A thermode fabric for personal cooling and a method of making the same

Abstract

This invention discloses a thermal diode fabric for personal cooling and its preparation method. The preparation method includes: preparing a spinning solution containing thermally conductive particles, a hydrophobic polymer, and a crosslinking agent; electrospinning under low humidity to obtain a dense heat-transferring fiber film; using the obtained dense heat-transferring fiber film as a receiving substrate, electrospinning under high humidity to obtain a fluffy heat-insulating fiber wadding layer; and finally performing a crosslinking heat treatment to obtain the thermal diode fabric. This invention utilizes a simple electrospinning process to prepare a fiber material with a double-layer asymmetric density structure in a single step by controlling humidity without changing the spinning solution. It exhibits unidirectional thermal conductivity similar to a thermal diode, effectively dissipating heat when the human body is in a hot environment and effectively insulating when the human body is in a cold environment, ensuring that the skin temperature is maintained even in situations with significant temperature changes, such as entering and exiting air-conditioned spaces in summer.

Description

Technical Field

[0001] This invention relates to a thermal diode fabric for personal cooling and its preparation method, belonging to the field of functional fiber materials technology. Background Technology

[0002] Due to global warming and other climate changes, summer temperatures are rising, leading to increasing attention on personal thermal management textiles. These textiles can regulate individual thermal and humidity comfort based on unique body characteristics, while also reducing energy consumption and environmental pollution from building cooling systems. Based on heat transfer methods, personal thermal management textiles can be categorized into four types: heat conduction, heat radiation, heat convection, and evaporative cooling. While radiation, convection, and evaporative cooling textiles have been extensively studied, conduction cooling, a crucial method for achieving cooling through the textile itself, has received significantly less innovation.

[0003] Thousands of years ago, humans discovered that hemp fibers have a cooling effect when worn. Later, with the development and prosperity of synthetic fibers, nylon fibers became the preferred material for making summer cooling clothing. This is because both hemp and nylon fibers have high thermal conductivity, allowing them to transfer heat generated by the human body to the environment more quickly and efficiently, thus achieving body cooling. Therefore, current research on thermally conductive textiles focuses on improving the thermal conductivity of fabrics through various methods. For example, Hu et al. used 3D printing to incorporate boron nitride nanosheets into fibers and weave them into fabrics (ACS Nano 2017, 11, 11513), while Pan et al. impregnated cotton fabrics with a dispersion of boron nitride nanosheets to improve the fabric's thermal conductivity (Adv. Funct. Mater. 2022, 33, 2210769).

[0004] However, according to the second law of thermodynamics, heat can only diffuse from high temperatures to low temperatures. Therefore, such highly thermally conductive textiles are only suitable for environments where the ambient temperature is lower than the body temperature (mostly indoors, such as homes, offices, and shopping malls). Once in high-temperature environments (mostly outdoors, and some special production workshops), heat will be transferred to the body, causing it to heat up instead of cooling down. Therefore, current technologies only increase the thermal conductivity of materials by adding thermally conductive fillers to individual fibers or by finishing the fabric. While this can diffuse body heat outwards to achieve cooling, when the body enters a high-temperature environment, external heat is rapidly conducted to the body, causing it to heat up. Therefore, such highly thermally conductive textiles are only suitable for wearing in air-conditioned rooms and cannot cool down in high-temperature environments or adapt to environmental changes. Therefore, the key challenge that urgently needs to be solved in thermally conductive cooling textiles is their inability to achieve cooling of the human body even in high-temperature environments. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a thermal diode fabric for personal cooling and its preparation method. This invention utilizes an electrospinning process to prepare a fiber fabric with a double-layer asymmetric density structure in one step by controlling humidity without altering the spinning solution. This fabric exhibits a unidirectional thermal conductivity similar to a thermal diode, enabling effective heat dissipation when the human body is in a hot environment and effective heat insulation when the human body is in a cold environment. This ensures that the human body maintains its skin temperature even in situations with significant temperature variations, such as entering and exiting air-conditioned spaces in summer, preventing sudden changes in body temperature.

[0006] To achieve the above objectives, the present invention provides a method for preparing a thermal diode fabric, comprising the following steps:

[0007] Step 1: Disperse the thermally conductive particles in a solvent to obtain a dispersion, then dissolve the hydrophobic polymer (molecular weight 10W~100W) and crosslinking agent in the dispersion to obtain a uniform and stable spinning solution;

[0008] Step 2: Electrospin the spinning solution in a low humidity environment with a relative humidity of ≤50% to obtain a dense heat transfer fiber film.

[0009] Step 3: Using the dense heat transfer fiber membrane obtained in Step 2 as the receiving substrate, electrospin the spinning solution in a high humidity environment with a relative humidity of ≥75% to obtain a fluffy heat insulation fiber floc layer.

[0010] Step 4: The two-layer composite fiber material obtained in Step 3 is heat-treated to crosslink, thus obtaining the thermal diode fabric.

[0011] Preferably, the molecular weight of the hydrophobic polymer is 10W to 100W; the spinnability of the solution depends on the viscosity, which is affected by both the molecular weight of the polymer and the concentration of the solution; in this invention, the range of molecular weight is not specifically limited, and the spinnability of the solution can be adjusted by adjusting the concentration.

[0012] Preferably, the thermally conductive particles in step 1 are selected from at least one of boron nitride, graphene, silicon nitride, aluminum nitride, silicon carbide, magnesium oxide, aluminum oxide, zinc oxide, and carbon nanotubes;

[0013] The solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, acetone, toluene, xylene, dioxane, tetrahydrofuran, dichloroethane, chloroform, N-methylpyrrolidone, and dimethyl sulfoxide.

[0014] Preferably, the hydrophobic polymer in step 1 is selected from at least one of polyurethane, polysulfone, polyethersulfone, polyarylsulfone, polyphenylene sulfone, polymethyl methacrylate, polystyrene, and styrene-methyl methacrylate copolymer resin;

[0015] The crosslinking agent is selected from at least one of isocyanate and aziridine.

[0016] In this invention, the type of crosslinking agent isocyanate is not limited, and the crosslinking effect is provided by the isocyanate group; any one or more combinations of monoisocyanates R-N=C=O, diisocyanates O=C=N-R-N=C=O, and polyisocyanates can be selected; the diisocyanates include, but are not limited to, toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), hexamethylene diisocyanate (HDI), and lysine diisocyanate (LDI).

[0017] Preferably, in the spinning solution obtained in step 1, the mass content of the hydrophobic polymer is 15-25%, the mass content of the thermally conductive particles is 2-10%, and the mass content of the crosslinking agent is 0.5-5%.

[0018] Preferably, the electrospinning process conditions in step 2 are as follows: electrospinning voltage is 20-40kV, receiving distance is 10-30cm, the injection rate of the spinning solution is 3-6mL / h, and the relative humidity is 30-50%.

[0019] Preferably, the electrospinning process conditions in step 3 are as follows: electrospinning voltage is 20-40kV, receiving distance is 10-30cm, the infusion rate of the spinning solution is 3-6mL / h, and the relative humidity is 75%-95%.

[0020] Preferably, the heat treatment temperature in step 4 is 100–140°C, and the time is 30–120 min.

[0021] This invention also provides a thermal diode fabric prepared by the above-described method. The resulting thermal diode fabric has a two-layer composite structure, with the upper layer being a loose, heat-insulating fiber wadding layer with a bulk density of 1–10 mg / cm³. 3 The average pore size is 20–40 μm, the porosity is greater than 99%, and the fiber diameter is 4–10 μm; the lower layer is a dense heat transfer fiber membrane with a bulk density of 50–200 mg / cm³. 3 The average pore size is 5–15 μm, the porosity is less than 95%, and the fiber diameter is 0.5–2 μm. When heat is transferred from the dense fiber membrane layer to the fluffy fiber floc layer, the thermal conductivity is greater than 200 mW / (m·K), while when heat is transferred from the fluffy fiber floc layer to the dense fiber membrane layer, the thermal conductivity is less than 50 mW / (m·K).

[0022] The present invention also provides the application of the thermal diode fabric prepared by the above preparation method in the preparation of cooling fabrics.

[0023] This invention utilizes a simple electrospinning process to prepare a fiber material with a bilayer asymmetric density structure in a single step by controlling humidity without altering the spinning solution. The principle behind this one-step humidity control for asymmetric structure lies in the fact that during electrospinning, the solvent in the jet continuously diffuses with water vapor in the environment. The hydrophobic polymer in the jet solidifies upon contact with water. Therefore, when the ambient humidity is low, the jet solidifies slowly and the stretching time is long, forming finer fibers that accumulate into a dense fiber membrane. Conversely, when the ambient humidity is high, the jet solidifies quickly and the stretching time is short, forming coarser fibers that support a fluffy fiber sheet.

[0024] The principle behind this asymmetric structure achieving the thermal diode effect lies in two aspects: First, the difference in the pore structure of the two layers results in different contact areas with the heat source. The dense fiber membrane, which is close to the skin, has small pores and low porosity, thus having a large contact area with the skin. This allows the fabric to absorb more heat from the heat source, facilitating heat diffusion through the skin. Conversely, the loose fiber wadding layer, facing the environment, has large pores and high porosity, resulting in a small contact area with the outside world. This reduces the amount of heat absorbed by the fabric and prevents heat conduction to the body. Second, the thermal conductivity of the two layers changes differently with temperature. The loose wadding layer, filled with numerous pores, stores a large amount of still air. Due to the extremely low thermal conductivity of still air, the loose layer has an extremely low thermal conductivity, which remains relatively stable with increasing temperature. In contrast, the dense fiber layer, with its tightly packed fibers and extensive heat transfer paths, has a high thermal conductivity that increases significantly with temperature. This hinders heat conduction when a heat source comes into contact with the loose layer. Even if heat is conducted to the dense layer, the limited amount of heat results in a low thermal conductivity in the dense layer, ultimately leading to a very low overall thermal conductivity of the material. Conversely, when a heat source comes into contact with the dense layer, the higher temperature causes a significantly higher thermal conductivity in the dense layer, allowing for almost unimpeded heat transfer. Heat is transferred to the loose layer and then diffuses to the outside. Therefore, these two factors result in the fabric having a unidirectional thermal conductivity similar to a thermal diode. This allows for effective heat dissipation when the human body is in a hot environment and effective insulation when the human body is in a cold environment. This ensures that the skin temperature remains consistently lower, preventing sudden changes in body temperature, even in situations with significant temperature fluctuations, such as moving between air-conditioned and cold environments in summer.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention utilizes a simple electrospinning process to prepare fiber materials with a double-layer asymmetric density structure in one step by simply adjusting the humidity without changing the spinning solution.

[0027] 2. The composite material of the present invention consists of an upper layer of fluffy heat-insulating fiber flakes and a lower layer of dense heat-transferring fiber membrane. The dense layer can receive more heat and has a high thermal conductivity to achieve heat diffusion, while the fluffy layer absorbs less heat and has a low thermal conductivity, which can block heat from being conducted to the human body.

[0028] 3. This invention utilizes an asymmetric density structure to achieve a diode-like effect, where when the environment is hotter than the human body, external heat is difficult to enter the human body, while when the human body is hotter than the environment, heat can be efficiently diffused outward. This is beneficial for cooling the human body in summer, which has never been reported in other products or studies. Attached Figure Description

[0029] Figure 1 Scanning electron microscope image of the thermal diode fabric prepared by this invention.

[0030] Figure 2 for Figure 1 Enlarged image. Detailed Implementation

[0031] To make the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0032] In the following examples, all materials and reagents used, unless otherwise specified, are commercially available products. Specifically, polyurethane (CAS number: 51852-81-4, molecular weight 35W) was purchased from Huntsman Polyurethanes Ltd., China; polysulfone (CAS number: 51852-81-4, molecular weight 50W) was purchased from Solvay Ltd., USA; and polystyrene (CAS number: 100-42-5, molecular weight 35W) was purchased from SECCO Petrochemical Co., Ltd., China.

[0033] Example 1

[0034] A method for preparing a thermal diode fabric for personal cooling includes the following steps:

[0035] 1. The thermally conductive boron nitride nanosheets are dispersed in a mixed solvent of acetone and N,N-dimethylacetamide at a mass ratio of 1:4. The boron nitride nanosheets are then sonicated to ensure uniform dispersion, resulting in a dispersion. The hydrophobic polymers polyurethane and polysulfone (mass ratio of 1:9) and the crosslinking agent isocyanate are then dissolved in the dispersion to obtain a uniform and stable spinning solution. The concentration of boron nitride nanosheets in the spinning solution is 10 wt%, the concentration of the polymer is 15 wt%, and the concentration of isocyanate is 0.5 wt%.

[0036] 2. The spinning solution is first electrospun in a low-humidity environment to obtain a dense heat transfer fiber film. The spinning process parameters are: voltage 40kV, receiving distance 30cm, injection speed 3mL / h, and relative humidity 33±3%.

[0037] 3. Using the obtained dense heat transfer fiber membrane as the receiving substrate, the spinning solution is electrospun in a high humidity environment to obtain a fluffy heat insulation fiber floc layer. The spinning process parameters are: voltage 40kV, receiving distance 30cm, injection speed 3mL / h, and relative humidity of the environment 78±3%.

[0038] 4. The obtained two-layer composite fiber material is placed in a 120℃ forced-air oven for 1 hour for heat treatment to crosslink, thus obtaining the thermal diode fabric.

[0039] The resulting secondary tube fabric morphology is as follows: Figures 1-2 As shown in the figure, the fabric has a two-layer composite structure: an upper layer of loose, heat-insulating fiber wadding and a lower layer of dense, heat-transferring fiber membrane. The lower fiber membrane has a diameter of approximately 0.5 μm and a bulk density of approximately 200 mg / cm³. 3 The average pore size is approximately 5 μm; the upper fluffy layer has a fiber diameter of approximately 4 μm and a bulk density of approximately 10 mg / cm³. 3 The average pore size is approximately 20 μm. Tests showed that the thermal conductivity of the fabric from the dense layer to the loose layer is approximately 300 mW / (m·K), and the thermal conductivity from the loose layer to the dense layer is approximately 40 mW / (m·K).

[0040] Example 2

[0041] A method for preparing a thermal diode fabric for personal cooling includes the following steps:

[0042] 1. The thermally conductive boron nitride nanosheets are dispersed in a mixed solvent of acetone and N,N-dimethylacetamide at a mass ratio of 1:4. The boron nitride nanosheets are then sonicated to ensure uniform dispersion, resulting in a dispersion. The hydrophobic polymers polyurethane and polysulfone (mass ratio 3:7) and the crosslinking agent isocyanate are then dissolved in the dispersion to obtain a uniform and stable spinning solution. The concentration of boron nitride nanosheets in the spinning solution is 2 wt%, the concentration of the polymer is 25 wt%, and the concentration of isocyanate is 5 wt%.

[0043] 2. The spinning solution is first electrospun in a low-humidity environment to obtain a dense heat transfer fiber film. The spinning process parameters are: voltage 20kV, receiving distance 10cm, injection speed 6mL / h, and relative humidity of the environment 47±3%.

[0044] 3. Using the obtained dense heat transfer fiber membrane as the receiving substrate, the spinning solution is electrospun in a high humidity environment to obtain a fluffy heat insulation fiber floc layer. The spinning process parameters are: voltage 20kV, receiving distance 10cm, injection speed 6mL / h, and relative humidity of the environment 80±3%.

[0045] 4. The obtained two-layer composite fiber material is placed in a 120℃ forced-air oven for 1 hour for heat treatment to crosslink, thus obtaining the thermal diode fabric.

[0046] The resulting secondary tube fabric has a two-layer composite structure: an upper layer of loose, insulating fiber wadding and a lower layer of dense heat-transferring fiber membrane. The lower fiber membrane has a diameter of approximately 2 μm and a bulk density of approximately 50 mg / cm³. 3 The average pore size is approximately 15 μm; the upper fluffy layer has a fiber diameter of approximately 10 μm and a bulk density of approximately 2 mg / cm³. 3 The average pore size is approximately 40 μm. Testing showed that the thermal conductivity of the fabric from the dense layer to the loose layer is approximately 200 mW / (m·K), and the thermal conductivity from the loose layer to the dense layer is approximately 50 mW / (m·K).

[0047] Example 3

[0048] A method for preparing a thermal diode fabric for personal cooling includes the following steps:

[0049] 1. Thermally conductive boron nitride nanosheets were dispersed in a mixed solvent of dioxane and N,N-dimethylacetamide at a mass ratio of 1:4. The boron nitride nanosheets were then sonicated to ensure uniform dispersion, resulting in a dispersion. Hydrophobic polymers polyurethane and polysulfone (mass ratio 2:8) and crosslinking agent aziridine were then dissolved in the dispersion to obtain a uniform and stable spinning solution. The concentration of boron nitride nanosheets in the spinning solution was 5 wt%, the polymer concentration was 20 wt%, and the aziridine concentration was 5 wt%.

[0050] 2. The spinning solution is first electrospun in a low-humidity environment to obtain a dense heat transfer fiber film. The spinning process parameters are: voltage 40kV, receiving distance 20cm, injection speed 5mL / h, and relative humidity of 40±3%.

[0051] 3. Using the obtained dense heat transfer fiber membrane as the receiving substrate, the spinning solution is electrospun in a high humidity environment to obtain a fluffy heat insulation fiber floc layer. The spinning process parameters are: voltage 40kV, receiving distance 20cm, injection speed 5mL / h, and relative humidity of the environment 85±3%.

[0052] 4. The obtained two-layer composite fiber material is placed in a 120℃ forced-air drying oven for 1 hour for heat treatment and crosslinking to obtain the thermal diode fabric.

[0053] The resulting secondary tube fabric has a two-layer composite structure: an upper layer of loose, heat-insulating fiber wadding and a lower layer of dense heat-transferring fiber membrane. The lower fiber membrane has a diameter of approximately 1 μm and a bulk density of approximately 100 mg / cm³. 3The average pore size is approximately 10 μm; the upper fluffy layer has a fiber diameter of approximately 7 μm and a bulk density of approximately 5 mg / cm³. 3 The average pore size is approximately 30 μm. Tests showed that the thermal conductivity from the dense layer to the loose layer is approximately 300 mW / (m·K), and the thermal conductivity from the loose layer to the dense layer is approximately 30 mW / (m·K).

[0054] Example 4

[0055] A method for preparing a thermal diode fabric for personal cooling includes the following steps:

[0056] 1. The thermally conductive boron nitride nanosheets are dispersed in a mixed solvent of acetone and N,N-dimethylacetamide at a mass ratio of 1:4. The boron nitride nanosheets are then sonicated to ensure uniform dispersion, resulting in a dispersion. Hydrophobic polymers polyurethane and polystyrene (mass ratio 2:8) and crosslinking agent isocyanate are then dissolved in the dispersion to obtain a uniform and stable spinning solution. The concentration of boron nitride nanosheets in the spinning solution is 5 wt%, the polymer concentration is 20 wt%, and the isocyanate concentration is 5 wt%.

[0057] 2. The spinning solution is first electrospun in a low-humidity environment to obtain a dense heat transfer fiber film. The spinning process parameters are: voltage 40kV, receiving distance 20cm, injection speed 5mL / h, and relative humidity of 40±3%.

[0058] 3. Using the obtained dense heat transfer fiber membrane as the receiving substrate, the spinning solution is electrospun in a high humidity environment to obtain a fluffy heat insulation fiber floc layer. The spinning process parameters are: voltage 40kV, receiving distance 20cm, injection speed 5mL / h, and relative humidity of the environment 85±3%.

[0059] 4. The obtained two-layer composite fiber material is placed in a 120℃ forced-air drying oven for 1 hour for heat treatment and crosslinking to obtain the thermal diode fabric.

[0060] The resulting secondary tube fabric has a two-layer composite structure: an upper layer of loose, heat-insulating fiber wadding and a lower layer of dense heat-transferring fiber membrane. The lower fiber membrane has a diameter of approximately 0.8 μm and a bulk density of approximately 120 mg / cm³. 3 The average pore size is approximately 8 μm; the upper fluffy layer has a fiber diameter of approximately 5 μm and a bulk density of approximately 8 mg / cm³. 3 The average pore size is approximately 25 μm. Tests showed that the thermal conductivity of the fabric from the dense layer to the loose layer is approximately 250 mW / (m·K), and the thermal conductivity from the loose layer to the dense layer is approximately 28 mW / (m·K).

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make several improvements and additions without departing from the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A method of preparing a thermodiode fabric, characterized by, The method comprises the following steps: Step 1: dispersing the heat-conducting particles in a solvent to obtain a dispersion liquid, and then dissolving the hydrophobic polymer and the crosslinking agent in the dispersion liquid to obtain a uniform and stable spinning solution; Step 2: electrospinning the spinning solution in a low-humidity environment with a relative humidity of ≤50% to obtain a dense heat-conducting fiber membrane layer; Step 3: electrospinning the spinning solution in a high-humidity environment with a relative humidity of ≥75% by taking the dense heat-conducting fiber membrane layer obtained in Step 2 as a receiving substrate to obtain a fluffy heat-insulating fiber flake layer; Step 4: heat treating the two-layer composite fiber material obtained in Step 3 to crosslink, thereby obtaining a thermal diode fabric; The heat-conducting particles in Step 1 are selected from at least one of boron nitride, graphene, silicon nitride, aluminum nitride, silicon carbide, magnesium oxide, aluminum oxide, zinc oxide, and carbon nanotubes; and the crosslinking agent is selected from at least one of isocyanate and aziridine; In the spinning solution obtained in Step 1: the mass content of the hydrophobic polymer is 15-25%, the mass content of the heat-conducting particles is 2-10%, and the mass content of the crosslinking agent is 0.5-5%; The temperature of the heat treatment in Step 4 is 100-140°C, and the time is 30-120 min.

2. The production method according to claim 1, wherein The solvent in Step 1 is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, acetone, toluene, xylene, dioxane, tetrahydrofuran, dichloroethane, chloroform, N-methylpyrrolidone, and dimethyl sulfoxide.

3. The production method according to claim 1, wherein The hydrophobic polymer in Step 1 is selected from at least one of polyurethane, polysulfone, polyether sulfone, polyaryl sulfone, polyphenylene sulfone, polymethyl methacrylate, polystyrene, and styrene-methyl methacrylate copolymer resin.

4. The production method according to claim 1, wherein The process conditions for electrospinning in Step 2 are as follows: the electrospinning voltage is 20-40 kV, the receiving distance is 10-30 cm, the perfusion speed of the spinning solution is 3-6 mL / h, and the environmental relative humidity is 30-50%.

5. The production method according to claim 1, wherein The process conditions for electrospinning in Step 3 are as follows: the electrospinning voltage is 20-40 kV, the receiving distance is 10-30 cm, the perfusion speed of the spinning solution is 3-6 mL / h, and the environmental relative humidity is 75%-95%.

6. The thermal diode fabric prepared by the preparation method in any one of claims 1-5.

7. The application of the thermal diode fabric prepared by the preparation method in any one of claims 1-5 in the preparation of a cooling fabric.

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