A phthalonitrile modified phenolic aerogel and a preparation method and application thereof

Abstract

The application discloses a phthalonitrile modified phenolic aerogel and a preparation method and application thereof, linear phenolic resin, 4-nitro-phthalonitrile and alkaline catalyst are dissolved in an organic solvent, a water bath reaction is carried out, and a phthalonitrile etherified phenolic resin is obtained by powdering; a mixed solvent is prepared, the linear phenolic resin and the phthalonitrile etherified phenolic resin are dissolved in the mixed solvent, and a mixed solution is obtained; a crosslinking agent is added into the mixed solution, a sol-gel reaction is carried out to obtain a wet gel, the wet gel is aged, is sectionally solidified, and is dried to obtain the phthalonitrile modified phenolic aerogel. The pyrolysis performance of the phenolic aerogel is improved, the phthalonitrile modified phenolic aerogel with high residual carbon and high thermal stability is obtained under the condition of low-temperature heating, and is suitable for application in the field of thermal protection system heat insulation and ablation of space equipment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ablation heat protection material preparation, and particularly relates to a phthalonitrile modified phenolic aerogel and a preparation method and application thereof. BACKGROUND

[0002] With the gradual deepening of human exploration of space, spacecrafts have to face more extreme and complex external environment tests. When the spacecrafts move at high speed in the atmosphere, they will have strong friction with the air, resulting in serious aerodynamic heating effect and a large amount of heat energy, so that the surface of the spacecrafts reaches a very high temperature. Therefore, in order to protect the normal operation of the internal system and equipment, the heat protection system is one of the indispensable systems in the space equipment. The return type spacecraft and the space return capsule need to brake and decelerate when returning, which is a compromise for the insufficient performance of the heat protection system. In the heat protection system, the ablation type heat protection system is mainly used for the return type spacecraft. The phenolic aerogel is widely used in this field due to its high residual carbon, low density, low thermal conductivity and excellent heat insulation and ablation capacity. The heat protection big bottom of the American "Dragon" spacecraft uses a carbon fiber reinforced phenolic aerogel composite material, which has extremely low thermal conductivity and good ablation and heat insulation performance.

[0003] At present, the phenolic aerogel is mainly prepared by using resorcinol and formaldehyde as raw materials, through a sol-gel reaction, solvent replacement and supercritical drying or freeze drying. The methylene bond of the phenolic aerogel is cracked too fast under the action of high temperature ablation, the residual carbon is relatively low, and the thermal stability is insufficient, which is not conducive to obtaining better heat insulation and ablation performance. Therefore, it is crucial to modify the phenolic aerogel to obtain a modified phenolic aerogel with higher residual carbon, good thermal stability and more excellent heat insulation and ablation performance. SUMMARY

[0004] The purpose of the present application is to introduce phthalonitrile into the skeleton of the phenolic aerogel, and to provide a phthalonitrile modified phenolic aerogel and a preparation method and application thereof. The phthalonitrile etherified phenolic is blended with the thermoplastic phenolic under suitable conditions to prepare the phthalonitrile modified phenolic aerogel, which has excellent performance of high residual carbon and high thermal stability. The method has low cost, mild conditions and simple preparation process and is easy to operate.

[0005] The present application is realized by the following technical scheme.

[0006] In one aspect of the present application, a preparation method of a phthalonitrile modified phenolic aerogel is provided, which comprises the following steps:

[0007] a. Dissolving linear phenolic, 4-nitrophthalonitrile and alkaline catalyst in an organic solvent according to the mass ratio of (5-8) :(2-5) :(2-5), stirring uniformly, water bath reaction, cooling, adjusting pH, powdering, to obtain phthalonitrile etherified phenolic resin;

[0008] b. Dissolve the purchased linear phenolic and o-phenylenedimethylene cyan etherified phenolic resin in a mixed solvent according to the mass ratio (5-8):(2-5), stir uniformly to obtain a mixed solution;

[0009] c. Add a crosslinking agent to the mixed solution according to the mass ratio of mixed solution:crosslinking agent 100:(2-4), stir uniformly to obtain a precursor solution;

[0010] d. Perform sol-gel reaction on the precursor solution to obtain a wet gel, and then age, segmentally solidify, and dry to obtain an o-phenylenedimethylene cyan modified phenolic aerogel.

[0011] As a preferred, the organic solvent is any one of pyrrolidone, dimethyl sulfoxide, dimethyl formamide or dimethyl acetamide.

[0012] The mixed solvent is configured according to the mass ratio of (5-8):(3-6) of a main solvent and a secondary solvent, the main solvent is ethanol, and the secondary solvent is ethyl acetate.

[0013] As a preferred, the alkaline catalyst is any one of NaOH, KOH, K2CO3, Na2CO3 or Ba(OH)2.

[0014] As a preferred, the crosslinking agent is hexamethylenetetramine.

[0015] As a preferred, in step a, the water bath reaction is performed at 80-90℃ for 5-10h, then the temperature is reduced to normal temperature, and the pH is adjusted to neutral.

[0016] As a preferred, in step d, the sol-gel reaction is performed at a temperature of 90-150℃ for 24-72h, and the aging is performed at room temperature for 1-3 days.

[0017] As a preferred, the segmental solidification process is: 90℃ / 0.5h, 110℃ / 1h, 140℃ / 2h, 150℃ / 3h, 180℃ / 2h, 200℃ / 2h, 220℃ / 4h, and normal pressure drying.

[0018] Another aspect of the present application provides an o-phenylenedimethylene cyan modified phenolic aerogel prepared by the method.

[0019] The present application has the following beneficial effects due to the above technical solutions:

[0020] 1.The application introduces o-phthalonitrile into the phenolic aerogel framework, and since o-phthalonitrile itself has good thermal stability, its introduction improves the pyrolysis performance of the phenolic aerogel, significantly improves the initial pyrolysis temperature, improves the thermal stability of the phenolic aerogel, and expands the application range of the phenolic aerogel in the field of thermal ablation, so that it can be applied to more severe environments. The prepared o-phthalonitrile modified phenolic aerogel can be applied in the thermal protection system of aerospace equipment.

[0021] 2.The application uses o-phthalonitrile etherified phenolic resin in the preparation of aerogel, introduces o-phthalonitrile into the phenolic resin to obtain BPN, and then blends BPN with phenolic resin, and obtains aerogel through gel-sol. The o-phthalonitrile is introduced into the phenolic aerogel framework at a lower temperature, and the use of mixed solvents enables the two resins with different solubilities to be blended to prepare aerogel. The application successfully expands the application of o-phthalonitrile to aerogel. The carbon residue rate of the aerogel prepared by the application can reach 68.14%, and the initial decomposition temperature and the maximum rate of thermal decomposition temperature are significantly improved compared with the phenolic aerogel. BRIEF DESCRIPTION OF DRAWINGS

[0022] The drawings described herein are used to provide further understanding of the application, form a part of the application, and do not constitute an improper limitation on the application. In the drawings:

[0023] Figure 1 The preparation flowchart of the application;

[0024] Figure 2 The TG curve of the o-phthalonitrile modified phenolic aerogel prepared by the application. DETAILED DESCRIPTION

[0025] The application will be described in detail below with reference to the drawings and specific examples. The schematic examples and descriptions of the application are used to explain the application, but do not constitute a limitation on the application.

[0026] The application provides a preparation method of o-phthalonitrile modified phenolic aerogel, as shown in the figure, comprising the following steps: Figure 1

[0027] a, linear phenolic resin: 4-nitro-o-phthalonitrile: alkaline catalyst are dissolved in organic solvent according to the mass ratio (5-8):(3-5):(4-6), stirred uniformly, reacted in 80-90℃ water bath for 5-10h, cooled, pH adjusted to neutral, powdered, and o-phthalonitrile etherified phenolic resin is obtained;

[0028] Among them, the alkaline catalyst is any one of NaOH, KOH, K2CO3, Na2CO3 or Ba(OH)2.

[0029] ​The organic solvent is any one of N-dimethylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) or dimethylacetamide (DMAC).

[0030] The used phthalonitrile is ortho-nitro-substituted phthalonitrile or meta-nitro-substituted phthalonitrile, and the amount is 0-100% of the molar number of phenolic hydroxyl groups of the phenol-formaldehyde phenol, but not 0, such as 50%-70%.

[0031] b. The main solvent (ethanol) and the auxiliary solvent (ethyl acetate) are configured into a mixed solvent according to a mass ratio (4-7):(3-6); the purchased linear phenol formaldehyde and the phthalonitrile etherified phenol formaldehyde resin are dissolved in the mixed solvent according to a mass ratio (5-8):(2-5), and stirred uniformly to obtain a mixed solution;

[0032] c. The mixed solution is added with a crosslinking agent according to a mass ratio of 100:(2-4), and stirred uniformly to obtain a precursor solution;

[0033] The crosslinking agent is any one of ammonium persulfate, potassium persulfate or hexamethylenetetramine.

[0034] d. The precursor solution is subjected to a sol-gel reaction at a temperature of 90-150℃ for 24-72h to obtain a wet gel, which is aged at room temperature for 1-3 days, and subjected to segmented curing and normal-pressure drying at 90℃ / 0.5h, 110℃ / 1h, 140℃ / 2h, 150℃ / 3h, 180℃ / 2h, 200℃ / 2h and 220℃ / 4h to obtain a phthalonitrile-modified phenolic aerogel.

[0035] Since the phthalonitrile resin itself has a high reaction temperature, which usually starts to cure at 270℃, the temperature is too high for most conditions for preparing aerogels. Therefore, the phthalonitrile is connected to the phenolic hydroxyl group of the phenol formaldehyde resin, so as to introduce the phthalonitrile into the phenol formaldehyde skeleton, and the phthalonitrile is introduced into the phenol formaldehyde aerogel skeleton by means of the lower temperature curing condition of the phenol formaldehyde.

[0036] Due to the difference in solubility of PF and BPN, the solubility of phenolic resin modified by phthalonitrile changes before and after modification. Phthalonitrile etherified phenolic resin can be dissolved in organic solvents such as acetone, ethyl acetate, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethyl sulfoxide and pyrrolidone, while linear phenolic resin is easily soluble in ethanol and most organic solvents. The solvent for preparing aerogel of phenolic resin at normal pressure is ethanol, but phthalonitrile etherified phenolic resin is difficult to dissolve in ethanol. Therefore, the mixed solvent of ethanol and ethyl acetate is used in the patent to successfully dissolve phthalonitrile etherified phenolic resin and linear phenolic resin, so that it is possible to introduce phthalonitrile into the skeleton of phenolic aerogel. Moreover, the aerogel prepared by dissolving resin in mixed solvent can be prepared by normal pressure drying, which simplifies the drying process and shortens the preparation time.

[0037] The method of the present application is further described in detail through different examples.

[0038] Example 1

[0039] Mass ratio: W (phenolic resin PF) : W (phthalonitrile etherified phenolic resin BPN) = 8:2

[0040] Linear phenolic resin: 4-nitrophthalonitrile: K2CO3 were dissolved in N-dimethylpyrrolidone (NMP) according to the mass ratio of 5:3:4, stirred uniformly, reacted at 90℃ water bath for 7h, cooled, adjusted pH to neutral, powdered, and phthalonitrile etherified phenolic resin was obtained;

[0041] 25g of ethanol and ethyl acetate solvent were mixed uniformly according to the mass ratio of 5:5 to obtain 50g of mixed solvent. Linear phenolic resin and phthalonitrile etherified phenolic resin were added to the mixed solvent according to the mass ratio of 8:2, stirred uniformly at room temperature until completely dissolved, and a mixed solution was obtained;

[0042] According to the mass ratio of 100:2 of mixed solution: crosslinking agent, hexamethylenetetramine was added to the mixed solution and stirred uniformly. After obtaining a uniform solution, it was placed in a reaction kettle and placed in a 90℃ constant temperature environment for sol-gel reaction for 72h. After the reaction was completed, the reaction kettle was taken out and cooled to room temperature. The wet gel was taken out and aged at room temperature for 2d. It was dried at 80℃ under normal pressure for 12h until the weight was unchanged. It was subjected to staged curing to obtain phthalonitrile modified phenolic aerogel.

[0043] The phthalonitrile modified phenolic aerogel prepared was tested to have a 10% compression strength of 2.13MPa, a room temperature thermal conductivity of 0.0390W / m / K, an initial pyrolysis temperature of 435.15℃, a maximum pyrolysis speed temperature of 584.73℃, and a residual carbon of 63.21%.

[0044] Example 2

[0045] Mass ratio: W (phenol formaldehyde PF): W (phthalonitrile etherified phenol formaldehyde BPN) = 7:3

[0046] Linear phenol formaldehyde: 4-nitro phthalonitrile: Na2CO3 were dissolved in dimethyl sulfoxide (DMSO) according to a mass ratio of 6:4:5, stirred uniformly, reacted in a 90°C water bath for 5h, cooled, adjusted to neutral pH, powdered, and phthalonitrile etherified phenol formaldehyde resin was obtained;

[0047] Ethanol and ethyl acetate solvents were mixed uniformly according to a mass ratio of 6:4 to obtain 50g of mixed solvent, and linear phenol formaldehyde and phthalonitrile etherified phenol formaldehyde resin were added to the mixed solvent according to a mass ratio of 7:3, stirred uniformly at room temperature until completely dissolved, and a mixed solution was obtained;

[0048] According to a mass ratio of 100:2.5 of mixed solution: crosslinking agent, potassium persulfate was added to the mixed solution and stirred uniformly, and after a uniform solution was obtained, it was placed in a reaction kettle and placed in a 100°C constant temperature environment for sol-gel reaction for 48h, and after the reaction was completed, the reaction kettle was removed and cooled to room temperature, the wet gel was removed and aged at room temperature for 3d, and dried at 80°C under normal pressure for 12h until the weight was unchanged, and the phthalonitrile modified phenolic aerogel was obtained by step curing.

[0049] The phthalonitrile modified phenolic aerogel prepared was tested to have a 10% compression strength of 2.34MPa, a room temperature thermal conductivity of 0.0391W / m / K, an initial pyrolysis temperature of 464.46°C, a maximum pyrolysis speed temperature of 610.36°C, and a residual carbon of 65.05%.

[0050] Example 3

[0051] Mass ratio: W (phenol formaldehyde PF): W (phthalonitrile etherified phenol formaldehyde BPN) = 6:4

[0052] Linear phenol formaldehyde: 4-nitro phthalonitrile: KOH were dissolved in N,N-dimethylformamide (DMF) according to a mass ratio of 7:4:6, stirred uniformly, reacted in a 85°C water bath for 8h, cooled, adjusted to neutral pH, powdered, and phthalonitrile etherified phenol formaldehyde resin was obtained;

[0053] Ethanol and acetone solvents were mixed uniformly according to a mass ratio of 7:3 to obtain 50g of mixed solvent, and phenol formaldehyde resin and phthalonitrile etherified phenol formaldehyde resin were added to the mixed solvent according to a mass ratio of 6:4, stirred uniformly at room temperature until completely dissolved, and a mixed solution was obtained;

[0054] According to the mixed solution: crosslinking agent mass ratio 100:3, add ammonium persulfate in the mixed solution and stir uniformly, after obtaining a uniform solution, place it in a reaction kettle, place it in a constant temperature environment of 150°C for sol-gel reaction for 24h, after the reaction is completed, take out the reaction kettle and cool it to room temperature, take out the wet gel and age it at room temperature for 2d, dry it at 80°C under normal pressure for 12h until the weight is unchanged, and perform segmented curing to obtain a phthalonitrile modified phenolic aerogel.

[0055] The prepared phthalonitrile modified phenolic aerogel is tested, and the 10% compression strength is 2.92MPa, the room temperature thermal conductivity coefficient is 0.0394W / m / K, the initial pyrolysis temperature is 495.08°C, the maximum pyrolysis speed temperature is 615.97°C, and the residual carbon can reach 68.14%.

[0056] Example 4

[0057] Mass ratio: W(phenolic PF):W(phthalonitrile etherified phenolic BPN) = 5:5

[0058] Dissolve linear phenolic, 4-nitrophthalonitrile and Ba(OH)2 in dimethylacetamide (DMAC) according to the mass ratio of 8:5:6, stir uniformly, react in a water bath at 80°C for 10h, cool down, adjust the pH to neutral, powder, and obtain phthalonitrile etherified phenolic resin;

[0059] Take 50g of mixed solvent by mixing ethanol and ethyl acetate solvents in a mass ratio of 4:6, add phenolic resin and phthalonitrile etherified phenolic resin to the mixed solvent in a mass ratio of 5:5, stir uniformly at room temperature until completely dissolved, and obtain a mixed solution;

[0060] According to the mixed solution: crosslinking agent mass ratio 100:4, add hexamethylenetetramine in the mixed solution and stir uniformly, after obtaining a uniform solution, place it in a reaction kettle, place it in a constant temperature environment of 120°C for sol-gel reaction for 36h, after the reaction is completed, take out the reaction kettle and cool it to room temperature, take out the wet gel and age it at room temperature for 1d, dry it at 80°C under normal pressure for 12h until the weight is unchanged, and perform segmented curing to obtain a phthalonitrile modified phenolic aerogel.

[0061] The prepared phthalonitrile modified phenolic aerogel is tested, and the 10% compression strength is 3.45MPa, the room temperature thermal conductivity coefficient is 0.0412W / M / K, the initial pyrolysis temperature is 513.12°C, the maximum pyrolysis speed temperature is 632.57°C, and the residual carbon can reach 67.96%.

[0062] Comparative Example 1

[0063] Mass ratio: W(phenolic PF):W(phthalonitrile etherified phenolic BPN) = 10:0

[0064] Take 25g of ethanol and ethyl acetate solvent respectively, mix them uniformly in a mass ratio of 1:1 to obtain 50g of mixed solvent, add 12.5g of phenolic resin into the mixed solvent, stir uniformly at room temperature until completely dissolved, add 1.875g of hexamethylenetetramine into the solution and stir uniformly, obtain a uniform solution, place it in a reaction kettle, place it in a constant temperature environment for sol-gel reaction for 3d, after the reaction is completed, take out the reaction kettle and cool it to room temperature, take out the wet gel and age it at room temperature for 2d, dry it at 80℃ under normal pressure for 12h until the weight does not change, carry out segmented curing, and obtain the phthalonitrile modified phenolic aerogel.

[0065] The phthalonitrile modified phenolic aerogel prepared is tested, and the 10% compression strength is 1.56MPa, the room temperature thermal conductivity is 0.0369W / m / K, the initial pyrolysis temperature is 364.21℃, the maximum pyrolysis rate temperature is 540.06℃, and the residual carbon can reach 55.39%.

[0066] The density, compression, simultaneous thermal analysis, performance test of Examples 1-4 are compared with those of Comparative Example 1.

[0067] The test results are shown in Table 1

[0068]

[0069] From Table 1 and Figure 2 The TG curve of the phthalonitrile modified phenolic aerogel prepared in the application can be seen that, with the increase of the content of phthalonitrile, the density, compression strength and thermal conductivity of the phthalonitrile modified phenolic aerogel prepared by the method of the application are improved, and at the same time, the thermal stability is also obviously improved, that is, the initial pyrolysis temperature is increased by 148.91℃, the maximum pyrolysis rate temperature is increased by 92.51℃, and the residual carbon rate is increased by 12.57%, and overall, when the content of BPN resin is less than 50%, the thermal stability of the aerogel gradually increases with the increase of the content of phthalonitrile. The introduction of phthalonitrile into the phenolic aerogel achieves the goal of improving the thermal stability of the phenolic aerogel and increasing the residual carbon rate without greatly increasing the density and thermal conductivity.

[0070] The application is not limited to the above examples, and based on the technical solutions disclosed in the application, those skilled in the art can make some substitutions and modifications to some technical features according to the disclosed technical content without creative labor, and these substitutions and modifications are all within the protection scope of the application.

Claims

1. A method of preparing a phthalonitrile-modified phenolic aerogel, characterized in that, The method comprises the following steps: a. Dissolving linear phenolic resin, 4-nitrophthalonitrile and alkaline catalyst in organic solvent according to the mass ratio of (5-8):(2-5):(2-5), stirring uniformly, water bath reaction, cooling, adjusting pH, powdering to obtain phthalonitrile etherified phenolic resin; b. Dissolving linear phenolic resin and phthalonitrile etherified phenolic resin in mixed solvent according to the mass ratio of (5-8):(2-5), stirring uniformly to obtain a mixed solution; c. Adding crosslinking agent to the mixed solution according to the mass ratio of 100:(2-4), stirring uniformly to obtain a precursor solution; d. The precursor solution is subjected to sol-gel reaction to obtain wet gel, and the wet gel is aged, sectionally solidified and dried to obtain phthalonitrile modified phenolic aerogel.

2. The method for preparing phthalonitrile-modified phenolic aerogel according to claim 1, characterized in that, The organic solvent is any one of pyrrolidone, dimethyl sulfoxide, dimethyl formamide or dimethyl acetamide.

3. The method for preparing phthalonitrile-modified phenolic aerogel according to claim 1, characterized in that, The mixed solvent is configured according to the mass ratio of (5-8):(2-5) of main solvent and auxiliary solvent, the main solvent is ethanol, and the auxiliary solvent is ethyl acetate or tetrahydrofuran.

4. The method for preparing phthalonitrile-modified phenolic aerogel according to claim 1, characterized in that, The alkaline catalyst is any one of NaOH, KOH, K2CO3, Na2CO3 or Ba(OH)2.

5. The method for preparing phthalonitrile-modified phenolic aerogel according to claim 1, characterized in that, The crosslinking agent is any one of ammonium persulfate, potassium persulfate or hexamethylenetetramine.

6. The method for preparing phthalonitrile-modified phenolic aerogel according to claim 1, characterized in that, In step a, the water bath reaction is performed at 80-90°C for 5-10h, the temperature is reduced to room temperature, and the pH is adjusted to neutral.

7. The method for preparing phthalonitrile-modified phenolic aerogel according to claim 1, characterized in that, In step d, the sol-gel reaction is performed at a temperature of 90-150°C for 24-72h, and the aging is performed at room temperature for 1-3 days.

8. The method for preparing phthalonitrile-modified phenolic aerogel according to claim 1, characterized in that, The sectionally solidification process is: 90°C / 0.5h, 110°C / 1h, 140°C / 2h, 150°C / 3h, 180°C / 2h, 200°C / 2h, 220°C / 4h, and normal pressure drying.

9. The phthalonitrile modified phenolic aerogel prepared by the method according to any one of claims 1-8.

10. The phthalonitrile modified phenolic aerogel according to claim 9 is applied in thermal protection system of space equipment.

Images