Normal-pressure low-cost silicon dioxide aerogel composite material and preparation method thereof

Abstract

The invention relates to the technical field of thermal insulation material preparation, in particular to a normal-pressure low-cost silicon dioxide aerogel composite material and a preparation method thereof, and the preparation method comprises four typical steps of precursor preparation, gelling, aging and drying. According to the method, methyltriethoxysilane is taken as a silicon source, water is taken as a unique solvent, water-soluble polyethylene fibers are taken as a fiber reinforced material, and gel is prepared by adopting an acid-base two-step method. And aging the wet gel at room temperature without solvent replacement, and drying at normal pressure to form the aerogel. The water-soluble ultra-high molecular weight polyethylene fiber is introduced into the silicon dioxide precursor, so that the yield of the silicon-based aerogel under the normal-pressure drying condition is increased, and the mechanical property of the silicon-based aerogel is remarkably improved. The problems that traditional silicon dioxide aerogel is long in preparation period, tedious in process, poor in mechanical property and prone to shrinkage and fragmentation in the drying process are effectively solved, and an innovative material which is excellent in performance and high in cost effectiveness is provided for the field of heat preservation and heat insulation.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal insulation material preparation, and particularly to an atmospheric-pressure low-cost silica aerogel composite material and a preparation method thereof. Background Art

[0002] With the rapid development of global science and technology and economy, factors such as industrialization, urbanization, and population growth have jointly driven a huge demand for energy, which not only intensifies the consumption of fossil fuels but also exerts great pressure on the environment. As a key energy-saving technical means, thermal insulation materials can effectively reduce energy loss during transmission and use, and improve energy utilization efficiency. By reducing heat loss in buildings, optimizing thermal energy management of industrial equipment, and enhancing the energy efficiency of various transportation tools, thermal insulation materials play an irreplaceable role in reducing energy waste and carbon emissions. It not only helps to relieve the pressure on energy supply but also makes an important contribution to environmental protection, and is an important support for achieving sustainable development. Therefore, the development and application of high-efficiency thermal insulation materials are of great significance for addressing energy and environmental challenges globally.

[0003] As a new type of lightweight, multifunctional, and environmentally friendly aerogel material, SiO2 aerogel material has attracted more and more extensive attention due to its unique properties (low density, high specific surface area, low thermal conductivity); it is lightweight, fire-resistant, heat-insulating, and environmentally friendly, and has unparalleled advantages compared with traditional thermal insulation materials. However, its fragile structure, insufficient mechanical properties, and long preparation time limit its wide application. In the field of atmospheric-pressure drying technology, traditional methods not only have a long preparation cycle and frequent solvent replacement, but also the obtained finished products are often fragile or have a high shrinkage rate, and the mechanical properties are difficult to meet the ideal requirements. Although there are numerous research literatures and patents on the preparation process of silica aerogel in recent years, examples of preparing silica composite aerogels with a short preparation cycle, non-fragile, and hydrophobic properties under atmospheric pressure are still quite rare.

[0004] Patent CN105692631B discloses a method for preparing silica aerogel at normal pressure, which uses tetraethyl orthosilicate or sodium silicate as a precursor, and uses metal salt compounds to modify the aged silica wet gel 2 to 5 times with an interval of 20 to 30 hours, and after 2 to 6 solvent replacements, it is dried at normal pressure to prepare silica aerogel. Patent CN101948296A provides a fiber-reinforced aerogel insulation material and a method for preparing the material, which uses silica hydrosol as a precursor, and uses one of quartz fiber, high silica fiber, aluminum silicate fiber and other fibers as a fiber material, and ages for 8 to 16 hours at room temperature or under heating conditions, and performs two solvent replacements with an interval of 24 to 120 hours, and then uses supercritical drying to prepare fiber-reinforced aerogel. Although these two patents can also prepare silica aerogel, the cycle for preparing aerogel is long, the process is cumbersome, and the mechanical properties of the silica aerogel obtained are poor.

[0005] In summary, the existing aerogel atmospheric pressure drying preparation method has the problems of long production cycle, poor mechanical properties, and easy cracking during drying, which greatly hinders the industrial application of aerogel materials. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a low-cost silica aerogel composite material at normal pressure and a preparation method thereof in view of the deficiencies of the above-mentioned prior art, including four typical steps of precursor preparation, gelation, aging and drying. The method uses methyltriethoxysilane as a silicon source, water as the only solvent, and water-soluble polyethylene fiber as a fiber reinforcement material. The gel is prepared by an acid-base two-step method. The wet gel is aged at room temperature without solvent replacement, and an aerogel is formed after gradient normal pressure drying. By introducing water-soluble ultra-high molecular weight polyethylene fiber into the silica precursor, not only the yield of silicon-based aerogel under normal pressure drying conditions is improved, but also its mechanical properties are significantly improved. The present invention effectively overcomes the problems of long preparation cycle, cumbersome process, poor mechanical properties, and easy shrinkage and fragmentation during the drying process of traditional silica aerogel, and provides an innovative material with excellent performance and high cost-effectiveness in the field of thermal insulation.

[0007] In order to solve the above technical problems, the present invention provides the following technical solution: a method for preparing a low-cost silica aerogel composite material at normal pressure, the method comprising the following steps: Step 1: Mix water and acid to form an acidic aqueous solution, then add a silicon source and a surfactant in proportion, stir and hydrolyze, then slowly add the fiber to the stirred hydrolyzed solution, stir evenly to obtain a precursor solution; Step 2: adding alkali to the precursor solution to adjust its pH to 6.5-7.5, continuing to stir for a certain period of time and then standing the gel until it is converted into a wet gel; Step 3: Aging the wet gel in air for a certain period of time; Step 4: Gradient atmospheric pressure drying is carried out on the wet gel that has been aged for a certain period of time, and an aerogel is obtained after drying.

[0008] Further, the acidic aqueous solution in Step 1 is obtained by mixing water and an acid and stirring, and the stirring method is one of magnetic stirring or mechanical stirring. The stirring time, temperature, and rotation speed are 3 - 5 min, 20 - 40 °C, and 400 - 800 r / min respectively; The stirring hydrolysis method is one of magnetic stirring or mechanical stirring, and the rotation speed is 500 - 800 r / min; The hydrolysis temperature is 10 °C - 60 °C, and the hydrolysis time is 4 - 20 h.

[0009] Further, the concentration of the acidic aqueous solution in Step 1 is 1 - 10 mmol / L. Among them, the water is one of ordinary water, distilled water, or deionized water, and the acidic catalyst is one of hydrofluoric acid, glacial acetic acid, or oxalic acid; The molar ratio of the silicon source to water is 1:(30 - 45). Among them, the silicon source is one of methyltriethoxysilane and methyltrimethoxysilane; The mass ratio of the surfactant to the silicon source is 0.001 - 0.005:1; among them, the surfactant is one of tetradecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, cetyltrimethylammonium bromide, and polyoxyethylene polyoxypropylene ether.

[0010] Further, the fiber in Step 1 is a hydrophilic water-soluble ultra-high molecular weight polyethylene fiber UHMWPE, with a particle size of 30 - 120 microns and a molecular weight Mw of 400 - 800 ten thousand; The method of adding the fiber is to slowly pour it into the solution being stirred, and 5 - 50 g is added per 1 mol of the silicon source.

[0011] Further, the base in Step 2 is at least one of NH4OH, NaH(CO)3, Na2(CO)3, NaOH, KOH, K2(CO)3, or KH(CO)3.

[0012] Further, the stirring temperature in Step 2 is 10 - 30 °C, and the stirring time is 5 - 20 min; The standing temperature is 10 - 30 °C, and the standing time is at least 4 h.

[0013] Further, the method for determining the conversion to the wet gel in Step 2 is to tilt the gel at 45°. If the gel has no fluidity, it means that the wet gel is successfully prepared.

[0014] Furthermore, the aging method in Step 3 is: standing in air for aging, with an aging time of 4 - 12 h and a temperature of 15 - 30 °C.

[0015] Furthermore, the process of gradient atmospheric pressure drying in Step 4 is: maintaining the temperature at 40 °C for 2 - 4 h, 80 °C for 2 - 4 h, and 100 °C for 2 - 4 h respectively; During the atmospheric pressure drying process, the heating rate is controlled at 0.1 - 2 °C / min.

[0016] Furthermore, the low - cost silica aerogel composite material prepared by the above - mentioned technical solution, using methyltriethoxysilane as the silicon source, water as the sole solvent, and water - soluble polyethylene fiber as the fiber - reinforcing material, is a low - cost silica aerogel composite material under atmospheric pressure.

[0017] By means of the above - mentioned technical solution, the present invention provides a low - cost silica aerogel composite material under atmospheric pressure and its preparation method, which has at least the following beneficial effects: (1) The preparation process of the present invention is carried out under atmospheric pressure conditions, without using organic solvents for solvent replacement, avoiding environmental pollution and safety hazards in solvent use, and reducing complex steps in the production process. The overall process cycle is short. In addition, the preparation method of the present invention has a low cost, and its simplicity and low cost make it have broad application potential in large - scale industrial production.

[0018] (2) By introducing ultra - high - molecular - weight polyethylene fiber (UHMWPE), the present invention enhances the three - dimensional network structure of the gel, effectively strengthens the mechanical support inside the gel, and improves its overall toughness and stability. Especially during the drying process of the aerogel, the cracks and cracking phenomena caused by drying shrinkage are significantly reduced, thereby improving the overall durability and service life of the material.

[0019] (3) The apparent density of the SiO2 aerogel prepared by the present invention is between 0.1 - 0.15 g / cm 3 , and this low - density characteristic makes it have significant advantages in thermal insulation materials and heat insulation applications. At the same time, the thermal conductivity of the aerogel is as low as 0.0453 W / (m·K), indicating that under the conditions of low cost and short cycle, its heat insulation performance can be comparable to that of existing aerogels, and it can effectively reduce heat transfer.

[0020] (4) The SiO2 aerogel block prepared by the present invention has good integrity and good mechanical properties, and is not easily damaged when subjected to external physical actions, thus ensuring its durability during long - term use.

[0021] (5) The contact angle between the SiO2 aerogel prepared by the present invention and water can reach 138.59°, which has good hydrophobicity, strong waterproof performance, can effectively prevent the penetration of moisture, and enables it to maintain its excellent physical properties in a wet or humid environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings: Figure 1 Schematic flow chart of the embodiment of the present invention.

[0023] Figure 2 Macromorphology diagram of the aerogel prepared in Example 1; Figure 3 Compressive stress-strain curve of the aerogel prepared in Example 1; Figure 4 Schematic diagram of the contact angle between the aerogel prepared in Example 2 and water; Figure 5 Scanning electron microscope schematic diagram of the aerogel prepared in Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the drawings and specific embodiments. Thereby, the implementation process of how the present application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0025] Although the steps in the present invention are arranged with reference numerals, they are not used to limit the order of the steps. Unless the order of the steps is clearly stated or the execution of a certain step requires other steps as a basis, the relative order of the steps can be adjusted. It can be understood that the term "and / or" used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. Example 1

[0026] The method for preparing an atmospheric-pressure low-cost silica aerogel composite material proposed in this Example 1 includes the following steps: Step 1: Add 0.054 mol of acetic acid to 3 mol of water, stir with a magnetic stirrer at 25 °C and 500 r / min for 5 min to mix into an acidic aqueous solution; then add 100 mmol of methyltriethoxysilane and 0.03 g of cetyltrimethylammonium bromide to the above solution, and stir and hydrolyze at 25 °C and 600 r / min for 6 h. Prepare 7.5 g of water-soluble ultra-high molecular weight polyethylene fibers with a particle size of 30 microns, slowly add them to the hydrolyzing solution that is being stirred, and obtain a precursor solution after stirring evenly.

[0027] Step 2: Adjust the pH to between 6.5 and 7.5 by dropping 2% ammonia water, stir at 25 °C and 600 r / min for 5 min, and then let it stand for 4 h. Until it is tilted 45°, and the gel has no fluidity, which indicates that the wet gel is successfully prepared.

[0028] Step 3: Age the wet gel in air at 25 °C for 4 h.

[0029] Step 4: Perform gradient atmospheric pressure drying on the wet gel, control the heating rate below 2 °C / min, and obtain an aerogel after holding at 40 °C for 4 h, 80 °C for 4 h, and 100 °C for 2 h respectively.

[0030] The density of this material is 0.112 g / cm 3 , and the thermal conductivity is 0.05656 W / (m·K). Example 2

[0031] The method for preparing an atmospheric pressure low-cost silica aerogel composite material proposed in this Example 2 includes the following steps: Step 1: Add 0.054 mol of acetic acid to 3 mol of water, stir with a magnetic stirrer at 25 °C and 500 r / min for 5 min to mix into an acidic aqueous solution; then add 100 mmol of methyltriethoxysilane and 0.03 g of cetyltrimethylammonium bromide to the above solution, and stir and hydrolyze at 25 °C and 600 r / min for 6 h. Prepare 15 g of water-soluble ultra-high molecular weight polyethylene fibers with a particle size of 30 microns, slowly add them to the hydrolyzing solution that is being stirred, and obtain a precursor solution after stirring evenly.

[0032] Step 2: Adjust the pH to between 6.5 and 7.5 by dropping 2% ammonia water, stir at 25 °C and 600 r / min for 5 min, and then let it stand for 4 h. Until it is tilted 45°, and the gel has no fluidity, which indicates that the wet gel is successfully prepared.

[0033] Step 3: Age the wet gel in air at 25 °C for 4 h.

[0034] Step 4: Gradient atmospheric pressure drying is carried out on the wet gel, with the heating rate controlled below 2 °C / min. After maintaining the temperature at 40 °C for 4 h, 80 °C for 4 h, and 100 °C for 2 h respectively, aerogels are obtained.

[0035] The density of this material is 0.126 g / cm 3 , and the thermal conductivity is 0.04530 W / (m·K). Example 3

[0036] The method for preparing an atmospheric pressure low-cost silica aerogel composite material proposed in this Example 3 includes the following steps: Step 1: Add 0.054 mol of acetic acid to 3 mol of water, stir for 5 min at 25 °C and 500 r / min using a magnetic stirrer to mix into an acidic aqueous solution; then add 100 mmol of methyltriethoxysilane and 0.03 g of cetyltrimethylammonium bromide to the above solution, and stir and hydrolyze for 6 h at 25 °C and 600 r / min. Prepare 30 g of water-soluble ultra-high molecular weight polyethylene fibers with a particle size of 30 microns, slowly add them to the hydrolyzing solution under stirring, and obtain a precursor solution after stirring evenly.

[0037] Step 2: Adjust the pH to between 6.5 and 7.5 by dropping 2% ammonia water, stir for 5 min at 25 °C and 600 r / min, and then let it stand for 4 h. Until it is tilted at 45°, and the gel has no fluidity, it indicates that the wet gel is successfully prepared.

[0038] Step 3: Age the wet gel in air at 25 °C for 4 h.

[0039] Step 4: Gradient atmospheric pressure drying is carried out on the wet gel, with the heating rate controlled below 2 °C / min. After maintaining the temperature at 40 °C for 4 h, 80 °C for 4 h, and 100 °C for 2 h respectively, aerogels are obtained.

[0040] The density of this material is 0.134 g / cm 3 , and the thermal conductivity is 0.05016 W / (m·K).

[0041] As Figures 1 - 5 shown, Figure 1 is the process flow schematic diagram of the method for preparing an atmospheric pressure low-cost silica aerogel composite material in this application; Figure 2 is the macroscopic morphology diagram of the aerogel prepared in Example 1 of this application. It can be seen that the aerogel prepared by this method exhibits a complete and uniform macroscopic morphology; Figure 3This is the compressive stress-strain curve graph of the aerogel prepared in Example 1 of this application. The stress of the aerogel at a strain of 50% is 0.07 MPa, and the compressive deformation can reach 80%, indicating that the aerogel prepared under the conditions of low cost and short cycle by this method has good deformation ability and compressive resistance, and can withstand compressive deformation within a large range without damage; Figure 4 This is the contact angle (138.59°) between the aerogel prepared in Example 2 of this application and water, indicating that the aerogel has good hydrophobic performance; Figure 5 This is the scanning electron microscope schematic diagram of the aerogel prepared in Example 2 of this application. The microstructure of the aerogel is mainly composed of macropores, which can effectively reduce the damage to the pores during the drying process, so that the drying can be directly completed without going through complex dissolution and replacement steps. This not only greatly shortens the preparation cycle, but also helps to maintain the integrity of the microstructure of the aerogel.

[0042] The present invention includes four typical steps: precursor preparation, gelation, aging and drying. This method uses methyltriethoxysilane as the silicon source, water as the only solvent, and water-soluble polyethylene fiber as the fiber reinforcing material, and prepares the gel by a two-step acid-base method. The wet gel is aged at room temperature without solvent replacement, and an aerogel is formed after gradient atmospheric drying. By introducing water-soluble ultra-high molecular weight polyethylene fiber into the silica precursor, not only the yield of the silica-based aerogel under atmospheric drying conditions is improved, but also its mechanical properties are significantly improved. The present invention effectively overcomes the problems of long preparation cycle, cumbersome process, poor mechanical properties, and easy shrinkage and fragmentation during the drying process of traditional silica aerogels, and provides an innovative material with excellent performance and high cost-effectiveness for the field of thermal insulation.

[0043] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0044] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A preparation method of an atmospheric-pressure low-cost silica aerogel composite material, characterized in that, The method comprises the following steps: Step 1: Mix water and acid to form an acidic aqueous solution, then add a silicon source and a surfactant in proportion, stir and hydrolyze, then slowly add the fiber to the stirred hydrolyzed solution, stir evenly to obtain a precursor solution; Step 2: adding alkali to the precursor solution to adjust its pH to 6.5-7.5, continuing to stir for a certain period of time and then standing the gel until it is converted into a wet gel; Step 3: placing the wet gel in air for aging for a certain period of time; Step 4: subjecting the wet gel aged for a certain period of time to gradient normal pressure drying to obtain aerogel after drying.

2. The preparation method according to claim 1, characterized in that, The acidic aqueous solution in step 1 is obtained by mixing water and acid and stirring them. The stirring method is magnetic stirring or mechanical stirring. The stirring time, temperature and speed are 3-5 min, 20-40° C. and 400-800 r / min respectively. The stirring hydrolysis method is one of magnetic stirring or mechanical stirring, and the rotation speed is 500-800 r / min; The hydrolysis temperature is 10°C to 60°C, and the hydrolysis time is 4 to 20 hours.

3. The preparation method according to claim 2, characterized in that, The concentration of the acidic aqueous solution in step 1 is 1-10 mmol / L, wherein the water is one of ordinary water, distilled water or deionized water, and the acidic catalyst is one of hydrofluoric acid, glacial acetic acid or oxalic acid; The molar ratio of the silicon source to water is 1:(30-45), wherein the silicon source is one of methyltriethoxysilane and methyltrimethoxysilane; The mass ratio of the surfactant to the silicon source is 0.001-0.005:1; wherein the surfactant is one of tetradecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and polyoxyethylene polyoxypropylene ether.

4. The preparation method according to claim 1, characterized in that, The fiber in step 1 is a hydrophilic water-soluble ultra-high molecular weight polyethylene fiber UHMWPE, with a particle size of 30 to 120 microns and a molecular weight Mw of 4 to 8 million; The fiber is added in a manner of slowly pouring it into the stirring solution, with 5-50 g added for every 1 mol of silicon source.

5. The preparation method according to claim 1, wherein The base in step 2 is at least one of NH4OH, NaH(CO)3, Na2(CO)3, NaOH, KOH, K2(CO)3 or KH(CO)3.

6. The preparation method according to claim 5, characterized in that, The stirring temperature in step 2 is 10-30°C and the stirring time is 5-20min; The standing temperature is 10-30° C., and the standing time is at least 4 hours.

7. The preparation method according to claim 1, characterized in that, The method for judging the conversion into wet gel in step 2 is to tilt the gel at 45°. If the gel has no fluidity, it means that the wet gel is successfully prepared.

8. The preparation method according to claim 1, characterized in that The aging method in step three is: standing in the air for 4 to 12 hours at a temperature of 15 to 30°C.

9. The preparation method according to claim 1, characterized in that, The process of gradient atmospheric pressure drying in step 4 is: keeping warm at 40°C for 2-4h, keeping warm at 80°C for 2-4h, and keeping warm at 100°C for 2-4h; During the normal pressure drying process, the heating rate is controlled at 0.1~2℃ / min.

10. An atmospheric-pressure low-cost silica aerogel composite material, characterized in that, Using the preparation method described in any one of the above claims 1-9, a low-cost silica aerogel composite material is obtained with methyltriethoxysilane as the silicon source, water as the sole solvent, and water-soluble polyethylene fiber as the fiber reinforcement material under atmospheric pressure.

Images