Flexible thermal insulation porous material and preparation method thereof

Abstract

The invention discloses a flexible thermal insulation porous material and a preparation method thereof. The method comprises the following steps: firstly, directionally freezing a solution, and in the freezing process, repelling a macromolecular solute into crystal domains which are distributed in a honeycomb shape by growing ice crystals to generate a high-concentration enrichment region; in the space-limited and high-concentration environment, the polymer solute begins phase separation and precipitation, and a certain dense accumulation unit similar to a crystalline region is generated due to accumulation and arrangement among molecular chains. Then the frozen polymer solution is put into an electrolyte solution to be soaked, due to the HofMichael effect, polymer solute can be further subjected to phase separation under the salting-out effect, intermolecular accumulation is tighter, more dense accumulation units similar to crystalline regions can be generated, the strength of the whole separated polymer material is improved, and the separation efficiency is improved. Therefore, the porous material is obtained under a non-freeze-drying condition and is expected to be applied to a filling layer of a warm-keeping and heat-insulating article.

Description

Technical Field

[0001] The invention relates to a flexible thermal insulation porous material and a preparation method thereof, belongs to the field of preparation of thermal management materials, and is expected to be applied to the filling layer of thermal insulation products. Background Art

[0002] Freeze casting is a kind of exclusivity by ice crystal or other crystal, the frozen solution or dispersion liquid is removed by freeze drying to obtain the preparation method of the porous structure material replicating the gap of frozen solvent, the solvent of the used solution or dispersion liquid can be liquid with higher melting point such as water, cyclohexane, or solid with lower melting point such as camphene (camphor terpene). Water has the advantages of environmental protection, cheap and easy to obtain, and is the most commonly used solvent of freeze casting. The porous material obtained by freeze casting with water as solvent has the unique honeycomb structure of ice crystal, and these porous materials depend on the property of raw material itself, and can have different functional properties, such as wave absorption and noise reduction, electromagnetic shielding, thermal insulation, buffer damping, etc.

[0003] Freeze casting technology can be used to prepare porous materials with good thermal insulation properties. Patent application CN110372908A describes a thermal insulation polyimide nanofiber aerogel and its preparation method, which is to mix polyamic acid nanofibers, water-soluble polyamic acid, and triethylamine in water, disperse them, obtain a dispersion, freeze and freeze-dry the dispersion, and then perform thermal imidization to obtain a polyimide nano aerogel with good thermal insulation effects. Patent application CN114805910A describes a method for preparing a super-hydrophobic, thermally insulating aerogel, which is to perform directional freezing and freeze-drying of a chitosan solution, and then perform chemical vapor deposition hydrophobic modification to obtain a hydrophobic chitosan aerogel with a layered / porous structure and excellent thermal insulation properties. Patent application CN114085418A describes a degradable highly hydrophobic aerogel porous material and a preparation method thereof. By freezing and freeze-drying a dispersion of L-polylactic acid, D-polylactic acid and a porogen, a polylactic acid-based degradable highly hydrophobic aerogel porous material having a three-dimensional porous structure, high porosity, low density and large specific surface area can be obtained.

[0004] The current method of preparing porous organic materials by freeze casting has the following disadvantages:

[0005] (1) Existing methods require time-consuming and energy-consuming freeze-drying technology to maintain the final porous structure of the material;

[0006] (2) Existing methods have poor versatility and can only be applied to specific raw material systems;

[0007] (3) Existing methods cannot expand the functions of porous materials during the preparation process. Summary of the invention

[0008] In order to improve the above-mentioned thermal insulation porous material and preparation method, the present invention provides a flexible thermal insulation porous material and a preparation method thereof. Through directional freezing, based on the freeze-precipitation effect and the Hofmeister salting-out effect, the dense stacking between polymer solutes can be promoted, and the structural strength of the overall frame can be improved. The quick preparation of porous materials without freeze-drying is realized, which makes up for the defect of traditional methods' dependence on freeze-drying technology, and is expected to be applied to the filling layer of thermal insulation products.

[0009] To achieve the above object, the specific technical solution of the present invention is a flexible thermal insulation porous material and a preparation method thereof, comprising the following steps:

[0010] (1) adding a polymer solute into water and stirring to dissolve it to obtain a polymer solution;

[0011] (2) placing the polymer solution in (1) into a freezing mold, and placing the mold into a low-temperature freezing liquid for directional freezing to obtain a frozen polymer solution;

[0012] (3) soaking the frozen polymer solution in (2) in an electrolyte solution to obtain a polymer gel;

[0013] (4) placing the polymer gel in (3) into a silane solution for hydrophobic treatment;

[0014] (5) The polymer gel after the hydrophobic treatment in (4) is left to dry at room temperature until the weight no longer changes, thereby obtaining a flexible thermal insulation porous material.

[0015] Furthermore, in the above technical solution, in order to give the flexible thermal insulation porous material properties or functions such as conductivity, photothermal or photocatalytic properties, corresponding functional auxiliary materials can be added to the polymer solution in step (1).

[0016] Furthermore, the polymer solute is one or more polymers such as chitosan, sodium alginate, gelatin, polyvinyl alcohol, polyacrylamide, polyethylene glycol, etc.

[0017] Furthermore, the temperature range of the directional freezing is -60°C to -120°C.

[0018] Furthermore, the speed of placing the freezing mold into the low-temperature freezing liquid is 0.5-5 mm / min.

[0019] Furthermore, the electrolyte is one or more of chloride, sulfate, carbonate, oxalate, citrate, nitrate and the like.

[0020] Furthermore, the concentration of the polymer solution ranges from 2wt% to 30wt%.

[0021] Furthermore, the material of the freezing mold is one or more plastics such as polytetrafluoroethylene, polypropylene, polycarbonate, and polyethylene high-density polyethylene.

[0022] The present invention also provides a flexible thermal insulation porous material prepared according to the method.

[0023] The principle of the present invention is that during the freezing process, the polymer solute will be repelled by the growing ice crystals into the honeycomb-shaped crystal domains, producing a high-concentration enrichment area. In this space-limited, high-concentration environment, the polymer solute begins to phase separate and precipitate, and due to the stacking arrangement between the molecular chains, a certain dense stacking unit of the quasi-crystalline area is produced. After the frozen polymer solution is placed in the electrolyte solution, due to the Hofmeister effect, the polymer solute will further phase separate due to the salting-out effect, and the molecular stacking will be more dense, and more dense stacking units of the quasi-crystalline area will be produced. These dense stacking units are distributed between the polymer flexible segments, thereby improving the strength of the entire precipitated polymer material while ensuring the overall flexibility of the material, so as to ensure the integrity of the overall structure during the melting of ice crystals and the volatilization of water.

[0024] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0025] 1. The present invention does not involve freeze drying, is simple to operate, and does not require expensive equipment.

[0026] 2. The present invention can be applied to different polymer systems, such as natural polymer chitosan, sodium alginate, gelatin, etc., and artificial polymer polyvinyl alcohol, polyacrylamide, polyethylene glycol, etc.

[0027] 3. The present invention can endow the flexible thermal insulation porous material with different functions by blending, that is, adding corresponding functional auxiliary materials to the polymer solution in step (1), such as by adding graphene, the flexible felt can be endowed with conductive and photothermal properties, and by adding titanium dioxide particles, the flexible felt can be endowed with photocatalytic properties, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flow chart is prepared for the present invention;

[0029] Figure 2 This is a scanning electron microscope image of the flexible thermal insulation porous material in Example 1. DETAILED DESCRIPTION

[0030] The following is combined with Figure 1 , Figure 2 The present invention is further described with examples:

[0031] Embodiment 1:

[0032] A flexible thermal insulation porous material and a preparation method thereof, comprising the following steps:

[0033] (1) Add 5 g of polyvinyl alcohol to 100 mL of pure water and stir to dissolve in a 70°C water bath to obtain a polyvinyl alcohol solution.

[0034] (2) The polyvinyl alcohol solution in (1) is placed in a freezing mold with a glass bottom and plastic sides, and then the mold is immersed in a low-temperature freezing liquid at -80°C at a speed of 1 mm / min until the liquid level of the polyvinyl alcohol solution in the mold is lower than the freezing liquid and is completely frozen, thereby obtaining a frozen polyvinyl alcohol solution.

[0035] (3) The frozen polyvinyl alcohol solution in (2) was completely immersed in a sodium citrate electrolyte solution with a concentration of 1.5 mol / mL and soaked for 4 days to obtain a polyvinyl alcohol gel.

[0036] (4) The polyvinyl alcohol gel in (3) was immersed in a 10% trimethylmethoxysilane ethanol solution for 24 hours for hydrophobic treatment.

[0037] (5) The hydrophobicized polyvinyl alcohol gel in (4) is air-dried at room temperature until the weight no longer changes, thereby obtaining a flexible thermal insulation porous material.

[0038] The density of the flexible thermal insulation porous material finally prepared is 0.12g / cm 3 The porosity is 92% and the room temperature thermal conductivity is 0.032W / (m·K).

[0039] Figure 2 This is a scanning electron microscope image of a flexible thermal insulation porous material. It can be seen that in the porous material prepared by directional freezing, the main body of polyethanol is distributed in layers.

[0040] Embodiment 2:

[0041] A flexible thermal insulation porous material and a preparation method thereof, comprising the following steps:

[0042] (1) 5 g of polyvinyl alcohol was added to 100 mL of a graphene oxide solution having a concentration of 10 mg / mL, and the mixture was stirred and dissolved in a 70° C. water bath. Then, 2 g of ascorbic acid was added and the mixture was stirred and dissolved to obtain a polyvinyl alcohol solution.

[0043] (2) The polyvinyl alcohol solution in (1) is placed in a freezing mold with a glass bottom and plastic sides, and then the mold is immersed in a low-temperature freezing liquid at -90°C at a speed of 1 mm / min until the liquid level of the polyvinyl alcohol solution in the mold is lower than the freezing liquid and is completely frozen, thereby obtaining a frozen polyvinyl alcohol solution.

[0044] (3) The frozen polyvinyl alcohol solution in (2) was completely immersed in a sodium citrate electrolyte solution with a concentration of 1.5 mol / mL and soaked for 4 days to obtain a polyvinyl alcohol gel.

[0045] (4) The polyvinyl alcohol gel in (3) was immersed in a 10% trimethylmethoxysilane ethanol solution for 24 hours for hydrophobic treatment.

[0046] (5) The hydrophobicized polyvinyl alcohol gel in (4) is air-dried at room temperature until the weight no longer changes, thereby obtaining a graphene-doped flexible thermal insulation porous material.

[0047] The density of the graphene-doped flexible thermal insulation porous material prepared is 0.18 g / cm 3 The porosity is 90% and the room temperature thermal conductivity is 0.036W / (m·K).

[0048] Embodiment 3:

[0049] A flexible thermal insulation porous material and a preparation method thereof, comprising the following steps:

[0050] (1) Add 10 g of sodium alginate into 100 mL of pure water, stir to dissolve, and remove bubbles by ultrasonication to obtain a sodium alginate solution.

[0051] (2) The sodium alginate solution in (1) is placed in a freezing mold with a glass bottom and plastic sides, and then the mold is immersed in a low-temperature freezing liquid at -80°C at a speed of 1 mm / min until the liquid level of the sodium alginate solution in the mold is lower than the freezing liquid and is completely frozen, thereby obtaining a frozen sodium alginate solution.

[0052] (3) The frozen sodium alginate solution in (2) was completely immersed in a sodium sulfate electrolyte solution with a concentration of 1.5 mol / mL for 4 days to obtain a sodium alginate gel.

[0053] (4) The sodium alginate gel in (3) was immersed in a 10% trimethylmethoxysilane ethanol solution for 24 hours for hydrophobic treatment.

[0054] (5) The hydrophobicized sodium alginate gel in (4) is left to dry at room temperature until the weight no longer changes, thereby obtaining a flexible thermal insulation porous material.

[0055] The density of the flexible thermal insulation porous material finally prepared is 0.23g / cm 3 The porosity is 87% and the room temperature thermal conductivity is 0.035 W / (m·K).

[0056] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and implement it accordingly. It can be understood by those skilled in the art that various replacements, changes and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the contents disclosed in the embodiments of this specification, and the scope of protection of the present invention shall be subject to the scope defined in the claims.

Claims

1. A method for preparing a flexible thermal insulation porous material, characterized in that: The following steps are involved: Adding a polymer solute into water and stirring to dissolve it to obtain a polymer solution; The polymer solution is loaded into a freezing mold, and the freezing mold is placed in a low-temperature freezing liquid for directional freezing to obtain a frozen polymer solution; soaking the frozen polymer solution in an electrolyte solution to obtain a polymer gel; The polymer gel is placed in a silane solution for hydrophobic treatment; The hydrophobized polymer gel is left to dry at room temperature until the weight no longer changes, thereby obtaining a flexible thermal insulation porous material.

2. The preparation method according to claim 1, characterized in that: The polymer solute is one or more of chitosan, sodium alginate, gelatin, polyvinyl alcohol, polyacrylamide and polyethylene glycol.

3. The preparation method according to claim 1, characterized in that: The temperature range of the directional freezing is -60°C to -120°C.

4. The preparation method according to claim 1, characterized in that: The speed of placing the freezing mold into the low-temperature freezing liquid is 0.5-5 mm / min.

5. The preparation method according to claim 1, characterized in that: The electrolyte is one or more of chloride, sulfate, carbonate, oxalate, citrate, and nitrate.

6. The preparation method according to claim 1, characterized in that: The concentration of the polymer solution is in the range of 2 wt % to 30 wt %.

7. The preparation method according to claim 1, characterized in that: The material of the freezing mold is one or more of polytetrafluoroethylene, polypropylene, polycarbonate, and high-density polyethylene.

8. The preparation method according to claim 1, characterized in that: Corresponding functional auxiliary materials are added to the polymer solution to realize the conductive, photothermal or photocatalytic functions of the flexible thermal insulation porous material.

9. A flexible thermal insulation porous material prepared according to the method according to any one of claims 1 to 8.

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