Flexible thermal insulation material with whisker / fiber secondary structure composite film layer and preparation method of flexible thermal insulation material

Abstract

The invention provides a whisker / fiber secondary structure composite film layer flexible thermal insulation material and a preparation method thereof, and belongs to the technical field of flexible thermal insulation materials. The preparation method comprises the following steps: preparing spinning sol from AN, TEOS, AIP, PEO, PVA, PVP and a porous thermal insulation material as raw materials, carrying out electrostatic spinning to prepare a fiber membrane, pre-sintering the fiber membrane, loading AlF3 and SiO2, and finally sintering to catalyze a secondary structure. Through structural design, whisker secondary structures which are different in direction and can be mutually lapped to form a frame grow on a fiber main body of the fiber membrane, the mechanical property of the fiber membrane layer is guaranteed, meanwhile, the porosity of the fiber membrane layer is further improved, the microstructure of the fiber membrane layer is improved, and the effect of reducing the thermal conductivity of loaded aerogel is developed. And another new way is provided for improving the thermal insulation performance of the composite material. The thermal conductivity of the obtained thermal insulation material is lower than 0.038 W / (m.K).

Description

Technical Field

[0001] The present invention relates to the technical field of flexible thermal insulation materials, and particularly relates to a whisker / fiber secondary structure composite film flexible thermal insulation material and a preparation method thereof. Background Art

[0002] In any system, as long as there is a temperature difference inside, heat will inevitably flow from the high-temperature part (or object) to the low-temperature part (or object), and this phenomenon is called heat transfer. Thermal insulation materials have heat preservation or cold preservation functions and heat shielding functions, and can reduce heat loss by affecting three heat transfer modes of heat conduction, convection and radiation, thereby improving the energy utilization efficiency.

[0003] At present, although the layered composite material of aerogel-fiber is an important research direction of high-performance flexible thermal insulation materials, there are still some problems to be improved: ① After the aerogel and the fiber are compounded, the thermal conductivity is still relatively high, and its thermal conductivity is generally above 0.03 W / (m·k), which is still difficult to meet the requirements of special fields in actual production; ② The uneven distribution and chaotic orientation of the fibers will affect the mechanical properties of the composite material. For the problem of low thermal conductivity mentioned above, the usual approach is to improve the performance of the aerogel to reduce the overall thermal conductivity of the composite material. However, by analyzing the reasons, it will be found that the main reason for its high thermal conductivity lies in the fiber layer. It is precisely because of the close contact between single fibers that the fiber layer is relatively dense, and the thermal conductivity cannot reach the same level as that of the aerogel; for the second problem mentioned above, if the fiber is replaced with a fiber membrane / mat, although it can well avoid the problems of uneven distribution and orientation of the fibers in the nanoporous material, it still cannot solve the problem of relative density of the fiber layer. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a whisker / fiber secondary structure composite film flexible thermal insulation material and a preparation method thereof.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention, a preparation method of a whisker / fiber secondary structure composite film flexible thermal insulation material, comprising the following steps:

[0007] Preparing a spinning sol with aluminum nitrate, tetraethyl orthosilicate, aluminum isopropoxide, polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone and a porous heat insulation material as raw materials;

[0008] Electrospinning the spinning sol to obtain a fiber membrane;

[0009] Drying and pre-burning the fiber membrane to obtain a green body fiber membrane;

[0010] Immerse the green body fiber membrane, AlF3, and SiO2 nanopowder in an ethanol solution, filter, and obtain a fiber membrane loaded with a catalyst.

[0011] Sinter the fiber membrane loaded with the catalyst to obtain the whisker / fiber secondary structure composite membrane layer flexible thermal insulation material.

[0012] The second technical solution of the present invention is a whisker / fiber secondary structure composite membrane layer flexible thermal insulation material prepared by the above preparation method.

[0013] The present invention discloses the following technical effects:

[0014] The present invention adopts a dry process to mix fibers with catalyst dry powder. During sintering, in-situ synthesis is used to generate fluffy mullite whiskers on the surface of the fibers, and a whisker / fiber secondary structure composite membrane layer flexible thermal insulation material is prepared by a simpler process.

[0015] Compared with the current industrial thermal insulation materials, the present invention reduces the content of organic substances, breaks through the limitation of the use temperature, and prepares a flexible thermal insulation material that can be used in the range of 600 - 1200 °C.

[0016] While maintaining the flexibility of the product, the present invention significantly reduces its thermal conductivity, and the thermal conductivity is lower than 0.038 W / (m·K). Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1 SEM scanning diagram of the whisker / fiber secondary structure composite membrane layer flexible thermal insulation material prepared in Comparative Example 1;

[0019] Figure 2 SEM scanning diagram of the whisker / fiber secondary structure composite membrane layer flexible thermal insulation material prepared in Example 1. Detailed Embodiments

[0020] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0021] It should be understood that the terms used in the present invention are only for describing particular embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0022] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0023] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the specification of the present invention, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0024] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0025] The present invention first uses AN, TEOS, AIP, PEO, PVA, PVP, and porous thermal insulation materials as raw materials to prepare a spinning sol, and then performs electrospinning to prepare a fiber membrane. After pre-burning the fiber membrane, it is co-filtered with catalysts AlF3 and SiO2, and finally sintered to obtain a composite material with a secondary structure. Through structural design, the present invention grows whisker secondary structures with different directions on the fiber main body of the fiber membrane, which can overlap with each other to form a framework. While ensuring the mechanical properties of the fiber membrane layer, it further improves its porosity and improves the microstructure of the fiber membrane layer, opening up a new way to improve the thermal insulation performance of the composite material in addition to reducing the thermal conductivity of the loaded aerogel.

[0026] Specifically, the first aspect of the present invention provides a method for preparing a whisker / fiber secondary structure composite membrane flexible thermal insulation material, comprising the following steps:

[0027] Using aluminum nitrate, tetraethyl orthosilicate, aluminum isopropoxide, polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, and porous thermal insulation materials as raw materials to prepare a spinning sol;

[0028] Electrospin the spinning sol to obtain a fiber membrane;

[0029] Dry and pre-burn the fiber membrane to obtain a green body fiber membrane;

[0030] Immerse the green body fiber membrane, AlF3 and SiO2 nanopowder in an ethanol solution, and filter to obtain a fiber membrane loaded with a catalyst;

[0031] Sinter the fiber membrane loaded with the catalyst to obtain the whisker / fiber secondary structure composite membrane flexible thermal insulation material.

[0032] In a preferred embodiment of the present invention, a spinning sol is prepared using aluminum nitrate (AN), tetraethyl orthosilicate (TEOS), aluminum isopropoxide (AIP), polyethylene oxide (PEO), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP) and a porous thermal insulation material as raw materials. Specifically: dissolve aluminum nitrate, tetraethyl orthosilicate and aluminum isopropoxide in water, and then adjust the pH value of the system to be acidic to obtain a precursor sol; dissolve polyethylene oxide, polyvinyl alcohol and polyvinylpyrrolidone in water, and then carry out a stirring reaction to obtain a spinning aid; after mixing the spinning aid and the precursor sol evenly, add a porous thermal insulation material, and then mix evenly to obtain a spinning sol, and then electrospin the spinning sol to obtain a fiber membrane;

[0033] In a preferred embodiment of the present invention, the mass ratio of aluminum nitrate, tetraethyl orthosilicate and aluminum isopropoxide is 20-40:10-30:10-50 (further preferably 30-40:20-30:40-50, 37:22:41); the mass ratio of polyethylene oxide, polyvinyl alcohol and polyvinylpyrrolidone is 1-2:1-5:0.5-2 (further preferably 1-2:1-2:0.5-1, 1:1:1); the mass ratio of the spinning aid to the precursor sol is 0.5-3:5 (further preferably 2-3:5, 2:5).

[0034] In the present invention, if the ratio of the raw materials is not within the above parameter range, it will cause problems such as being unable to obtain uniform fibers with a suitable porosity during electrospinning. On the one hand, the fibers cannot be formed due to poor spinnability of the fibers and fall in the form of droplets. On the other hand, the conductivity of the spinning solution is too poor, and the fibers cannot fall to the negative electrode in time after fiber formation and a series of other problems.

[0035] In a preferred embodiment of the present invention, when dissolving aluminum nitrate, tetraethyl orthosilicate and aluminum isopropoxide in water, the mass ratio of aluminum nitrate to water is 1:1; when dissolving polyethylene oxide, polyvinyl alcohol and polyvinylpyrrolidone in water, the mass ratio of polyethylene oxide to water is 1:1.

[0036] In the present invention, if there is too little solvent (water), it cannot be effectively dissolved, and if there is too much, the concentration time will be prolonged, reducing the production efficiency.

[0037] In a preferred embodiment of the present invention, the pH value is 5; the solution used to adjust the pH value is oxalic acid and glacial acetic acid with a volume ratio of 1:1.

[0038] In the present invention, if the pH value is not appropriate, the catalytic effect cannot be achieved, resulting in the inability to obtain linear-structured molecules and affecting the spinnability of the sol.

[0039] In a preferred embodiment of the present invention, the stirring reaction is specifically as follows: first stir at 60 - 90 °C (more preferably 80 °C) for 5 - 20 h (more preferably 8 - 12 h, 10 h) under the condition of condensation reflux, and then cool to room temperature and stir for another 5 - 20 h (more preferably 8 h).

[0040] In the present invention, if the reaction time and conditions are not appropriate, the reaction will not be reproducible, the sol structure cannot obtain a linear structure, or the composition is uneven. It will also affect the sol concentration, resulting in problems during the electrospinning process.

[0041] In a preferred embodiment of the present invention, the porous thermal insulation material is SiO2 aerogel, Al2O3 aerogel or SiC porous ceramic particles; the mass percentage of the porous thermal insulation material in the spinning sol is 2 - 12% (more preferably 3 - 7%, 5%).

[0042] In a preferred embodiment of the present invention, the particle size range of the SiO2 aerogel is 10 - 15 μm, the purity is ≥99%, and it has strong hydrophobicity. Inappropriate aerogel particle size will result in damaged fiber continuity after spinning, too short and fragmented fibers, affecting the final performance.

[0043] In a preferred embodiment of the present invention, the parameters of the electrospinning are set as follows: the positive voltage is 15 kV, the negative voltage is 13 kV, the pushing speed of the micro pump is 1 - 1.5 mL / h, the spinning distance is 15 - 20 cm, the ambient temperature is 25 °C, and the ambient humidity is 20 - 30%. Inappropriate spinning parameters will prevent smooth spinning, fiber formation, or directly result in liquid drops dripping, or low spinning efficiency.

[0044] In a preferred embodiment of the present invention, the drying temperature is 75 °C and the time is 1 - 2 h. Poor drying will easily cause surface cracks in the gel fibers, affecting the quality after sintering.

[0045] In a preferred embodiment of the present invention, the pre-sintering temperature is 800 °C and the time is 0.5 - 2 h (more preferably 1 h).

[0046] In a preferred embodiment of the present invention, the mass ratio of the green body fiber membrane, AlF3, and SiO2 nanoflour is 2 - 5:1 - 3:1 - 3 (more preferably, 2:1:1).

[0047] In the present invention, if the above parameters are not within this range, the catalytic effect will be affected and the secondary structure cannot be catalyzed.

[0048] In a preferred embodiment of the present invention, the impregnation time is 2 - 3 h. Insufficient impregnation will lead to uneven catalysis.

[0049] In a preferred embodiment of the present invention, the sintering temperature is 1200 - 1500 °C (more preferably, 1250 °C), and the time is 0.5 - 3 (more preferably, 1 h). If the sintering process is not within the parameter range of the present invention, the secondary structure cannot be catalyzed, or the final product will not be flexible.

[0050] In the present invention: the control of the in-situ growth process of the whisker secondary structure. The length of the mullite secondary structure and its density on the fiber need to be strictly controlled. If the whiskers grow too little, they cannot play the role of increasing the specific surface area, and if they grow too long, there is a risk of damaging the mechanical properties of the original film layer. The present invention realizes the control of the in-situ growth process of the whisker secondary structure by controlling the proportion of the catalyst and the sintering parameters, etc.

[0051] In the present invention, the method of mixing evenly can be selected by the conventional technical means of those skilled in the art, for example: stirring.

[0052] The second aspect of the present invention provides a whisker / fiber secondary structure composite film flexible thermal insulation material prepared by the above preparation method.

[0053] The technical solutions of the present invention, unless otherwise specified, are all conventional solutions in the art. The reagents or raw materials used, unless otherwise specified, are all purchased from commercial channels or have been made public.

[0054] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments only.

[0055] In the examples, the particle size range of the silica aerogel used is 10 - 15 μm, the purity is above 99%, and it has strong hydrophobicity.

[0056] Example 1

[0057] A preparation method of a whisker / fiber secondary structure composite film flexible thermal insulation material (referred to as thermal insulation material for short) is as follows:

[0058] 1. Preparation of the precursor sol

[0059] After dissolving aluminum nitrate in water, tetraethyl orthosilicate and aluminum isopropoxide were added successively. Among them, the mass ratio of AN:TEOS:AIP was 37:22:41, and the mass ratio of AN to water was 1:1. After magnetic stirring for 1 min, oxalic acid and glacial acetic acid with a volume ratio of 1:1 were added, and the pH value of the system was adjusted to about 5. Then, magnetic stirring was carried out at a speed of 300 r / min for 20 h to obtain a transparent sol.

[0060] 2. Preparation of spinning aid

[0061] Polyethylene oxide, polyvinyl alcohol and polyvinylpyrrolidone were dissolved in deionized water. Among them, the mass ratio of PEO:PVA:PVP:deionized water was 1:1:1:1. Stirring was carried out at 80 °C for 10 h in a condensing reflux device, and then cooled to room temperature and stirred for another 8 h to obtain a spinning aid.

[0062] 3. Preparation of spinning sol

[0063] The spinning aid was slowly added dropwise to the precursor sol (the mass ratio of the spinning aid to the precursor sol was 2:5), and magnetic stirring was carried out at a speed of 500 r / min for 1 h. Then, silica aerogel with a mass fraction of 5% of the spinning sol was added, and stirring was continued for 20 h to obtain a translucent spinning sol.

[0064] 4. Preparation of fiber membrane by electrospinning

[0065] Electrospinning was carried out under the conditions of a positive voltage of 15 kV, a negative voltage of 13 kV, a micro-pump pushing speed of 1 - 1.5 mL / h, a spinning distance of 15 - 20 cm, an ambient temperature of 25 °C, and an ambient humidity of 20 - 30% to obtain a uniform, dense and flexible fiber membrane.

[0066] 5. Catalysis of secondary structure

[0067] The fiber membrane obtained in step (4) was dried in an oven at 75 °C for 2 h, and then pre-fired in a muffle furnace at 800 °C for 1 h to obtain a green body fiber membrane.

[0068] Then, 2 g of the green body fiber membrane was soaked in ethanol together with 1 g of AlF3 and 1 g of SiO2 nanopowder for 2 h, and then filtered together to obtain a fiber membrane loaded with a catalyst.

[0069] The fiber membrane loaded with a catalyst was sintered in a muffle furnace at 1250 °C for 1 h to obtain a thermal insulation material.

[0070] The thermal conductivity and high-temperature performance of the thermal insulation material obtained in this example were tested by the transient plane heat source test method. The thermal insulation material obtained in this example has a high use temperature, reaching 600 - 1200 °C, and at the same time maintains the flexible characteristics. The thermal conductivity is 0.38 W / (m·K).

[0071] Comparative Example 1

[0072] The difference from Example 1 is only that the 2g green body fiber membrane, 1g AlF3 and 1g SiO2 nanoflour are replaced with 7g green body fiber membrane, 4g AlF3 and 4g SiO2 nanoflour, and other parameters and steps are the same as those in Example 1.

[0073] It can be seen from Figure 1 and Figure 2 that the thermal insulation material prepared in this application has an obvious secondary structure.

[0074] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a whisker / fiber secondary structure composite film flexible thermal insulation material, characterized in that, Comprising the following steps: Preparing a spinning sol using aluminum nitrate, tetraethyl orthosilicate, aluminum isopropoxide, polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, and a porous thermal insulation material as raw materials; Electrospinning the spinning sol to obtain a fibrous membrane; Drying and pre-firing the fibrous membrane to obtain a green body fibrous membrane; Immersing the green body fibrous membrane, AlF3, and SiO2 nanoflour in an ethanol solution, and filtering to obtain a fibrous membrane loaded with a catalyst; Sintering the fibrous membrane loaded with the catalyst to obtain the whisker / fiber secondary structure composite membrane layer flexible thermal insulation material.

2. The preparation method of the whisker / fiber secondary structure composite film flexible thermal insulation material according to claim 1, characterized in that, Preparing the spinning sol using aluminum nitrate, tetraethyl orthosilicate, aluminum isopropoxide, polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, and a porous thermal insulation material as raw materials, specifically: dissolving aluminum nitrate, tetraethyl orthosilicate, and aluminum isopropoxide in water, then adjusting the pH value of the system to acidic to obtain a precursor sol; dissolving polyethylene oxide, polyvinyl alcohol, and polyvinylpyrrolidone in water, then performing a stirring reaction to obtain a spinning aid; after uniformly mixing the spinning aid with the precursor sol, adding the porous thermal insulation material, and then mixing uniformly to obtain the spinning sol.

3. The preparation method of the whisker / fiber secondary structure composite film layer flexible thermal insulation material according to claim 1 or 2, characterized in that, The mass ratio of aluminum nitrate, tetraethyl orthosilicate, and aluminum isopropoxide is 20-40:10-30:10-50; the mass ratio of polyethylene oxide, polyvinyl alcohol, and polyvinylpyrrolidone is 1-2:1-5:0.5-2; the mass ratio of the spinning aid to the precursor sol is 0.5-3:

5.

4. The preparation method of the whisker / fiber secondary structure composite film flexible thermal insulation material according to claim 2, wherein The stirring reaction is specifically: first stirring at 60-90°C for 5-20 h under reflux condensation conditions, and then cooling to room temperature and stirring for another 5-20 h.

5. The preparation method of the whisker / fiber secondary structure composite film flexible thermal insulation material according to claim 1 or 2, characterized in that, The porous thermal insulation material is SiO2 aerogel, Al2O3 aerogel, or SiC porous ceramic particles; the mass percentage of the porous thermal insulation material in the spinning sol is 2-12%.

6. The preparation method of the whisker / fiber secondary structure composite film layer flexible thermal insulation material according to claim 1, characterized in that, The parameter settings for the electrospinning are: positive voltage is 15 kV, negative voltage is 13 kV, the pushing speed of the micro pump is 1-1.5 mL / h, the spinning distance is 15-20 cm, the ambient temperature is 25°C, and the ambient humidity is 20-30%.

7. The preparation method of the whisker / fiber secondary structure composite film layer flexible thermal insulation material according to claim 1, wherein, The temperature of the pre-firing is 800°C, and the time is 0.5-2 h.

8. The preparation method of the whisker / fiber secondary structure composite film layer flexible thermal insulation material according to claim 1, characterized in that, The mass ratio of the green body fibrous membrane, AlF3, and SiO2 nanoflour is 2-5:1-3:1-3.

9. The preparation method of the whisker / fiber secondary structure composite film flexible thermal insulation material according to claim 1, characterized in that, The temperature of the sintering is 1200-1500°C, and the time is 0.5-3 h.

10. A whisker / fiber secondary structure composite membrane layer flexible thermal insulation material prepared by the preparation method according to any one of claims 1-9.

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