components and inorganic components, and a coating formed by using the organic-inorganic sol-gel not only has good flexibility and adhesive ability of the organic components, but also has high hardness of the inorganic components and good compatibility with a cement matrix.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials, and particularly relates to an organic-inorganic sol-gel preparation method and its application in fiber modification. Background Art

[0002] In the composite material system of steel fiber reinforced concrete, the strengthening effect of steel fibers mainly depends on the effective stress transfer between them and the matrix. However, the surface of steel fibers is mostly composed of metallic iron phase and low-active oxide layer, and its chemical inertness makes it difficult to provide effective nucleation sites for hydration products on the surface, delaying or reducing the directional deposition and growth of calcium silicate hydrate gel in the interfacial zone, resulting in a loose structure, high porosity, and insufficient interfacial bonding strength in the interfacial transition zone between steel fibers and concrete matrix. The ultra-high mechanical properties of steel fibers are not fully utilized, and when there are chloride ions or other corrosive media in the environment, this defect channel will accelerate the diffusion of corrosive media to the surface of steel fibers, affecting the durability of the material.

[0003] Chemical coating technology can improve the chemical activity of the steel fiber surface, induce or promote the attachment and growth of hydration products on the fiber surface, thereby enhancing the denseness of the interfacial transition zone and improving the bonding between steel fibers and the concrete matrix. Commonly used chemical coatings are divided into organic coatings and inorganic coatings. Organic coatings (such as polyurethane, PU) have good flexibility, can effectively absorb stress, and reduce the generation of cracks. However, the compatibility between organic components and inorganic mineral phases is poor. In contrast, inorganic coatings (such as tetraethoxysilane, TEOS) have the advantages of high hardness, wear resistance, and good compatibility with the cement matrix, but organic coatings are very brittle and prone to cracking under load.

[0004] Developing an organic-inorganic hybrid coating to improve the chemical compatibility at the interface of multiphase materials and enhance the interfacial bonding performance between steel fibers and the concrete matrix is a powerful guarantee for improving the stress transfer efficiency of steel fibers in the cement matrix and the long-term service ability of concrete. However, the chemical properties of organic materials and inorganic materials are significantly different. In a simple blend or copolymer system, the interaction between organic and inorganic components is weak, it is difficult to achieve uniform dispersion and strong chemical cross-linking at the molecular level, and phase separation is likely to occur.

[0005] Therefore, how to closely combine inorganic materials and organic materials is an urgent problem to be solved at present. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems in the related art to some extent. To this end, an embodiment of the present invention provides a method for preparing an organic-inorganic sol-gel, and the obtained sol-gel realizes the tight cross-linking of organic components and inorganic components. The coating formed on the surface of steel fibers using this sol-gel not only has the good flexibility and adhesion ability of the organic components, but also has the high hardness of the inorganic components and good compatibility with the cement matrix.

[0007] The method for preparing an organic-inorganic sol-gel according to an embodiment of the present invention includes the following steps:

[0008] (1) Hydrolyze tetraethoxysilane and then add a coupling agent for condensation reaction to obtain a silicone network;

[0009] (2) Add aqueous polyurethane to the silicone network obtained in step (1) for cross-linking reaction.

[0010] The advantages and technical effects brought by the method for preparing an organic-inorganic sol-gel according to an embodiment of the present invention are as follows: 1. In the method of the embodiment of the present invention, an organic-inorganic hybrid sol-gel is prepared by the sol-gel method, and the organic components and inorganic components are tightly cross-linked into an interpenetrating structure at the nanoscale, thereby effectively avoiding the phase separation problem that easily occurs in organic or inorganic coatings in a blend or copolymer system; 2. In the method of the embodiment of the present invention, the prepared organic-inorganic sol-gel is used to prepare a coating for steel fibers, which not only endows the coating with the good flexibility and adhesion ability of the organic components, but also endows the coating with the high hardness of the inorganic components and good compatibility with the cement matrix; the prepared organic-inorganic hybrid coating can significantly improve the bonding performance between steel fibers and the concrete interface, and improve the interface stability and mechanical properties of steel fiber reinforced concrete materials.

[0011] In some embodiments, in step (1), the hydrolysis reaction includes: mixing tetraethoxysilane and ethanol, first adding deionized water and then adding an acid solution to adjust the pH for hydrolysis reaction.

[0012] In some embodiments, the volume ratio of tetraethoxysilane, ethanol and deionized water is 1:(2-4):(1-3);

[0013] and / or, the acid solution includes at least one of acetic acid solution, citric acid solution, oxalic acid solution or glycolic acid solution;

[0014] and / or, adjust the pH to 4-5;

[0015] and / or, the temperature of the hydrolysis reaction is 25-40°C, and the time of the hydrolysis reaction is 3-4 h;

[0016] And / or, the hydrolysis reaction is carried out under stirring, and the rotation speed of the stirring is 500 - 700 rpm.

[0017] In some embodiments, in the step (1), the coupling agent includes at least one of γ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, or 3-glycidoxypropyltriethoxysilane;

[0018] And / or, the molar ratio of the tetraethoxysilane to the coupling agent is (10 - 20):1;

[0019] And / or, the temperature of the condensation reaction is 25 - 40 °C, and the time of the condensation reaction is 0.5 - 1.5 h.

[0020] In some embodiments, in the step (2), it further includes: first diluting the aqueous polyurethane with deionized water and then carrying out a cross-linking reaction with the silicone network.

[0021] In some embodiments, in the step (2), the solid content of the aqueous polyurethane is 50 - 70%;

[0022] And / or, in the step (2), the volume ratio of the tetraethoxysilane to the aqueous polyurethane is 1:(0.5 - 2).

[0023] In some embodiments, in the step (2), the temperature of the cross-linking reaction is 25 - 40 °C, and the time of the cross-linking reaction is 0.5 - 2 h;

[0024] And / or, the reaction is carried out under stirring, and the rotation speed of the stirring is 500 - 700 rpm.

[0025] And / or, the aqueous polyurethane is added to the silicone network step by step.

[0026] The embodiment of the present invention also provides an organic-inorganic sol-gel prepared by the above method.

[0027] The embodiment of the present invention also provides the application of the organic-inorganic sol-gel prepared by the above method or the above organic-inorganic sol-gel in fibers.

[0028] In some embodiments, the application includes coating the organic-inorganic sol-gel on the surface of the fiber and obtaining an organic-inorganic sol-gel coating after standing and drying. Description of the Drawings

[0029] Figure 1 It is a schematic flow chart of preparing the organic-inorganic sol-gel and modifying the steel fiber in Example 1;

[0030] Figure 2It is a schematic diagram of the contact angle of unmodified steel fibers and organo-inorganic sol-gel modified steel fibers;

[0031] Figure 3 are the interfacial bond strengths of unmodified steel fibers and organo-inorganic sol-gel modified steel fibers with the concrete matrix;

[0032] Figure 4 are the micrographs of the interfacial transition zone between unmodified steel fibers and organo-inorganic sol-gel modified steel fibers and the concrete matrix. Detailed implementation mode

[0033] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0034] The preparation method of the organo-inorganic sol-gel in the embodiments of the present invention includes the following steps:

[0035] (1) Hydrolyze tetraethoxysilane (TEOS) and then add a coupling agent (KH-550) for condensation reaction to obtain a silicone network;

[0036] (2) Add waterborne polyurethane (PU) to the silicone network obtained in step (1) for crosslinking reaction.

[0037] The preparation method of the organo-inorganic sol-gel in the embodiments of the present invention uses a sol-gel method to prepare an organo-inorganic hybrid sol-gel, which tightly crosslinks the organic component and the inorganic component into a nanoscale interpenetrating structure, thus effectively avoiding the phase separation problem that easily occurs in the organic or inorganic coating in the blend or copolymer system; using the prepared organo-inorganic sol-gel to prepare the coating of steel fibers not only endows the coating with good flexibility and adhesion ability of the organic component, but also endows the coating with high hardness of the inorganic component and good compatibility with the cement matrix. The prepared organo-inorganic hybrid coating can significantly improve the bonding performance between the steel fibers and the concrete interface, and improve the interface stability and mechanical properties of the steel fiber reinforced concrete material.

[0038] In some embodiments, preferably, in step (1), the hydrolysis reaction includes: mixing tetraethoxysilane and ethanol, first adding deionized water and then adding acetic acid solution to adjust the pH for hydrolysis reaction. Further preferably, the deionized water and the acid solution are added dropwise.

[0039] In some embodiments, preferably, the volume ratio of tetraethoxysilane, ethanol and deionized water is 1:(2-4):(1-3);

[0040] And / or, the acid solution includes at least one of acetic acid solution, citric acid solution, oxalic acid solution or glycolic acid solution;

[0041] And / or, adjust the pH to 4 - 5;

[0042] And / or, the temperature of the hydrolysis reaction is 25 - 40 °C, and the time of the hydrolysis reaction is 3 - 4 h;

[0043] And / or, the hydrolysis reaction is carried out under stirring, and the rotation speed of the stirring is 500 - 700 rpm.

[0044] In some embodiments, preferably, in the step (1), the coupling agent includes at least one of γ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane or 3-glycidylpropyltriethoxysilane;

[0045] And / or, the molar ratio of the tetraethoxysilane to the coupling agent is (10 - 20):1;

[0046] And / or, the temperature of the condensation reaction is 25 - 40 °C, and the time of the condensation reaction is 0.5 - 1.5 h.

[0047] In the embodiments of the present invention, the content of the coupling agent is optimized, which can not only ensure the formation of the silicone network but also not interfere too much with the bonding performance of the formed coating; if the dosage of the coupling agent is too low, the interfacial adhesion of the formed coating may be improved, but the silicone network is not dense enough; if the dosage of the coupling agent is too high, the interfacial bonding performance is insufficient, and the formed coating may become relatively brittle and is prone to cracking or peeling.

[0048] In some embodiments, preferably, in the step (2), it further includes: first diluting the waterborne polyurethane with deionized water and then carrying out a crosslinking reaction with the silicone network. The dosage of deionized water does not need to be particularly limited as long as it can reduce the viscosity of the waterborne polyurethane; diluting the waterborne polyurethane with water to reduce its viscosity before carrying out the crosslinking reaction is beneficial to the progress of the crosslinking reaction.

[0049] In some embodiments, preferably, in the step (2), the solid content of the waterborne polyurethane is 50 - 70%; and / or, in the step (2), the volume ratio of the tetraethoxysilane to the waterborne polyurethane is 1:(0.5 - 2). Further preferably, the solid content of the waterborne polyurethane is 60%, and the volume ratio of the tetraethoxysilane to the waterborne polyurethane is 1:1.7.

[0050] In the embodiments of the present invention, waterborne polyurethane and tetraethoxysilane are preferably selected, which is beneficial to form a uniform organic-inorganic composite coating, taking into account hardness and flexibility, and improving the bonding strength at the interface between steel fibers and concrete and the durability of the coating. If the dosage of waterborne polyurethane is too low, the formed coating has enhanced rigidity, but the flexibility and interfacial adhesion decrease, which may lead to coating cracking or interfacial failure. If the dosage of waterborne polyurethane is too high, the formed coating has enhanced flexibility, but the siloxane network is insufficient, and the coating hardness and durability decrease, which may lead to coating failure.

[0051] In some embodiments, preferably, in step (2), the temperature of the crosslinking reaction is 25-40°C, and the time of the crosslinking reaction is 0.5-2 h;

[0052] And / or, the reaction is carried out under stirring, and the rotation speed of the stirring is 500-700 rpm.

[0053] And / or, the waterborne polyurethane is added step by step into the siloxane network.

[0054] The embodiments of the present invention also provide an organic-inorganic sol-gel prepared by the above method.

[0055] The embodiments of the present invention also provide the application of the organic-inorganic sol-gel prepared by the above method or the above organic-inorganic sol-gel in fibers.

[0056] In some embodiments, preferably, the application includes coating the organic-inorganic sol-gel on the surface of the fiber, and after standing and drying, an organic-inorganic sol-gel coating is obtained. Further preferably, the fiber includes steel fibers, and the application includes: first soaking the steel fibers in a sodium hydroxide solution to remove lipids and impurities on the surface of the steel fibers, and then washing with water and ethanol to remove the residual sodium hydroxide solution; the standing time is 10-14 h, the drying temperature is 70-90°C, and the drying time is 2-4 h.

[0057] The technical solutions of the present invention will be described in detail below in conjunction with specific embodiments and drawings.

[0058] Example 1

[0059] In this example, the process for preparing the organic-inorganic sol-gel and modifying the steel fibers is as Figure 1 shown:

[0060] (1) Mix 50 mL of tetraethoxysilane (0.224 mol) and 150 mL of ethanol, stir with a magnetic stirrer at room temperature for 10 minutes at a stirring rate of 600 rpm; dropwise add 100 mL of deionized water to the mixed solution of tetraethoxysilane (TEOS) and ethanol, control to complete within 10 minutes, and then dropwise add acetic acid solution to adjust the pH value of the solution to 4; maintain a stirring rate of 600 rpm during the addition process, and then continue to stir with a magnetic stirrer at a rate of 600 rpm for 3 hours of hydrolysis reaction at room temperature;

[0061] (2) After hydrolysis is completed, add 3 mL (0.013 mol) of γ-aminopropyltriethoxysilane (KH550), and continue to stir at room temperature for 1 hour;

[0062] (3) In another container, mix 85 mL of aqueous polyurethane with a solid content of 60% and 50 mL of deionized water at room temperature and stir for 20 minutes at 400 rpm;

[0063] (4) Slowly add the diluted aqueous polyurethane to the sol, add it step by step over 15 minutes, ensure sufficient stirring after each addition, and continue to stir at 600 rpm for 1 hour;

[0064] (5) Immerse the steel fibers in sodium hydroxide solution for 30 minutes to remove surface lipids and impurities, and then wash the steel fibers with water and ethanol to remove the residual NaOH;

[0065] (6) Then evenly coat the prepared sol on the surface of the steel fibers and let it stand at room temperature for 12 hours to form a sol-gel coating, and then dry the steel fibers in a vacuum drying oven at 80 °C for 3 hours to complete the modification of the steel fiber organic-inorganic sol-gel coating.

[0066] Example 2

[0067] The preparation method of this example is the same as that of Example 1, except that the volume ratio of tetraethoxysilane (TEOS) to aqueous polyurethane (PU) is 1:0.67.

[0068] Example 3

[0069] The preparation method of this example is the same as that of Example 1, except that the volume ratio of tetraethoxysilane (TEOS) to aqueous polyurethane (PU) is 1:1.5.

[0070] Comparative Example 1

[0071] Prepare a tris(hydroxymethyl)aminomethane (TRIS) solution with a pH of 7.8 and a concentration of 0.01 mol / L (1.21 g / L) as a buffer solution. Add dopamine hydrochloride to the buffer solution to prepare a 3 g / L dopamine solution. Immerse the steel fibers in the prepared dopamine solution and soak for 24 h. Then take out the steel fibers from the dopamine solution and rinse with water to remove the residual dopamine. After that, dry the steel fibers at 60 °C for 24 h and weigh the steel fibers every 2 h until the difference between adjacent weighing results is less than 0.01%, obtaining steel fibers with a surface modified by dopamine.

[0072] Comparative Example 2

[0073] (1) Clean the steel fibers with sodium hydroxide solution to remove the grease and impurities on their surfaces, and then rinse with deionized water until the pH value of the final rinse water reaches about 7, and then air-dry the steel fibers.

[0074] (2) Use 1000 ml of absolute ethanol as a solvent, add 80 ml of tetraethyl orthosilicate and 1% (by mass of the solvent) of the ionic surfactant cetyltrimethylammonium bromide. To provide an alkaline reaction environment, add 40 ml of concentrated ammonia, and ultrasonically process the mixed solution for 30 min to obtain a surface treatment agent.

[0075] (3) Immerse the air-dried steel fibers in step (1) into the surface treatment agent obtained in step (2), maintain in a constant temperature water bath at 45 °C for 12 h, and then age at room temperature for another 24 h.

[0076] (4) After taking out the steel fibers, wash them repeatedly with deionized water, dry at 80 °C, and store in a dry environment to complete the surface modification, obtaining steel fibers with a surface loaded with a nano-silica coating.

[0077] Test Example

[0078] 1. Contact Angle

[0079] Perform contact angle tests on the organo-inorganic sol-gel modified steel fibers and unmodified steel fibers prepared in Example 1, and the results are as Figure 2 shown. It can be seen from Figure 2 that the contact angle of the unmodified steel fibers is 90.3°, showing hydrophobicity; while the contact angle of the organo-inorganic sol-gel modified steel fibers is 48.8°, showing hydrophilicity, indicating that the coating can significantly improve the surface wettability of the steel fibers, thereby improving their compatibility with the concrete matrix and enhancing the interfacial bonding performance.

[0080] 2. Interfacial Bonding Strength:

[0081] Test method: The length of the steel fiber used is 18 mm, and the diameter is 0.2 mm. The positions of 4 steel fibers are fixed by foam board and polyvinyl chloride with a spacing of 15 mm, and the length of the fiber pull-out end is controlled to be 7 mm. It is clamped into the mortar figure-8 mold. After pouring both ends with cement mortar respectively, it is cured in a standard curing room at 20°C ± 2°C and a relative humidity of 95% for 28 days, and then the fiber pull-out test is carried out using a universal testing machine. The pull-out rate is 1 mm / min. The calculation formula for the steel fiber-matrix bond strength is as follows:

[0083] In the formula: τ is the bond strength, MPa; F m is the peak load, kN; n is the number of fibers; d f is the fiber diameter, mm; l e is the bond length of the fiber pull-out end, mm.

[0084] Among them, the results of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1:

[0085] Table 1

[0086] Bond strength (MPa) Pull-out energy (N·mm) Example 1 6.33 517.63 Example 2 6.03 463.90 Example 3 5.71 493.37 Comparative Example 1 4.45 159.78 Comparative Example 2 4.02 203.56

[0087] The results of the modified steel fiber and the unmodified steel fiber in Example 1 are as Figure 3 shown. It can be seen from Figure 3 that the bond strength between the unmodified steel fiber and the concrete matrix is 3.65 MPa, and the pull-out energy is 267.17 N·mm; after being modified by the organic-inorganic sol-gel, the bond strength and pull-out energy between the steel fiber and the concrete matrix are 6.33 MPa and 517.63 N·mm respectively, which are increased by 73.42% and 93.75% respectively compared with the unmodified steel fiber. It can be seen that the organic-inorganic sol-gel can effectively enhance the interfacial bond performance between the steel fiber and the concrete matrix.

[0088] 3. Microscopic morphology of the interfacial transition zone

[0089] The steel fibers modified by the organic-inorganic sol-gel and the unmodified steel fibers are respectively mixed with the concrete matrix, and the obtained composites are characterized by scanning electron microscopy. The results are as Figure 4 shown. It can be seen from Figure 4 that there are obvious defects in the interfacial transition zone between the unmodified steel fiber and the concrete matrix, the structure is relatively loose, and the interfacial combination is poor; while there are basically no defects in the transition zone between the steel fiber modified by the organic-inorganic sol-gel and the concrete matrix, the structure is relatively dense, and the combination between the two is closer, and the bond performance is significantly improved.

[0090] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0091] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Variations, modifications, substitutions, and alterations made by those of ordinary skill in the art to the above embodiments are all within the scope of protection of the present invention.

Claims

1. A method for preparing an organic-inorganic sol-gel, characterized in that: The following steps are involved: (1) hydrolyzing tetraethoxysilane and then adding a coupling agent to carry out a condensation reaction to obtain a siloxane network; (2) adding waterborne polyurethane to the siloxane network obtained in step (1) to carry out a cross-linking reaction.

2. The method for preparing the organic-inorganic sol-gel according to claim 1, characterized in that: In the step (1), the hydrolysis reaction comprises: after mixing tetraethoxysilane and ethanol, first adding deionized water and then adding an acid solution to adjust the pH, and then performing a hydrolysis reaction.

3. The method for preparing the organic-inorganic sol-gel according to claim 2, characterized in that: The volume ratio of tetraethoxysilane, ethanol and deionized water is 1:(2-4):(1-3); and / or, the acid solution comprises at least one of an acetic acid solution, a citric acid solution, an oxalic acid solution or a glycolic acid solution; and / or, adjusting the pH to 4-5; And / or, the temperature of the hydrolysis reaction is 25-40° C., and the time of the hydrolysis reaction is 3-4 hours; And / or, the hydrolysis reaction is carried out under stirring, and the stirring speed is 500-700 rpm.

4. The method for preparing the organic-inorganic sol-gel according to claim 1, characterized in that: In the step (1), the coupling agent includes at least one of γ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane or 3-glycidylpropyltriethoxysilane; And / or, the molar ratio of tetraethoxysilane to coupling agent is (10-20):1; And / or, the temperature of the condensation reaction is 25-40° C., and the time of the condensation reaction is 0.5-1.5 h.

5. The method for preparing the organic-inorganic sol-gel according to claim 1, characterized in that: The step (2) also includes: diluting the waterborne polyurethane with deionized water and then performing a cross-linking reaction with the siloxane network.

6. The method for preparing the organic-inorganic sol-gel according to claim 1, characterized in that: In the step (2), the solid content of the waterborne polyurethane is 50-70%; And / or, in the step (2), the volume ratio of the tetraethoxysilane to the aqueous polyurethane is 1:(0.5-2).

7. The method for preparing an organic-inorganic sol-gel according to claim 1, 5 or 6, characterized in that: In the step (2), the temperature of the cross-linking reaction is 25 to 40° C., and the time of the cross-linking reaction is 0.5 to 2 hours; And / or, the cross-linking reaction is carried out under stirring, and the stirring speed is 500-700 rpm. And / or, the waterborne polyurethane is added to the siloxane network in steps.

8. An organic-inorganic sol-gel, characterized in that: The method is prepared by the method according to any one of claims 1 to 7.

9. Use of the organic-inorganic sol-gel prepared according to the preparation method of any one of claims 1 to 7 or the organic-inorganic sol-gel according to claim 8 in fibers.

10. The use according to claim 9, characterized in that: The method comprises coating the organic-inorganic sol-gel on the surface of the fiber and drying the fiber to obtain the organic-inorganic sol-gel coating.

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