Wood-based heat storage material and preparation method thereof

Abstract

The present invention provides a wood-based heat storage material and a preparation method thereof. The wood-based heat storage material has a plurality of wood fiber layers, the wood fiber layers are derived from wood fibers, wherein the wood fiber layers are connected to the wood fiber layers, and at least part of the wood fiber layers have a pore structure, and the pore structure is formed by the collapse of wood ray tissue. The wood-based heat storage material of the present invention has excellent photothermal conversion performance, a very high photothermal conversion rate, and excellent elasticity and shape recovery. Furthermore, the preparation method of the present invention can expose the benzene ring carbon skeleton of lignin, thereby obtaining a wood-based heat storage material with excellent photothermal conversion performance, and the preparation method of the present invention is simple and easy, the raw materials are easy to obtain, and it is suitable for mass production.

Description

Technical Field

[0001] The invention relates to a wood-based heat storage material and a preparation method thereof, and belongs to the field of wood. Background Art

[0002] Photothermal porous materials mainly include semiconductor particles, carbon matrix and plasmon materials, which can convert absorbed light energy into heat energy, thereby achieving the characteristic of local high temperature. Based on this characteristic, photothermal porous materials are widely used in the fields of crude oil adsorption recovery, seawater desalination, heat storage and insulation, and also have wide applications in the fields of solar energy utilization and biomedicine.

[0003] In the prior art, nano-photothermal materials such as carbon nanotubes, graphene / reduced graphene oxide, MXene, black phosphorus quantum dots, etc. are often used to modify organic polymers to prepare porous materials with photothermal effects. However, nano-photothermal materials such as graphene / reduced graphene oxide, carbon nanotubes, MXene, black phosphorus quantum dots, etc. have problems such as complex preparation, high cost, and biological toxicity. In addition, the porous materials obtained by modifying organic polymers with the above materials also have problems such as weak mechanical strength, poor reusability, and non-renewability.

[0004] Wood is one of the most abundant renewable resources on earth, and is known as one of the four major materials in the world today, along with steel, plastic, and cement. Due to its high mechanical strength, low cost, and good machinability, wood has been widely used in all aspects of human life, including buildings, furniture, chemical products, and textiles. However, many production and processing departments will generate a large amount of waste in the process of using wood resources. For example, many early sawmills will generate a lot of solid waste such as wood chips and wood slag when processing wood into boards, resulting in a waste of resources.

[0005] Due to its abundance and scalability, wood has gradually been used to make wood-based heat storage materials. The preparation methods are generally divided into the following two methods, namely direct carbonization and surface coating. Among them, direct carbonization is the two most common wood carbonization methods, which are treatment in a high temperature environment or flame burning. Reference 1 reported that by cutting logs perpendicular to the growth direction of the wood and carbonizing the top surface at 500°C, a surface carbonized wood can be obtained, which can achieve an ultra-high optical absorption rate of about 99% in the wavelength range of 250-2500nm. Reference 2 reported that by cutting logs along the growth direction of the wood and carbonizing the side surface at 500°C, a wood-based photothermal conversion material was also obtained, which can achieve a high optical absorption rate of about 97% in the wavelength range of 250-2500nm, and under the illumination intensity of 1 sun, the wet sample increased from 20°C to 30.2°C within 300s. This method is a direct carbonization method, which has high energy consumption and is not conducive to achieving carbon neutrality. In addition, the photothermal conversion efficiency is low and the temperature rise of the sample surface is small.

[0006] Surface coating refers to the method of coating one material on the surface of another material, which mainly includes electroplating technology, spraying technology and deposition technology. By taking advantage of the stability and scalability of wood, photothermal materials can be coated on the surface of wood to prepare wood-based photothermal conversion materials with excellent performance. Related research mainly includes carbon nanotube coating, polydopamine coating, graphene coating and metal nanoparticle deposition.

[0007] Reference 3 uses graphene to spray on the surface of wood. In the wavelength range of 200-2500nm, the absorbance is higher than 95%. Under the illumination intensity of 1 sun, the temperature of the wet sample rises from 21°C to 38°C within 10 minutes. It can be made into a large-scale wood-based photothermal conversion material. Reference 4 deposits palladium, gold and silver nanoparticles on the surface of wood to obtain a plasma wood with excellent photothermal performance. In the wavelength range of 200-2500nm, the material can achieve a light absorption rate of about 99%, the surface temperature can reach 30.6°C under the illumination intensity of 1 sun, and the surface temperature can reach 55°C under the illumination intensity of 5 suns, indicating that it has high light absorption rate and strong photothermal conversion ability. The preparation process of nanomaterials such as graphene, palladium, gold and silver is complicated and costly, which is not conducive to the large-scale application of products. In addition, although the above-mentioned wood-based composite materials have high light absorption rate, the photothermal conversion efficiency is low, and the material heating effect is not obvious (the heating effect is poor).

[0008] References:

[0009] Cited literature 1: Zhu M, Li Y, Chen G, et al. Tree-inspired design for high-efficiency water extraction [J]. Advanced Materials, 2017, 29(44): 1704107.1-1704107.9.

[0010] Cited literature 2: Liu, Chen C, Chen G, et al. High-performance solar steam with layered channels: artificial tree with a reversed design [J]. Advanced Energy Materials, 2018, 8(8): 1701616.

[0011] Cited literature 3: Li T, Liu H, Zhao

[0012] Cited literature 4: Zhu M, Li Y, Chen F, et al. Plasmonic wood for high-efficiency solar steam generation [J]. Advanced Energy Materials, 2018, 8(4): 1701028.1-1701028.7. Summary of the invention

[0013] Problem that the invention aims to solve

[0014] The benzene ring carbon skeleton carried by lignin, one of the main components of wood, is an ideal photothermal material. However, the existing benzene ring carbon skeleton of lignin is wrapped by the oxygen-containing side chains and hemicellulose it carries, and cannot achieve photothermal conversion and heat storage. The inventors found that if the benzene ring carbon skeleton in the wood can be exposed, combined with the natural porous structure of the wood, an environmentally friendly wood-based heat storage material can be obtained. In view of the above technical problems existing in the prior art, the present invention first provides a wood-based heat storage material. The wood-based heat storage material of the present invention has excellent photothermal conversion performance, a very high photothermal conversion rate, and excellent elasticity and shape recovery.

[0015] Furthermore, the present invention also provides a method for preparing a wood-based heat storage material, which can expose the benzene ring carbon skeleton of lignin, thereby obtaining a wood-based heat storage material with excellent photothermal conversion performance.

[0016] Solutions for solving problems

[0017] The present invention provides a wood-based heat storage material, wherein the wood-based heat storage material has a plurality of wood fiber layers, wherein the wood fiber layers are derived from wood fibers, wherein:

[0018] The wood fiber layers are connected to the wood fiber layers, and,

[0019] At least part of the wood fiber layers have a pore structure between the wood fiber layers, and the pore structure is formed by the collapse of wood ray tissue.

[0020] According to the wood-based heat storage material of the present invention, the wood fiber layer has a porous structure, and the average pore size of the wood fiber layer is 1 μm to 500 μm.

[0021] According to the wood-based heat storage material of the present invention, the wood fiber layer contains cellulose, hemicellulose and lignin; wherein,

[0022] Taking the total mass of the wood-based heat storage material as 100%, the content of the cellulose is more than 50%, the content of the hemicellulose is less than 10%, and the content of the lignin is less than 20%.

[0023] The present invention also provides a method for preparing the wood-based heat storage material according to the present invention, which comprises the step of collapsing the wood ray tissue of the wood raw material.

[0024] The preparation method according to the present invention comprises the following steps:

[0025] Chemically treating wood raw materials with alkaline substances and / or oxides to obtain wood-based materials;

[0026] Drying the wood-based material to obtain a dried product;

[0027] The dried product is subjected to heat treatment to obtain a wood-based heat storage material.

[0028] According to the preparation method of the present invention, the alkaline substance includes one or a combination of two or more of KOH, NaOH, Na2SO3, K2SO3, Na2CO3, K2CO3; the oxide includes one or a combination of two or more of H2O2, NaClO2, NaClO, KClO2, KClO; and the time of the chemical treatment is 2h to 72h.

[0029] According to the preparation method of the present invention, the drying includes one or a combination of two or more of air drying, freeze drying or supercritical drying.

[0030] According to the preparation method of the present invention, the air drying comprises drying at a temperature of 10°C to 60°C for 6h to 72h;

[0031] The freeze drying comprises freezing at a temperature of -196°C to -10°C for 0.5h to 24h, and then drying at a vacuum degree of 0.1μPa to 120Pa and a temperature of -65°C to -45°C for 24h to 72h;

[0032] The supercritical drying comprises introducing liquid carbon dioxide and performing supercritical drying at a temperature of 10° C. to 60° C. and a pressure of 1 MPa to 30 MPa for 1 hour to 36 hours.

[0033] According to the preparation method of the present invention, before drying, it also includes a step of washing the wood-based material with an alcohol solvent.

[0034] According to the preparation method of the present invention, the heat treatment comprises heating the temperature to 190°C to 1000°C at a heating rate of 1°C / min to 10°C / min for 1h to 5h.

[0035] Effects of the Invention

[0036] The wood-based heat storage material of the present invention has excellent light-to-heat conversion performance, a very high light-to-heat conversion rate, and excellent elasticity and shape recovery.

[0037] Furthermore, the preparation method of the present invention can expose the benzene ring carbon skeleton of lignin, thereby obtaining a wood-based heat storage material with excellent photothermal conversion performance. The preparation method of the present invention is simple and easy, the raw materials are easy to obtain, and it is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A photograph showing the wood-based heat storage material of the present invention;

[0039] Figure 2 The electron microscope images of the wood-based heat storage material of the present invention are shown, wherein a is a schematic diagram of a cross section of the wood-based heat storage material; b is a schematic diagram of a chord section of the wood-based heat storage material; and c is a schematic diagram of the pores of the wood-based heat storage material;

[0040] Figure 3 The photothermal conversion effect diagram of the wood-based heat storage material of Example 1 of the present invention is shown;

[0041] Figure 4 The chemical composition evolution of the wood-based heat storage material from natural balsa wood to the wood-based heat storage material of Example 1 of the present invention is shown;

[0042] Figure 5 The compressive stress-strain curve of the wood-based heat storage material of Example 1 of the present invention is shown;

[0043] Figure 6 The photographs showing the water contact angles of the balsa wood and the wood-based heat storage material of Example 1 of the present invention are shown, wherein the left picture is the balsa wood and the right picture is the wood-based heat storage material;

[0044] Figure 7 A schematic plan view of the water contact angle of balsa wood and wood-based heat storage material according to Example 1 of the present invention is shown, wherein the left figure is balsa wood and the right figure is the wood-based heat storage material. DETAILED DESCRIPTION

[0045] The following is a detailed description of the present invention. The following description of the technical features is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0046] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0047] In this specification, unless otherwise stated, "multiple" in "multiple", "multiple", "plurality", etc. means a numerical value of 2 or more.

[0048] In the present specification, the term “substantially”, “essentially”, “generally” or “substantially” means that the error is less than 5%, or less than 3% or less than 1% compared with the relevant perfect standard or theoretical standard.

[0049] In this specification, unless otherwise specified, "%" means mass percentage.

[0050] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0051] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 10-40°C.

[0052] In this specification, unless otherwise specified, the "water" used may be tap water, distilled water, deionized water, ion exchange water, high-purity water, purified water, or other water available in the art.

[0053] In the present specification, "optional" or "optionally" means that the event or situation described below may or may not occur, and the description includes cases where the event occurs and cases where it does not occur.

[0054] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0055] <First aspect>

[0056] A first aspect of the present invention provides a wood-based heat storage material, wherein the wood-based heat storage material has a plurality of wood fiber layers, wherein the wood fiber layers are derived from wood fibers,

[0057] The wood fiber layers are connected to the wood fiber layers, and,

[0058] At least part of the wood fiber layers have a pore structure between the wood fiber layers, and the pore structure is formed by the collapse of wood ray tissue.

[0059] The wood-based heat storage material of the present invention has excellent light-to-heat conversion performance, a very high light-to-heat conversion rate, and excellent elasticity and shape recovery.

[0060] The wood fiber of the present invention is a mechanical tissue composed of lignified thickened cell walls and fiber cells with round pores, and is one of the main components of the xylem. The wood fiber of the present invention is relatively completely retained in the wood-based heat storage material and forms a layered structure.

[0061] Furthermore, in the present invention, the wood fiber layers are connected to each other. The present invention retains the original structure of the wood fiber, and the wood fiber layers are not broken, so that the layers can still be connected relatively tightly at positions other than the wood ray tissue, so that they can be presented as the skeleton structure of the wood-based heat storage material.

[0062] In the present invention, at least part of the wood fiber layers have a channel structure, and the channel structure is formed by the collapse of wood ray tissue. Wood ray tissue is a vascular ray located in the secondary xylem within the cambium, which plays a role in lateral conduction and nutrient storage in wood. In the cross section of the wood, wood rays can be seen that are perpendicular to the growth rings of the wood and arranged radially. On the tangential section, the rays are longitudinal or spindle-shaped. On the radial section, the rays are arranged in lines or sheets of different heights.

[0063] In the present invention, the pore structure is formed by collapsing the wood ray tissue. The existence of the pore structure enables the wood-based porous material of the present invention to exhibit excellent elasticity and shape recovery.

[0064] In some specific embodiments, the wood fiber layer of the present invention has a porous structure, and the average pore size of the wood fiber layer is 1 μm to 500 μm, for example: 10 μm, 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, etc. Since the wood fiber layer of the present invention has a porous structure, it helps to improve the elasticity and shape recovery of the wood-based heat storage material.

[0065] Furthermore, in some other specific embodiments, the wood fiber layer contains cellulose, hemicellulose and lignin; wherein,

[0066] Taking the total mass of the wood-based heat storage material as 100%, the content of the cellulose is more than 50%, preferably 50-70%; for example: 52%, 55%, 58%, 60%, 62%, 65%, 68%, etc.; the content of the hemicellulose is less than 10%, preferably 1-10%, for example: 2%, 4%, 6%, 8%, etc.; the content of the lignin is less than 20%, preferably 5-20%, for example: 6%, 8%, 10%, 12%, 14%, 16%, 18%, etc. When the content of cellulose, hemicellulose and lignin in the present application is within the above range, it is beneficial to reduce the hydrophilic group of the wood-based heat storage material and fully expose the benzene ring structure of lignin, thereby ensuring the light-heat conversion efficiency of the material and making the material have a better warming effect.

[0067] In addition, it should be noted that the wood-based heat storage material of the present invention contains not only cellulose, hemicellulose and lignin. Since the wood raw materials contain some pectin, minerals, plant proteins and water in addition to cellulose, hemicellulose and lignin, after a series of chemical treatments to form wood-based heat storage materials, some of the components (including cellulose, hemicellulose and lignin, etc.) will undergo chemical evolution to form other substances. For example, after chemical treatment, some characteristic groups of lignin will be completely processed, and only part of the skeleton will remain on it. Therefore, during detection, this part of the skeleton essentially no longer belongs to the category of lignin. Since these other substances have little impact on the present invention, they will no longer be tested and limited.

[0068] <Second Aspect>

[0069] The second aspect of the present invention provides a method for preparing the wood-based heat storage material according to the first aspect of the present invention, comprising the step of collapsing the wood ray tissue of the wood raw material. The present invention forms a pore structure by collapsing the wood ray tissue, so that the wood-based porous material of the present invention exhibits excellent elasticity and shape recovery.

[0070] Specifically, the method for preparing the wood-based heat storage material of the present invention comprises the following steps:

[0071] Chemically treating wood raw materials with alkaline substances and / or oxides to obtain wood-based materials;

[0072] Drying the wood-based material to obtain a dried product;

[0073] The dried product is subjected to heat treatment to obtain a wood-based heat storage material.

[0074] Chemical treatment

[0075] In the present invention, the wood raw material is not particularly limited, and can be any commonly used wood raw material with wood ray tissue in the art. For example: coniferous wood, hardwood, balsa wood, basswood, poplar, birch, basswood, oak, etc. During preparation, the wood raw material can be cut into smaller sizes for easy preparation. The present invention does not particularly limit the specific size, and can be cut as needed.

[0076] The present invention first uses alkaline substances and / or oxides to chemically treat wood raw materials to obtain wood-based materials; specifically, the time of the chemical treatment is 2h to 72h, preferably 2h to 40h; for example: 5h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h, 50h, 55h, 60h, 65h, 70h, etc. The inventors of the present invention have found that the time of chemical treatment has a certain influence on the performance of the product, and the present invention does not recommend that the time of chemical treatment is too long. When the time of chemical treatment is too long, it may cause too much lignin to be removed, which will cause the wood-based heat storage material of the present invention to have no heat storage function. Further, when the time of the chemical treatment is 2h to 40h, it is easier to obtain the desired wood-based material. In addition, if the size of the wood raw material is too large, the time of its chemical treatment should be extended to a certain extent to obtain the desired product.

[0077] Generally speaking, when only alkaline substances are used to chemically treat wood raw materials, the lignin content will be relatively high, making the heat storage effect more excellent, but the elastic performance is poor. Therefore, the present invention preferably uses oxides to chemically treat wood raw materials to obtain wood-based materials; or first uses alkaline substances to chemically treat wood raw materials to remove part of hemicellulose to obtain an alkali-treated product, and then uses oxides to chemically treat the alkali-treated product to remove part of the lignin to obtain a wood-based material.

[0078] In some specific embodiments, when the present invention uses oxides to chemically treat wood raw materials, it is possible to consider using some oxides with strong oxidizing ability (such as hydrogen peroxide, etc.) or to appropriately extend the oxidation time to obtain wood-based heat storage materials with excellent performance. This is because when the oxidizing ability of the oxide is strong or the oxidation time is long, hemicellulose and lignin can be basically removed at the same time.

[0079] In other specific embodiments, the present invention first uses alkaline substances to chemically treat wood raw materials to remove part of hemicellulose to obtain an alkali-treated product; then uses oxides to chemically treat the alkali-treated product to remove part of lignin. This can also be more conducive to heat treatment. After heat treatment, the lignin benzene ring structure in the wood fiber can be completely exposed, so that the wood-based heat storage material can achieve photothermal conversion and heat storage.

[0080] The present invention does not make any particular limitation on the alkaline substance, which may be an alkaline substance commonly used in the art. Specifically, the alkaline substance includes one or a combination of two or more of KOH, NaOH, Na2SO3, K2SO3, Na2CO3, K2CO3, etc.

[0081] Furthermore, when using alkaline substances for chemical treatment, the wood raw material can be soaked in a solution of the alkaline substance to obtain an alkali-treated product. Specifically, the alkaline substance can be dissolved in a solvent to obtain the alkaline-treated product. The present invention does not specifically limit the specific solvent, and can be a polar solvent commonly used in the art, such as water. Specifically, the mass fraction of the alkaline substance in the solution of the alkaline substance is 1% to 20%, such as 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, etc.

[0082] In some specific embodiments, when using alkaline substances for chemical treatment, a heating method can be used to accelerate the removal of hemicellulose. Specifically, the heating temperature can be 60°C to 150°C, for example: 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, etc.; the heating time is 1h to 10h, for example: 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, etc.

[0083] Further, the alkali-treated product is oxidized by an oxide to remove part of the lignin. The oxide is not particularly limited in the present invention and can be an oxide commonly used in the art. Specifically, the oxide can include one or a combination of two or more of H2O2, NaClO2, NaClO, KClO2, KClO, etc.

[0084] Furthermore, when the oxide is used for chemical treatment, the wood raw material can be soaked in a solution of the oxide to obtain a wood-based material. Specifically, the oxide can be dissolved in a solvent to obtain the wood-based material. The present invention does not specifically limit the specific solvent, and the wood-based material can be a polar solvent commonly used in the art, such as water. Specifically, the mass fraction of the oxide in the solution of the oxide is 0.5% to 30%, such as 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, etc.

[0085] In addition, in order to better achieve oxidation treatment, when NaClO2, NaClO, KClO2, KClO, etc. are used as oxides and when preparing the oxide solution, glacial acetic acid needs to be added to adjust the pH of the oxide solution to be acidic. The specific pH value can be 3 to 5, preferably 3.5 to 5, for example: 3.2, 3.8, 4, 4.2, 4.8, etc.

[0086] In some specific embodiments, when chemical treatment is performed using oxides, a heating method can be used to accelerate the removal of lignin. Specifically, the heating temperature can be 30°C to 100°C, for example, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, etc.; the heating time is 1h to 17h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, etc.

[0087] dry

[0088] After the chemical treatment, the wood-based material is dried to obtain a dried product. Specifically, the wood-based material can be washed with a polar solvent to neutralize it so as to facilitate drying later. The polar solvent can be water or an alcohol solvent. Further, before drying, if the wood-based material is washed with water, an alcohol solvent can be used to wash the wood-based material again, so as to replace the solvent and facilitate drying.

[0089] In some specific embodiments, the drying comprises one or a combination of two or more of air drying, freeze drying or supercritical drying. The drying procedure is beneficial to the subsequent heat treatment.

[0090] As for air drying, in the present invention, the air drying includes drying at a temperature of 10°C to 60°C, for example, 20°C, 30°C, 40°C, 50°C, etc., for 6h to 72h, for example, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h, 50h, 55h, 60h, 65h, 70h, etc.

[0091] For freeze drying, in the present invention, the freeze drying includes freezing at a temperature of -196°C to -10°C, such as -185°C, -160°C, -150°C, -135°C, -120°C, -105°C, -90°C, -75°C, -60°C, -45°C, -30°C, -15°C, etc. for 0.5h to 24h, such as 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, etc., and then placing it in a vacuum degree of 0.1μPa to 120Pa, such as 10μPa, 100μPa, 200 The temperature is -65℃~-45℃, such as -62℃, -60℃, -58℃, -55℃, -52℃, -50℃, -48℃, etc., and the drying time is 24h~72h, such as 25h, 30h, 35h, 40h, 45h, 50h, 55h, 60h, 65h, 70h, etc.

[0092] For supercritical drying, in the present invention, the supercritical drying includes introducing liquid carbon dioxide, at a temperature of 10°C to 60°C, for example, 20°C, 30°C, 40°C, 50°C, etc., and a pressure of 1MPa to 30MPa, for example, 2MPa, 5MPa, 8MPa, 10MPa, 12MPa, 15MPa, 18MPa, 20MPa, 22MPa, 25MPa, 28MPa, etc., for supercritical drying for 1h to 36h, for example, 2h, 5h, 8h, 10h, 12h, 15h, 18h, 20h, 22h, 25h, 28h, 30h, 32h, 35h, etc. During supercritical drying, the pressure increase rate can be 0.5-5 MPa / min, for example: 1 MPa / min, 1.5 MPa / min, 2 MPa / min, 2.5 MPa / min, 3 MPa / min, 3.5 MPa / min, 4 MPa / min, 4.5 MPa / min, etc.

[0093] Furthermore, when supercritical drying is performed, supercritical drying can be repeated 3 to 5 times to obtain the desired dried product. In addition, pressure relief is performed after drying, and the pressure relief rate can be 0.1-1.5 MPa / min, for example: 0.2 MPa / min, 0.4 MPa / min, 0.6 MPa / min, 0.8 MPa / min, 1.0 MPa / min, 1.2 MPa / min, 1.4 MPa / min, etc.

[0094] Heat Treatment

[0095] The present invention obtains a wood-based heat storage material by heat-treating the dried product. The present invention can expose the benzene ring structure of the remaining lignin through heat treatment, thereby obtaining a wood-based heat storage material. The wood-based heat storage material realizes light-heat conversion and heat storage.

[0096] Specifically, the heat treatment may include, under the protection of an inert gas, heating the dried product to a heat treatment temperature for heat treatment, thereby obtaining a wood-based heat storage material.

[0097] As for the conditions for heat treatment, preferably, the heat treatment temperature is 190℃~1000℃, for example: 200℃, 250℃, 300℃, 350℃, 400℃, 500℃, 600℃, 700℃, 800℃, etc.; the heat treatment time is 1-5h, for example: 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, etc.; the heating rate is 1℃ / min~10℃ / min.

[0098] The present invention does not specifically limit the inert gas, and it can be some inert gases commonly used in the art, such as nitrogen and rare gases, such as argon, helium, etc. It should be noted that the inert gas in the present invention refers to a gas that does not undergo relevant reactions during the heat treatment process of the present invention.

[0099] The present invention does not specifically limit the heat treatment apparatus, and the heat treatment may be performed in any apparatus commonly used in the art, for example, in a muffle furnace, a tubular furnace, or a vacuum furnace.

[0100] Example

[0101] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0102] Example 1

[0103] A balsa wood block with a size of 20 mm × 20 mm × 20 mm was immersed in 500 mL of KOH solution (wherein the mass fraction of KOH was 2 wt%), heated to 90°C for reaction for 4 h, and the sample was taken out to obtain a pretreated product. The pretreated product was transferred to 500 mL of NaClO2 solution (wherein the mass fraction of NaClO2 was 1 wt%), the pH of the NaClO2 solution was adjusted to 4 with glacial acetic acid, and heated to 60°C for reaction for 10 h to obtain a wood-based material.

[0104] After the reaction, the sample was thoroughly washed with deionized water until neutral, and then placed in tert-butyl alcohol for displacement washing for 4 hours. The wood-based material was then placed in a refrigerator at a temperature of -20°C for 12 hours, and then transferred to a freeze dryer at a temperature of -60°C and a vacuum degree of 10 mPa for 24 hours to obtain a wood-based skeleton with a natural light wood structure, i.e., a dried product.

[0105] The dried product was placed in a muffle furnace, the heating rate of the muffle furnace was set to 4° / min, heated to 230°C for 180 min, and the sample was taken out after the muffle furnace was cooled to room temperature to obtain a wood-based heat storage material.

[0106] Example 2

[0107] A poplar wood block with a size of 50mm×50mm×50mm was soaked in 1000mL of a mixed solution of NaOH and NaSO3 (wherein the mass fraction of NaOH was 10% and the mass fraction of NaSO3 was 5%), reacted at 80°C for 6h, and the sample was taken out to obtain a pretreated product. The pretreated product was transferred to 100mL of a NaClO2 solution (the mass fraction of NaClO2 was 1wt%), the pH of the NaClO2 solution was adjusted to 5 with glacial acetic acid, and heated to 80°C for 6h. After the reaction, the sample was thoroughly washed with deionized water until it was neutral to obtain a wood-based material.

[0108] The sample was soaked in anhydrous ethanol for cleaning and replacement, and the anhydrous ethanol was replaced every 3 hours for three times. The sample was placed in the supercritical dryer pressure chamber, and liquid CO2 was poured in. The temperature in the chamber was set to 45°C, the pressure increase rate was 2MPa / min, and the pressure was increased to 10MPa for supercritical CO2 drying. The pressure was released after 2 hours, and the pressure release rate was 0.8MPa / min. After drying, a wood-based skeleton with the natural structure of poplar wood was obtained, that is, the dried product.

[0109] The dried product was placed in a tubular furnace, the air in the furnace was evacuated with a vacuum pump, nitrogen was introduced, the heating rate was set to 5° / min, heated to 300°C and reacted for 4 hours, and the sample was taken out after the temperature was cooled to room temperature to obtain a wood-based heat storage material.

[0110] Example 3

[0111] An oak wood board with a size of 400 mm×400 mm×5 mm was immersed in 1000 mL of H2O2 solution (wherein the mass fraction of H2O2 was 30%), heated to 85°C for reaction for 36 hours, and then the sample was thoroughly washed with deionized water to obtain a wood-based material.

[0112] The wood-based material is soaked in anhydrous ethanol for cleaning and replacement, and the anhydrous ethanol is replaced every 3 hours for three times. The wood-based material is then transferred to isopropanol for cleaning and replacement, and the isopropanol is replaced every 3 hours for two times. The wood-based material is then placed in an air-dried environment at room temperature (about 25°C) for 48 hours to obtain a wood-based skeleton with a natural poplar wood structure, i.e., a dried product.

[0113] The dried product was placed in a vacuum heating box, the heating temperature was set to 5° / min, heated to 210° for 4 hours, and the sample was taken out after the temperature cooled to room temperature to obtain a wood-based heat storage material.

[0114] Example 4

[0115] A balsa wood block with a size of 20 mm×20 mm×20 mm was immersed in 500 mL of KOH solution (wherein the mass fraction of KOH was 2 wt %), heated to 90° C. and reacted for 4 h, and the sample was taken out to obtain a wood-based material.

[0116] After the reaction, the sample was thoroughly washed with deionized water until neutral, and then placed in tert-butyl alcohol for displacement washing for 4 hours. The wood-based material was then placed in a refrigerator at a temperature of -20°C for 12 hours, and then transferred to a freeze dryer at a temperature of -60°C and a vacuum degree of 10 mPa for 24 hours to obtain a wood-based skeleton with a natural light wood structure, i.e., a dried product.

[0117] The dried product was placed in a muffle furnace, the heating rate of the muffle furnace was set to 4° / min, heated to 230°C for 180 min, and the sample was taken out after the muffle furnace was cooled to room temperature to obtain a wood-based heat storage material.

[0118] Performance Testing

[0119] 1. Content of lignin, cellulose and hemicellulose

[0120] The cellulose, hemicellulose and lignin contents were determined according to the national standard GB / T 35818-2018: Analysis method of forestry biomass raw materials - Determination of polysaccharide and lignin content. The results are shown in Table 1 below:

[0121] Table 1

[0122]

[0123] It can be seen from Table 1 that the contents of lignin, cellulose and hemicellulose in the wood-based heat storage material of the present invention are appropriate, which is beneficial to reducing the hydrophilic groups of the wood-based heat storage material and fully exposing the benzene ring structure of lignin, thereby ensuring the photothermal conversion efficiency of the material and making the material have a better warming effect.

[0124] 2. Photothermal conversion test

[0125] A xenon lamp was used to simulate solar radiation (1500W / m 2 ) irradiated the wood-based heat storage material of Example 1, and used an infrared thermal imager to record the real-time temperature of the sample surface. The results are as follows Figure 3 shown.

[0126] Depend on Figure 3 It can be seen that the surface temperature of the wood-based heat storage material of Example 1 reaches 50°C within 10 seconds, and the surface temperature is as high as 80°C at 145 seconds.

[0127] Furthermore, the photothermal conversion test was conducted on the wood-based heat storage materials of Examples 2-4 according to the above method, and the results are shown in Table 2 below.

[0128] Table 2

[0129]

[0130] It can be seen from Table 2 that the surface temperature of the wood-based heat storage materials of Examples 2 and 3 reaches above 50°C within 10 seconds, and the surface temperature is as high as above 80°C at 145 seconds, which is basically equivalent to Example 1. Due to the high lignin content of Example 4, its surface temperature reaches above 60°C within 10 seconds, and the surface temperature is as high as above 100°C at 145 seconds.

[0131] 3. Chemical composition change test

[0132] The chemical composition changes of the wood-based heat storage material of Example 1 were characterized by using an infrared scanner, with a scanning range of 4000-400 cm -1 , scanning frequency 4° / min, the results are as follows Figure 4 shown.

[0133] Depend on Figure 4 It can be seen that most of the hemicellulose in the wood-based skeleton obtained by chemical treatment has been removed. The hydrophilic groups such as phenolic hydroxyl and methoxy groups on the surface of the wood-based heat storage material obtained by heat treatment have been greatly reduced, and the lignin benzene ring structure has been exposed.

[0134] 4. Mechanical properties test

[0135] The compression-rebound performance of the wood-based heat storage material of Example 1 was tested using a universal mechanical testing machine, wherein the compression rate was 1 mm / min and the maximum compression strain was 60%. The results are as follows: Figure 5 shown.

[0136] Depend on Figure 5 It can be seen that the wood-based heat storage material exhibits excellent elasticity and shape recovery. The material can still rebound to its original height after experiencing a compressive strain of up to 60%.

[0137] Furthermore, the mechanical properties of the wood-based heat storage materials of Examples 2-4 were tested again using a universal mechanical testing machine according to the above method, with a maximum compression strain of 60%. The results are shown in Table 3 below.

[0138] Table 3

[0139]

[0140] As can be seen from Table 3, due to the relatively low lignin content in Examples 1-3 of the present invention, Examples 1-3 all exhibit excellent elasticity and shape recovery, and the material can still rebound to the original height after experiencing a compression strain of up to 60%. However, due to the high lignin content in Example 4, its elasticity and shape recovery are poor, and the compression strain cannot reach 60%.

[0141] 5. Contact angle test

[0142] The water contact angle of the wood-based porous heat storage material before and after treatment in Example 1 was measured using a contact angle meter. The water droplet was in contact with the sample surface for 30 seconds, and a photo was taken after the state was stable. Five different areas of each sample were randomly selected for measurement, and the average value was taken as the final result. The results are shown in the figure. Figure 6 and Figure 7 shown.

[0143] Depend on Figure 6 and Figure 7 It can be seen that the water contact angle of natural wood is zero, showing hydrophilic properties, while the water contact angle of wood-based heat storage materials is as high as 152°, showing superhydrophobic properties.

[0144] It should be noted that, although the technical solution of the present invention is introduced with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0145] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A wood-based heat storage material, characterized in that: The wood-based heat storage material has a plurality of wood fiber layers, wherein the wood fiber layers are derived from wood fibers, The wood fiber layers are connected to the wood fiber layers, and, At least part of the wood fiber layers have a pore structure between the wood fiber layers, and the pore structure is formed by the collapse of wood ray tissue; The wood fiber layer contains cellulose, hemicellulose and lignin; wherein, Taking the total mass of the wood-based heat storage material as 100%, the content of cellulose is more than 50%, the content of hemicellulose is less than 10%, and the content of lignin is less than 16%.

2. The wood-based heat storage material according to claim 1, characterized in that: The wood fiber layer has a porous structure, and the average pore size of the wood fiber layer is 1 μm to 500 μm.

3. A method for preparing a wood-based heat storage material according to claim 1 or 2, characterized in that: The method comprises the step of collapsing the wood ray tissue of the wood raw material.

4. The preparation method according to claim 3, characterized in that: The following steps are involved: Chemical treatment of wood raw materials with alkaline substances and / or oxides to obtain wood-based materials; Drying the wood-based material to obtain a dried product; The dried product is subjected to heat treatment to obtain a wood-based heat storage material.

5. The preparation method according to claim 4, characterized in that: The alkaline substance includes one or a combination of two or more of KOH, NaOH, Na2SO3, K2SO3, Na2CO3, and K2CO3; the oxide includes one or a combination of two or more of H2O2, NaClO2, NaClO, KClO2, and KClO; and the chemical treatment time is 2 hours to 72 hours.

6. The preparation method according to claim 4 or 5, characterized in that: The drying includes one or a combination of two or more of air drying, freeze drying or supercritical drying.

7. The preparation method according to claim 6, characterized in that: The air drying comprises drying at a temperature of 10°C to 60°C for 6h to 72h; The freeze drying comprises freezing at a temperature of -196°C to -10°C for 0.5h to 24h, and then drying at a vacuum degree of 0.1μPa to 120Pa and a temperature of -65°C to -45°C for 24h to 72h; The supercritical drying comprises introducing liquid carbon dioxide and performing supercritical drying at a temperature of 10° C. to 60° C. and a pressure of 1 MPa to 30 MPa for 1 hour to 36 hours.

8. The preparation method according to claim 6, characterized in that: Before drying, the method further includes the step of washing the wood-based material with an alcohol solvent.

9. The preparation method according to any one of claims 4 or 5, characterized in that: The heat treatment includes heating the temperature to 190° C. to 1000° C. at a heating rate of 1° C. / min to 10° C. / min for 1 hour to 5 hours.

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