Thermal diode fabric for personal cooling and preparation method thereof

Abstract

The invention discloses a thermal diode fabric for personal cooling and a preparation method thereof. The preparation method comprises the following steps: preparing a spinning solution containing heat-conducting particles, a hydrophobic polymer and a cross-linking agent; performing electrostatic spinning in a low-humidity environment to obtain a compact heat transfer fiber membrane layer; carrying out electrostatic spinning in a high-humidity environment by taking the obtained compact heat-transfer fiber membrane layer as a receiving base material to obtain a fluffy heat-insulation fiber flocculus layer; and finally, carrying out cross-linking heat treatment to obtain the thermal diode fabric. According to the preparation method, a simple electrostatic spinning preparation process is utilized, and the fiber material with a double-layer asymmetric density structure is prepared in one step only by regulating and controlling the humidity under the condition that a spinning solution is not changed; the one-way heat conduction effect similar to that of a hot diode is achieved, effective heat dissipation when the human body is in a cold environment and effective heat insulation when the human body is in a hot environment can be achieved, and the skin temperature is kept under the situation that the temperature change difference is large when the human body enters and exits an air-conditioning place in summer.

Description

Technical Field

[0001] The invention relates to a thermal diode fabric for personal cooling and a preparation method thereof, belonging to the technical field of functional fiber materials. Background Art

[0002] Due to climate change such as global warming, summer temperatures are getting higher and higher, and personal thermal management textiles have received more and more attention because they can adjust individual thermal and moisture comfort according to each person's different physical characteristics, while also reducing energy consumption and environmental pollution of building refrigeration equipment. According to the mode of heat transfer, personal thermal management textiles can be divided into four categories: thermal conduction, thermal radiation, thermal convection and evaporative cooling. Among them, radiation, convection and evaporative cooling textiles have been extensively studied, while conduction cooling, as an important way for textiles themselves to achieve cooling, is seriously lacking in innovation.

[0003] Thousands of years ago, humans discovered that hemp fiber is cool to wear. Later, with the development and prosperity of synthetic fibers, nylon fiber became the preferred material for making summer cooling clothing. This is because both hemp fiber and nylon fiber have high thermal conductivity, which can transfer the heat generated by the human body to the environment faster and more efficiently, thereby achieving human body cooling. Therefore, current research on thermal conductive textiles is mostly to improve 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), and Pan et al. immersed cotton fabrics in a dispersion of boron nitride nanosheets to improve the thermal conductivity of fabrics (Adv. Funct. Mater. 2022, 33, 2210769).

[0004] However, according to the second law of thermodynamics, heat can only diffuse from high temperature to low temperature. Therefore, this kind of high thermal conductivity textile is only suitable for places where the ambient temperature is lower than the body (mostly indoors, such as homes, offices, shopping malls, etc.). Once entering a high temperature place (mostly outdoors, and there are also some special production workshops), heat will be transmitted to the human body, not only can it not cool down, but it will increase the temperature. Therefore, the existing technology only improves the thermal conductivity of the material by adding thermal conductive fillers to the single fiber or finishing the fabric. Although this can diffuse the body heat outward to achieve cooling, when the human body enters a high temperature environment, the external heat is quickly transferred to the human body, causing the human body to heat up. Therefore, this kind of high thermal conductivity textile is only suitable for wearing in air-conditioned rooms, and cannot cool down in a high temperature environment, nor can it adapt to environmental changes. Therefore, the key problem that thermal conductive cooling textiles urgently need to solve is that they cannot still achieve human body cooling when the environment is high temperature. Summary of the invention

[0005] The purpose of the present invention is: to address the deficiencies in the prior art, the present invention provides a thermal diode fabric for personal cooling and a preparation method thereof. The present invention uses an electrostatic spinning process to prepare a fiber fabric with a double-layer asymmetric density structure by regulating the humidity without changing the spinning solution. The fiber fabric has a unidirectional heat conduction effect similar to a thermal diode, and can achieve effective heat dissipation when the human body's thermal environment is cold, and effective heat insulation when the human body's cold environment is hot, ensuring that the human body maintains skin temperature in a situation where the temperature changes greatly when entering and leaving air-conditioned places in summer, and does not cause the human body temperature to fluctuate between hot and cold.

[0006] In order to achieve the above object, 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, and then dissolve a hydrophobic polymer (molecular weight 10W to 100W) and a cross-linking agent in the dispersion to obtain a uniform and stable spinning solution;

[0008] Step 2: electrospinning the spinning solution in a low humidity environment with a relative humidity of ≤50% to obtain a dense heat transfer fiber membrane layer;

[0009] Step 3: using the dense heat transfer fiber membrane layer obtained in step 2 as a receiving substrate, electrospinning the spinning solution in a high humidity environment with a relative humidity of ≥75% to obtain a fluffy heat insulating fiber flake layer;

[0010] Step 4: heat-treat the two layers of composite fiber materials obtained in step 3 to cross-link them, thereby obtaining 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, and the viscosity is affected by the polymer molecular weight and the solution concentration; in the present invention, the range of molecular weight is not specifically limited, and the spinnability of the solution can be adjusted by 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, polyphenylenesulfone, polymethyl methacrylate, polystyrene and styrene-methyl methacrylate copolymer resin;

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

[0016] In the present invention, the type of cross-linking agent isocyanate is not limited, and the cross-linking effect is provided by the isocyanate group; any one or more combinations of monoisocyanate R-N=C=O, diisocyanate O=C=N-R-N=C=O and polyisocyanate can be selected; the diisocyanate includes but is 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 thermal conductive particles is 2-10%, and the mass content of the cross-linking agent is 0.5-5%.

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

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

[0020] Preferably, the heat treatment in step 4 is carried out at a temperature of 100 to 140° C. and for a time of 30 to 120 minutes.

[0021] The present invention also provides a thermal diode fabric prepared by the above preparation method. The obtained thermal diode fabric has a two-layer composite structure, the upper layer is a fluffy thermal insulation fiber flake layer, and the volume density is 1-10 mg / cm 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 layer with a volume density of 50-200 mg / cm 3 The average pore size is 5 to 15 μm, the porosity is less than 95%, and the fiber diameter is 0.5 to 2 μm; when heat is transferred from the dense fiber membrane layer to the fluffy fiber flake layer, the thermal conductivity is greater than 200 mW / (m·K), and when heat is transferred from the fluffy fiber flake layer to the dense fiber membrane layer, the thermal conductivity is less than 50 mW / (m·K).

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

[0023] The present invention uses a simple preparation process of electrospinning to prepare a fiber material with a double-layer asymmetric density structure in one step by regulating humidity without changing the spinning solution; the principle that the preparation of this asymmetric structure can be achieved in one step by regulating humidity is that during the electrospinning process, the solvent in the jet continuously diffuses with the water vapor in the environment, and the hydrophobic polymer in the jet solidifies when it encounters water, so when the ambient humidity is low, the jet solidifies slowly and the stretching time is long, forming thinner fibers and accumulating into a dense fiber film. When the ambient humidity is high, the jet solidifies quickly and the stretching time is short, forming thicker fibers to support fluffy fiber flakes.

[0024] The principle of this asymmetric structure to achieve the thermal diode effect lies in two aspects: First, due to the difference in the pore structure of the two layers of materials, the contact area between the two and the heat source is different. The dense fiber membrane close to the skin has a small pore size and a low porosity, so the contact area between the fiber and the skin is large, and the fabric absorbs more heat from the heat source, which is conducive to the diffusion of skin heat; while the fluffy fiber flake layer facing the environment has a large pore size and a high porosity, so the contact area between the fiber and the outside world is small, and the fabric absorbs less heat in the environment, avoiding the conduction of heat to the human body. Second, the thermal conductivity of the two layers of materials changes differently with temperature. The fluffy flake layer is filled with a large number of pores, so it stores a large amount of still air. Due to the extremely low thermal conductivity of still air, the fluffy layer has an extremely low thermal conductivity, and the thermal conductivity does not change much with the increase of temperature; while the dense fiber layer has a high thermal conductivity because the fibers are in close contact and the heat transmission path is wide, and the thermal conductivity increases significantly with temperature. This means that when the heat source contacts the fluffy layer, heat conduction is hindered. Even if it is conducted to the dense layer, the less heat leads to a low thermal conductivity of the dense layer, and the thermal conductivity of the material as a whole is ultimately very low. When the heat source contacts the dense layer, the higher temperature makes the thermal conductivity of the dense layer significantly higher, and almost unimpeded transfer can be achieved. After the heat is transferred to the fluffy layer, it continues to diffuse to the outside. Therefore, these two reasons make the fabric have a unidirectional heat conduction effect similar to a thermal diode, which can effectively dissipate heat when the human body is in a cold thermal environment, and effectively insulate when the human body is in a hot cold environment. This ensures that when the human body enters and exits air-conditioned places in summer, where the temperature changes greatly, the skin temperature is always cooled down, and the human body temperature will not fluctuate.

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

[0026] 1. The present invention utilizes a simple electrospinning preparation process to prepare a fiber material 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 is composed of an upper fluffy heat-insulating fiber flake layer and a lower dense heat-conducting fiber membrane layer, wherein the dense layer can receive more heat and has a higher thermal conductivity to achieve heat diffusion, and the fluffy layer absorbs less heat and has a lower thermal conductivity to block heat conduction to the human body;

[0028] 3. The present invention utilizes an asymmetric density structure to achieve a diode-like effect in which 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, the heat can efficiently diffuse outward, which is beneficial for cooling the human body in summer. This has never been reported in other products or studies. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0030] Figure 2 for Figure 1 Magnified image of . DETAILED DESCRIPTION

[0031] In order to make the present invention more clearly understood, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0032] In the following examples, the materials, reagents, etc. used, unless otherwise specified, are conventional commercially available products; among them, the CAS number of polyurethane is 51852-81-4, the molecular weight is 35W, purchased from Huntsman Polyurethane Co., Ltd. of China; the CAS number of polysulfone is 51852-81-4, the molecular weight is 50W, purchased from Solvay Co., Ltd. of the United States; the CAS number of polystyrene is 100-42-5, the molecular weight is 35W, purchased from China Secco Petrochemical Co., Ltd.

[0033] Example 1

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

[0035] 1. Disperse the thermal conductive particle boron nitride nanosheets in a mixed solvent of acetone and N,N-dimethylacetamide in a mass ratio of 1:4, and uniformly disperse the boron nitride nanosheets by ultrasound to obtain a dispersion liquid. Then, dissolve the hydrophobic polymer polyurethane and polysulfone (mass ratio 1:9) and the cross-linking agent isocyanate in the dispersion liquid to obtain a uniform and stable spinning solution; the concentration of the boron nitride nanosheets in the spinning solution is 10wt%, the concentration of the polymer is 15wt%, and the concentration of the isocyanate is 0.5wt%.

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

[0037] 3. Taking the obtained dense heat transfer fiber membrane layer as the receiving substrate, the spinning solution is continued to be electrostatically spun in a high humidity environment to obtain a fluffy heat insulating fiber flake layer; the spinning process parameters are: voltage 40kV, receiving distance 30cm, infusion speed 3mL / h, and environmental relative humidity of 78±3%.

[0038] 4. The obtained two-layer composite fiber material is placed in a 120° C. forced air oven for heat treatment for 1 h for cross-linking to obtain a thermal diode fabric.

[0039] The morphology of the obtained secondary tube fabric is as follows Figures 1-2 As shown in the figure, the fabric has a two-layer composite structure. The upper layer is a fluffy heat-insulating fiber flake layer, and the lower layer is a dense heat-transfer fiber membrane layer. The diameter of the lower fiber membrane is about 0.5 μm, and the volume density is about 200 mg / cm 3 The average pore size is about 5 μm; the fiber diameter of the upper fluffy layer is about 4 μm, and the volume density is about 10 mg / cm 3 The average pore size is about 20 μm. According to the test, the thermal conductivity of the fabric from the dense layer to the fluffy layer is about 300 mW / (m·K), and the thermal conductivity of the fabric from the fluffy layer to the dense layer is about 40 mW / (m·K).

[0040] Example 2

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

[0042] 1. Disperse the thermal conductive particle boron nitride nanosheets in a mixed solvent of acetone and N,N-dimethylacetamide in a mass ratio of 1:4, and uniformly disperse the boron nitride nanosheets by ultrasound to obtain a dispersion liquid. Then, dissolve the hydrophobic polymer polyurethane and polysulfone (mass ratio 3:7) and the cross-linking agent isocyanate in the dispersion liquid to obtain a uniform and stable spinning solution; the concentration of the boron nitride nanosheets in the spinning solution is 2wt%, the concentration of the polymer is 25wt%, and the concentration of the isocyanate is 5wt%.

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

[0044] 3. Taking the obtained dense heat transfer fiber membrane layer as the receiving substrate, the spinning solution is continued to be electrostatically spun in a high humidity environment to obtain a fluffy heat insulating fiber flake layer; the spinning process parameters are: voltage 20kV, receiving distance 10cm, infusion speed 6mL / h, and environmental relative humidity of 80±3%.

[0045] 4. The obtained two-layer composite fiber material is placed in a 120° C. forced air oven for heat treatment for 1 h for cross-linking to obtain a thermal diode fabric.

[0046] The obtained secondary tube fabric has a two-layer composite structure. The upper layer is a fluffy heat-insulating fiber flake layer, and the lower layer is a dense heat-transfer fiber membrane layer. The diameter of the lower fiber membrane is about 2 μm, and the volume density is about 50 mg / cm 3 The average pore size is about 15 μm; the fiber diameter of the upper fluffy layer is about 10 μm, and the volume density is about 2 mg / cm 3 The average pore size is about 40 μm. According to the test, the thermal conductivity of the fabric from the dense layer to the fluffy layer is about 200 mW / (m·K), and the thermal conductivity of the fabric from the fluffy layer to the dense layer is about 50 mW / (m·K).

[0047] Example 3

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

[0049] 1. Disperse thermal conductive particle boron nitride nanosheets in a mixed solvent of dioxane and N,N-dimethylacetamide in a mass ratio of 1:4, and uniformly disperse the boron nitride nanosheets by ultrasound to obtain a dispersion liquid. Then, hydrophobic polymers polyurethane and polysulfone (mass ratio 2:8) and a cross-linking agent aziridine are dissolved in the dispersion liquid to obtain a uniform and stable spinning solution; the concentration of boron nitride nanosheets in the spinning solution is 5wt%, the concentration of the polymer is 20wt%, and the concentration of aziridine is 5wt%.

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

[0051] 3. Taking the obtained dense heat transfer fiber membrane layer as the receiving substrate, the spinning solution is continued to be electrostatically spun in a high humidity environment to obtain a fluffy heat insulating fiber flake layer; the spinning process parameters are: voltage 40kV, receiving distance 20cm, infusion speed 5mL / h, and environmental relative humidity of 85±3%.

[0052] 4. The obtained two-layer composite fiber material is placed in a 120° C. forced air oven for heat treatment for 1 hour to dry and cross-link, thereby obtaining a thermal diode fabric.

[0053] The obtained secondary tube fabric has a two-layer composite structure. The upper layer is a fluffy heat-insulating fiber flake layer, and the lower layer is a dense heat-transfer fiber membrane layer. The diameter of the lower fiber membrane is about 1 μm, and the volume density is about 100 mg / cm 3The average pore size is about 10 μm; the fiber diameter of the upper fluffy layer is about 7 μm, and the volume density is about 5 mg / cm 3 The average pore size is about 30 μm. According to the test, the thermal conductivity of the fabric from the dense layer to the fluffy layer is about 300 mW / (m·K), and the thermal conductivity of the fabric from the fluffy layer to the dense layer is about 30 mW / (m·K).

[0054] Example 4

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

[0056] 1. Disperse the thermal conductive particle boron nitride nanosheets in a mixed solvent of acetone and N,N-dimethylacetamide in a mass ratio of 1:4, and uniformly disperse the boron nitride nanosheets by ultrasound to obtain a dispersion liquid. Then, dissolve the hydrophobic polymer polyurethane and polystyrene (mass ratio 2:8) and the cross-linking agent isocyanate in the dispersion liquid to obtain a uniform and stable spinning solution; the concentration of the boron nitride nanosheets in the spinning solution is 5wt%, the concentration of the polymer is 20wt%, and the concentration of the isocyanate is 5wt%.

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

[0058] 3. Taking the obtained dense heat transfer fiber membrane layer as the receiving substrate, the spinning solution is continued to be electrostatically spun in a high humidity environment to obtain a fluffy heat insulating fiber flake layer; the spinning process parameters are: voltage 40kV, receiving distance 20cm, infusion speed 5mL / h, and environmental relative humidity of 85±3%.

[0059] 4. The obtained two-layer composite fiber material is placed in a 120° C. forced air oven for heat treatment for 1 hour to dry and cross-link, thereby obtaining a thermal diode fabric.

[0060] The obtained secondary tube fabric has a two-layer composite structure. The upper layer is a fluffy heat-insulating fiber flake layer, and the lower layer is a dense heat-transfer fiber membrane layer. The diameter of the lower fiber membrane is about 0.8 μm, and the volume density is about 120 mg / cm 3 The average pore size is about 8μm; the fiber diameter of the upper fluffy layer is about 5μm, and the volume density is about 8mg / cm 3 The average pore size is about 25 μm. According to the test, the thermal conductivity of the fabric from the dense layer to the fluffy layer is about 250 mW / (m·K), and the thermal conductivity of the fabric from the fluffy layer to the dense layer is about 28 mW / (m·K).

[0061] The above description is only a preferred embodiment of the present invention and is not any formal or substantial limitation of the present invention. It should be pointed out that a person skilled in the art can make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a thermal diode fabric, It is characterized in that The following steps are involved: Step 1: Dispersing the thermally conductive particles in a solvent to obtain a dispersion, and then dissolving a hydrophobic polymer and a cross-linking agent in the dispersion 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 transfer fiber membrane layer; Step 3: using the dense heat transfer fiber membrane layer obtained in step 2 as a receiving substrate, electrospinning the spinning solution in a high humidity environment with a relative humidity of ≥75% to obtain a fluffy heat insulating fiber flake layer; Step 4: heat-treat the two layers of composite fiber materials obtained in step 3 to cross-link them, thereby obtaining thermal diode fabric.

2. The preparation method according to claim 1, It is characterized in that 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; 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.

3. The preparation method according to claim 1, It is characterized in that 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; The cross-linking agent is selected from at least one of isocyanate and aziridine.

4. The preparation method according to claim 1, It is characterized in that In the spinning solution obtained in step 1, the mass content of the hydrophobic polymer is 15-25%, the mass content of the thermal conductive particles is 2-10%, and the mass content of the cross-linking agent is 0.5-5%.

5. The preparation method according to claim 1, It is characterized in that The process conditions of electrospinning in step 2 are as follows: electrospinning voltage is 20-40 kV, receiving distance is 10-30 cm, perfusion speed of spinning solution is 3-6 mL / h, and relative humidity of environment is 30-50%.

6. The preparation method according to claim 1, It is characterized in that The process conditions of electrospinning in step 3 are as follows: electrospinning voltage is 20-40 kV, receiving distance is 10-30 cm, perfusion speed of spinning solution is 3-6 mL / h, and relative humidity of environment is 75%-95%.

7. The preparation method according to claim 1, It is characterized in that The heat treatment temperature in step 4 is 100-140° C. and the time is 30-120 min.

8. The thermal diode fabric prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the thermal diode fabric prepared by the preparation method according to any one of claims 1 to 7 in the preparation of cooling fabrics.

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