Boron sol modified phenolic aerogel and preparation method thereof

Abstract

The invention discloses boron sol modified phenolic aerogel and a preparation method thereof, and belongs to the technical field of aerogel materials. In order to solve the problem that boron modification of phenolic aerogel is limited by active sites, boron sol and phenolic sol are mainly adopted to be blended, and a boron oxide-phenolic quasi-dual-network structure is formed through curing and drying processes. The molten boron oxide can be used for coating the carbon skeleton in the material ablation process, the residual carbon rate is increased, the oxidation resistance is enhanced, and the material can be applied to an ablation thermal insulation material in a thermal protection system.

Description

Technical Field

[0001] The present invention relates to a boron sol-modified phenolic aerogel and a preparation method thereof, belonging to the technical field of aerogel materials. Background Art

[0002] Phenolic aerogel is a nano-porous organic material with properties such as light weight, heat insulation, and ablation heat protection, and is widely used in thermal protection systems. However, in an aerobic environment, when the temperature reaches 600 °C or higher, phenolic aerogel can be completely ablated, and the char residue rate is almost zero. Therefore, in order to meet the requirements of the thermal protection system for the ablation resistance of ablation materials in the service environment, it is necessary to perform ablation-resistant modification on phenolic aerogel. Boron modification is one of the currently feasible methods to improve the ablation resistance of phenolic aerogel. The ablation-resistant mechanism of boron-modified phenolic aerogel has two aspects. On the one hand, the C-C bonds in the molecular chain are replaced by B-O bonds and B-C bonds with higher bond energies, improving the thermal properties and crosslinking degree of phenolic aerogel. On the other hand, boron oxide is generated during the ablation process of boron-modified phenolic aerogel. Boron oxide will turn into a liquid state above 450 °C, and the liquid boron oxide can flow and wrap the surrounding phenolic aerogel to isolate oxygen erosion, thereby increasing the char residue rate of phenolic aerogel.

[0003] Generally, there are two paths to prepare boron-modified phenolic aerogel. One is to add a boron modifier during the sol-gel process of phenolic sol to directly generate boron-modified phenolic aerogel. The other is to first perform boron modification on phenolic resin, and then use boron phenolic as the raw material to prepare boron-modified phenolic resin. Patent application CN112175230A discloses a preparation method of boron-modified phenolic aerogel. In this method, linear phenolic resin and organic borates such as tributyl borate are dissolved in ethanol, and then a boron composite phenolic wet gel is obtained through a sol-gel process. During the high-temperature gel process, organic boron sources such as tributyl borate graft-react with phenol aldehyde to achieve chemical bond connection and compounding. Finally, boron-modified phenolic aerogel is obtained through atmospheric drying. Patent application CN117917450A discloses a high-char residue phenolic aerogel thermal insulation material and a preparation method thereof. In this method, thermosetting boron phenolic and linear phenolic are mixed in an organic solvent, and then after sol-gel and atmospheric drying, boron-modified phenolic aerogel is obtained. Patent application CN111234299A discloses a heat-resistant phenolic aerogel and a preparation method thereof. In this method, boron-modified phenolic resin is first prepared by reacting phenol, formaldehyde, a catalyst, and boric acid in a certain proportion, and then boron phenolic and a curing accelerator are mixed and subjected to a sol-gel reaction, and boron-modified phenolic aerogel is obtained after atmospheric drying.

[0004] The prior art has the following defects: (1) Introducing boron-containing functional groups depends on active sites such as hydroxymethyl in the phenolic aerogel itself, and the upper limit of boron element introduction is relatively low. (2) The preparation of boron-modified phenolic aerogels is limited to a certain specific phenolic system, and the universality is poor. (3) In order to achieve the preparation of phenolic aerogels, it is often necessary to first prepare boron-modified phenolic resins to serve as raw materials. Summary of the Invention

[0005] The object of the present invention is to provide a boron sol-modified phenolic aerogel and its preparation method, which realizes simple and efficient boron modification of phenolic aerogels, makes up for the problem that existing boron modification is restricted by active sites in phenolic aerogels, and can be applied to ablation heat insulation materials in thermal protection systems.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A preparation method of a boron sol-modified phenolic aerogel, comprising the following steps:

[0008] (1) Prepare boron sol and phenolic sol;

[0009] (2) After mixing the boron sol and the phenolic sol evenly, a reaction precursor solution is obtained;

[0010] (3) Load the reaction precursor solution into a closed reaction kettle for heating and curing;

[0011] (4) Immerse the cured wet gel in an alkaline solution and an anhydrous ethanol / water mixture for a period of time in sequence;

[0012] (5) Carry out atmospheric drying on the soaked wet gel to finally obtain a boron-modified phenolic aerogel.

[0013] Further, the volume ratio range of the boron sol to the phenolic sol in step (1) is 0 to 1.

[0014] Further, the concentration range of the boron sol in step (1) is 10 to 60 wt%.

[0015] Further, the concentration range of the phenolic sol in step (1) is 10 to 60 wt%.

[0016] Further, the boron source of the boron sol in step (1) is a borate ester, and the borate ester is selected from one or more of tributyl borate, triisopropyl borate, and triphenyl borate.

[0017] Further, the phenolic sol in step (1) is one or more of a phenol-formaldehyde system, a resorcinol-formaldehyde system, and a resorcinol-furfural system.

[0018] Further, the curing temperature in step (3) ranges from 80 to 120 °C, and a stepped curing method is adopted, with the total curing duration being 60 to 96 h.

[0019] Further, the alkaline solution in step (4) is an aqueous solution of one or more of NaOH, KOH, Na2CO3, and K2CO3, with a concentration of 0.01 to 0.1 mol / L.

[0020] Further, the soaking duration in step (4) is 24 to 48 h.

[0021] Further, the atmospheric drying method in step (5) is as follows: first, air-dry at room temperature until the mass no longer changes, and then place it in an oven to dry until the mass no longer changes.

[0022] A boron sol-modified phenolic aerogel is prepared by the above preparation method.

[0023] The principle of the present invention is: by mixing boron sol and phenolic sol and selecting a suitable curing process, a boron oxide and phenolic quasi-binary network structure is formed during the sol-gel process, ensuring the uniform and stable distribution of boron oxide in the phenolic aerogel. When the phenolic aerogel is ablated by heat, the molten boron oxide can effectively coat the phenolic aerogel skeleton and its pyrolyzed carbon skeleton, thereby isolating oxygen to prevent further oxidation, promoting the formation of a shape, and increasing the char yield.

[0024] The present invention has the following advantages compared with the prior art:

[0025] 1. The present invention does not require modification of phenolic resin and can directly realize the preparation of boron-modified phenolic aerogel.

[0026] 2. The boron element functional groups in the present invention do not need to react and combine with specific functional groups on the phenolic aerogel skeleton, greatly increasing the upper limit of the introduced amount of boron element.

[0027] 3. The boron element in the present invention exists in the form of a three-dimensional network and can be uniformly distributed in the phenolic aerogel skeleton.

[0028] 4. Soaking the wet gel in the alkaline solution in the present invention can, on the one hand, remove excess reaction raw materials, and on the other hand, improve the stability of the boron skeleton. Brief Description of the Drawings

[0029] Figure 1 is the preparation flow chart of the boron sol-modified phenolic aerogel of the present invention. Detailed Description of the Invention

[0030] To make the technical features and advantages or technical effects in the above technical solutions of the present invention more obvious and understandable, the following is a detailed description through examples.

[0031] Example 1

[0032] A preparation method of boron sol modified phenolic aerogel, comprising the following steps:

[0033] (1) Mix 8 mL of tributyl borate, 24 mL of absolute ethanol, 12 mL of pure water and 2 mL of glacial acetic acid evenly by stirring at room temperature to obtain boron sol. Mix 19 g of phenol, 32 g of formaldehyde solution (formalin, concentration 37%) and 40 mL of absolute ethanol evenly by stirring at room temperature to obtain phenolic sol.

[0034] (2) Slowly add the boron sol to the phenolic sol while stirring, and mix evenly to obtain a reaction precursor solution.

[0035] (3) Put the reaction precursor solution into a sealed reaction kettle, and place the reaction kettle in an oven. Heat it at 80 °C for 48 h and then at 120 °C for 24 h in sequence for curing.

[0036] (4) After the reaction kettle cools down, take out the cured wet gel and soak it in 0.01 mol / L NaOH solution and anhydrous ethanol / water mixture (volume ratio 3 / 1) for 24 h in sequence.

[0037] (5) After the soaked wet gel is left to stand at room temperature until its mass no longer changes, then put it in an oven at 100 °C and dry it until its mass no longer changes, finally obtaining boron modified phenolic aerogel.

[0038] The density of the finally prepared boron modified phenolic aerogel is 0.35 g / cm 3 , the residue weight at 800 °C in nitrogen atmosphere is 68%, and the residue weight at 800 °C in air atmosphere is 22%.

[0039] Example 2

[0040] A preparation method of boron sol modified phenolic aerogel, comprising the following steps:

[0041] (1) Mix 8 mL of tributyl borate, 24 mL of absolute ethanol, 12 mL of pure water and 2 mL of glacial acetic acid evenly by stirring at room temperature to obtain boron sol. Mix 22 g of resorcinol, 30 g of furfural, 20 mL of pure water and 40 mL of absolute ethanol evenly by stirring at room temperature to obtain phenolic sol.

[0042] (2) Slowly add the boron sol to the phenolic sol while stirring, and mix evenly to obtain a reaction precursor solution.

[0043] (3) Put the reaction precursor solution into a sealed reaction kettle, and place the reaction kettle in an oven. Heat it at 90 °C for 36 h and then at 120 °C for 24 h in sequence for curing.

[0044] (4) After the reaction kettle is cooled, the solidified wet gel is taken out and soaked in a 0.1 mol / L Na2CO3 solution and an anhydrous ethanol / water mixture (volume ratio 3 / 1) for 36 h in sequence.

[0045] (5) After the soaked wet gel is left to dry at room temperature until its mass remains unchanged, it is then placed in an oven at 100 °C and dried until its mass no longer changes, finally obtaining boron-modified phenolic aerogel.

[0046] The density of the finally prepared boron-modified phenolic aerogel is 0.38 g / cm 3 , the residual weight at 800 °C in a nitrogen atmosphere is 72%, and the residual weight at 800 °C in an air atmosphere is 27%.

[0047] Example 3

[0048] A preparation method of boron sol-modified phenolic aerogel, comprising the following steps:

[0049] (1) 8 mL of triisopropyl borate, 24 mL of anhydrous ethanol, 12 mL of pure water and 1 g of oxalic acid are stirred and mixed evenly at room temperature to obtain boron sol. 22 g of resorcinol, 32 g of formaldehyde solution (formalin, concentration 37%) and 40 mL of anhydrous ethanol are stirred and mixed evenly at room temperature to obtain phenolic sol.

[0050] (2) While stirring, the boron sol is slowly added to the phenolic sol and mixed evenly to obtain a reaction precursor solution.

[0051] (3) The reaction precursor solution is filled into a sealed reaction kettle, and the reaction kettle is placed in an oven and heated at 80 °C for 48 h and then at 120 °C for 48 h in sequence for curing.

[0052] (4) After the reaction kettle is cooled, the solidified wet gel is taken out and soaked in a 0.01 mol / L NaOH solution and an anhydrous ethanol / water mixture (volume ratio 3 / 1) for 48 h in sequence.

[0053] (5) After the soaked wet gel is left to dry at room temperature until its mass remains unchanged, it is then placed in an oven at 100 °C and dried until its mass no longer changes, finally obtaining boron-modified phenolic aerogel.

[0054] The density of the finally prepared boron-modified phenolic aerogel is 0.41 g / cm 3 , the residual weight at 800 °C in a nitrogen atmosphere is 66%, and the residual weight at 800 °C in an air atmosphere is 18%.

[0055] Although the present invention has been disclosed above with examples, it is not intended to limit the present invention. Appropriate modifications or equivalent replacements made by those of ordinary skill in the art to the technical solutions of the present invention should all be covered within the protection scope of the present invention, and the protection scope of the present invention shall be subject to that defined by the claims.

Claims

1. A preparation method of boron sol modified phenolic aerogel, characterized in that, It includes the following steps: (1) Prepare boron sol and phenolic sol; (2) After mixing the boron sol and the phenolic sol evenly, obtain a reaction precursor solution; (3) Load the reaction precursor solution into a sealed reaction kettle for heating and curing; (4) Immerse the cured wet gel in an alkaline solution and an anhydrous ethanol / water mixture in sequence for a period of time; (5) Carry out atmospheric drying on the immersed wet gel to finally obtain a boron-modified phenolic aerogel.

2. The preparation method according to claim 1, characterized in that, The volume ratio range of the boron sol to the phenolic sol in step (1) is 0 to 1.

3. The preparation method according to claim 1 or 2, characterized in that, The concentration range of the boron sol in step (1) is 10 to 60 wt%, and the concentration range of the phenolic sol is 10 to 60 wt%.

4. The preparation method according to claim 1, wherein The boron source of the boron sol in step (1) is a borate ester, and the borate ester is selected from one or more of tributyl borate, triisopropyl borate, and triphenyl borate.

5. The preparation method according to claim 1, characterized in that, The phenolic sol in step (1) is one or more of a phenol-formaldehyde system, a resorcinol-formaldehyde system, and a resorcinol-furfural system.

6. The preparation method according to claim 1, characterized in that, The curing temperature range in step (3) is 80 to 120 °C, and a stepwise curing method is adopted, and the total curing duration is 60 to 96 h.

7. The preparation method according to claim 1, characterized in that, The alkaline solution in step (4) is an aqueous solution of one or more of NaOH, KOH, Na2CO3, and K2CO3, and the concentration is 0.01 to 0.1 mol / L.

8. The preparation method according to claim 1, characterized in that, The immersion duration in step (4) is 24 to 48 h.

9. The preparation method according to claim 1, characterized in that, The atmospheric drying method in step (5) is: first air-dry at room temperature until the mass does not change, and then place it in an oven to dry until the mass no longer changes.

10. A boron sol-modified phenolic aerogel, characterized in that, Prepared by the preparation method described in any one of claims 1-9.

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