A method for preparing aramid micro / nano fibers and their application in aramid paper.

Abstract

This invention discloses a method for preparing aramid micro / nanofibers and their application in aramid paper. The invention prepares aramid micro / nanofibers via spray drying. The principle is as follows: aramid micro / nanofiber droplets or fine streams are formed through atomization. When the viscosity of the solution and the frequency of the centrifugal atomizer reach certain values, these droplets or streams are further elongated, forming longer streams. These streams then come into contact with hot gas, undergoing sufficient heat exchange and quickly vaporizing and removing the solvent, thereby forming dried aramid micro / nanofibers. The resulting aramid micro / nanofibers have a diameter of 50 nm to 10 μm and a length of 10 μm to 200 μm. Applying the aramid micro / nanofibers obtained by this invention to the preparation of aramid paper imparts excellent mechanical strength and electrical properties to the paper. Furthermore, the preparation method of this invention is simple, low-cost, and highly efficient, and the organic solvent used can be recycled in a green manner, making it suitable for large-scale application.

Description

Technical Field

[0001] This invention relates to the field of polymer nanomaterial preparation technology, and in particular to a method for preparing aramid nanofibers and their application in aramid paper. Background Technology

[0002] Nanomaterials possess unique surface and interface properties, exhibiting physical or chemical properties not found in conventional macroscopic materials, and have been widely applied in various scientific and industrial fields.

[0003] Aramid precipitated fiber is a fully aromatic polyamide synthetic material produced by high-speed centrifugal shearing of aramid spinning dope in a coagulation bath. It has excellent liquid phase dispersion properties and composite reinforcement effect, and has been widely used as one of the raw materials for high-performance aramid paper.

[0004] Currently, domestically produced aramid paper is mostly prepared by blending short aramid fibers obtained from wet spinning with precipitated fibers, followed by external hot pressing. However, the resulting aramid paper has several problems: 1. Poor cohesion and adhesion between the precipitated and short fibers; 2. Low paper density and significant retention of porous structures; 3. Poor mechanical and electrical properties. The main reason for this is that the aramid precipitated fibers obtained through the traditional coagulation bath shearing method have a core-sheath structure in their outer layer, resulting in complete surface hydrogen bonding and few oxygen-containing sites. Furthermore, this traditional coagulation bath shearing method also suffers from a series of problems, including long preparation cycles, low yield, high cost, environmental pollution from organic solvents, and difficulty in dispersion in water.

[0005] To address the aforementioned issues, numerous methods for preparing aramid fibers have been reported, including electrospinning, chemical splitting, jet spinning, and one-step polymerization. Chinese patent CN104562650A discloses a method for preparing aramid nanofibers using chemical splitting in an alkaline medium. However, this method still faces many challenges in terms of large-scale production, material form, and properties, such as long preparation time and low production efficiency, making it difficult to apply for large-scale industrial production. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of this invention is to provide a method for preparing aramid micro / nano fibers and their application in aramid paper.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides a method for preparing aramid micro / nano fibers, comprising the following steps:

[0009] S1. Dissolve the aramid polymer in a chloride salt / organic solvent system to obtain an aramid polymer solution with a concentration of 5-20 wt%;

[0010] S2. Spray dry the aramid polymer solution from step S1 to obtain aramid micro / nano fibers;

[0011] The spray drying conditions are set as follows: the flow rate of the peristaltic pump is 100-3000 mL / h, the nozzle size is 0.5-2.0 mm, the atomizer frequency is 150-500 Hz, the inlet temperature is 175-250℃, the outlet temperature is 120-200℃, and the carrier gas is 99% high-purity nitrogen.

[0012] Preferably, in step S1, the aramid polymer is poly(m-phenylene isophthalamide) (m-aramid, PMIA) or poly(p-phenylene terephthalamide) (p-aramid, PPTA); the organic solvent is any one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP);

[0013] Preferably, in step S1, the chloride salt is CaCl2 or LiCl, and the mass fraction of CaCl2 or LiCl in the chloride salt / organic solvent system is 2-10 wt%.

[0014] A second aspect of the present invention provides aramid micro / nano fibers obtained by the above preparation method, wherein the aramid micro / nano fibers have a diameter of 50 nm to 10 μm and a length of 10 μm to 200 μm.

[0015] A third aspect of the present invention provides the application of the above-mentioned aramid micro / nano fibers in the preparation of aramid paper.

[0016] The present invention has the following beneficial effects:

[0017] (1) This invention uses aramid polymer solution as raw material to prepare aramid micro / nano fibers with diameters of 50 nm to 10 μm and lengths of 10 μm to 200 μm by spray drying. The principle is as follows: aramid micro / nano droplets or fine streams are formed through atomization. When the viscosity of the solution and the frequency of the centrifugal atomizer reach a certain value, these micro / nano droplets or fine streams are further elongated to form longer streams. Furthermore, these streams come into contact with hot gas, undergoing sufficient heat exchange, and the solvent is vaporized and removed in a short time, forming dried aramid micro / nano fibers. The prepared aramid micro / nano fibers also have the advantages of high yield and high purity, and have broad application prospects in industry.

[0018] (2) The aramid micro-nano fibers prepared by the method of the present invention have low solvent content and abundant oxygen-containing sites on their surface. When the aramid micro-nano fibers are used to prepare aramid paper, when the aramid micro-nano fibers are mixed with aramid short fibers, the abundant oxygen-containing sites on the surface of the obtained aramid micro-nano fibers are fully bonded to the aramid short fibers under hot pressing, thereby minimizing the residual pores between the aramid short fibers in the aramid paper, thereby improving the interfacial cohesion and the density of the paper, giving the obtained aramid paper excellent mechanical strength and electrical properties, enabling it to be used in high-end applications, while reducing the use of chemicals.

[0019] (3) The preparation method of the present invention has the characteristics of simple process, low cost and high production efficiency, and the organic solvent used can be recycled in a green way, which is suitable for large-scale promotion and application. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 SEM and TEM images of the aramid micro / nano fibers prepared in Example 1;

[0022] Figure 2 SEM image of the cross section of the aramid paper prepared in Experimental Example 1;

[0023] Figure 3 The image shows a cross-sectional SEM image of the aramid paper prepared in Experiment Example 2. Detailed Implementation

[0024] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention may be implemented in other embodiments without these specific details.

[0025] Example 1

[0026] A method for preparing aramid micro / nano fibers, the specific steps of which are as follows:

[0027] 3.0 g of poly(m-phenylene isophthalamide) (PMIA) was dissolved in 60 mL of a mixed solvent of N,N-dimethylacetamide (DMAc) and 9% LiCl. The solution was heated to 60 °C and stirred at 500 rpm until it was completely dissolved to obtain a PMIA solution.

[0028] The obtained PMIA solution was injected into a centrifugal spray dryer using a peristaltic pump at a rate of 1000 mL / h. The process parameters were set as follows: 1 mm nozzle size, 300 Hz atomizer frequency, 230 °C inlet temperature, 180 °C outlet temperature, and 99% high-purity nitrogen as carrier gas. After injection, the instrument was shut down, yielding monodisperse aramid micro / nano fibers with a solvent content of 1.3% and a yield of 96.2%.

[0029] The aramid micro / nano fiber product obtained in Example 1 was characterized, and the scanning electron microscope (SEM) image and transmission electron microscope (TEM) image are shown below. Figure 1 .Depend on Figure 1 The results showed that the aramid micro / nano fibers prepared in Example 1 had a length of 20 μm and a diameter of 100 nm.

[0030] Example 2

[0031] 3.0 g of poly(m-phenylene isophthalamide) (PMIA) was dissolved in 60 mL of a mixed solvent of N,N-dimethylacetamide (DMAc) and 9% LiCl. The solution was heated to 60 °C and stirred at 500 rpm until it was completely dissolved to obtain a PMIA solution.

[0032] The obtained PMIA solution was injected into a centrifugal spray dryer at a rate of 500 mL / h using a peristaltic pump. The process parameters were set as follows: 0.5 mm nozzle size, 500 Hz atomizer frequency, 230 °C inlet temperature, 180 °C outlet temperature, and 99% high-purity nitrogen as carrier gas. After injection, the instrument was shut down, yielding monodisperse aramid micro / nanofibers with a solvent content of 0.8% and a yield of 95.2%. The obtained aramid micro / nanofibers had a length of 10 μm and a diameter of 50 nm.

[0033] Example 3

[0034] Dissolve 9g of poly(m-phenylene isophthalamide) (PMIA) in 60mL of a mixed solvent of N,N-dimethylacetamide (DMAc) and 9% LiCl, heat to 60℃, and stir at 500rpm to completely dissolve it, thus obtaining a PMIA solution.

[0035] The obtained PMIA solution was injected into a centrifugal spray dryer at a rate of 1000 mL / h using a peristaltic pump. The process parameters were set as follows: 1 mm nozzle size, 400 Hz atomizer frequency, 200 °C inlet temperature, 160 °C outlet temperature, and 99% high-purity nitrogen as carrier gas. After injection, the instrument was shut down, yielding monodisperse aramid micro / nano fibers with a solvent content of 3.3% and a yield of 96.7%. The obtained aramid micro / nano fibers had a length of 100 μm and a diameter of 1 μm.

[0036] Example 4

[0037] Dissolve 6g of poly(m-phenylene isophthalamide) (PMIA) in 60mL of a mixed solvent of N,N-dimethylacetamide (DMAc) and 9% LiCl, heat to 60℃, and stir at 500rpm to completely dissolve it, thus obtaining a PMIA solution.

[0038] The obtained PMIA solution was injected into a centrifugal spray dryer at a rate of 3000 mL / h using a peristaltic pump. The process parameters were set as follows: 1 mm nozzle size, 150 Hz atomizer frequency, 250 °C inlet temperature, 160 °C outlet temperature, and 99% high-purity nitrogen as carrier gas. After injection, the instrument was shut down, yielding monodisperse aramid micro / nano fibers with a solvent content of 1.1% and a yield of 95.6%. The obtained aramid micro / nano fibers had a length of 180 μm and a diameter of 5 μm.

[0039] Example 5

[0040] 12g of poly(m-phenylene isophthalamide) (PMIA) was dissolved in 60mL of a mixed solvent of N,N-dimethylacetamide (DMAc) and 9% LiCl. The solution was heated to 60℃ and stirred at 500rpm until it was completely dissolved to obtain a PMIA solution.

[0041] The obtained PMIA solution was injected into a centrifugal spray dryer at a rate of 100 mL / h using a peristaltic pump. The process parameters were set as follows: 2 mm nozzle size, 250 Hz atomizer frequency, 175 °C inlet temperature, 140 °C outlet temperature, and 99% high-purity nitrogen as carrier gas. After injection, the instrument was shut off, yielding monodisperse aramid micro / nano fibers with a solvent content of 5% and a yield of 98.7%. The obtained aramid micro / nano fibers had a length of 200 μm and a diameter of 10 μm.

[0042] Comparative Example 1

[0043] Dissolve 6g of poly(m-phenylene isophthalamide) (PMIA) in 60mL of a mixed solvent of N,N-dimethylacetamide (DMAc) and 9% LiCl, heat to 60℃, and stir at 500rpm to completely dissolve it, thus obtaining a PMIA solution.

[0044] The obtained PMIA solution was injected into a centrifugal spray dryer at a rate of 2000 mL / h using a peristaltic pump. The process parameters were set as follows: nebulizer nozzle size 1 mm, nebulizer frequency 400 Hz, inlet temperature 250 °C, outlet temperature 90 °C, and carrier gas 99% high-purity nitrogen. After injection, the instrument was shut down. Ultimately, no solid sample was obtained. This is because the vaporized DMAc circulated with the nitrogen to the outlet, and the excessively low outlet temperature caused the solvent to condense upon contact with the condenser, leading to the re-dissolution of the solid sample.

[0045] Experimental Example 1

[0046] The aramid micro / nano fibers obtained in Example 1 were blended with micron-sized aramid chopped fibers as fillers, and then industrial aramid paper was prepared by oblique wire papermaking. The specific steps are as follows:

[0047] (1) Aramid micro-nano fibers and aramid short-cut fibers were placed in an aqueous solution at a mass ratio of 4:6. The solution was then stirred at 10,000 rpm for 5 minutes using a high-speed desolvation machine to obtain a mixed fiber dispersion with a concentration of 1.5‰.

[0048] (2) The obtained mixed fiber dispersion was transferred to the inside of an inclined wire paper machine and paper was formed using the inclined wire paper machine. Finally, it was placed on a roll calender for hot pressing. The hot pressing conditions of the roll calender were: temperature 180℃, pressure 12 MPa, and time 18 min, to obtain high-performance aramid paper. The obtained high-performance aramid paper was characterized, and the scanning electron microscope images of the surface and cross-section of the prepared aramid paper are shown in the figure. Figure 2 .

[0049] Figure 2 Scanning electron microscopy results showed that the aramid paper prepared in Example 1 had few residual pores in its cross-section, good surface coating, and good interfacial cohesion.

[0050] The physical properties of the aramid paper prepared in this experiment are: thickness 0.05 mm, basis weight 40.1 g / m². 2 Tensile strength: 78 N / cm longitudinally, 32 N / cm transversely; elongation: 7.4% longitudinally, 5.6% transversely; initial tear strength: 11.6 N longitudinally, 7.8 N transversely; dielectric strength: 25.1 kV / mm.

[0051] Experimental Example 2

[0052] Similar to Example 1, except that aramid paper was prepared using aramid fibers obtained by a wet process, the specific steps of which are described in CN116971205A. The obtained aramid paper was characterized, and the scanning electron microscope images of its surface and cross-section are shown below. Figure 3 .

[0053] Figure 3 Scanning electron microscopy results revealed that the aramid paper prepared in Experiment Example 2 had many large residual pores, poor cohesion between the chromatographic fibers and the short aramid fibers, and a clear interface.

[0054] The physical properties of the aramid paper prepared in this experiment are: thickness 0.048 mm, basis weight 39.5 g / m². 2 Tensile strength: 43 N / cm longitudinally, 15 N / cm transversely; elongation: 4.1% longitudinally, 3.1% transversely; initial tear strength: 8.1 N longitudinally, 4.5 N transversely; dielectric strength: 12.2 kV / mm.

[0055] Compared to the aramid paper prepared in Example 2, the aramid paper prepared in Example 1 by blending the aramid micro / nano fibers obtained by spray drying according to this invention with aramid chopped fibers not only showed significant improvements in thermal stability and mechanical and electrical properties, but also exhibited higher tensile strength and thermal stability than aramid paper prepared by conventional wet processing with precipitated fibers, compared to traditional precipitated fibers. This is because, compared to traditional precipitated fibers, the aramid micro / nano fibers prepared by this invention have a lower solvent content and abundant oxygen-containing sites on their surface, allowing for thorough adhesion with the aramid chopped fibers under hot pressing. This minimizes the residual porosity between the aramid chopped fibers in the aramid paper, improving interfacial cohesion and paper density. Consequently, the resulting aramid paper has higher density and better mechanical and electrical properties.

[0056] This invention is not limited to the specific embodiments described above. Any modifications made by those skilled in the art based on the above concept without creative effort are within the scope of protection of this invention.

Claims

1. The application of aramid micro / nano fibers in the preparation of aramid paper, characterized in that, The method for preparing the aramid micro / nano fibers includes the following steps: (1) Dissolve 3.0 g of poly(m-phenylene isophthalamide) in 60 mL of a mixed solvent of N,N-dimethylacetamide and 9% LiCl, heat to 60 °C, and stir at 500 rpm to completely dissolve it to obtain a PMIA solution; inject the obtained PMIA solution into a centrifugal spray dryer at a injection rate of 1000 mL / h using a peristaltic pump, and set the process parameters as follows: 1 mm nozzle size, 300 Hz atomizer frequency, 230 °C inlet temperature, 180 °C outlet temperature, and 99% high-purity nitrogen as carrier gas. After the injection is completed, turn off the instrument to obtain monodisperse aramid micro / nano fibers. Alternatively (2) Dissolve 3.0 g of poly(m-phenylene isophthalamide) in 60 mL of a mixed solvent of N,N-dimethylacetamide and 9% LiCl, heat to 60 °C, and stir at 500 rpm to completely dissolve it to obtain a PMIA solution; inject the obtained PMIA solution into a centrifugal spray dryer at a rate of 500 mL / h using a peristaltic pump, and set the process parameters as follows: the atomizer nozzle size is 0.5 mm, the atomizer frequency is 500 Hz, the inlet temperature is 230 °C, the outlet temperature is 180 °C, and the carrier gas is 99% high-purity nitrogen. After the injection is completed, turn off the instrument to obtain monodisperse aramid micro-nano fibers. The length of the obtained aramid micro-nano fibers is 10 μm and the diameter is 50 nm. Alternatively (3) Dissolve 9g of poly(m-phenylene isophthalamide) in a mixed solvent of 60mL of N,N-dimethylacetamide and 9% LiCl, heat to 60℃, and stir at 500rpm to completely dissolve it to obtain a PMIA solution; inject the obtained PMIA solution into a centrifugal spray drying device at a rate of 1000mL / h using a peristaltic pump, and set the process parameters as follows: the size of the atomizer nozzle is 1mm, the atomizer frequency is 400Hz, the inlet temperature is 200℃, the outlet temperature is 160℃, and the carrier gas is 99% high-purity nitrogen. After the injection is completed, turn off the instrument to obtain monodisperse aramid micro-nano fibers. The length of the obtained aramid micro-nano fibers is 100μm and the diameter is 1μm. Alternatively (4) dissolve 6g of poly(m-phenylene isophthalamide) in a mixed solvent of 60mL of N,N-dimethylacetamide and 9% LiCl, heat to 60℃, and stir at 500rpm to completely dissolve it to obtain a PMIA solution; inject the obtained PMIA solution into a centrifugal spray dryer at a rate of 3000mL / h using a peristaltic pump, and set the process parameters as follows: the atomizer nozzle size is 1mm, the atomizer frequency is 150Hz, the inlet temperature is 250℃, the outlet temperature is 160℃, and the carrier gas is 99% high-purity nitrogen. After the injection is completed, turn off the instrument to obtain monodisperse aramid micro-nano fibers. The length of the obtained aramid micro-nano fibers is 180μm and the diameter is 5μm. Alternatively (5) dissolve 12g of poly(m-phenylene isophthalamide) in a mixed solvent of 60mL of N,N-dimethylacetamide and 9% LiCl, heat to 60℃, and stir at 500rpm to completely dissolve it to obtain a PMIA solution; inject the obtained PMIA solution into a centrifugal spray dryer at a rate of 100mL / h using a peristaltic pump, and set the process parameters as follows: the atomizer nozzle size is 2mm, the atomizer frequency is 250Hz, the inlet temperature is 175℃, the outlet temperature is 140℃, and the carrier gas is 99% high-purity nitrogen. After the injection is completed, turn off the instrument to obtain monodisperse aramid micro-nano fibers with a length of 200μm and a diameter of 10μm.

Images