Electrospun high thermal conductive two-dimensional polyamide nanofiber membrane and method thereof

Abstract

The application discloses a high-thermal-conductivity two-dimensional polyamide nanofiber membrane prepared by electrostatic spinning and a method thereof. By using a high-concentration two-dimensional polyamide solution and ultrahigh-molecular-weight polyethylene oxide as a spinning solution, a molecular chain entanglement structure is introduced into the spinning solution, the spinning solution has tensibility, and by changing the content of the polyethylene oxide, a nanofiber membrane with adjustable diameter can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of spinning technology, specifically relating to a high thermal conductivity two-dimensional polyamide nanofiber membrane prepared by electrospinning and its method. Background Technology

[0002] In recent years, electrospinning technology has attracted widespread attention in the field of nanofiber preparation due to its simplicity, versatility, and high continuity. This technology can produce ultrafine fibers with diameters ranging from tens to hundreds of nanometers, and its internal structure can be controlled, such as hollow, porous, and core-shell structures. Furthermore, the fiber surface or internal structure can be further modified using nanoparticles. Currently, nanofibers obtained through electrospinning have been applied in multiple fields, including filtration membranes, biosensors, surface coatings, tissue engineering, and energy storage.

[0003] The raw materials for electrospun nanofibers are diverse, including polymers, ceramics, small molecules, and their composites. One-dimensional polymers, due to their linear or branched molecular chain structure, can provide sufficient molecular entanglement, thus endowing the spinning solution with good stretchability. Two-dimensional polymers, however, typically exist in crystalline powder form. The strong π-π stacking between layers makes it difficult for them to spontaneously disperse into a single layer or few layers in solvents, thus hindering the formation of a uniform and stable dispersion. Furthermore, the lamellar structure of two-dimensional polymers cannot form entanglement, resulting in a dispersion lacking stretchability and unable to form a stable jet. These limitations currently prevent the preparation of two-dimensional polymer nanofibers using electrospinning. Currently, two-dimensional polymer nanofibers are mainly obtained through in-situ epitaxial growth on the surface of one-dimensional polymer nanofibers. However, the resulting nanofibers are merely loosely packed aggregates of two-dimensional polymer particles with weak mechanical properties and lack practical application value. Two-dimensional polymers are often used as fillers in electrospinning to obtain composite fibers when mixed with one-dimensional polymers. However, as composite fillers, they cannot fully utilize the intrinsic advantages of the two-dimensional topology of two-dimensional polymers, such as high thermal conductivity, high electrical conductivity, high carrier mobility, low resistance, and high selectivity in molecular ion sieving. Therefore, there is an urgent need for a spinning process that can directly prepare two-dimensional polymers into nanofilms to further expand the application fields and development prospects of two-dimensional polymer materials. Summary of the Invention

[0004] To address the challenge of directly preparing highly thermally conductive two-dimensional polymer nanofilms using existing technologies, this invention proposes a method for preparing highly thermally conductive two-dimensional polyamide nanofiber membranes via electrospinning. By using a high-concentration two-dimensional polyamide solution and ultra-high molecular weight polyethylene oxide (Mv~7900000) as the spinning solution, an entangled molecular chain structure is introduced into the spinning solution, giving it stretchability. Furthermore, by varying the amount of polyethylene oxide added, nanofiber membranes with adjustable diameters can be obtained.

[0005] One of the technical solutions of the present invention is to provide a method for electrospinning to produce a high thermal conductivity two-dimensional polyamide nanofiber membrane, comprising the following steps: (1) Preparation of two-dimensional polyamide; (2) Preparation of spinning solution: 40-45 wt.% of two-dimensional polyamide dispersion and 2-5 wt.% of polyethylene oxide solution are heated at 60°C and mixed evenly until there is no transparent gel-like precipitate in the solution to obtain spinning solution; in spinning solution, the mass ratio of polyethylene oxide to polyamide is 1:(20-50); the solvent of the two-dimensional polyamide dispersion and polyethylene oxide solution is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; (3) Electrospinning: Use a spinning needle with a specification of 22G-30G as the spinning nozzle, use a receiving device covered with PET copper-plated film as the receiving device to take in the yarn, turn on the switch of the electrospinning device to perform electrospinning, and form a uniform nanofiber film on the PET copper-plated film.

[0006] Furthermore, the receiving device is a high-speed receiving device, which includes a roller whose axis is perpendicular to the voltage direction of electrospinning; and the roller rotates at high speed along its axis, with a rotation speed of 300-3000 rpm.

[0007] Furthermore, in step 3, the spinning needle is 10-20 cm away from the high-speed receiving device.

[0008] Furthermore, during the electrospinning process, the positive electrode voltage is 10-16 kV, and the negative electrode voltage is -3 to -6 kV.

[0009] Furthermore, the method for preparing the two-dimensional polyamide described in step 1 is as follows: (1) Melamine and acyl chloride compounds are added to N-methylpyrrolidone and stirred until homogeneous. A catalyst is added and the mixture is stirred at 25-40°C for 24 hours. The acyl chloride compounds are 1,3,5-benzenetricarboxylic acid chloride or terephthaloyl chloride. (2) The reaction product obtained in step 1 is added to the washing solution at a volume ratio of 1:8. After washing, the product is centrifuged to obtain powder. The washing solution is water, ethanol or acetone. (3) The powder was dried at 60°C for 12 h and then transferred to a vacuum oven to continue drying at 60°C for 6 h to obtain two-dimensional polyamide.

[0010] Furthermore, in step 1 of the preparation of the two-dimensional polyamide, the concentration of melamine in the mixture of catalyst and N-methylpyrrolidone is 0.1 mol / L; when the acyl chloride compound is 1,3,5-benzenetricarboxyl chloride, the concentration in the above mixture is 0.1 mol / L, and when it is terephthaloyl chloride, the concentration in the above mixture is 0.15 mol / L.

[0011] Furthermore, the catalyst used in step 1 of the preparation of the two-dimensional polyamide is pyridine.

[0012] The two-dimensional aromatic polyamide powder synthesized in this invention is composed of stacked small-sized two-dimensional sheets, with many small crystalline regions arranged randomly within each sheet. Therefore, the interaction between the sheets is weak, allowing the stacked sheets to disperse into single or several extremely thin layered molecules under mechanical stirring, forming a stable, high-concentration dispersion. Two-dimensional aromatic polyamide can form a high-concentration dispersion of up to 45%. However, the solution formed by stacked two-dimensional nanosheets has poor stretchability. Therefore, ultra-high molecular weight polyethylene oxide (PEO) is introduced. Its long molecular chains form a physical cross-linking network through dense entanglement, significantly increasing the chain entanglement concentration of the solution. This imparts sufficient viscoelasticity and tensile strength to the spinning solution, thereby suppressing jet instability (dropletization) and bending instability (fiber wobbling and breakage), ensuring the continuity of the jet during stretching and solvent evaporation. Simultaneously, the addition of PEO allows for precise control of fiber diameter by adjusting the concentration—high concentration PEO improves the stretchability of the solution, which is beneficial for forming fine, continuous fibers.

[0013] In some embodiments of the present invention, the specific operation of electrospinning is as follows: A spinning device is installed. In the electrospinning equipment chamber, a 1ml syringe is used to draw the prepared electrospinning solution. A 22G spinning needle is then installed as a spinning nozzle. The syringe is then installed on the electrospinning apparatus in the equipment chamber to form the electrospinning device. Subsequently, a high-speed collection and control orientation device and the electrospinning equipment are connected. A PET copper-plated film is then fixed on the rotating shaft of the high-speed receiving device. The distance between the nozzle and the receiving device is adjusted to 10cm-25cm. Two infrared lamps are then installed and aligned with the take-up shaft to ensure rapid solvent evaporation. The equipment is turned on, and the speed of the high-speed receiving device is adjusted to 300-3000rpm, the injection speed to 0.1mm / min, and the positive and negative voltmeters are turned on. The positive voltage is adjusted to 10-16kV, and the negative voltage to -3 to -6kV for spinning. Under the action of a high electric field, the extruded spinning solution forms a charged jet, which is collected by the receiving shaft.

[0014] The second technical solution of the present invention is to provide a high thermal conductivity two-dimensional polyamide nanofiber membrane prepared by the above method.

[0015] The prepared two-dimensional polyamide nanofibers have diameters ranging from 80 to 800 nm, and their thermal conductivity can reach up to 8.7 W / (m²). K).

[0016] The beneficial effects of the present invention are as follows: (1) A high thermal conductivity two-dimensional polyamide nanofiber membrane is directly prepared by electrospinning. The prepared nanofiber membrane has good thermal conductivity, reaching 8.7 W / (m²). K).

[0017] (2) The highly conjugated two-dimensional framework of two-dimensional polymers provides an efficient thermal conduction pathway, while the layered structure reduces phonon scattering. Therefore, directly assembling two-dimensional polymers into nanofibers is expected to obtain nanofiber materials with high thermal conductivity. Attached Figure Description

[0018] Figure 1 The molecular formula of the polyamide described in this invention is [insert molecular formula here].

[0019] Figure 2 SEM image of the nanofiber membrane in Example 1. Detailed Implementation

[0020] The basic principle of electrospinning is to use a high-voltage electric field to generate a strong electric force between the spinning nozzle and the receiving device, charging droplets in the polymer solution or melt. When an electric field is applied, the charges on the droplet surface repel each other, overcoming their surface tension, causing the droplet to gradually stretch and form a conical structure, namely a Taylor cone. As the electric field strength further increases, a charged jet forms at the top of the Taylor cone, continuously stretching and thinning under the action of the high electric field, and forming nanofibers after solvent evaporation or cooling and solidification. For the electrospinning solution, a sufficient concentration of polymer chain entanglement is required to stably form continuous fibers. When the solution concentration is below the minimum spinnable concentration, the interaction between polymer chains is weak and cannot overcome Rayleigh instability, leading to interruption of the jetting and the formation of droplets, resulting in bead-like structures or spherical particles in the fibers, making it impossible to obtain a uniform nanofiber membrane.

[0021] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all terms are parts by weight and weight percentages.

[0022] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0023] The embodiments of the present invention will be further described below with reference to several examples.

[0024] It should be understood that the described embodiments are only some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0025] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0026] Example 1 Melamine and 1,3,5-benzenetriformyl chloride were added to N-methylpyrrolidone and stirred until homogeneous. A catalyst was then added, and the mixture was stirred at 25°C for 24 hours. The concentration of melamine in the mixture of catalyst and N-methylpyrrolidone was 0.1 mol / L; the concentration of 1,3,5-benzenetriformyl chloride in the same mixture was also 0.1 mol / L. (2) Add the reaction product obtained in step 1 to water at a volume ratio of 1:8, wash and centrifuge to obtain powder; (3) The powder was dried at 60°C for 12 h and then transferred to a vacuum oven to continue drying at 60°C for 6 h to obtain two-dimensional polyamide (MA-2DPA-1).

[0027] (4) Weigh 0.4g of two-dimensional polyamide (MA-2DPA-1) powder and add it to 0.6g of N,N-dimethylformamide (DMF) solvent to obtain a 40 wt.% polyamide (MA-2DPA-1) dispersion.

[0028] (5) Weigh 0.2g of polyethylene oxide and add 9.8g of N,N-dimethylformamide (DMF) under magnetic stirring at 60 degrees Celsius and 300 rpm to prepare a 2 wt.% polyethylene oxide solution. The solvent is N,N-dimethylformamide (DMF).

[0029] (6) Prepare spinning solution: Heat and stir the solutions obtained in steps (4) and (5) at 60°C for 30 min to obtain spinning solution; the mass ratio of polyethylene oxide (PEO) to polyamide (MA-2DPA-1) in the spinning solution is 1:50.

[0030] (7) Install the spinning device. In the electrospinning equipment chamber, use a 1ml syringe to draw the prepared electrospinning solution, then install a 22G spinning needle as the spinning nozzle. Then install the syringe on the electrospinning instrument in the equipment chamber to form the electrospinning device. Then fix the PET copper-plated film on the receiving shaft, with the spinning needle 10cm away from the high-speed receiving device. Then install two infrared lamps, aiming them at the take-up shaft to ensure rapid solvent evaporation.

[0031] (8) Using electrospinning, turn on the equipment, adjust the receiving speed of the high-speed receiving device to 300 rpm and the injection speed to 0.1 mm / min, turn on the positive and negative voltage meters, adjust the positive voltage to 10 kV and the negative voltage to -3 kV, and carry out spinning. Under the action of high electric field, the extruded spinning liquid forms a charged jet and is collected by the receiving shaft.

[0032] (9) The two-dimensional polyamide (MA-2DPA-1) nanofiber membrane obtained in (8) is dried in an oven at 60 degrees Celsius to obtain the two-dimensional polyamide (MA-2DPA-1) nanofiber membrane.

[0033] The thermal conductivity of the two-dimensional polyamide nanofiber membrane was tested by capturing temperature changes with an infrared camera. The obtained thermal conductivity result for the two-dimensional polyamide (MA-2DPA-1) nanofiber membrane was 2.3 W / (m²). K).

[0034] Example 2: (1) Melamine and terephthaloyl chloride were added to N-methylpyrrolidone and stirred until homogeneous. A catalyst was added and the mixture was stirred at 40°C for 24 hours. The concentration of melamine in the mixture of catalyst and N-methylpyrrolidone was 0.1 mol / L. The concentration of terephthaloyl chloride in the mixture was 0.15 mol / L.

[0035] (2) Add the reaction product obtained in step 1 to ethanol at a volume ratio of 1:8, wash and centrifuge to obtain powder; (3) The powder was dried at 60°C for 12 h and then transferred to a vacuum oven to continue drying at 60°C for 6 h to obtain two-dimensional polyamide (MA-2DPA-2).

[0036] (4) Weigh 0.4g of two-dimensional polyamide (MA-2DPA-2) powder and add it to 0.6g of N,N-dimethylformamide (DMF) solvent to obtain a 40 wt.% polyamide (MA-2DPA-2) dispersion.

[0037] (5) Weigh 0.2g of polyethylene oxide and add 9.8g of N,N-dimethylformamide (DMF) under magnetic stirring at 60 degrees Celsius and 300 rpm to prepare a 2 wt.% polyethylene oxide solution. The solvent is N,N-dimethylformamide (DMF).

[0038] (6) Prepare spinning solution: Heat and stir the solutions obtained in steps (4) and (5) at 60°C for 30 min to obtain spinning solution; the mass ratio of polyethylene oxide (PEO) to polyamide (MA-2DPA-2) in the spinning solution is 1:50.

[0039] (7) Install the spinning device. In the electrospinning equipment chamber, use a 1ml syringe to draw the prepared electrospinning solution, then install a 22G spinning needle as the spinning nozzle. Install the syringe on the electrospinning machine in the equipment chamber to form the electrospinning device. Then fix the PET copper-plated film on the receiving shaft, with the spinning needle 20cm away from the high-speed receiving device. Install two infrared lamps and align them with the take-up shaft to ensure rapid solvent evaporation.

[0040] (8) Using electrospinning, turn on the equipment, adjust the receiving speed of the take-up shaft to 300 rpm and the injection speed to 0.1 mm / min, turn on the positive and negative voltage meters, adjust the positive voltage to 14 kV and the negative voltage to -3 kV, and carry out spinning. Under the action of high electric field, the extruded spinning liquid forms a charged jet and is collected by the receiving shaft.

[0041] (9) The two-dimensional polyamide (MA-2DPA-2) nanofiber membrane obtained in (8) is dried in an oven at 60 degrees Celsius to obtain the two-dimensional polyamide (MA-2DPA-2) nanofiber membrane.

[0042] The obtained two-dimensional polyamide (MA-2DPA-2) nanofiber membrane has a thermal conductivity of 1.6 W / (m²). K).

[0043] Example 3: (1) Weigh 0.4g of two-dimensional polyamide (MA-2DPA-1) powder and add it to 0.6g of N,N-dimethylacetamide solvent to obtain a 40 wt.% polyamide (MA-2DPA-1) dispersion.

[0044] (2) Weigh 0.2g of polyethylene oxide and add 9.8g of N,N-dimethylacetamide under magnetic stirring at 60 degrees Celsius and 300 rpm to prepare a 2 wt.% polyethylene oxide solution. The solvent is N,N-dimethylformamide (DMF).

[0045] (3) Prepare spinning solution. Heat and stir the solution obtained in steps (4) and (5) at 60°C for 30 min to obtain spinning solution. The mass ratio of polyethylene oxide (PEO) to polyamide (MA-2DPA-1) in the spinning solution is 1:50.

[0046] (4) Install the spinning device. In the electrospinning equipment chamber, use a 1ml syringe to draw the prepared electrospinning solution, then install a 22G specification spinning needle as a spinning nozzle, and then install the syringe on the electrospinning instrument in the equipment chamber to form an electrospinning device. (5) Connect the high-speed collection control orientation device and the electrospinning equipment, fix the PET copper-plated film on the receiving shaft, and keep the spinning needle 10cm away from the high-speed receiving device. Then install two infrared lamps and align them with the take-up shaft to ensure rapid solvent evaporation.

[0047] (6) Using electrospinning, turn on the equipment, adjust the speed of the high-speed receiving device to 2000 rpm and the injection speed to 0.1 mm / min, turn on the positive and negative voltage meters, adjust the positive voltage to 16 kV and the negative voltage to -3 kV, and carry out spinning. Under the action of high electric field, the extruded spinning liquid forms a charged jet and is collected by the receiving shaft.

[0048] (7) The two-dimensional polyamide (MA-2DPA-1) nanofiber membrane obtained in (6) is dried in an oven at 60 degrees Celsius to obtain the two-dimensional polyamide (MA-2DPA-1) nanofiber membrane.

[0049] The obtained two-dimensional polyamide (MA-2DPA-1) nanofiber membrane has a thermal conductivity of 8.7 W / (m²). K).

[0050] Example 4: (1) Weigh 0.45g of two-dimensional polyamide (MA-2DPA-2) powder and add it to 0.55g of dimethyl sulfoxide solvent to obtain a 45wt.% polyamide (MA-2DPA-2) dispersion.

[0051] (2) Weigh 0.5g of polyethylene oxide and add 9.5g of dimethyl sulfoxide under magnetic stirring at 60 degrees Celsius and 300 rpm to prepare a 5 wt.% polyethylene oxide solution. The solvent is N,N-dimethylformamide (DMF).

[0052] (3) Prepare spinning solution. Heat and stir the solution obtained in steps (4) and (5) at 60°C for 30 min to obtain spinning solution. The mass ratio of polyethylene oxide (PEO) to polyamide (MA-2DPA-2) in the spinning solution is 1:20.

[0053] (4) Install the spinning device. In the electrospinning equipment chamber, use a 1ml syringe to draw the prepared electrospinning solution, then install a 30G spinning needle as a spinning nozzle, and then install the syringe on the electrospinning instrument in the equipment chamber to form an electrospinning device. (5) Connect the high-speed collection control orientation device and the electrospinning equipment, fix the PET copper-plated film on the receiving shaft, and keep the spinning needle 20cm away from the high-speed receiving device. Then install two infrared lamps and align them with the take-up shaft to ensure rapid solvent evaporation.

[0054] (6) Using electrospinning, turn on the equipment, adjust the speed of the high-speed receiving device to 3000 rpm, the injection speed to 0.1 mm / min, turn on the positive and negative voltage meters, adjust the positive voltage to 14 kV and the negative voltage to -6 kV, and carry out spinning. Under the action of high electric field, the extruded spinning liquid forms a charged jet and is collected by the receiving shaft.

[0055] (7) The two-dimensional polyamide (MA-2DPA-2) nanofiber membrane obtained in (6) is dried in an oven at 60 degrees Celsius to obtain the two-dimensional polyamide (MA-2DPA-2) nanofiber membrane.

[0056] The obtained two-dimensional polyamide (MA-2DPA-2) nanofiber membrane has a thermal conductivity of 5.4 W / (m²). K).

[0057] Comparative Example 1 The difference from Example 1 is that a 30 wt.% two-dimensional polyamide solution was used as a raw material to prepare the spinning solution, and the resulting product was nanofibers and droplets with beaded strings, and a non-uniform and stable nanofiber structure.

[0058] Comparative Example 2 The difference from Example 1 is that a 35 wt.% two-dimensional polyamide solution was used as a raw material to prepare the spinning solution, and the resulting product was partially uniform nanofibers and a small number of spherical droplets, and the jet was unstable.

[0059] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A method of electrospinning for preparing a high thermally conductive two-dimensional polyamide nanofiber membrane, characterized in that, It includes the following steps: (1) Preparation of two-dimensional polyamide; the preparation method of the two-dimensional polyamide is as follows: 1) Melamine and acyl chloride compounds are added to N-methylpyrrolidone and stirred until homogeneous. A catalyst is added, and the mixture is stirred and reacted at 25-40°C for 24 hours. The acyl chloride compound is 1,3,5-benzenetricarboxylic acid chloride or terephthaloyl chloride. 2) Add the reaction product obtained in step 1 to the washing solution at a volume ratio of 1:8, wash and centrifuge to obtain powder. The washing solution is water, ethanol or acetone. 3) The powder was dried at 60°C for 12 h, and then transferred to a vacuum oven to continue drying at 60°C for 6 h to obtain two-dimensional polyamide; (2) Preparation of spinning solution: 40-45 wt.% of two-dimensional polyamide dispersion and 2-5 wt.% of polyethylene oxide solution are heated at 60°C and mixed evenly until no transparent gel-like precipitate is found in the solution to obtain the spinning solution; in the spinning solution, the mass ratio of polyethylene oxide to two-dimensional polyamide is 1:(20-50); the solvent of the two-dimensional polyamide dispersion and polyethylene oxide solution is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; the viscosity-average molecular weight of the polyethylene oxide is 7,900,000; (3) Electrospinning: Use a 22G-30G spinning needle as a spinning nozzle, use a receiving device covered with PET copper-plated film to take in the yarn, turn on the switch of the electrospinning device to perform electrospinning, and form a uniform nanofiber film on the PET copper-plated film.

2. The method of claim 1, wherein, The receiving device is a high-speed receiving device, including a roller, the axis of which is perpendicular to the voltage direction of electrospinning; and the roller rotates at high speed along its axis, with a rotation speed of 300-3000 rpm.

3. The method according to claim 2, characterized in that, The spinning needle should be 10-20cm away from the high-speed receiving device.

4. The method according to claim 1, characterized in that, During the electrospinning process, the positive electrode voltage is 10-16 kV and the negative electrode voltage is -3 to -6 kV.

5. The method according to claim 1, characterized in that, In step 1), the concentration of melamine in the mixture of catalyst and N-methylpyrrolidone is 0.1 mol / L; when the acyl chloride compound is 1,3,5-benzenetricarboxyl chloride, the concentration in the above mixture is 0.1 mol / L, and when it is terephthaloyl chloride, the concentration in the above mixture is 0.15 mol / L.

6. The method according to claim 1, characterized in that, The catalyst in step 1) is pyridine.

7. A high thermal conductivity two-dimensional polyamide nanofiber membrane prepared by the method of claim 1.

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