Method for manufacturing aerogel sheet, aerogel sheet and use thereof

Abstract

The present invention provides a simple, environmentally friendly method for manufacturing aerogel panels. This method surpasses the laboratory-scale limitations of conventional freeze-casting techniques, which typically produce panels smaller than 5 centimeters. It enables the production of large-scale aerogel panels with uniform pore sizes and parallel pore channels. The aerogel panels produced using this method exhibit ultra-low thermal conductivity and high light reflectivity across their thickness, making them suitable for practical applications in thermal insulation and / or heat preservation, such as exterior walls and roofs of buildings.

Description

Technical Field

[0001] The present invention relates to the field of aerogel plate manufacturing, and more particularly, provides a novel method for manufacturing aerogel plates, an aerogel plate manufactured by the method and uses thereof. Background Art

[0002] Aerogel materials have attracted much attention in thermal insulation applications due to their low density, high porosity and low thermal conductivity. Due to the extensive use of air conditioners during the hot summer, aerogel materials with low thermal conductivity show great potential to reduce the high energy consumption of buildings. In order to achieve ultra-low thermal conductivity and excellent thermal insulation performance, anisotropic aerogels with pores arranged in a predetermined direction can be manufactured using a unidirectional freeze casting technique. Although the thermal insulation performance of highly anisotropic aerogels in the radial direction is very promising, for example, their thermal conductivity is less than 24m Wm -1 K -1 However, conventional freeze-casting apparatus and the physical limitations of ice crystal growth (due to thermal conductivity limitations) greatly hinder the large-scale production of aerogel materials for practical thermal insulation applications.

[0003] Several factors, including the cooling rate of the heat sink and the temperature gradient between the heat sink and the surrounding environment, influence the solidification pattern of the colloidal solution, which in turn determines the pore arrangement in the aerogel. In practice, when using a single heat sink, a constant freezing rate can only be achieved over a few centimeters. Using dual-sided heat sinks can achieve a constant freezing rate over longer distances. However, the size of aerogels with uniform pore arrangement is still limited by the short freezing length. Several existing methods exist for producing large-scale aerogels. However, these methods aim to produce aerogels with pores aligned along the thickness using a bottom heat sink. When used as insulation, these methods promote heat transfer between the roof and the building's exterior environment. Therefore, these methods are not suitable for producing aerogels for building insulation. In addition to low thermal conductivity through the thickness, aerogels should also be able to effectively reflect sunlight to avoid heat gain due to daytime solar radiation. However, the optical reflectivity of aerogels reported in the prior art is not ideal, requiring additional reflective coatings or finishes for practical applications.

[0004] In view of the above situation, there is a need in the art for a universal and easy-to-operate method for manufacturing aerogel panels, which can manufacture large-sized aerogel panels with ultra-low thermal conductivity and high light reflectivity. Summary of the Invention

[0005] As previously mentioned, there is a need in the art for a large-scale aerogel sheet with uniformly arranged and parallel porous channels perpendicular to the thickness direction. This helps achieve ultra-low thermal conductivity and high light reflectivity in the thickness direction, and can therefore be used as a thermal insulation material for building exterior walls and roofs. Based on this, the inventors of the present invention have designed the following method for manufacturing aerogel sheets.

[0006] In a first aspect of the present invention, there is provided a method for manufacturing an aerogel sheet, comprising the following steps:

[0007] 1) providing a water-based colloidal solution;

[0008] 2) freeze-casting the aqueous colloidal solution piece by piece in a freezing mold using a movable side cooling source, thereby obtaining a frozen sample;

[0009] 3) Freeze-drying the frozen sample to obtain an aerogel plate.

[0010] In a second aspect, an aerogel plate is provided, wherein the aerogel plate has pore channels parallel to the plane of the aerogel plate, with uniform pore diameters and uniform arrangement.

[0011] In a third aspect, there is provided use of the aerogel board manufactured by the method of the first aspect or the aerogel board of the second aspect for construction applications such as roofs and exterior walls of buildings.

[0012] The benefits of the present invention are that the method for manufacturing aerogel panels of the present invention is simple to operate and environmentally friendly. It can not only manufacture aerogel panels with ultra-low thermal conductivity and high light reflectivity, but also break through the laboratory scale that is usually less than 5 cm and can realize the manufacture of large-scale aerogel panels, making it suitable for actual building insulation, heat preservation and other applications as a thermal insulation material. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, together with the embodiments of the present invention, provide further explanation of the present invention and constitute a part of the specification. It should be understood that the drawings described below relate only to some embodiments of the present invention and do not limit the present invention. It will be apparent to those skilled in the art that other embodiments can be derived from these drawings without inventive effort.

[0014] Figure 1 A schematic diagram showing a manufacturing apparatus and its mechanism for manufacturing an aerogel plate by freeze casting using a movable side cooling source according to one embodiment of the method of the present invention.

[0015] Figure 2 Digital photos and scanning electron microscope (SEM) photos of aerogel samples manufactured according to the method of the present invention are shown, wherein AI shows different areas of the aerogel plate.

[0016] Figure 3 A photograph (a) showing an aerogel plate manufactured using a movable side cooling source according to an embodiment of the present invention, and a transverse dimension (20×20 cm) of the aerogel plate. 2)(b) and thickness (≤1cm)(c) tests.

[0017] Figure 4 Shown are measurements of thermal conductivity and light reflectivity of different regions of an aerogel sheet according to one embodiment of the present invention.

[0018] Figure 5 The high flexibility of the aerogel sheet sample according to one embodiment of the present invention is shown.

[0019] Figure 6 UV-vis spectra of homemade WPU solid films, expanded polystyrene (EPS) foam coated with commercial reflective coatings, silica (SiO2)-based aerogels, WPU aerogels according to the present invention, and BNNS / WPU composite aerogels are shown.

[0020] Figure 7 A diagram showing field tests of aerogel panels according to one embodiment of the present invention, aerogels with highly reflective coatings (commercial EPS), silica (SiO2)-based aerogels, and glass for applications in thermal insulation and light reflectivity.

[0021] Figure 8 Graph showing temperature variations over time of an aerogel panel according to one embodiment of the present invention, a silicon dioxide (SiO2) based aerogel with a highly reflective coating (commercial EPS), the inside of glass, and the ambient temperature during field testing. DETAILED DESCRIPTION

[0022] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. It should be understood that the following description is merely illustrative of the present invention and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be subject to the appended claims. Furthermore, those skilled in the art will appreciate that the technical solutions of the present invention may be modified without departing from the spirit and purpose of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0023] 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 the subject matter of the present invention belongs. Before describing the present invention in detail, the following definitions are provided for a better understanding of the present invention.

[0024] Where a numerical range is provided, such as a concentration range, a percentage range, or a ratio range, it is understood that each intervening value, to the tenth of the unit of the lower limit, between the upper and lower limits of the range and any other stated or intervening values ​​in the stated range are encompassed within the subject matter unless the context clearly dictates otherwise. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges, and such embodiments are also encompassed within the subject matter, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also encompassed within the subject matter.

[0025] Throughout the application, many embodiments use the expressions "comprising", "including" or "consisting essentially / mainly of..." The expressions "comprising", "including" or "consisting essentially / mainly of..." can generally be understood as open-ended expressions, indicating that not only the elements, components, assemblies, method steps, etc. specifically listed after the expression are included, but also other elements, components, assemblies, method steps, etc. are included. In addition, in this document, the expressions "comprising", "including" or "consisting essentially / mainly of..." can also be understood as closed-ended expressions in some cases, indicating that only the elements, components, assemblies, method steps specifically listed after the expression are included, but no other elements, components, assemblies, method steps are included. In this case, the expression is equivalent to the expression "consisting of..."

[0026] For a better understanding of the present teachings and without limiting the scope of the present teachings, all numbers and other numerical values ​​expressing quantities, percentages or ratios used in the specification and claims should be understood as being modified in all cases by the term "about", unless otherwise indicated. Therefore, unless indicated to the contrary, the numerical parameters set forth in the following specification and the appended claims are approximate values ​​that may vary depending on the desired properties sought to be obtained. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0027] As mentioned above, for practical building insulation applications, the art urgently needs a universal and simple aerogel board manufacturing method, which can produce aerogel boards with large sizes, ultra-low thermal conductivity and high light reflectivity that are different from laboratory scale (less than 5 cm). The manufactured aerogel boards thus have the potential to be used as insulation materials for the exterior of buildings.

[0028] In a first aspect of the present invention, there is provided a method for manufacturing an aerogel sheet, comprising the following steps:

[0029] 1) providing a water-based colloidal solution;

[0030] 2) freeze-casting the aqueous colloidal solution piece by piece in a freezing mold using a movable side cooling source, thereby obtaining a frozen sample;

[0031] 3) Freeze-drying the frozen sample to obtain an aerogel plate.

[0032] In a specific embodiment, the aqueous colloidal solution comprises:

[0033] - polymer particles having at least one dimension ranging from 1 nm to 1 μm in a concentration in the range of 1% to 10% by weight; and

[0034] - Inorganic and / or organic nanofillers having at least one dimension smaller than 100 nanometers, representing from 0% to 60% by weight of the sum of the weight of the polymer particles and the nanofillers.

[0035] In a preferred embodiment, the concentration of the polymer particles is in the range of 1 wt % to 5 wt %, for example, 1.4 wt % or 2.5 wt %.

[0036] In a more preferred embodiment, the concentration of the polymer particles is in the range of 1.4 wt%.

[0037] In another embodiment, the inorganic and / or organic nanofillers comprise 1 wt%, 5 wt%, 10 wt%, 20 wt%, or 50 wt%, e.g., 5 wt% to 20 wt%, of the combined weight of the polymer particles and the nanofillers.

[0038] Aerogels, made from aqueous colloidal solutions containing polymers and, optionally, inorganic or organic nanoparticles, are promising materials for building insulation applications. A simple and environmentally friendly method for large-scale production of aerogel panels is freeze-casting aqueous colloidal solutions, as this method does not require a complex setup. A temperature gradient between a movable lateral cooling source and the surroundings (or, in other words, the closed end of the freezing mold) enables ice crystal growth, which in turn pushes particles in the aqueous colloidal solution toward the boundaries of the ice crystals. The subsequent freeze-drying step causes the ice to sublime, forming parallel porous channels surrounded by solid chamber walls.

[0039] As used herein, the term "aqueous colloidal solution" refers to a colloidal solution formed by dispersing particles of at least one polymer molecule in water, wherein at least one dimension of the particles of the at least one polymer molecule is in the range of 1 nanometer to 1 micrometer.

[0040] In a more specific embodiment, the polymer particles are waterborne polyurethane (WPU) particles, waterborne polyvinyl alcohol particles, waterborne polyimide particles, preferably waterborne polyurethane particles.

[0041] In yet a more specific embodiment, the inorganic or organic nanofiller is boron nitride nanosheets (BNNS).

[0042] In a preferred embodiment, the polymer particles are waterborne polyurethane particles with a concentration of 1.4 wt %; the nanofiller is boron nitride nanosheets (BNNS), which accounts for 10 wt % of the total weight of the waterborne polyurethane particles and the BNNS.

[0043] The addition of at least one inorganic and / or organic nanofiller to the aqueous colloidal solution of polymer particles is intended to further modify the properties of the aerogel sheet. For example, boron nitride nanosheets can be used to modulate thermal conductivity in the alignment direction, further reducing heat transfer through the thickness without compromising the aerogel sheet's high light reflectivity.

[0044] As used herein, the term "nanofiller" refers to an organic and / or inorganic filler having a size of less than 100 nanometers in at least one dimension.

[0045] The choice of raw materials for the aqueous colloidal solution depends on the desired properties of the aerogel. All raw materials disclosed herein are, in principle, suitable for providing aerogels with low thermal conductivity and high light reflectivity. However, due to differences in the manufacturing process, the microstructure of the resulting aerogel can also vary.

[0046] In a specific embodiment, step 1) of the method of the present invention comprises:

[0047] 1-1) The polymer particles are dispersed in water, thereby obtaining the water-based alternating solution.

[0048] In another specific embodiment, step 1) of the method of the present invention comprises:

[0049] 1-2-1) dispersing the inorganic and / or organic nanofiller in water, for example, by subjecting it to ultrasonic treatment in an ultrasonic bath at 15° C. to 30° C. for 10 minutes to 2 hours, thereby obtaining a nanofiller dispersion; and

[0050] 1-2-2) mixing the nanofiller dispersion with an aqueous solution obtained by dispersing the polymer particles in water, for example by stirring at 15° C. to 30° C. for at least 10 hours, for example 12 hours, 16 hours, 20 hours, or 24 hours, to obtain the water-based colloidal solution.

[0051] In a preferred embodiment, step 1) comprises:

[0052] 1-2-1′) dispersing the inorganic and / or organic nanofiller in water, for example, by subjecting it to ultrasonic treatment in an ultrasonic bath at 20° C. for 30 minutes, thereby obtaining a nanofiller dispersion; and

[0053] 1-2-2′) Mixing the nanofiller dispersion with an aqueous solution obtained by dispersing the polymer particles in water, for example, by stirring at room temperature for 12 hours, thereby obtaining the water-based colloidal solution.

[0054] In a specific embodiment, step 2) of the method of the present invention comprises:

[0055] 2-1) moving the movable side cooling source so that its proximal end is spaced apart from the side closed end of the freezing mold by an effective freezing distance, thereby forming a freezing space in the freezing mold;

[0056] 2-2) pouring the aqueous colloidal solution into the freezing space and waiting for a time sufficient for the aqueous colloidal solution to solidify into a block, for example, waiting for at least 10 minutes, for example, 15 minutes;

[0057] Optionally, repeat steps 2-1) and 2-2) to obtain a frozen sample of a desired length.

[0058] As used herein, the term "removable side cooling source" refers to a movable cooling source positioned opposite the closed end of the freezing mold, with its proximal end in direct contact with the aqueous colloidal solution to be frozen, for freezing the aqueous colloidal solution. The term "side" refers to a surface opposite / parallel to the closed end of the freezing mold. The term "proximal end" refers to the end of the movable side cooling source in contact with the aqueous colloidal solution to be frozen.

[0059] By spacing the proximal end of the movable side cooling source from the side closed end of the freezing mold by an effective freezing distance, a freezing space defined by the proximal end of the movable side cooling source and the side closed end of the freezing mold can be formed in the freezing mold.

[0060] A previous study compared the pore density of cross sections at two different locations about 1 cm apart in the growth direction of the ice crystals. The results showed that the pore density decreased by 30% when the distance from the cold source was about 1 cm. This means that the pore size increases as the distance from the cold source increases. This uneven pore size along the growth direction of the ice crystal can be attributed to the increase in freezing temperature as the solidification front moves away from the cold source. When the solidification front is too far away from the cold source, the temperature of the solidification front is ultimately unable to remain low enough to drive the directional growth of the ice crystals, resulting in randomly arranged pores far away from the cold source. One of the biggest challenges in using freeze casting technology to manufacture large-scale aerogel plates is to maintain a consistent pore size across the entire size of the sample.

[0061] As used herein, the term "freezing front" refers to the boundary between the solidified portion and the unsolidified portion in the water-based colloidal solution, and the boundary gradually moves away from the lateral cooling source as ice crystals continue to grow.

[0062] Therefore, in one embodiment, the freezing effective distance is no more than 15 mm, for example, no more than 14 mm, no more than 13 mm, no more than 12 mm, no more than 11 mm or no more than 10 mm, or any numerical value in the range of any two of the above numerical values. In a preferred embodiment, the freezing effective distance range is 10 mm to 15 mm. Without wishing to be bound by theory, the inventors have found that the aerogel plate obtained according to this preferred embodiment of the present invention has pore channels that are parallel to each other (or in other words, highly oriented) and evenly arranged. Such pore channels that are parallel to each other can significantly reduce the heat conduction in the thickness direction of the aerogel plate, thereby achieving thermal insulation.

[0063] As used herein, the term "freezing effective distance" refers to the distance between the proximal end of the movable side cold source and the side closed end of the freezing mold so that the aerogel block obtained according to the method of the present invention can have pore channels with basically uniform pore size, uniform arrangement and parallel to each other.

[0064] In yet another specific embodiment, the movable side cooling source provides a low temperature as low as -170°C.

[0065] In a further specific embodiment, the movable side cooling source is a metal container filled with a cold medium such as liquid nitrogen.

[0066] In a further specific embodiment, the metal is a thermally conductive metal material such as a single metal such as aluminum, copper, etc., or an alloy such as stainless steel, etc.

[0067] As used herein, the term "thermally conductive metal" refers to a metal material having relatively high thermal conductivity.

[0068] Figure 1The exemplary schematic diagram of the freeze pouring device used according to the method of the present invention is shown. The movable side cold source can be a metal container filled with liquid nitrogen. Therefore, the temperature of this movable side cold source can be about -170 ℃. The freezing mold is made of a material such as polytetrafluoroethylene that can withstand low temperatures, for example -170 ℃. The metal container is placed in the freezing mold. The near end of the cold source and the closed end of the freezing mold are separated by a certain distance, such as 15 mm, thereby forming a freezing space for freezing the water-based colloidal solution in the freezing mold. The water-based colloidal solution to be frozen is poured into the freezing space in the freezing mold and solidified under the temperature gradient driven between the near end of the metal container (such as, about -170 ℃) and the closed end of the freezing mold (such as, room temperature). After solidification is completed, the metal container is continued to move a distance (such as 15 mm) in the direction away from the closed end of the freezing mold, thereby forming another freezing space in the freezing mold. Another aqueous colloidal solution is then poured into the additional freezing space, and freeze casting is continued to form new aerogel blocks, which are connected to the previously solidified aerogel blocks. The above steps can be repeated several times, thereby freeze casting the aqueous colloidal solution piece by piece. In addition, it will be understood that the freezing distance in each freeze casting step can be the same or different, depending on the specific circumstances. In addition, it will be understood that the size of the aerogel plate can be determined by customizing the size of the freezing mold (more specifically, the width dimension) and the total number of solidified aerogel blocks.

[0069] As used herein, the term "block by block" refers to obtaining aerogel blocks having a freezing effective distance by freezing a water-based colloidal solution by repeating steps 2-1) and 2-2), thereby obtaining aerogel plates of the desired size (lateral size).

[0070] In a specific embodiment, the freeze drying in step 3) of the method of the present invention is carried out under vacuum conditions at a temperature at least 20° C. lower than the freezing point of the aqueous colloidal solution for at least 48 hours.

[0071] The frozen sample is freeze-dried under vacuum conditions to remove ice by sublimation. Freeze-drying can be performed using equipment familiar to those skilled in the art, such as a commercially available freeze dryer. Furthermore, those skilled in the art can appropriately increase or decrease the drying time based on the vacuum conditions of the freeze dryer used.

[0072] In a further specific embodiment, the vacuum condition may be a low pressure condition of 0.1 mbar to 0.4 mbar. Preferably, the vacuum condition may be a low pressure condition of 0.2 mbar to 0.3 mbar.

[0073] In a further specific embodiment, the freeze-drying temperature may be -40° C. Those skilled in the art can reasonably select the freeze-drying temperature according to the aqueous colloidal solution used.

[0074] In a preferred embodiment, a longer freeze-drying time can be used to ensure that all moisture in the aerogel is removed. For example, freeze-drying can be performed for at least 96 hours, 120 hours, 144 hours, etc. Generally, the less moisture remaining in the aerogel, the lower the density and the higher the porosity of the resulting aerogel. A person skilled in the art can select a reasonable drying time based on actual needs, such as the performance of the freeze dryer and the properties of the aqueous colloidal solution used.

[0075] After freeze drying step 3), aerogel sheets of desired size can be obtained. The desired size of the aerogel sheet can be achieved by customizing the size of the freezing mold and determining the total number of frozen aerogel blocks.

[0076] In a second aspect, an aerogel plate is provided, wherein the aerogel plate has pore channels parallel to the plane of the aerogel plate, with uniform pore diameters and uniform arrangement.

[0077] As previously described, the temperature gradient between the movable side cooling source and the surrounding environment (or the closed end of the freezing mold) enables the continuous growth of ice crystals, which in turn pushes particles in the aqueous colloidal solution toward the boundaries of the ice crystals. The subsequent freeze-drying step causes the ice to sublime, thereby forming porous channels parallel to the direction of ice crystal growth and surrounded by solid chamber walls. The inventors further selected an appropriate freezing distance to ensure that the pore diameters in the frozen block are substantially uniform. After ice sublimation, the resulting pore channels are (highly) parallel to each other, thereby forming an aerogel sheet with reduced heat transfer through the thickness direction.

[0078] As used herein, the term "uniform pore size" means that the pores in the aerogel sheet all have a diameter ranging from 15 to 30 microns. Those skilled in the art will understand that, in general, the pore size will vary with the distance between the solidification front and the lateral cooling source along the direction of ice crystal growth in the aerogel sheet, and will generally increase as this distance increases.

[0079] As used herein, the term "uniformly arranged" means that the pore channels in the aerogel plate are evenly distributed, without being particularly dense or particularly loose. Those skilled in the art will clearly understand the meaning of this term.

[0080] In a preferred embodiment, the aerogel sheet has pore channels that are parallel to each other throughout the entire length of the aerogel sheet.

[0081] As used herein, the term "parallel to each other" means that the pore channels in the aerogel block are arranged in parallel, or in other words, the pore channels in the aerogel block are highly oriented. In this way, heat conduction can be further reduced and light reflection can be increased.

[0082] Figure 2 Digital photos and scanning electron microscope (SEM) photos of aerogel samples manufactured according to the aforementioned mechanism are shown. The SEM photos show that uniformly arranged pores are formed in the freezing direction in different areas of the aerogel sheet. Because the freezing distance of each block is relatively short, the pore arrangement in the entire aerogel sheet is uniform, and the pore size range of different areas of the aerogel sheet is 15 microns to 30 microns. At the same time, the SEM images also show that two frozen blocks with comparable pore sizes and parallel pore channels can be well connected.

[0083] As previously mentioned, the size of the aerogel sheet of the present invention can be determined by tailoring the size of the freezing mold and the total number of solidified aerogel blocks.

[0084] The dimensions of an aerogel sheet include thickness, length, and width, which are also referred to herein as "transverse dimensions." The thickness can be adjusted by the height of the freezing mold and the volume of aqueous colloidal solution used for each aerogel block. The length, which is the dimension of the aerogel sheet along the direction of ice crystal growth, is determined by the effective freezing distance and the total number of aerogel blocks freeze-cast. The width, which is the inner width of the freezing mold, is the width of the inner surface of the freezing mold.

[0085] Accordingly, the term "large size" refers to the lateral dimensions of aerogels relative to laboratory-scale aerogels that are smaller than 5 cm, for example 20 x 20 cm2, or larger sizes that can be used for building exterior walls and roofs.

[0086] Figure 3 A photograph showing an aerogel sheet manufactured using a movable side cooling source according to one embodiment of the present invention shows that the aerogel sheet manufactured by one embodiment of the present invention has a lateral dimension of about 20×20 square centimeters and a thickness of about 1 centimeter.

[0087] In another specific embodiment, the density of the aerogel plate is 20 mg / cm 3 Up to 60mg / cm 3 , for example 25 mg / cm 3 、30mg / cm 3 、35mg / cm 3 , 40mg / cm 3 , 45mg / cm 3 、50mg / cm 3 、55mg / cm 3 .

[0088] In a preferred embodiment, the density of the aerogel plate is 20 mg / cm 3 Up to 30mg / cm 3 .

[0089] In another specific embodiment, the porosity of the aerogel sheet is not less than 90%. In a preferred embodiment, the porosity of the aerogel sheet is not less than 95%. In a more preferred embodiment, the porosity of the aerogel sheet is 95% to 98%.

[0090] In yet another specific embodiment, the thermal conductivity of the aerogel sheet is less than 24 mW m -1 K -1 For example, 17mW m -1 K -1 、18mW m -1 K -1 、19mW m -1 K -1 、20mW m -1 K -1 、21mW m -1 K -1 、22mW m -1 K -1 、22.5mW m -1 K -1 wait.

[0091] In a preferred embodiment, the thermal conductivity of the aerogel sheet is less than 20 mW m -1 K -1 , for example 17mW m -1 K -1 .

[0092] In another specific embodiment, the light reflectivity of the aerogel plate is not less than 90%.In a preferred embodiment, the light reflectivity of the aerogel plate is 92% to 95%.

[0093] Due to the strong light scattering inside the aerogel, the present invention provides a method with a light intensity of less than 24 mW m in the thickness direction. - 1 K -1 The aerogel panels have ultra-low thermal conductivity (even lower than that of air) and high light reflectivity of no less than 90%. When applied to the roof or exterior walls of a building, they can significantly reduce the amount of heat absorbed from sunlight and the amount of heat conducted from the surrounding environment into the building.

[0094] Figure 4The thermal conductivity and reflectivity measurements of different regions of an aerogel sheet according to one embodiment of the present invention are shown. The thermal conductivity and reflectivity of different regions of the aerogel sheet are highly consistent, with standard deviations not exceeding 10% and 3%, respectively. The thermal conductivity and reflectivity of the aerogel sheet can be measured using methods well known in the art, such as a Hot Disk TPS 2500S thermal constant analyzer and a Perkin Elmer Lambda 950 UV-Visible Near-Infrared spectrometer, but are not limited thereto.

[0095] In another specific embodiment, the aerogel sheet is manufactured by the method described in the first aspect.

[0096] In a third aspect, there is provided use of the aerogel panel produced by the method of the first aspect or the aerogel panel of the second aspect for construction applications.

[0097] In a specific embodiment, the aerogel board is used for roofs and exterior walls of buildings.

[0098] In yet another specific embodiment, the aerogel sheet is used for thermal insulation and / or light reflection.

[0099] As mentioned above, aerogel panels made of polymers and optional nanofillers are promising materials for building insulation applications. In particular, the aerogel panels manufactured according to the method of the present invention have uniform pore channels that are parallel to each other and have a consistent pore size in the direction perpendicular to the thickness, which is ideal for thermal insulation and heat preservation of building roofs and exterior walls because the parallel pore channels can significantly reduce heat conduction in the thickness direction. In addition, nanofillers can achieve further modification of the aerogel panels. For example, the addition of boron nitride nanosheets can be used to adjust the heat conduction in the direction of parallel pore channels, thereby further reducing heat transfer in the thickness direction without affecting the high light reflectivity of the aerogel panels. Therefore, when the aerogel panels of the present invention are applied to the roofs and exterior walls of buildings, the heat absorbed from sunlight and the heat conduction from the surrounding environment to the interior of the building can be significantly reduced, thereby achieving thermal insulation and heat preservation of the building.

[0100] The benefits of the present invention are that the method for manufacturing aerogel panels is simple and environmentally friendly. It can not only produce aerogel panels with ultra-low thermal conductivity and high light reflectivity, but also break through the laboratory scale that is usually less than 5 cm, and realize the production of large-scale aerogel panels with practical potential, making them suitable for actual building insulation applications.

[0101] Example

[0102] The following examples will use waterborne polyurethane (WPU) and boron nitride nanosheets (BNNS) as raw materials to prepare large-scale BNNS / WPU aerogel panels and verify the thermal insulation and light reflectivity effects of the large-scale aerogel panels designed according to the present invention. Unless otherwise specified, the test methods used are conventional methods, and unless otherwise specified, the test materials used in the following examples are purchased from conventional reagent stores. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs.

[0103] The following examples are provided to better illustrate the claimed invention and are not to be construed as limiting the scope of the present invention in any way. All of the following specific compounds, materials and methods fall within the scope of the present invention in whole or in part. These specific compounds, materials and methods are not intended to limit the present invention, but are only used to illustrate specific embodiments within the scope of the present invention. Those skilled in the art may make any modifications and variations to the present invention embodied therein. These modifications and variations are also considered to be within the scope of the present invention.

[0104] Materials and Equipment

[0105] Waterborne polyurethane (WPU): purchased from DSM R-610

[0106] Boron nitride nanosheets (BNNS): Prepared using urea-assisted ball milling. The hydrophilic amino groups in urea and the high ball milling speed help effectively exfoliate hexagonal boron nitride (h-BN) bulk into nanosheets a few nanometers thick. Excess urea is completely removed by repeated washing and dialysis before use.

[0107] Expanded polystyrene (EPS): purchased from VFP

[0108] Silica (SiO2) aerogel: purchased from Wuzhen Technology Hebei Co., Ltd.

[0109] Freeze dryer: Scientz 10N / A

[0110] Desktop scanning electron microscope (SEM): Hitachi TM3030

[0111] Thermal Constant Analyzer: Hot Disk TPS 2500S

[0112] UV-visible-near-infrared spectrometer: Perkin Elmer Lambda 950

[0113] Example 1: Preparation of BNNS / WPU aerogel sheet

[0114] First, 10 g of homemade BNNS was dissolved in 250 ml of deionized water, and the BNNS solution was sonicated in an ultrasonic bath at 20° C. for 120 min to ensure that the BNNS was evenly dispersed in the deionized water.

[0115] Next, 40 ml of the BNNS solution was introduced into 960 ml of the 1.5 wt % WPU solution, and the resulting mixture was mechanically stirred at room temperature for 12 h before the freeze-casting process to obtain a BNNS / WPU colloidal solution for subsequent freeze-casting.

[0116] Then, in Figure 1 In the freeze casting apparatus shown, the BNNS / WPU colloidal solution is freeze cast, and the detailed steps are as follows:

[0117] (i) A metal container was placed in a polytetrafluoroethylene mold (21 cm in width) at a distance of 15 mm from the closed end of the mold, thereby forming a freezing space.

[0118] (ii) Fill the metal container with liquid nitrogen and wait for a period of time until the surface temperature of the metal container stabilizes at approximately -170° C. To ensure a constant freezing temperature, the metal container is continuously filled with liquid nitrogen at a rate of 1 L / min.

[0119] (iii) A certain volume of BNNS / WPU colloidal solution was poured into the freezing space in the mold and waited for a period of time until the colloidal solution was completely solidified.

[0120] (iv) The metal container is moved 15 mm in the opposite direction to the growth of ice crystals, thereby forming a new frozen space.

[0121] (v) Pour the same volume of BNNS / WPU colloidal solution into the newly formed freezing space and wait for a while until the colloidal solution is completely solidified.

[0122] (vi) Repeat steps (iv) and (v) until an aerogel of the desired length (e.g., 21 cm) is obtained.

[0123] Finally, the frozen BNNS / WPU sheet was freeze-dried in a freeze dryer with a cold trap temperature of −40 °C and a pressure of 0.1 mbar for 96 h to obtain a large-sized aerogel sheet.

[0124] Example 2: Characterization of BNNS / WPU aerogel sheets

[0125] The aerogel plate manufactured by the method of Example 1 was characterized in terms of structure, thermal conductivity, light reflectivity and other properties.

[0126] The microstructure of the aerogel sheet was characterized using a desktop scanning electron microscope (SEM, Hitachi TM3030). Figure 2 shown. Figure 2 The SEM images show uniformly aligned pores in different regions of the aerogel sheet, aligned along the freezing direction. Due to the short freezing distance between each block, the pores are uniformly distributed throughout the aerogel sheet, with pore sizes ranging from 15 to 30 microns across the different regions. The SEM images also demonstrate that two frozen blocks with comparable pore sizes and parallel pore channels can be well connected.

[0127] Figure 3 The macroscopic structure of the aerogel plate manufactured by the method of Example 1 is further shown. It can be seen that its lateral size is about 20×20 square centimeters (the size of the aerogel plate shrinks after freeze-drying) and the thickness is about 1 centimeter.

[0128] The thermal conductivity of the aerogel sheet was measured using a Hot Disk Thermal Constants Analyzer (Hot Disk TPS 2500S), and the light reflectivity of the aerogel sheet in the wavelength range of 0.25 μm to 2.5 μm was measured using a UV-visible near-infrared spectrometer (Perkin Elmer Lambda 950). The average weighted light reflectivity was calculated according to ASTM G173-03.

[0129] Figure 4 The results show that the thermal conductivity and light reflectivity of the BNNS / WPU aerogel plate of the present invention are 22.2±1.1 mW m -1 K -1 The average thermal conductivity of regions A, B, and C is 23.5 mW m -1 K -1 、21.4mW m -1 K -1 and 21.8mW m -1 K -1 The thermal conductivity of the aerogel board of the present invention is 27% lower than that of commercial EPS foam and even lower than the thermal conductivity of air (24 mW m -1 K -1 ). In addition, the average weighted light reflectivity of the aerogel sheet of the present invention is 92.6±1.2% (the light reflectivity of regions A, B, and C are 92.4%, 93.6%, and 91.7%, respectively), which is about 10% higher than the high reflectivity (about 85%) coating available on the market. As used in this embodiment, the term "average" refers to the average value of properties measured from different regions of at least 3 samples. In addition, by Figure 4The results show that the thermal conductivity and light reflectivity of different regions of the BNNS / WPU aerogel plate of the present invention are highly consistent, and the standard deviations do not exceed 10% and 3%, respectively.

[0130] In addition, according to the measurement, the aerogel plate has a -3 The material has an extremely low density and a high porosity of 97.2±0.1%.

[0131] Figure 5 The photographs show the aerogel sheet of the present invention being bent in two directions, along the boundary direction and perpendicular to the boundary direction. It can be seen that the aerogel sheet exhibits good mechanical flexibility and strength when bent, making it easier to roll up for transportation and unfold.

[0132] Example 3: Comparison with prior art

[0133] First, this example tests the UV-vis spectra of a homemade WPU solid film, EPS foam coated with a commercial reflective coating, a silica (SiO2)-based aerogel, a 1.4 wt% WPU aerogel (without nanofiller) prepared by the method of the present invention, and a 1.4 wt% WPU / BNNS composite aerogel (wherein BNNS accounts for 10 wt% of the sum of the weights of WPU and BNNS). The light reflectance of each sample in the wavelength range of 0.25 μm to 2.5 μm is calculated, and the results are shown as follows: Figure 6 As shown, the WPU solid film is essentially unable to reflect sunlight. However, compared to EPS foam coated with commercial reflective coatings, the aerogel produced by the method of the present invention, regardless of whether nanofillers are added, exhibits significantly higher light reflectivity. The addition of nanofillers has also been shown to further improve the light reflectivity of the aerogel sheet.

[0134] Then, the actual thermal insulation performance of each sample was tested by exposing silica (SiO2)-based aerogel, commercial expanded polystyrene (EPS), glass, and the WPU / BNNS composite aerogel of the present invention to sunlight and monitoring the temperature on the other side (inside) using a thermocouple. The field test device is as follows Figure 7 The test device was exposed to direct sunlight for 5 hours, and a thermocouple was used to monitor the ambient temperature and the temperature inside the sample. The temperature of each sample changed with time as shown in the figure below. Figure 8As shown in the figure, the WPU / BNNS aerogel board of the present invention is superior to glass, commercial EPS and SiO2-based aerogel in reducing the internal temperature exposed to sunlight. In addition, during the hottest time of the day (e.g., between 2 p.m. and 3 p.m.), the internal temperature of the WPU / BNNS aerogel board of the present invention is even lower than the ambient temperature, which proves that the WPU / BNNS aerogel board of the present invention has more effective sunlight reflection performance.

Claims

1. A method for manufacturing an aerogel sheet, comprising the following steps: 1) providing a water-based colloidal solution; 2) freeze-casting the aqueous colloidal solution piece by piece in a freezing mold using a movable side cooling source, thereby obtaining a frozen sample; 3) Freeze-drying the frozen sample to obtain an aerogel plate.

2. The method according to claim 1, wherein The water-based colloidal solution comprises: - polymer particles having at least one dimension ranging from 1 nm to 1 μm in a concentration in the range of 1% to 10% by weight; and - Inorganic and / or organic nanofillers having at least one dimension smaller than 100 nanometers, representing from 0% to 60% by weight of the sum of the weight of the polymer particles and the nanofillers.

3. The method according to claim 2, wherein: The polymer particles are waterborne polyurethane particles, waterborne polyvinyl alcohol particles or waterborne polyimide particles.

4. The method according to claim 2, wherein: The concentration of the polymer particles ranges from 1 wt% to 5 wt%.

5. The method according to claim 2, wherein: The inorganic and / or organic nanofiller accounts for 5 to 20 wt % of the sum of the weight of the polymer particles and the nanofiller.

6. The method according to claim 2, wherein: Step 1) includes: 1-1) dispersing the polymer particles in water to obtain the water-based colloidal solution; or 1-2-1) dispersing the inorganic and / or organic nanofiller in water to obtain a nanofiller dispersion; and 1-2-2) The nanofiller dispersion is mixed with an aqueous solution obtained by dispersing the polymer particles in water, thereby obtaining the water-based colloidal solution.

7. The method according to claim 6, wherein: In step 1-2-1), a nanofiller dispersion is obtained by subjecting a solution obtained by dispersing the inorganic and / or organic nanofiller in water to ultrasonic treatment in an ultrasonic bath at 15° C. to 30° C. for 10 minutes to 2 hours.

8. The method according to claim 7, wherein: The temperature of the ultrasonic bath was 20°C.

9. The method according to claim 7, wherein: The ultrasonic treatment time was 30 minutes.

10. The method according to claim 6, wherein: In step 1-2-2), the aqueous colloidal solution is obtained by mixing the nanofiller dispersion with an aqueous solution obtained by dispersing the polymer particles in water at 15° C. to 30° C. and stirring the solution for at least 10 hours.

11. The method according to claim 10, wherein: Stirring was carried out at room temperature.

12. The method according to claim 10, wherein: The stirring time is 12 hours, 16 hours, 20 hours, or 24 hours.

13. The method according to claim 1, wherein Step 2) includes: 2-1) moving the movable side cooling source so that its proximal end is spaced apart from the side closed end of the freezing mold by an effective freezing distance, thereby forming a freezing space in the freezing mold; 2-2) Pour the water-based colloidal solution into the freezing space and wait for a time sufficient for the water-based colloidal solution to solidify into blocks.

14. The method according to claim 13, wherein In step 2-2), the waiting time is at least 10 minutes.

15. The method according to claim 14, wherein The waiting time is 15 minutes.

16. The method according to claim 13, wherein: Repeat steps 2-1) and 2-2) to obtain frozen samples of the desired length.

17. The method according to claim 13, wherein: The effective freezing distance does not exceed 15 mm.

18. The method according to claim 17, wherein The effective freezing distance is 15 mm.

19. The method according to any one of claims 1 to 18, wherein The movable side cooling source provides low temperature down to -170°C.

20. The method according to claim 19, wherein The movable side cooling source is a metal container filled with a cooling medium.

21. The method according to claim 20, wherein The cold medium is liquid nitrogen.

22. The method according to claim 20 or 21, wherein The metal is a heat-conducting metal material.

23. The method according to claim 22, wherein The heat-conducting metal material is a single metal.

24. The method according to claim 23, wherein The elemental metal is aluminum, copper, or an alloy.

25. The method according to claim 24, wherein The alloy is stainless steel.

26. The method according to any one of claims 1 to 18, wherein Step 3) is carried out under vacuum conditions at a temperature range of at least 20° C. lower than the freezing point of the water-based colloidal solution, and the freeze-drying time is at least 48 hours.

27. The method according to claim 26, wherein Step 3) is carried out under low pressure conditions of 0.1 mbar to 0.4 mbar.

28. The method according to claim 27, wherein Step 3) is carried out under low pressure conditions of 0.2 mbar to 0.3 mbar.

29. The method according to claim 26, wherein The temperature at least 20°C lower than the freezing point of the water-based colloidal solution is -40°C.

30. The method of claim 26, wherein: The freeze-drying time is 96 hours.

31. An aerogel plate, manufactured by the method according to any one of claims 1 to 30, and having pore channels parallel to the plane of the aerogel plate, with consistent pore diameters and uniform arrangement.

32. The aerogel sheet according to claim 31, wherein The aerogel sheet has pore channels that are parallel to each other throughout the entire length of the aerogel sheet.

33. The aerogel sheet according to claim 31, wherein The density of the aerogel plate is 20 to 60 mg / cm 3 .

34. The aerogel sheet according to claim 33, wherein The density of the aerogel plate is 20 to 30 mg / cm 3 .

35. The aerogel sheet according to claim 31, wherein The porosity of the aerogel plate is not less than 90%.

36. The aerogel sheet according to claim 35, wherein The porosity of the aerogel plate is not less than 95%.

37. The aerogel sheet according to claim 36, wherein The porosity of the aerogel sheet is 95% to 98%.

38. The aerogel sheet according to claim 31, wherein The thermal conductivity of the aerogel plate is lower than 24 mW m -1 K -1 .

39. The aerogel sheet according to claim 38, wherein The thermal conductivity of the aerogel plate is less than 20 mW m -1 K -1 .

40. The aerogel sheet according to claim 39, wherein The thermal conductivity of the aerogel plate is 17 mW m -1 K -1 .

41. The aerogel sheet according to claim 31, wherein The light reflectivity of the aerogel plate is not less than 90%.

42. The aerogel sheet according to claim 41, wherein The light reflectivity of the aerogel plate is 92% to 95%.

43. Use of an aerogel sheet according to any one of claims 31 to 42 for construction applications.

44. The use according to claim 43, wherein The architectural application is a roof or an exterior wall of a building.

45. The use according to claim 43 or 44, wherein The aerogel panels are used for heat insulation and / or light reflection of buildings.

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