A low-cost method for preparing fiber-reinforced aerogel

Abstract

The invention discloses a method for preparing a low-cost fiber-reinforced aerogel, comprising the following steps: S1) oxidizing nanopowder and preparing a nanopowder aqueous solution; S2) soaking a porous material in the nanopowder aqueous solution and performing ultrasonic vibration treatment so that the nanopowder is evenly distributed in the pores of the porous material; S3) placing the porous material after ultrasonic immersion in a microwave drying oven for drying and sintering; S4) repeating steps S2-S3 until an aerogel that meets the density requirements is obtained. The low-cost fiber-reinforced aerogel preparation method provided by the invention has good toughness and mechanical strength that ordinary aerogels do not have, can be extruded, and does not break or deform after extrusion; it also has extremely high corrosion resistance, heat insulation, sound insulation performance and unique air permeability, and has low manufacturing cost and can be mass-produced.

Description

[0001] A low-cost method for preparing fiber-reinforced aerogel Technical Field

[0002] The invention relates to a method for preparing an aerogel, and in particular to a method for preparing a low-cost fiber-reinforced aerogel. Background Art

[0003] Aerogel is a new type of lightweight nanoporous material with a three-dimensional nanoscale pore structure and extremely high porosity. It has many advantages such as low density, low thermal conductivity, and good wave absorption performance. It has broad application prospects in aerospace, sound insulation, heat insulation, and fireproof materials. However, due to the weak interaction between the solid particles of ordinary aerogels, it has the disadvantages of low strength, poor toughness, and easy breakage, making it difficult to use on a large scale in practical applications. At the same time, the preparation process of aerogel requires the use of freeze-drying equipment, vacuum equipment, etc., which has high requirements for equipment and a long production cycle, making the manufacturing cost of aerogel much higher than other materials. Therefore, how to prepare an aerogel with high mechanical strength, flexibility, and low cost has always been a focus of attention in academia and industry. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a low-cost method for preparing fiber-reinforced aerogel, which has good toughness and mechanical strength that ordinary aerogels do not have, can be extruded, and will not break or deform after extrusion; at the same time, it also has extremely high corrosion resistance, heat insulation, sound insulation performance and unique air permeability, and has low manufacturing cost and can be mass-produced.

[0005] The technical solution adopted by the present invention to solve the above technical problems is to provide a low-cost method for preparing fiber-reinforced aerogel, comprising the following steps: S1) oxidizing nanopowder and preparing a nanopowder aqueous solution; S2) immersing a porous material in the nanopowder aqueous solution and performing ultrasonic vibration treatment so that the nanopowder is evenly distributed in the pores of the porous material; S3) placing the porous material after ultrasonic immersion in a microwave drying oven for drying and sintering; S4) repeating steps S2-S3 until an aerogel meeting the density requirements is obtained.

[0006] Further, the step S1 comprises: S11) first adding nano powder, 98% concentrated sulfuric acid and potassium permanganate; S12) then pouring in distilled water and stirring continuously at 50-80°C for 30-90 minutes; S13) then adding 30% hydrogen peroxide to the mixture, and centrifuging the solution at a speed of 10000-15000rpm for 5-15 minutes; S14) then washing the solution with deionized water and 3-5% dilute hydrochloric acid until the pH value is 7; S15) finally, placing the mixture in an ultrasonic machine for ultrasonic vibration treatment to obtain an aqueous solution in which the nano powder is dispersed.

[0007] Further, the molar ratio of the nano powder, 98% concentrated sulfuric acid and potassium permanganate is 1:2-5:0.1-0.5. Most preferably, the molar ratio of the nano powder, 98% concentrated sulfuric acid and potassium permanganate is 1:3:0.3.

[0008] Furthermore, the nano powder is boron nitride, molybdenum disulfide, graphite or carbon nanotubes, and the particle size of the nano powder is between 50 nanometers and 50 micrometers.

[0009] Further, the molar ratio of the 30% hydrogen peroxide to the nano powder is 3-10: 1. Most preferably, the molar ratio of the 30% hydrogen peroxide to the nano powder is 5:1.

[0010] Further, the molar ratio of the distilled water to the nano powder is 300-400: 1. Most preferably, the molar ratio of the distilled water to the nano powder is 350:1.

[0011] Furthermore, in the step S2, the porous material with a relatively soft material (porous material made of extrudable flexible material that can be restored after extrusion, such as polyester sponge, polyurethane sponge, slow rebound memory foam, melamine sponge, etc.) is uniformly extruded to squeeze out the bubbles inside the porous material, so that the nanopowder in the aqueous solution can enter the internal pores of the porous material; for the porous material with a relatively hard material (porous material made of hard material that is difficult to restore after extrusion, such as glass fiber, metal porous material, etc.), vacuum defoaming is used to remove the bubbles in the porous material.

[0012] Furthermore, in step S2, the softer porous material is polyurethane foam or polyester fiber foam, and the harder porous material is glass fiber foam.

[0013] Furthermore, the step S3 includes: S31) pre-sintering: controlling the microwave power per square meter to 100-150W, and the microwave heating time to 5-10 minutes, so that the nano powder forms a preliminary bond in the pores of the porous material; S32) sintering: controlling the microwave power per square meter to 300-400W, and the microwave heating time to 5-10 minutes, so that the nano powder is gradually firmly combined in the pores of the porous material to form a nanoporous structure of the aerogel; S33) drying: controlling the microwave power per square meter to 150-300W, and the microwave heating time to 20-40 minutes, to remove the remaining aqueous solution in the porous medium.

[0014] Furthermore, the number of steps S2-S3 repeated in S4 is 3-9 times, the water content of the porous material is controlled between 90%-100% during each pre-sintering, the water content of the porous material is controlled between 60%-90% during each sintering, and the weight of the aerogel after each drying increases by 1 / 30-3 / 30.

[0015] Compared with the prior art, the present invention has the following beneficial effects: the low-cost fiber-reinforced aerogel preparation method provided by the present invention utilizes microwave heating and sintering technology to enable various nano powders (such as boron nitride, molybdenum disulfide, graphite, carbon nanotubes, etc.) to be combined in the macroscopic pores of porous materials (such as polyurethane foam, polyester fiber foam, glass fiber foam, etc.) to form microscopic nanopore aerogel. It utilizes the pore structure of the porous material as a support for the nanopores of the aerogel, which can protect the nanopores of the aerogel from being damaged by external forces. It is characterized by having good toughness and mechanical strength that ordinary aerogels do not have, being extrudable, and not breaking or deforming after extrusion. At the same time, it also has the extremely high corrosion resistance, heat insulation, and sound insulation performance of ordinary aerogels, and its unique air permeability can also be used for nano-level filtration, and it also has the characteristics of low manufacturing cost, mass production, and easy processing and forming. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The figure is a schematic diagram of the preparation process of the low-cost fiber-reinforced aerogel of the present invention;

[0017] Figure 2 A schematic diagram of the nanoporous structure of the low-cost fiber-reinforced aerogel of the present invention;

[0018] Figure 3 This is a diagram showing the sound absorption performance of the fiber-reinforced aerogel in Example 3 of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0020] Figure 1 The figure is a schematic diagram of the preparation process of the low-cost fiber-reinforced aerogel of the present invention.

[0021] See also Figure 1 The present invention provides a method for preparing a low-cost fiber-reinforced aerogel, and the specific process is as follows:

[0022] Step S1, preparation of nano powder aqueous solution

[0023] When preparing the aqueous solution, the nanopowder must first be oxidized. After the oxidation of the nanopowder, oxygen-containing groups can be formed on the surface of the nanopowder. The oxygen-containing groups can increase the hydrophilicity of the nanopowder, making it easier for the nanopowder to disperse in the aqueous solution and prevent it from agglomerating. When combined with a porous material later, it can more easily penetrate into the pores of the porous material.

[0024] (1) Stirring nanopowder (such as boron nitride, molybdenum disulfide, graphite, carbon nanotubes, etc.) and 98% concentrated sulfuric acid by mass in a beaker, and then adding potassium permanganate and mixing evenly; the molar ratio of nanopowder, 98% concentrated sulfuric acid and potassium permanganate is 1:3:0.3, and the particle size of the nanopowder is between 50 nanometers and 50 micrometers, preferably between 100 nanometers and 2 micrometers; to ensure that only the surface of the nanopowder is oxidized, to avoid excessive oxidation or even complete oxidation and decomposition of the nanopowder, thereby losing its original properties and morphology;

[0025] (2) Pour distilled water into a beaker and continue stirring at 50-80°C for 30-90 minutes; the molar ratio of distilled water to nanopowder is preferably 350:1;

[0026] (3) then adding 30% by mass concentration of hydrogen peroxide to the mixture, and repeatedly centrifuging the solution at a speed of 10000-15000 rpm for 5-15 minutes; the molar ratio of 30% hydrogen peroxide to nanopowder is preferably 5:1;

[0027] (4) Use deionized water and 3-5% mass percent dilute hydrochloric acid to clean the solution until the pH value is 7, so that it does not contain acid and alkali, does not affect the subsequent immersion of materials, and does not produce acid and alkali substances that are harmful to the human body, materials and the environment;

[0028] (5) Finally, the mixture was placed in an ultrasonic machine for 2 hours for dispersion to obtain a nanopowder dispersion in water.

[0029] Step S2: Soaking the porous material in the nano powder aqueous solution

[0030] (1) For some soft porous materials (such as polyurethane foam, polyester fiber foam, etc., the pore size of the porous material is between 100 microns and 1000 microns, preferably 200-500 microns), the porous material can be immersed in the prepared nanopowder aqueous solution, and the porous material can be uniformly squeezed to squeeze out the bubbles inside the porous material, so that the nanopowder in the aqueous solution can enter the internal pores of the porous material;

[0031] (2) For some porous materials with relatively hard materials (such as glass fiber foam cotton, etc., the pore size of the porous material is between 100 microns and 1000 microns, preferably 200-500 microns), the porous material can be immersed in the prepared nanopowder aqueous solution, and the bubbles in the porous material can be removed by vacuum defoaming to facilitate the nanopowder in the aqueous solution to enter the internal pores of the porous material;

[0032] (3) The porous material from which the bubbles have been removed in the nanopowder aqueous solution is further immersed in the nanopowder aqueous solution and subjected to ultrasonic vibration for 10-20 minutes to allow the nanopowder to be evenly distributed in the pores of the porous material.

[0033] Step S3: microwave drying and sintering

[0034] Ordinary aerogel manufacturing requires high vacuum equipment, freeze-drying equipment, etc., and the drying time takes more than 24 hours. The present invention places the porous material after ultrasonic soaking in nanopowder aqueous solution in a microwave drying oven for drying and sintering, which only takes 1 hour, greatly improving the preparation efficiency of aerogel. However, how to control the microwave drying and sintering process is very important. If the microwave power is too low, the drying and sintering effect will be greatly affected, while if the microwave power is too high, the sintering temperature will overheat and burn the porous medium, and even sparks will occur in severe cases. To this end, the applicant has repeatedly experimented and adopted the following three-step method to control the microwave power and time per square meter:

[0035] (1) Pre-sintering: The microwave power is 100-150W per square meter, and the microwave heating time is 5-10 minutes, so that the nanopowder forms a weak bond in the pores of the porous material. If the power is too high, the nanopowder will flow out of the pores with the aqueous solution. The water content of the porous material after pre-sintering is about 90%-100%.

[0036] (2) Sintering: The microwave power is 300-400W per square meter, and the microwave heating time is 5-10 minutes. At this stage, the nanopowders are gradually firmly combined in the pores of the porous material and form the nanoporous structure of the aerogel. The water content of the porous material after sintering is about 60%-90%.

[0037] (3) Drying: The microwave power is 150-300W per square meter, and the microwave heating time is 20-40 minutes. In order to prevent the microwave sintering temperature from overheating, the original porous medium (such as polyurethane, polyester fiber, etc.) will be burned. Therefore, the microwave power is reduced to heat and dry the remaining aqueous solution. Due to the large specific surface area of ​​the porous medium, the internal aqueous solution can generally be completely dried by microwave in about half an hour.

[0038] After the microwave drying and sintering treatment, the weight of the aerogel increases by 1 / 30-3 / 30 each time after drying. Repeating steps S2-S3 for 3-9 times can adjust the density of the aerogel, and then adjust the corrosion resistance, heat insulation, sound insulation, fire resistance, and filtration performance of the aerogel.

[0039] Example 1

[0040] 4 g of carbon nanotubes (average particle size 10 microns), 74 g of 98% concentrated sulfuric acid and 12 g of potassium permanganate were mixed and poured into 2 liters of distilled water and stirred continuously at 60 °C for 1 hour. Then 1 liter of 30% hydrogen peroxide was added to the mixed solution, and the solution was repeatedly centrifuged at 15000 rpm for 10 minutes. The solution was then cleaned with deionized water and 3-5% mass percent dilute hydrochloric acid until the pH value was 7, so that it was free of acid and alkali. Finally, the mixture was placed in an ultrasonic machine for ultrasonic vibration for 2 hours to disperse and prepare an oxidized carbon nanotube soaking solution. The polyester fiber foam was cut into a 75 cm × 75 cm × 2 cm porous sponge board, soaked in the oxidized carbon nanotube soaking solution, squeezed to defoam, and then ultrasonically vibrated for 15 minutes. Then it was taken out and placed in a microwave sintering furnace for pre-sintering, with a pre-sintering microwave power of 80 W and a pre-sintering time of 10 minutes. Then it was continuously sintered in a microwave sintering furnace, with a sintering microwave power of 225 W and a sintering time of 10 minutes. Finally, the excess water was dried by microwave, with a microwave power of 100 W and a drying time of 20 minutes. The soaking and sintering were repeated 3 times to obtain the finished aerogel.

[0041] The finished aerogel has high sintering strength, good mechanical properties, fast rebound after repeated pressing, no cracking, and no powder falling.

[0042] Example 2

[0043] 2 grams of carbon nanotubes (average particle size 23 microns), 0.2 grams of molybdenum disulfide powder (average particle size 30 microns), 74 grams of 98% concentrated sulfuric acid and 12 grams of potassium permanganate were mixed and poured into 2 liters of distilled water and stirred continuously at 50°C for 1 hour. Then 1 liter of 30% hydrogen peroxide was added to the mixed solution, and the solution was repeatedly centrifuged at 15000rpm for 10 minutes. The solution was then washed with deionized water and 3-5% mass percent dilute hydrochloric acid until the pH value was 7, so that it was free of acid and alkali. Finally, the mixture was placed in an ultrasonic machine for ultrasonic vibration for 2 hours to disperse and prepare a nanopowder soaking solution. The polyurethane foam was cut into a porous sponge board of 75cm×75cm×5cm, soaked in the nanopowder soaking solution, and ultrasonically vibrated for 20 minutes after vacuum defoaming. After that, it was taken out and placed in a microwave sintering furnace for pre-sintering. The pre-sintering microwave power was 60W and the pre-sintering time was 10 minutes. Then continue to sinter in a microwave sintering furnace, the sintering microwave power is 200W, and the sintering time is 5 minutes. Finally, use microwave to dry the excess water, the drying microwave power is 100W, and the drying time is 40 minutes. Repeat the soaking and sintering for 4 times to obtain the finished aerogel.

[0044] The pores between the finished aerogels are composed of nanopowders, which are easier to absorb sound, and the sound absorption performance is better than that of existing nano sound-absorbing materials, such as Figure 3 shown.

[0045] Example 3

[0046] 1 gram of boron nitride nanopowder (average particle size 15 microns), 2 grams of carbon nanotubes (average particle size 20 microns), 74 grams of 98% concentrated sulfuric acid and 12 grams of potassium permanganate were mixed and poured into 2 liters of distilled water and stirred continuously at 80°C for 1 hour. Then 1 liter of 30% hydrogen peroxide was added to the mixed solution, and the solution was repeatedly centrifuged at 15,000 rpm for 10 minutes. The solution was then washed with deionized water and 3-5% mass percent dilute hydrochloric acid until the pH value was 7, so that it was free of acid and alkali. Finally, the mixture was placed in an ultrasonic machine for ultrasonic vibration for 2 hours to disperse and prepare a nanopowder soaking solution. The polyurethane sponge was cut into a porous sponge plate of 75cm×75cm×5cm, soaked in the nanopowder soaking solution, squeezed to defoam, and then ultrasonically vibrated for 10 minutes. After that, it was taken out and placed in a microwave sintering furnace for pre-sintering. The pre-sintering microwave power was 60W and the pre-sintering time was 10 minutes. Then continue to sinter in a microwave sintering furnace, the sintering microwave power is 200W, and the sintering time is 5 minutes. Finally, use microwave to dry the excess water, the drying microwave power is 100W, and the drying time is 40 minutes. Repeat the soaking and sintering for 2 times to obtain the finished aerogel.

[0047] The finished aerogel uses flame-retardant boron nitride nanopowder and oxidized carbon nanopowder to form a good flame-retardant and heat-insulating layer between the polyurethane sponge skeleton and pores, thereby turning the originally flammable polyurethane sponge into a sponge that is difficult to burn.

[0048] The reinforced fiber aerogel prepared by the present invention has the following performance advantages:

[0049] 1. Nanopore structure

[0050] The fiber-reinforced aerogel prepared by the method of the present invention is a nano-powder firmly connected in the pores of a porous material, thereby forming a stable aerogel nano-pore structure (the porous material is a polymer porous material, such as polyurethane foam, polyester fiber foam, etc.). The pore size of the aerogel nano-pore can be controlled to be 50 nanometers to 1 micron, and the porosity can reach more than 97.5%. Figure 2 shown.

[0051] 2. Mechanical properties

[0052] The fiber-reinforced aerogel prepared by the method of the present invention is elastic, maintains its original shape without deformation under repeated pressing, has extremely high flexibility and mechanical strength (the porous material is a polymer porous material, such as polyurethane foam, polyester fiber foam, etc.), and solves the defect of ordinary aerogel being easy to break.

[0053] 3. Fire prevention effect

[0054] The fiber-reinforced aerogel prepared by the method of the present invention has fireproof and fire-resistant properties. Since the surface of the nanopowder has been oxidized and cannot be burned when preparing the aqueous solution, the oxidized nanopowder covered on the porous material can play a certain fireproof protection role and is difficult to ignite with ordinary open flames. It can replace ordinary polyurethane foam and be applied in the fields of construction, thermal insulation, fire prevention, etc.

[0055] 4. Sound insulation effect

[0056] The most preferred repetition for wave absorption performance is 7-9 times. It is generally believed that the smaller the internal nanopore size, the higher the porosity, and the better the wave absorption effect. In the preparation, the more times of repeated immersion, the smaller the pore size, but the porosity also becomes lower. When repeated 7-9 times, the wave absorption effect of the material is the best. Taking the sample prepared by repeated immersion 8 times as an example, the sound absorption coefficient of the fiber reinforced aerogel prepared by the method of the present invention and other traditional sound absorbing materials is compared as shown in the following table.

[0057]

[0058] It can be seen from the above that the overall sound absorption coefficient of the fiber reinforced aerogel prepared by the method of the present invention is higher than that of other sound insulation materials, especially in the high-frequency stage, and its sound absorption coefficient can be close to 1.

[0059] 5. Filtering effect

[0060] As for the filtering effect, it is found through experiments that it is preferably repeated 5-6 times. If the pore size of the material is not small enough for less than 5 times, some nanoparticles will flow out and cannot be completely filtered out. If it is repeated more than 6 times, the pore size of the material surface will be too small or even blocked, and it will be difficult for water and air to pass through. Taking 6 times of repetition as an example, the nano powder is placed on the fiber reinforced aerogel prepared by the method of the present invention, and then washed with water. The nano powder is completely filtered out by the reinforced fiber aerogel, and what drips is pure water without impurities.

[0061] The nanopores of the fiber-reinforced aerogel prepared by the method of the present invention can effectively filter harmful gases such as PM2.5 without affecting air permeability, and can be applied to anti-PM2.5 masks. Its flexibility can make the mask fit the human face better and be more beautiful.

[0062] 6. Corrosion resistance

[0063] The fiber-reinforced aerogel prepared by the method of the present invention has extremely high corrosion resistance. Since the surface of the nano powder has been oxidized when preparing the aqueous solution, it is not easy to react with acids and alkalis. Therefore, the oxidized nano powder covered on the porous material can play a certain anti-corrosion role. In the corrosion resistance test of acid (10% hydrochloric acid, 10% sulfuric acid, 90% acetic acid), alkali (50% sodium hydroxide), alcohol (methanol, ethanol) and gasoline and other solutions and solvents, it shows very good stability, and no obvious dissolution and softening phenomenon occurs.

[0064] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make some modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be based on the definition of the claims.

Claims

1. A method for preparing a low-cost fiber-reinforced aerogel, characterized in that: The steps include: S1) oxidizing the nanopowder and preparing a nanopowder aqueous solution; S2) immersing the porous material in a nanopowder aqueous solution and subjecting it to ultrasonic vibration treatment so that the nanopowder is evenly distributed in the pores of the porous material; S3) placing the porous material after ultrasonic immersion in a microwave drying oven for drying and sintering; S4) repeating steps S2-S3 until an aerogel meeting the density requirements is obtained; Wherein, the nano powder is boron nitride, molybdenum disulfide, graphite or carbon nanotube; the particle size of the nano powder is between 50 nanometers and 50 micrometers; The porous material is polyurethane foam, polyester fiber foam or glass fiber foam cotton; the pore size of the porous material is between 100 microns and 1000 microns; The step S3 comprises: S31) Pre-sintering: Control the microwave power to 100-150W per square meter and the microwave heating time to 5-10 minutes, so that the nanopowder forms a preliminary bond in the pores of the porous material; S32) Sintering: Control the microwave power to 300-400W per square meter and the microwave heating time to 5-10 minutes, so that the nano powders are gradually and firmly combined in the pores of the porous material to form a nanoporous structure of the aerogel; S33) Drying: Control the microwave power to 150-300 W per square meter and the microwave heating time to 20-40 minutes to remove the remaining aqueous solution in the porous medium.

2. The method for preparing low-cost fiber-reinforced aerogel according to claim 1, characterized in that: The step S1 comprises: S11) firstly add nano powder, 98% concentrated sulfuric acid and potassium permanganate; S12) Then pour in distilled water and continue stirring at 50-80°C for 30-90 minutes; S13) then adding 30% hydrogen peroxide to the mixture, and centrifuging the solution at 10000-15000 rpm for 5-15 minutes; S14) washing the solution with deionized water and 3-5% dilute hydrochloric acid until the pH value is 7; S15) Finally, the mixture is placed in an ultrasonic machine for ultrasonic vibration treatment to obtain a nanopowder aqueous solution.

3. The method for preparing low-cost fiber-reinforced aerogel according to claim 2, characterized in that: The molar ratio of the nano powder, 98% concentrated sulfuric acid and potassium permanganate is 1:2-5:0.1-0.

5.

4. The method for preparing low-cost fiber-reinforced aerogel according to claim 3, characterized in that: The molar ratio of the nano powder, 98% concentrated sulfuric acid and potassium permanganate is 1:3:0.

3.

5. The method for preparing low-cost fiber-reinforced aerogel according to claim 2, characterized in that: The molar ratio of the 30% hydrogen peroxide to the nano powder is 3-10:

1.

6. The method for preparing low-cost fiber-reinforced aerogel according to claim 5, characterized in that: The molar ratio of 30% hydrogen peroxide to nano powder is 5:

1.

7. The method for preparing low-cost fiber-reinforced aerogel according to claim 2, characterized in that: The molar ratio of the distilled water to the nano powder is 300-400:

1.

8. The method for preparing low-cost fiber-reinforced aerogel according to claim 7, characterized in that: The molar ratio of the distilled water to the nano powder is 350:

1.

9. The method for preparing low-cost fiber-reinforced aerogel according to claim 1, characterized in that: In the step S2, the porous material is uniformly squeezed to squeeze out the bubbles inside the porous material, so that the nano powder in the aqueous solution can enter the internal pores of the porous material; or the bubbles in the porous material are removed by vacuum defoaming.

10. The method for preparing low-cost fiber-reinforced aerogel according to claim 1, characterized in that: The number of steps S2-S3 repeated in S4 is 3-9 times, the water content of the porous material is controlled between 90%-100% in each pre-sintering, the water content of the porous material is controlled between 60%-90% in each sintering, and the weight of the aerogel after each drying increases by 1 / 30-3 / 30.

Images