High-thermal-conductivity two-dimensional polyamide nanofiber membrane prepared by electrostatic spinning and preparation method thereof

Abstract

The invention discloses a high-thermal-conductivity two-dimensional polyamide nanofiber membrane prepared by electrostatic spinning and a preparation method thereof. A high-concentration two-dimensional polyamide solution and ultrahigh-molecular-weight polyoxyethylene are used as spinning solutions, an entanglement structure of a molecular chain is introduced into the spinning solutions, so that the spinning solutions have stretchability, and the nanofiber membrane with the adjustable diameter can be obtained by changing the content of the added polyoxyethylene.

Description

Technical Field

[0001] The invention belongs to the technical field of spinning, and in particular relates to a high thermal conductivity two-dimensional polyamide nanofiber membrane prepared by electrostatic spinning and a method thereof. Background Art

[0002] In recent years, electrospinning technology has received extensive 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 can regulate the internal structure, such as hollow, porous, core-shell structure, etc. In addition, the fiber surface or internal structure can be further modified by nanoparticles. At present, nanofibers obtained by electrospinning have been applied in many fields, including filtration membranes, biosensors, surface coatings, tissue engineering and energy storage.

[0003] The raw material types of electrospinning nanofibers are rich, such as polymers, ceramics, small molecules and their complexes. Among them, one-dimensional polymer materials can provide enough molecular entanglements due to their linear or branched molecular chain structures, thereby giving spinning solution good stretchability. Two-dimensional polymers are usually present in the form of crystalline powders, and the strong Π-Π stacking effect between layers makes it difficult to spontaneously disperse to a single layer or few layers in a solvent, so it is difficult to form a uniform and stable dispersion. At the same time, the two-dimensional polymers of the lamellar structure cannot form entanglements, so the dispersion does not have stretchability and cannot form a stable jet. The above restrictive conditions make it impossible to utilize electrospinning to realize the preparation of two-dimensional polymer nanofibers. At present, two-dimensional polymer nanofibers are mainly obtained by in-situ epitaxial growth on the surface of one-dimensional polymer nanofibers, but the nanofibers obtained in this way are only loose accumulations of two-dimensional polymer particles, and mechanical properties are very weak and do not have practical application value. Two-dimensional polymers are also often used as fillers and mixed with one-dimensional polymers for electrospinning to obtain composite fibers. However, as composite fillers, they cannot fully utilize the intrinsic advantages of the two-dimensional topological structure of two-dimensional polymers, such as high thermal conductivity, high electrical conductivity, high carrier mobility, low resistance and high selectivity of molecular ion screening, etc. Therefore, there is an urgent need for a spinning process that can directly prepare two-dimensional polymers into nanofilms to further expand the application field and development prospects of two-dimensional polymer materials. Summary of the invention

[0004] In view of the difficulty of directly preparing a highly thermally conductive two-dimensional polymer nanofilm with existing technology, the present invention proposes a highly thermally conductive two-dimensional polyamide nanofiber membrane prepared by electrospinning and a method thereof. By using a high-concentration two-dimensional polyamide solution and ultra-high molecular weight polyethylene oxide (Mv~7900000) as a spinning solution, an entangled structure of molecular chains is introduced into the spinning solution, so that the spinning solution has stretchability, and by changing the content of polyethylene oxide added, a nanofiber membrane with adjustable diameter can be obtained.

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

[0006] Furthermore, the receiving device is a high-speed receiving device, which includes 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 300-3000rpm.

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

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

[0009] Furthermore, the method for preparing the two-dimensional polyamide in step 1 is: (1) adding melamine and an acyl chloride compound to N-methylpyrrolidone and stirring to mix evenly, adding a catalyst, and stirring to react at 25-40° C. for 24 hours; the acyl chloride compound is 1,3,5-benzenetricarboxylic acid chloride or terephthaloyl chloride; (2) adding a washing liquid to the reaction product obtained in step 1 at a volume ratio of 1:8, washing and centrifuging to obtain a powder, wherein the washing liquid is water, ethanol or acetone; (3) The powder was dried at 60 °C for 12 h and then transferred to a vacuum oven and dried at 60 °C for another 6 h to obtain a two-dimensional polyamide.

[0010] Furthermore, in the step 1 of preparing the two-dimensional polyamide, the concentration of melamine in the mixture of the catalyst and N-methylpyrrolidone is 0.1 mol / L; when the acyl chloride compound is 1,3,5-benzenetricarboxylic acid 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 in step 1 of preparing the two-dimensional polyamide is pyridine.

[0012] The two-dimensional aromatic polyamide powder synthesized by the present invention is formed by stacking small-sized two-dimensional sheets, and the interior of the sheet is formed by many small crystal regions arranged in disorder, so the interaction between the sheets is weak, so that the stacked sheets can be dispersed into a single layer or several layers of extremely thin layered molecules under mechanical stirring to form a stable high-concentration dispersion. The two-dimensional aromatic polyamide can form a high-concentration dispersion of up to 45%. However, the solution formed by the stacking of two-dimensional nanosheets has poor stretchability, so ultra-high molecular weight polyethylene oxide (PEO) is introduced, and its long molecular chains form a physical cross-linking network through dense entanglement, which significantly increases the chain entanglement concentration of the solution, giving the spinning solution sufficient viscoelasticity and tensile resistance, thereby suppressing the instability (dropletization) and bending instability (fiber swing breakage) of the jet, and ensuring that the jet maintains continuity during stretching and solvent volatilization. At the same time, the addition of PEO can achieve precise control of the fiber diameter by adjusting the concentration-high concentration PEO improves the stretchability of the solution, which is conducive to the formation of thin and continuous fibers.

[0013] In some embodiments of the present invention, the specific operation of electrospinning is as follows: install the spinning device, extract the prepared electrospinning solution with a 1ml syringe needle in the electrospinning equipment warehouse, install the spinning needle of 22G specification as the spinning nozzle, and then install the syringe on the electrospinning instrument in the equipment cabin to form the electrospinning device. Then connect the high-speed collection control orientation device and the electrospinning equipment, then fix the PET copper-plated film on the high-speed receiving device rotating shaft, adjust the distance between the nozzle and the receiving device to 10cm-25cm, and then install two infrared lamps, aim at the silk collecting shaft to ensure that the solvent evaporates quickly. Turn on the equipment, adjust the high-speed receiving device speed to 300-3000rpm, the injection speed to 0.1mm / min, turn on the positive and negative voltage meter, adjust the positive voltage to 10-16Kv, and the negative voltage to -3- -6kV for spinning. Under the action of high electric field, the extruded spinning solution forms a jet with a point, 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 diameter of the prepared two-dimensional polyamide nanofibers is 80-800 nm, and the thermal conductivity of the nanofibers can reach up to 8.7 W / (m 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, and the prepared nanofiber membrane has good thermal conductivity, which can reach 8.7 W / (m K).

[0017] (2) The highly conjugated two-dimensional skeleton of two-dimensional polymers provides an efficient thermal conductivity pathway, while the layered structure reduces the scattering of phonons. Therefore, directly assembling two-dimensional polymers into nanofibers is expected to obtain highly thermally conductive nanofiber materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the molecular formula of the polyamide of the present invention.

[0019] Figure 2 This is the SEM of the nanofiber membrane of Example 1. DETAILED DESCRIPTION

[0020] The basic principle of electrospinning is to use a high voltage electric field to generate a strong electric field force between the spinning nozzle and the receiving device, so that the droplets in the polymer solution or melt are charged. When the electric field is applied, the charges on the surface of the droplets repel each other, overcome their surface tension, and gradually stretch the droplets to form a conical structure, namely the Taylor cone. As the electric field intensity increases further, a charged jet is formed at the top of the Taylor cone, which is continuously stretched and thinned under the action of the high electric field, and forms nanofibers after the solvent evaporates or cools and solidifies. For the electrospinning solution, it must have a sufficient concentration of polymer chain entanglements to stably form continuous fibers. When the solution concentration is lower than the minimum spinnable concentration, the interaction between the polymer chains is weak, and the Rayleigh instability cannot be overcome, resulting in jet interruption and the formation of droplets, thereby producing a beaded structure or spherical particles in the fiber, and a uniform nanofiber membrane cannot be obtained.

[0021] The following examples are used to further illustrate the present invention, and their purpose is to illustrate the present invention and should not be construed as limiting the scope of the present invention. Unless otherwise specified, all parts by weight and weight percentages are used below.

[0022] The raw materials used in the present invention, unless otherwise specified, are conventional commercially available products; the methods used in the present invention, unless otherwise specified, are conventional methods in the art.

[0023] The embodiments of the present invention are further described below with reference to a plurality of embodiments.

[0024] It should be clear that the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0025] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0026] Example 1 Add melamine and 1,3,5-benzenetricarboxylic acid chloride to N-methylpyrrolidone and stir to mix evenly, add catalyst, and stir to react at 25°C for 24 hours; the concentration of melamine in the mixture of catalyst and N-methylpyrrolidone is 0.1 mol / L; the concentration of 1,3,5-benzenetricarboxylic acid chloride in the above mixture is 0.1 mol / L; (2) adding water to the reaction product obtained in step 1 at a volume ratio of 1:8, washing and centrifuging to obtain a powder; (3) The powder was dried at 60 °C for 12 h and then transferred to a vacuum oven and dried at 60 °C for another 6 h to obtain a two-dimensional polyamide (MA-2DPA-1).

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

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

[0029] (6) Preparing a spinning solution, heating the solutions obtained in steps (4) and (5) at 60° C. and stirring and mixing for 30 minutes to obtain a spinning solution; in the spinning solution, the mass ratio of polyethylene oxide (PEO) to polyamide (MA-2DPA-1) is 1:50.

[0030] (7) Install the spinning device. In the electrospinning equipment compartment, use a 1 ml syringe to extract the prepared electrospinning solution, then install a 22G spinning needle as a spinning nozzle, and then install the syringe on the electrospinning instrument in the equipment compartment to form an electrospinning device. Then fix the PET copper-plated film on the receiving shaft, and the spinning needle is 10 cm away from the high-speed receiving device. Then install two infrared lamps and aim them at the receiving shaft to ensure that the solvent evaporates quickly.

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

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

[0033] The thermal conductivity test of the two-dimensional polyamide nanofiber membrane was carried out by capturing the temperature change with an infrared camera. The thermal conductivity result of the two-dimensional polyamide (MA-2DPA-1) nanofiber membrane was 2.3 W / (m K).

[0034] Embodiment 2: (1) Melamine and terephthaloyl chloride are added to N-methylpyrrolidone and stirred to mix evenly, a catalyst is added, and the mixture is stirred and reacted at 40°C for 24 hours; the concentration of melamine in the mixture of the catalyst and N-methylpyrrolidone is 0.1 mol / L; the concentration of terephthaloyl chloride in the above mixture is 0.15 mol / L.

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

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

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

[0038] (6) Preparing a spinning solution, heating the solutions obtained in steps (4) and (5) at 60° C. and stirring and mixing for 30 minutes to obtain a spinning solution; in the spinning solution, the mass ratio of polyethylene oxide (PEO) to polyamide (MA-2DPA-2) is 1:50.

[0039] (7) Install the spinning device. In the electrospinning equipment compartment, use a 1ml syringe to extract the prepared electrospinning solution, then install a 22G spinning needle as a spinning nozzle, and then install the syringe on the electrospinning instrument in the equipment compartment to form an electrospinning device. Then fix the PET copper-plated film on the receiving shaft, and the spinning needle is 20cm away from the high-speed receiving device. Then install two infrared lamps and aim them at the receiving shaft to ensure that the solvent evaporates quickly.

[0040] (8) Using electrospinning, turn on the equipment, adjust the receiving speed of the receiving shaft to 300 rpm, the injection speed to 0.1 mm / min, turn on the positive and negative voltage meters, adjust the positive pressure to 14 kV, and the negative pressure to -3 kV, and start spinning. Under the action of the 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 placed in an oven at 60 degrees Celsius for drying to obtain a two-dimensional polyamide (MA-2DPA-2) nanofiber membrane.

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

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

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

[0045] (3) Preparing a spinning solution: heating the solutions obtained in steps (4) and (5) at 60° C. and stirring and mixing for 30 minutes to obtain a spinning solution; in the spinning solution, the mass ratio of polyethylene oxide (PEO) to polyamide (MA-2DPA-1) is 1:50.

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

[0047] (6) Using electrospinning, turn on the equipment, adjust the speed of the high-speed receiving device to 2000rpm, the injection speed to 0.1mm / min, turn on the positive and negative voltage meters, adjust the positive pressure to 16kV, and the negative pressure to -3kV, and start spinning. Under the action of the high electric field, the extruded spinning solution 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 placed in an oven at 60 degrees Celsius for drying to obtain a two-dimensional polyamide (MA-2DPA-1) nanofiber membrane.

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

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

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

[0052] (3) Preparing a spinning solution: heating the solutions obtained in steps (4) and (5) at 60° C. and stirring and mixing for 30 minutes to obtain a spinning solution; in the spinning solution, the mass ratio of polyethylene oxide (PEO) to polyamide (MA-2DPA-2) is 1:20.

[0053] (4) Install the spinning device. In the electrospinning equipment compartment, use a 1 ml syringe to extract 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 compartment to form an electrospinning device. (5) Connect the high-speed collection and orientation control device to the electrospinning equipment, fix the PET copper-coated film on the receiving shaft, and keep the spinning needle 20 cm away from the high-speed receiving device. Then install two infrared lamps and aim them at the receiving shaft to ensure rapid evaporation of the solvent.

[0054] (6) Using electrospinning, turn on the equipment, adjust the speed of the high-speed receiving device to 3000rpm, the injection speed to 0.1mm / min, turn on the positive and negative voltage meters, adjust the positive pressure to 14kV, and the negative pressure to -6kV, and start spinning. Under the action of the 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 placed in an oven at 60 degrees Celsius for drying to obtain a two-dimensional polyamide (MA-2DPA-2) nanofiber membrane.

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

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

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

[0059] The above embodiments describe in detail the structure, features and effects of the present invention. The above are only preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which do not exceed the scope covered by the specification, should be within the protection scope of the present invention.

Claims

1. A method for preparing a high thermal conductivity two-dimensional polyamide nanofiber membrane by electrospinning, characterized in that: The following steps are involved: (1) Preparation of two-dimensional polyamide; (2) preparing a spinning solution: heating 40-45 wt.% of a two-dimensional polyamide dispersion and 2-5 wt.% of a polyethylene oxide solution at 60°C and mixing them uniformly until there is no transparent colloidal precipitate in the solution, thereby obtaining a spinning solution; in the spinning solution, the mass ratio of polyethylene oxide to polyamide is 1:(20-50); the solvents of the two-dimensional polyamide dispersion and the polyethylene oxide solution are 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 spinning needle of 22G-30G as the spinning nozzle, use a receiving device covered with a PET copper-coated film to collect the filaments, turn on the switch of the electrospinning device to perform electrospinning, and form a uniform nanofiber membrane on the PET copper-coated film.

2. The method according to claim 1, characterized in that: The receiving device is a high-speed receiving device, comprising 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 is 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 10-16KV, and the negative electrode voltage is -3- -6kV.

5. The method according to claim 1, characterized in that The method for preparing two-dimensional polyamide described in step 1 is: (1) adding melamine and an acyl chloride compound to N-methylpyrrolidone and stirring to mix evenly, adding a catalyst, and stirring to react at 25-40° C. for 24 hours; the acyl chloride compound is 1,3,5-benzenetricarboxylic acid chloride or terephthaloyl chloride; (2) adding a washing liquid to the reaction product obtained in step 1 at a volume ratio of 1:8, washing and centrifuging to obtain a powder, wherein the washing liquid is water, ethanol or acetone; (3) The powder was dried at 60 °C for 12 h and then transferred to a vacuum oven and dried at 60 °C for another 6 h to obtain a two-dimensional polyamide.

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

7. The method according to claim 5, characterized in that The catalyst in step 1 is pyridine.

8. A high thermal conductivity polyamide nanofiber membrane prepared by the method according to claim 1.

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