Method for preparing copolymerized aromatic polyamide fibrid by one-step method

Abstract

The invention belongs to the field of preparation of high-performance organic fibers and paper, and particularly provides a method for preparing a copolymerized aromatic polyamide fibrid by a one-step method, which comprises the following steps: (1) preparing a copolymerized aramid polymerization product by a one-step method, and enabling the viscosity of the copolymerized aramid polymerization product to be 1000-100000cp; (2) diluting the obtained product into a polymerization stock solution with certain dynamic viscosity by using a diluent in a blending kettle; and (3) preparing the polymerization stock solution into a vaporific stock solution by an atomizer, enabling the vaporific stock solution to be in contact with a coagulating bath to be coagulated into floccules, and treating the floccules by high-speed shearing equipment to form membrane-shaped or strip-shaped fibrid. The method is simple and easy to implement, equipment is easy and convenient to operate, controllability is high, the prepared fibrid is of an excellent film-shaped structure and is good in size uniformity, and the uniformity and the mechanical property of downstream products are effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of new polymer materials and relates to a one-step method for preparing copolymerized aromatic polyamide fibrids. Background Art

[0002] High-performance paper-based materials are mainly meta-aramid paper, para-aramid paper and a small amount of meta-aramid mixed paper. Aramid paper has excellent physical and mechanical properties, excellent dielectric properties, mechanical properties, high temperature resistance, chemical corrosion resistance and flexible designability, and is widely used in high-end insulation, aerospace, rail transportation and other fields.

[0003] Mixed aramid paper is mainly made of meta-aramid fibers and para-aramid staple fibers. Aramid copolymerized aramid fibers have low molecular chain rigidity and are easily broken into fibers under certain shearing action, forming ribbon-like or film-like aramid fibers with large specific surface area and more surface groups. This can achieve an organic combination of the excellent properties of para-aramid, high modulus and high temperature resistance, and meta-aramid flame retardancy and electrical insulation properties, improve the performance of aramid fibers from the molecular structure level, and broaden the application range of aramid fibers.

[0004] At present, the preparation method of precipitated fibers generally utilizes the high-speed shear force of the precipitator to inject aramid stock solution and a large amount of precipitating agent at the same time to obtain precipitated fibers in the form of films, strips or ribbons. The morphology and uniformity of precipitated fibers have a crucial impact on the indicators of downstream products. Fibers with uniform size and high degree of fibrillation have excellent bonding effect when aramid paper is formed, and can better combine with short-cut fibers to improve the uniformity and strength of paper-based materials. The aramid precipitated fibers currently prepared by the existing process have the disadvantages of incomplete membrane structure, large fiber morphology differences, and non-concentrated length distribution and insufficient uniformity. In addition, the equipment required is complex, and the fiberization process requires a large amount of coagulation bath, which is difficult to post-process and has high cost. Summary of the invention

[0005] In order to solve the problems of non-concentrated length distribution and insufficient uniformity of fiber analysis in the prior art, the present invention provides a one-step method for preparing co-aromatic polyamide fiber analysis, the steps comprising: (1) preparing a co-aramid polymerization product in one step, so that its viscosity is 1000-100000cp; (2) diluting the obtained product with a diluent in a mixing kettle to form a polymerization stock solution with a certain dynamic viscosity; (3) preparing the polymerization stock solution into a mist stock solution through an atomizer, the mist stock solution is contacted with a coagulation bath to coagulate into flocs, and is treated with a high-speed shearing device to form a film or ribbon-shaped fiber analysis. The above method is simple and easy to operate, the equipment is easy to operate, and the controllability is strong. The prepared fiber analysis presents an excellent film structure and good size uniformity, which effectively improves the uniformity and mechanical properties of downstream products.

[0006] The one-step method for preparing co-aromatic polyamide fibrid provided by the present invention specifically comprises the following steps:

[0007] (1) polymerization: preparing a solution of a certain concentration with a second monomer and a solvent, and carrying out solution polymerization in a reaction kettle with a molar ratio of the first monomer to the second monomer of 0.995 to 1.02:1;

[0008] (2) Dilution: The obtained product is diluted with a diluent in a mixing kettle to form a polymerization stock solution with a certain dynamic viscosity;

[0009] (3) Fiberization: The polymerization stock solution is prepared into a mist stock solution by an atomizer, the mist stock solution is coagulated into floccules by contact with a coagulation bath, and then treated by a high-speed shearing device to form film-like or ribbon-like precipitated fibers.

[0010] Preferably, in step (1), the first monomer comprises one or both of terephthaloyl chloride and isophthaloyl chloride, the second monomer comprises one or both of p-phenylenediamine and m-phenylenediamine, and the solvent is a mixture of one or more of N-methylpyrrolidone, N,N-dimethylacetamide, dimethyl sulfoxide and a chloride salt, wherein the mass fraction of the chloride salt in the second monomer solution system is 4 to 10%; and the chloride salt comprises calcium chloride or lithium chloride, which mainly plays a solubilizing role.

[0011] Preferably, the concentration of the second monomer solution is 0.1 to 0.8 mol / L, and the reaction temperature is -15 to 80°C;

[0012] More preferably, the concentration of the second monomer solution is 0.3-0.6 mol / L, and the molar ratio of the first monomer to the second monomer is (1-1.016):1;

[0013] More preferably, in step (1), the solution polymerization is low-temperature solution polymerization, first reacting at -15 to 10°C for 3 to 7 minutes, and then controlling the reaction temperature to 30 to 80°C for 20 to 50 minutes.

[0014] During the reaction of step (1), the temperature is adjusted according to the progress of the reaction. The purpose is to control the initial reaction of the monomers into a uniform oligomer system through low-temperature polymerization. When the molecular weight grows to a certain extent, the reaction temperature needs to be increased to increase the collision probability of the oligomers in the system and promote the further growth of the molecular chain.

[0015] Preferably, a shearing device is provided between the reaction kettle and the mixing kettle for mixing and conveying, so that the components can be conveyed to the mixing kettle in a uniformly mixed state for dilution and adjustment of dynamic viscosity; more preferably, the shearing device is a homogenizer.

[0016] In step (2), the diluent is one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide, and the dynamic viscosity of the obtained polymerization stock solution is 1000 to 100000 cp.

[0017] More preferably, the dynamic viscosity of the polymerization stock solution is 10,000 to 50,000 cp.

[0018] When the dynamic viscosity is too high, the molecules are rigid and have poor solubility in solvents. They will precipitate the moment they come into contact with the coagulation bath. Under the action of shear force, the degree of fiber fibrillation is poor and the fibers are small. When the dynamic viscosity is too low, the product molecular weight is low, and the polymer cannot solidify in time after contacting the coagulation bath, forming small fibers under the action of high-speed shear force.

[0019] Preferably, in step (3), the atomizer used is a pressure atomizer, specifically an LPG-50 atomizer selected from Wuxi World Rotary Atomization Technology Co., Ltd.

[0020] The spray pressure of the atomizer is 1-5 bar, the aperture of the atomizing disk is 10-70 μm, and when the polymer stock solution with a certain viscosity is atomized, due to the extrusion expansion effect, the size of the generated mist stock solution will be larger than the aperture of the atomizing disk, so the size of the mist stock solution is 10-200 μm; the size of the mist stock solution can be adjusted by changing the aperture and pressure of the atomizing disk, so that the fiber size is concentrated in the range of 10-3000 μm.

[0021] More preferably, the size of the mist stock solution is 10 to 100 μm.

[0022] Preferably, in step (3), the coagulation bath comprises deionized water and an organic solvent, wherein the organic solvent comprises a mixture of one or two of N-methylpyrrolidone and N,N-dimethylacetamide; the mass concentration of the organic solvent in the coagulation bath is 0-40%, and more preferably, the mass concentration of the organic solvent in the coagulation bath is 5-35%. When the organic solvent accounts for too low a proportion, the surface of the stock solution solidifies quickly, and the internal product enters the shearing device before solidifying, resulting in coarse fibers; when the organic solvent accounts for too high a proportion, the stock solution solidifies slowly and is easily broken into fine fibers under the action of high-speed shear force; the coagulation bath temperature is 10-50°C.

[0023] Preferably, the high-speed shearing device is selected from a precipitator, a hydraulic pulper, and a high-speed shearing machine.

[0024] In the prior art, during the preparation of fiber precipitation, the polymer solution is directly contacted with the coagulation bath and prepared by a precipitator. The morphology of the obtained fiber precipitation is not controlled, the size is not uniform, the degree of fiber fibrillation varies greatly, and the proportion of fibers with a larger aspect ratio is higher. However, the present invention controls the dynamic viscosity of the polymer stock solution to ensure its good processing performance, and obtains a mist stock solution with uniform and stable size after passing through the atomizing disk. These mist stock solutions precipitate immediately after contacting the coagulation bath, and form film-like or ribbon-like fibers under the action of high-speed shearing force, and their sizes are mainly distributed in 10 to 3000 μm.

[0025] The atomization process of the present invention is: the liquid prepared to a certain dynamic viscosity is input into the material tray by a diaphragm pump at high pressure, the temperature of the material system is adjusted to be stable, the mist droplets are sprayed, and then compressed air is used to flow down to obtain the required spherical mist stock liquid of a certain size ratio. Under the action of the coagulation bath, the film-shaped and ribbon-shaped precipitated fibers with uniform and adjustable size are prepared by strong mechanical shearing of the equipment.

[0026] The preparation method of the present invention is conducive to the formation of film-like or ribbon-like morphology of precipitated fibers, with uniform fiber structure and concentrated length distribution, and can prepare paper-based materials with uniform uniformity, high strength and high performance. At the same time, this molding method greatly reduces the amount of coagulation liquid used, and the equipment is simple and convenient to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a process flow chart for preparing co-aromatic polyamide fibrids in one step.

[0028] Figure 2 This is a microscope image of the fibrillation product prepared in Example 1.

[0029] Figure 3 This is a microscope picture of the fiber analysis product prepared in Comparative Example 1. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below in conjunction with specific embodiments. These embodiments are only used to illustrate the technical solution of the present invention in more detail and should not be construed as limiting the protection scope of the present invention.

[0031] All substances and reagents used are commercially available unless otherwise specified; concentrations are by mass unless otherwise specified.

[0032] The atomizer used was an LPG-50 atomizer produced by Wuxi World Rotary Atomization Technology Co., Ltd.

[0033] The materials and reagents used in the embodiments, unless otherwise specified, are all commercially available products.

[0034] Unless otherwise specified, the following percentages are all by mass.

[0035] Performance testing:

[0036] In the implementation case of the present invention, the prepared fibrids were prepared into paper-based materials for performance testing to compare their enhancement effects. The testing standards used were as follows:

[0037] The paper sample weight is based on GBT451.2-2002 "Determination of the weight of paper and paperboard";

[0038] The thickness of paper samples shall comply with GBT451.3-2002 "Determination of thickness of paper and paperboard";

[0039] The tensile strength and elongation of paper samples are based on GBT12914-2008 "Determination of tensile strength of paper and paperboard";

[0040] The tear strength of paper samples adopts GB / T455-2002 "Determination of tear strength of paper and paperboard".

[0041] When testing the dynamic viscosity, the measuring instrument needs to be connected to a constant temperature device and its temperature is controlled to be maintained at 50°C. After the sample is balanced in the test cylinder for 10 minutes, the test program is started and the test data is read. The test instrument is a Brabender electronic viscometer.

[0042] Example 1

[0043] The one-step method for preparing copolyaramid fiberized fibers specifically comprises the following steps: Figure 1 As shown,

[0044] (1) adding a first monomer and a second monomer solution with a concentration of 0.35 mol / L into a reaction kettle at a molar ratio of the first monomer to the second monomer of 1:1, controlling the initial reaction temperature at 10° C., controlling the kettle temperature at 60° C. after reacting for 3 minutes, and reacting for 50 minutes to obtain a polymerization product;

[0045] The solvent of the second monomer solution is a mixture of N-methylpyrrolidone and calcium chloride, wherein the mass fraction of calcium chloride in the second monomer solution is 6.5%; the first monomer is terephthaloyl chloride;

[0046] The second monomer is a mixture of p-phenylenediamine and m-phenylenediamine in a mass ratio of 6:4, and is prepared into a solution with the solvent at a concentration of 0.35 mol / L;

[0047] (2) preparing the polymerization product and N-methylpyrrolidone in a mixing kettle to form a polymerization stock solution with a dynamic viscosity of 10000 cp;

[0048] A homogenizer is set between the reactor and the mixing reactor as a mixing conveyor to transport the materials from the reactor to the mixing reactor in a uniformly mixed state;

[0049] (3) The polymerization stock solution obtained in step (2) is passed into an atomizer, and an atomizing disk with a pore size of 10 μm is selected to obtain a mist stock solution at a pressure of 1.5 bar, and the size of the mist stock solution is 10 to 30 μm; the atomizer is precipitated in a coagulation bath at a temperature of 25° C., wherein the coagulation bath is an N-methylpyrrolidone aqueous solution, wherein the mass fraction of N-methylpyrrolidone is 5%, and the volume ratio of the polymerization stock solution to the coagulation bath is 1:1. After the organic solvent is removed by a high-speed shearing machine and water washing, a precipitated fiber with uniform size is obtained. The length distribution of the precipitated fiber is shown in Table 1.

[0050] Table 1 Distribution of Fibers in Example 1

[0051]

[0052] The method for detecting the proportion of components of different lengths in Table 1 is: observing the samples using a microscope, counting the proportions of components of different lengths, and the number of point samples is ≥100.

[0053] from Figure 2 It can be seen that the precipitated fibers prepared by this method have small size differences, uniform size, and a film-like fiber morphology.

[0054] Example 2

[0055] The one-step method for preparing co-aromatic polyamide fibrid comprises the following steps:

[0056] (1) adding a first monomer and a second monomer solution with a concentration of 0.4 mol / L into a reaction kettle at a molar ratio of the first monomer to the second monomer of 1.003:1, controlling the initial reaction temperature at 5° C., controlling the kettle temperature at 55° C. after reacting for 5 minutes, and reacting for 30 minutes to obtain a polymerization product;

[0057] The solvent of the second monomer solution is a mixture of N-methylpyrrolidone and calcium chloride, wherein the mass fraction of calcium chloride in the second monomer solution is 6.5%; the first monomer is terephthaloyl chloride;

[0058] The second monomer is a mixture of p-phenylenediamine and m-phenylenediamine in a mass ratio of 5:5, and is prepared into a solution with the solvent at a concentration of 0.4 mol / L;

[0059] (2) preparing the polymerization product and N-methylpyrrolidone in a mixing kettle to form a polymerization stock solution with a dynamic viscosity of 25000 cp;

[0060] A homogenizer is set between the reactor and the mixing reactor as a mixing conveyor to transport the materials from the reactor to the mixing reactor in a uniformly mixed state;

[0061] (3) The polymerization stock solution obtained in step (2) is passed into an atomizer, and an atomizing disk with a pore size of 50 μm is selected to obtain a mist stock solution at a pressure of 3.5 bar, the size of which is 50 to 80 μm, and precipitated in a coagulation bath at a temperature of 40° C. and a mass concentration of 20%, wherein the coagulation bath is an N-methylpyrrolidone aqueous solution, wherein the mass fraction of N-methylpyrrolidone is 20%, and the volume ratio of the polymerization stock solution to the coagulation bath is 1:2. After being subjected to a high-speed shearing machine and washed with water to remove the organic solvent, precipitated fibers of uniform size are obtained. The length distribution of the precipitated fibers is shown in Table 2.

[0062] Table 2 Distribution of Fibers in Example 2

[0063]

[0064] Example 3

[0065] The one-step method for preparing co-aromatic polyamide fibrid comprises the following steps:

[0066] (1) adding a first monomer and a second monomer solution with a concentration of 0.6 mol / L into a reaction kettle at a molar ratio of the first monomer to the second monomer of 1.010:1, controlling the initial reaction temperature at -5°C, controlling the kettle temperature at 30°C after reacting for 7 minutes, and reacting for 25 minutes to obtain a polymerization product;

[0067] The solvent of the second monomer solution is a mixture of N-methylpyrrolidone and calcium chloride, wherein the mass fraction of calcium chloride in the second monomer solution is 7%; the first monomer is terephthaloyl chloride;

[0068] The second monomer is a mixture of p-phenylenediamine and m-phenylenediamine in a mass ratio of 4:6, and is prepared into a solution with the solvent at a concentration of 0.6 mol / L;

[0069] (2) preparing the polymerization product and N-methylpyrrolidone in a reaction kettle to form a polymerization stock solution with a dynamic viscosity of 20,000 cp;

[0070] A homogenizer is set between the reactor and the mixing reactor as a mixing conveyor to transport the materials from the reactor to the mixing reactor in a uniformly mixed state;

[0071] (3) The polymerization stock solution obtained in step (2) is passed into an atomizer, and an atomizing disk with a pore size of 70 μm is selected. A mist stock solution with a size of 70 to 120 μm is obtained under a pressure of 1.5 bar. The mist stock solution is precipitated in a coagulation bath at a temperature of 25° C. and a mass concentration of 15%. The coagulation bath is an N-methylpyrrolidone aqueous solution, wherein the mass fraction of N-methylpyrrolidone is 15%, and the volume ratio of the polymerization stock solution to the coagulation bath is 1:2. After being subjected to a high-speed shearing machine and washed with water to remove the organic solvent, precipitated fibers of uniform size are obtained. The length distribution of the precipitated fibers is shown in Table 3.

[0072] Table 3 Distribution of Fibers in Example 3

[0073]

[0074] Example 4

[0075] The one-step method for preparing co-aromatic polyamide fibrid comprises the following steps:

[0076] (1) adding a first monomer and a second monomer solution with a concentration of 0.45 mol / L into a reaction kettle at a molar ratio of the first monomer to the second monomer of 1.008:1, controlling the initial reaction temperature at 0° C., controlling the kettle temperature at 20° C. after reacting for 7 minutes, and reacting for 30 minutes to obtain a polymerization product;

[0077] The solvent of the second monomer solution is a mixture of N-methylpyrrolidone and calcium chloride, wherein the mass fraction of calcium chloride in the second monomer solution is 6.8%; the first monomer is terephthaloyl chloride;

[0078] The second monomer is a mixture of p-phenylenediamine and m-phenylenediamine in a mass ratio of 5:5, and is prepared into a solution with the solvent at a concentration of 0.45 mol / L;

[0079] (2) preparing the polymerization product and N-methylpyrrolidone in a reaction kettle to form a polymerization stock solution with a dynamic viscosity of 50,000 cp;

[0080] A homogenizer is set between the reactor and the mixing reactor as a mixing conveyor to transport the materials from the reactor to the mixing reactor in a uniformly mixed state;

[0081] (3) The polymerization stock solution obtained in step (2) is passed into an atomizer, and an atomizing disk with a pore size of 70 μm is selected. A mist stock solution with a size of 70 to 150 μm is obtained at a pressure of 3.5 bar. The mist stock solution is precipitated in a coagulation bath at a temperature of 30° C. and a mass concentration of 20%. The coagulation bath is an N-methylpyrrolidone aqueous solution, wherein the mass fraction of N-methylpyrrolidone is 20%, and the volume ratio of the polymerization stock solution to the coagulation bath is 1:1.5. After being subjected to a high-speed shearing machine and washing with water to remove the organic solvent, film-like precipitated fibers of uniform size are obtained. The length distribution of the precipitated fibers is shown in Table 4.

[0082] Table 4 Example 4 Fiber distribution

[0083]

[0084] Example 5

[0085] The one-step method for preparing co-aromatic polyamide fibrid comprises the following steps:

[0086] (1) adding a first monomer and a second monomer solution with a concentration of 0.8 mol / L into a reaction kettle at a molar ratio of the first monomer to the second monomer of 1:1.016, controlling the initial reaction temperature at -15°C, controlling the kettle temperature at 60°C after reacting for 7 minutes, and reacting for 40 minutes to obtain a polymerization product;

[0087] The solvent of the second monomer solution is a mixture of N-methylpyrrolidone and calcium chloride, wherein the mass fraction of calcium chloride in the second monomer solution is 6.5%; the first monomer is terephthaloyl chloride; the second monomer is a mixture of p-phenylenediamine and m-phenylenediamine in a mass ratio of 5:5, and is configured with the solvent at 0.8 mol / L to form a solution;

[0088] (2) preparing the polymerization product and N-methylpyrrolidone in a mixing kettle to form a polymerization stock solution with a dynamic viscosity of 100,000 cp;

[0089] A homogenizer is set between the reactor and the mixing reactor as a mixing conveyor to transport the materials from the reactor to the mixing reactor in a uniformly mixed state;

[0090] (3) The polymerization stock solution obtained in step (2) is passed into an atomizer, and an atomizing disk with a pore size of 70 μm is selected to obtain a mist stock solution at a pressure of 4 bar, wherein the mist stock solution has a size of 70 to 200 μm, and is precipitated in a coagulation bath at a temperature of 40° C. and a mass concentration of 35%, wherein the coagulation bath is an N-methylpyrrolidone aqueous solution, wherein the mass fraction of N-methylpyrrolidone is 35%, and the volume ratio of the polymerization stock solution to the coagulation bath is 1:2. After being subjected to a high-speed shearing machine and water washing to remove the organic solvent, a film-like precipitated fiber of uniform size is obtained.

[0091] Example 6

[0092] The one-step method for preparing co-aromatic polyamide fibrid comprises the following steps:

[0093] (1) adding a first monomer and a second monomer solution with a concentration of 0.1 mol / L into a reaction kettle at a molar ratio of the first monomer to the second monomer of 1:1, controlling the initial reaction temperature at 10° C., controlling the kettle temperature at 80° C. after reacting for 3 minutes, and reacting for 50 minutes to obtain a polymerization product;

[0094] The solvent of the second monomer solution is a mixture of N-methylpyrrolidone and calcium chloride, wherein the mass fraction of calcium chloride in the second monomer solution is 6.5%; the first monomer is terephthaloyl chloride;

[0095] The second monomer is a mixture of p-phenylenediamine and m-phenylenediamine in a mass ratio of 6:4, and is prepared into a solution with the solvent at a concentration of 0.1 mol / L;

[0096] (2) preparing the polymerization product and N-methylpyrrolidone in a mixing kettle to form a polymerization stock solution with a dynamic viscosity of 1000 cp;

[0097] A homogenizer is set between the reactor and the mixing reactor as a mixing conveyor to transport the materials from the reactor to the mixing reactor in a uniformly mixed state;

[0098] (3) The polymerization stock solution obtained in step (2) is passed into an atomizer, and an atomizing disk with a pore size of 10 μm is selected to obtain a mist stock solution at a pressure of 1.5 bar, wherein the mist stock solution has a size of 10 to 20 μm, and is precipitated in a coagulation bath at a temperature of 15° C. and a mass concentration of 5%, wherein the coagulation bath is an N-methylpyrrolidone aqueous solution, wherein the mass fraction of N-methylpyrrolidone is 5%, and the volume ratio of the polymerization stock solution to the coagulation bath is 1:1. After being subjected to a high-speed shearing machine and water washing to remove the organic solvent, a film-like precipitated fiber of uniform size is obtained.

[0099] Comparative Example 1

[0100] The one-step method for preparing co-aromatic polyamide fibrid comprises the following steps:

[0101] (1) adding a first monomer and a second monomer solution with a concentration of 0.35 mol / L into a reaction kettle at a molar ratio of the first monomer to the second monomer of 1:1, controlling the initial reaction temperature at 10° C., controlling the kettle temperature at 60° C. after reacting for 3 minutes, and reacting for 50 minutes to obtain a polymerization product;

[0102] The solvent of the second monomer solution is a mixture of N-methylpyrrolidone and calcium chloride salt, wherein the mass fraction of calcium chloride in the second monomer solution is 6.5%; the first monomer is terephthaloyl chloride;

[0103] The second monomer is a mixture of p-phenylenediamine and m-phenylenediamine in a mass ratio of 6:4, and is prepared into a solution with the solvent at a concentration of 0.35 mol / L;

[0104] (2) preparing the polymerization product N-methylpyrrolidone into a polymerization stock solution with a dynamic viscosity of 10000 cp in a reactor;

[0105] (3) The polymer stock solution obtained in step (2) and a coagulation bath with a mass concentration of 10% are measured in a volume ratio of 1:5, and directly poured into a coagulation machine with a rotation speed of 2950 r / min in the form of strands to mix with the coagulation bath, and the solution strands are dispersed and coagulated in the coagulation bath to obtain a precipitated fiber slurry. The slurry is separated and washed to obtain a precipitated fiber.

[0106] The size of the precipitated fibers prepared by this method varies greatly. The fiber morphology is mostly filamentous and long and thin. Figure 3 The distribution of fiber length is shown in Table 5.

[0107] Table 5 Comparative Example 1 Fiber Distribution

[0108]

[0109] The inventors compared the fibrils obtained in Examples 1-4 and Comparative Example 1, and the results are shown in Table 6:

[0110] Table 6

[0111]

[0112]

[0113] It can be seen from Table 6 that the fibrils prepared in Examples 1-4 mainly present a film-like structure, and have a concentrated size distribution and strong controllability. In addition, while the fibrils obtained in Examples 1-4 have better performance, the amount of coagulation liquid in the coagulation bath is also significantly reduced compared with Comparative Example 1 (volume ratio of stock solution to coagulation bath is 1:5).

[0114] Comparative Example 1: The precipitated fibers prepared by directly entering the high-speed precipitator in a thin stream form are mainly in the form of long filaments with a wide size distribution. Figure 2 , Figure 3 It can be clearly seen that the fibrils prepared by the two preparation methods have different morphologies. The size and morphology of the fibrils directly affect the strength and appearance of downstream application products. The film-like fibrils (example product) show stronger binding force in the paper-based material, while improving its apparent uniformity and processability.

[0115] Experimental example

[0116] Preparation of paper-based materials: para-aramid chopped fibers are deflaked by a deflaking machine, and the deflaking concentration is controlled to be 0.03% to prepare para-aramid chopped fiber slurry; the prepared fibrids in the above-mentioned embodiment and comparative example are pulped, and the pulping concentration is 0.5% to obtain aramid copolymerized fibrid slurry;

[0117] According to the mass percentage (calculated according to the absolute dry weight of the fibers in each slurry), 50% of the para-aramid short-cut fiber slurry and 50% of the aramid copolymerized precipitated fiber slurry are mixed and placed in a slurry preparation kettle, and the slurry concentration is adjusted to 0.1% with deionized water; the prepared fiber slurry is wet-coated by an inclined mesh method to form a continuous and uniformly distributed wet paper sheet, and the finished paper is obtained after the steps of pressing and dehydrating, hot roller drying, and high-temperature calendering.

[0118] The fibrids obtained in Examples 1-4 and Comparative Example 1 were prepared into paper by the above method and tested. The properties thereof are shown in the following table:

[0119] Table 7 Comparison of paper properties between the examples and the comparative examples

[0120]

[0121] It can be observed from Table 7 that the paper prepared by using the fibrids of Examples 1-4 has significantly improved tensile strength and tear resistance, and higher elongation, compared with Comparative Example 1.

[0122] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A one-step method for preparing co-aromatic polyamide fibrids, characterized in that: The following steps are involved: (1) Polymerization: The second monomer and the solvent are prepared into a solution of a certain concentration, and the first monomer and the second monomer solution are polymerized in a reaction kettle at a molar ratio of 0.995 to 1.02:1; (2) Dilution: The obtained product is diluted with a diluent in a mixing kettle to form a polymerization stock solution with a certain dynamic viscosity; (3) Fiberization: The polymerization stock solution is prepared into a mist stock solution by an atomizer, the mist stock solution is coagulated into floccules by contact with a coagulation bath, and then treated by a high-speed shearing device to form film-like or ribbon-like precipitated fibers.

2. The method for preparing co-aromatic polyamide fibrids by one step according to claim 1, characterized in that: In step (1), the first monomer is one or both of terephthaloyl chloride and isophthaloyl chloride; the second monomer is one or both of p-phenylenediamine and m-phenylenediamine; the solvent is a mixture of one or more of N-methylpyrrolidone, N,N-dimethylacetamide, dimethyl sulfoxide and chloride salt, wherein the mass fraction of chloride salt in the second monomer solution system is 4-10%; the chloride salt is selected from calcium chloride or lithium chloride; the concentration of the second monomer solution is 0.1-0.8 mol / L, the reaction temperature is -15-80°C, and the molar ratio of the first monomer to the second monomer is (1-1.016):

1.

3. The method for preparing co-aromatic polyamide fibrids in one step according to claim 2, characterized in that: The solution polymerization in step (1) is low-temperature solution polymerization, first reacting at -15 to 10°C for 3 to 7 minutes, then controlling the reaction temperature to 30 to 80°C for 20 to 50 minutes; the concentration of the second monomer solution is 0.3 to 0.6 mol / L.

4. The method for preparing co-aromatic polyamide fibrids in one step according to claim 1, characterized in that: In step (2), the dynamic viscosity of the polymerization stock solution is 1000-100000 cp, and the diluent is one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide.

5. The method for preparing co-aromatic polyamide fibrids in one step according to claim 4, characterized in that: The dynamic viscosity of the polymerization stock solution is 10000~50000cp.

6. The method for preparing co-aromatic polyamide fibrids by one step according to any one of claims 1 to 5, characterized in that: The atomizer used in step (3) is a pressure atomizer, the atomizer spray pressure is 1-5 bar, the aperture of the atomizing disk is 10-70 μm, and the size of the mist stock solution is 10-200 μm.

7. The method for preparing co-aromatic polyamide fibrids by one step according to any one of claims 1 to 5, characterized in that: The coagulation bath in step (3) comprises deionized water and an organic solvent, wherein the organic solvent comprises one or a mixture of two of N-methylpyrrolidone and N,N-dimethylacetamide; the mass concentration of the organic solvent in the coagulation bath is 0 to 40%, and the temperature of the coagulation bath is 10-50°C.

8. The method for preparing co-aromatic polyamide fibrids in one step according to claim 7, characterized in that: In step (3), the mass concentration of the organic solvent in the coagulation bath is 5 to 35%.

9. The method for preparing co-aromatic polyamide fibrids by one step according to any one of claims 1 to 5, characterized in that: The high-speed shearing equipment in step (3) is selected from a precipitator, a hydraulic pulper, and a high-speed shearing machine.

10. The method for preparing co-aromatic polyamide fibrids in one step according to claim 1, characterized in that: A homogenizer is installed between the reaction kettle and the mixing kettle.

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