Whisker / fiber secondary structure composite film layer flexible thermal insulation material and preparation method thereof

Abstract

The application 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 application prepares a spinning sol by taking AN, TEOS, AIP, PEO, PVA, PVP and porous thermal insulation material as raw materials, then electrostatic spinning is carried out to prepare a fiber film, the fiber film is pre-burned, AlF3 and SiO2 are loaded, and finally sintering is carried out to catalyze the secondary structure. Through the structural design, the whisker secondary structure with different directions and capable of being mutually overlapped to form a frame is grown on the fiber main body of the fiber film, the porosity of the fiber film layer is further improved, the microstructure of the fiber film layer is improved, another new way of improving the thermal insulation performance of the composite material is opened up in addition to reducing the thermal conductivity of the loaded aerogel, and the thermal conductivity of the obtained thermal insulation material is lower than 0.038 W / (m*K).

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible thermal insulation materials, in particular to a whisker / fiber secondary structure composite membrane layer flexible thermal insulation material and a preparation method thereof. BACKGROUND

[0002] No matter what 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), which is called heat transfer. Thermal insulation materials have heat preservation or cooling function and heat shielding function, which can reduce heat loss by affecting heat conduction, convection and radiation, and thus improve the utilization efficiency of energy.

[0003] At present, although the layered composite material of aerogel-fiber is an important research direction of high-performance flexible thermal insulation material, there are still some problems to be improved: ① the thermal conductivity of aerogel after being combined with fiber is still high, and the thermal conductivity is generally above 0.03 W / (m·k), which is still difficult to meet the needs of special fields in actual production; ② the uneven distribution and chaotic orientation of the fiber will affect the mechanical properties of the composite material. For the problem of low thermal conductivity mentioned above, the usual way is to improve the performance of aerogel to reduce the overall thermal conductivity of the composite material. However, it can be found that the main reason for the high thermal conductivity is the fiber layer. It is 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 the aerogel. For the second problem mentioned above, if the fiber is replaced by fiber membrane / mat, the uneven distribution and orientation of the fiber in the nano-porous material can be well avoided, but the problem of relatively dense fiber layer cannot be solved. SUMMARY

[0004] Therefore, the present application aims to provide a whisker / fiber secondary structure composite membrane layer flexible thermal insulation material and a preparation method thereof.

[0005] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0006] One of the technical schemes of the present application is a preparation method of a whisker / fiber secondary structure composite membrane layer flexible thermal insulation material, comprising the following steps:

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

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

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

[0010] The green fiber membrane, AlF3 and SiO2 nano powder are dipped in an ethanol solution, filtered to obtain the fiber membrane loaded with catalyst;

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

[0012] The whisker / fiber secondary structure composite membrane layer flexible thermal insulation material prepared by the preparation method.

[0013] The present application has the following technical effects:

[0014] The present application adopts a dry process, mixes the fiber and catalyst dry powder, generates the wool-like mullite whisker on the surface of the fiber by using in-situ synthesis method during sintering, and prepares the whisker / fiber secondary structure composite membrane layer flexible thermal insulation material by a simpler process.

[0015] The present application reduces the content of organic matter in the current industrial thermal insulation material, breaks through the limitation of use temperature, and prepares the flexible thermal insulation material capable of being used in the range of 600-1200 DEG C.

[0016] The present application greatly reduces the thermal conductivity while keeping the flexibility of the product, and the thermal conductivity is lower than 0.038 W / (m*K). BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced below, and obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

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

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

[0020] Now, various exemplary embodiments of the present application will be described in detail, and the detailed description should not be considered as a limitation of the present application, but should be understood as a more detailed description of some aspects, characteristics and embodiments of the present application.

[0021] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Additionally, for a range of values, the disclosure herein shall be interpreted as disclosing every value and sub-range within the range. Every middle point of the range or the sub-range is disclosed. The upper limit and the lower limit of these smaller ranges can be independently included or excluded in the ranges.

[0022] Unless otherwise defined, 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 application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All publications mentioned in this specification are herein incorporated by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The citation of any reference is not construed as an admission that it is prior art with respect to the present application.

[0023] Many modifications and variations of this application of the application can be made without departing from its spirit or scope, which will be apparent to those skilled in the art. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are exemplary only.

[0024] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended and do not exclude additional, unrecited elements or method steps.

[0025] The present application first prepares a spinning sol with AN, TEOS, AIP, PEO, PVA, PVP and porous thermal insulation material as raw materials, then electrospins to prepare a fiber membrane, pre-burns the fiber membrane, and co-filters the fiber membrane with catalysts AlF3 and SiO2, and finally sintering to obtain a composite material with secondary structure. Through structural design, the present application grows whisker secondary structures with different directions on the fiber body of the fiber membrane, which can be mutually overlapped to form a framework, thereby ensuring the mechanical properties of the fiber membrane layer, further improving the porosity and improving the microstructure of the fiber membrane layer, and opening up another 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 present application provides a preparation method of a whisker / fiber secondary structure composite membrane layer flexible thermal insulation material, including the following steps:

[0027] Preparation of a spinning sol with aluminum nitrate, tetraethyl orthosilicate, aluminum isopropoxide, polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone and porous thermal insulation material as raw materials;

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

[0029] drying and pre-burning the fiber membrane to obtain a green fiber membrane;

[0030] immersing the green fiber membrane, AlF3 and SiO2 nano-powder in an ethanol solution, filtering to obtain a fiber membrane loaded with catalyst;

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

[0032] In the preferred embodiment of the present application, the spinning sol is prepared by using aluminum nitrate (AN), tetraethyl orthosilicate (TEOS), aluminum isopropoxide (AIP), polyethylene oxide (PEO), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP) and 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 be acidic to obtain a precursor sol; dissolving polyethylene oxide, polyvinyl alcohol and polyvinylpyrrolidone in water, then stirring and reacting to obtain a spinning aid; mixing the spinning aid and the precursor sol uniformly, then adding porous thermal insulation material, then mixing uniformly to obtain a spinning sol, then electrospinning the spinning sol to obtain a fiber membrane.

[0033] In the preferred embodiment of the present application, the mass ratio of the 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 the 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 and the precursor sol is 0.5-3:5 (further preferably, 2-3:5, 2:5).

[0034] In the present application, if the proportion of raw materials is not within the above-mentioned parameter range, it will result in that uniform fiber with suitable porosity cannot be obtained during electrospinning, on the one hand, the fiber cannot be spun due to too poor spinnability of the fiber, and the fiber falls in the form of liquid droplets, on the other hand, the fiber cannot fall to the negative electrode in time due to too poor conductivity of the spinning solution and a series of problems.

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

[0036] In the present application, if the solvent (water) is too little to be dissolved effectively, or too much to prolong the concentration time and reduce the production efficiency.

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

[0038] In the present application, if the pH value is not appropriate, the catalytic effect cannot be achieved, resulting in that the molecular structure cannot be linear, and the sol can be affected.

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

[0040] In the present application, if the reaction time and conditions are not appropriate, the reaction cannot be repeated, the sol structure cannot be linear, or the composition is not uniform. It also affects the sol concentration, resulting in problems in the electrostatic method.

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

[0042] In the preferred embodiment of the present application, the particle size of the SiO2 aerogel is 10-15μm, and the purity is ≥99%, which has strong hydrophobicity. If the particle size of the aerogel is not appropriate, the continuity of the fiber after spinning will be damaged, the fiber will be too short and too broken, and the final performance will be affected.

[0043] In the preferred embodiment of the present application, the parameters of the electrospinning are set as follows: the positive voltage is 15kV, the negative voltage is 13kV, the micro pump pushing speed is 1-1.5mL / h, the spinning distance is 15-20cm, the environmental temperature is 25°C, and the environmental humidity is 20-30%. If the spinning parameters are not appropriate, the spinning cannot be successfully carried out, the fiber cannot be formed, or the spinning efficiency is low.

[0044] In the preferred embodiment of the present application, the drying temperature is 75°C, and the time is 1-2h. If the drying is not good, the gel fiber is easy to have surface cracks, which affects the quality after sintering.

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

[0046] In the preferred embodiment of the present application, the mass ratio of the green fiber membrane, AlF3 and SiO2 nanopowder is 2-5:1-3:1-3 (further preferably, 2:1:1).

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

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

[0049] In the preferred embodiment of the present application, the sintering temperature is 1200-1500℃ (further preferably, 1250℃), and the time is 0.5-3 (further preferably, 1h). If the sintering process is not within the parameter range of the present application, the secondary structure cannot be catalyzed, or the final product does not have flexibility.

[0050] In the present application: 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 whisker is too short, it cannot increase the specific surface area, and if it is too long, it has the risk of damaging the original membrane mechanical properties. The present application 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.

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

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

[0053] The technical solutions of the present application, if not specifically stated, are conventional solutions in the art. The reagents or raw materials used, if not specifically stated, are purchased from commercial channels or have been disclosed.

[0054] In order to better understand the present application, the content of the present application will be further illustrated by the following examples, but the content of the present application is not limited to the following examples.

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

[0056] Example 1

[0057] A preparation method of a whisker / fiber secondary structure composite membrane layer flexible thermal insulation material (referred to as thermal insulation material), the steps are as follows:

[0058] 1. Preparation of precursor sol

[0059] Dissolve aluminum nitrate in water, then add tetraethyl orthosilicate and aluminum isopropoxide in sequence, wherein the mass ratio of AN:TEOS:AIP is 37:22:41, and the mass ratio of AN to water is 1:1, and then add oxalic acid and glacial acetic acid in a volume ratio of 1:1 after magnetic stirring for 1 min, adjust the pH value of the system to about 5, then magnetically stir at a speed of 300 r / min for 20 h, and a transparent sol is obtained.

[0060] 2. Preparation of a spinning aid

[0061] Dissolve polyethylene oxide, polyvinyl alcohol and polyvinylpyrrolidone in deionized water, wherein the mass ratio of PEO:PVA:PVP:deionized water is 1:1:1:1, stir at 80°C in a condensation reflux device for 10 h, then cool to room temperature and stir for another 8 h, and a spinning aid is obtained.

[0062] 3. Preparation of a spinning sol

[0063] Slowly drop the spinning aid into the precursor sol (the mass ratio of the spinning aid to the precursor sol is 2:5), magnetically stir at a speed of 500 r / min for 1 h, then add 5% silica aerogel by mass fraction to the spinning sol, and continue to stir for 20 h, and a semi-transparent spinning sol is obtained.

[0064] 4. Preparation of a fiber membrane by electrospinning

[0065] Carry out electrospinning under the following conditions: a positive voltage of 15 kV, a negative voltage of 13 kV, a micro pump push 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%, and a uniform, dense and flexible fiber membrane is obtained.

[0066] 5. Catalysis of a secondary structure

[0067] Dry the fiber membrane obtained in step (4) in an oven at 75°C for 2 h, then place it in a muffle furnace and pre-burn at 800°C for 1 h, and a green fiber membrane is obtained.

[0068] Then immerse 2 g of the green fiber membrane in ethanol together with 1 g of AlF3 and 1 g of SiO2 nano powder for 2 h, then filter together, and a fiber membrane loaded with a catalyst is obtained.

[0069] Sinter the fiber membrane loaded with the catalyst in a muffle furnace at 1250°C for 1 h, and a thermal insulation material is obtained.

[0070] Test the thermal conductivity and high-temperature performance of the thermal insulation material obtained in this embodiment by using the transient plane heat source test method. The thermal insulation material obtained in this embodiment has a high use temperature, which can reach 600-1200°C, while maintaining the flexibility feature. The thermal conductivity is 0.38 W / (m·K).

[0071] Comparative Example 1

[0072] The difference between Example 1 and Comparative Example 1 is that 2 g of the base fiber membrane is replaced by 7 g of the base fiber membrane, 1 g of AlF3 and 1 g of SiO2 nano powder are replaced by 4 g of AlF3 and 4 g of SiO2 nano powder, and the other parameters and steps are the same as those of Example 1.

[0073] The thermal insulation material prepared in the present application has a clear secondary structure. Figure 1 and Figure 2 It can be seen that the thermal insulation material prepared in the present application has a clear secondary structure.

[0074] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled persons in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing a flexible thermal insulation material of a whisker / fiber secondary structure composite film layer, characterized in that, The method comprises the following steps: The spinning sol is prepared by using aluminum nitrate, tetraethyl orthosilicate, aluminum isopropoxide, polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone and porous thermal insulation material as raw materials, specifically, the aluminum nitrate, tetraethyl orthosilicate and aluminum isopropoxide are dissolved in water, then the pH value of the system is adjusted to be acidic to obtain a precursor sol; the polyethylene oxide, polyvinyl alcohol and polyvinylpyrrolidone are dissolved in water, then stirring reaction is carried out to obtain a spinning aid; the spinning aid and the precursor sol are uniformly mixed, then the porous thermal insulation material is added and uniformly mixed to obtain the spinning sol; The spinning sol is electrospun to obtain a fiber membrane; The fiber membrane is dried and pre-fired to obtain a green fiber membrane; The green fiber membrane, AlF3 and SiO2 nano powder are immersed in an ethanol solution and filtered to obtain a fiber membrane loaded with catalyst; The fiber membrane loaded with catalyst is sintered to obtain the whisker / fiber secondary structure composite membrane layer flexible thermal insulation material; The porous thermal insulation material is SiO2 aerogel, and the particle size of the SiO2 aerogel ranges from 10 to 15 μm; The pre-firing temperature is 800 ℃, and the time is 0.5-2 h; The mass ratio of the green fiber membrane, AlF3 and SiO2 nano powder is 2-5:1-3:1-3; The sintering temperature is 1200-1500 ℃, and the time is 0.5-3 h; The spinning sol is prepared by using aluminum nitrate, tetraethyl orthosilicate, aluminum isopropoxide, polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone and porous thermal insulation material as raw materials, specifically, the aluminum nitrate, tetraethyl orthosilicate and aluminum isopropoxide are dissolved in water, then the pH value of the system is adjusted to be acidic to obtain a precursor sol; the polyethylene oxide, polyvinyl alcohol and polyvinylpyrrolidone are dissolved in water, then stirring reaction is carried out to obtain a spinning aid; the spinning aid and the precursor sol are uniformly mixed, then the porous thermal insulation material is added and uniformly mixed to obtain the spinning sol; The mass ratio of the aluminum nitrate, tetraethyl orthosilicate and aluminum isopropoxide is 20-40:10-30:10-50; the mass ratio of the polyethylene oxide, polyvinyl alcohol and polyvinylpyrrolidone is 1-2:1-5:0.5-2; the mass ratio of the spinning aid and the precursor sol is 0.5-3:5; The stirring reaction is specifically as follows: first, stirring is carried out at 60-90 ℃ under condensation reflux for 5-20 h, then the temperature is cooled to room temperature and stirring is carried out again for 5-20 h.

2. The method for preparing the flexible thermal insulation material with a whisker / fiber secondary structure composite film layer according to claim 1, characterized in that, The mass percentage of the porous thermal insulation material in the spinning sol is 2-12%.

3. The method for preparing the flexible thermal insulation material with a whisker / fiber secondary structure composite film layer according to claim 1, characterized in that, The parameters of the electrospinning are as follows: positive voltage is 15 kV, negative voltage is 13 kV, micro pump pushing speed is 1-1.5 mL / h, spinning distance is 15-20 cm, ambient temperature is 25 ℃, and ambient humidity is 20-30%.

4. The whisker / fiber secondary structure composite membrane layer flexible thermal insulation material prepared by the preparation method according to any one of claims 1-3.

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