Method for increasing solid content of polyacrylonitrile spinning solution

Abstract

The present invention relates to a method for increasing the solid content of a polyacrylonitrile spinning solution, which method comprises: heating a mixture comprising a solvent and polyacrylonitrile in a CO 2 gas atmosphere, pressurizing to make the CO 2 in a supercritical state for reaction, and after the reaction is completed, cooling and depressurizing to obtain a polyacrylonitrile spinning solution. The preparation method described in the present invention utilizes supercritical carbon dioxide-assisted treatment to increase the solubility of polyacrylonitrile in the solvent. This preparation method has the advantages of environmental protection, controllable reaction, reduction of the use of chemical reagents, etc. The polyacrylonitrile spinning solution described in the present invention has great industrial application value.

Description

Technical Field

[0001] The present invention relates to a method for increasing the solid content of a polyacrylonitrile spinning solution. Background Art

[0002] Polyacrylonitrile (PAN)-based carbon fiber is an inorganic fiber material prepared from PAN precursor filaments through high-temperature treatment above 1000 °C, and has a series of excellent properties such as high specific strength, high specific modulus, high temperature resistance, corrosion resistance, fatigue resistance, radiation resistance, electrical conductivity, heat transfer, shock absorption, noise reduction, and low relative density. As a high-tech material for both military and civilian use, carbon fiber has been widely used in cutting-edge fields such as aerospace and national defense, as well as civilian industries such as high-grade sports goods and medical devices. The development and application of carbon fiber are playing an increasingly important role in enhancing the national military strength and the competitiveness of industrial products.

[0003] Common solvents used in polyacrylonitrile spinning solutions include N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide, and aqueous sodium thiocyanate solution. Aqueous sodium thiocyanate solution is non-toxic compared with other solvents and is an excellent solvent used in the polyacrylonitrile spinning process. However, when polyacrylonitrile is dissolved in aqueous sodium thiocyanate solution, gelation and other phenomena are likely to occur during the dissolution process, and the solubility is relatively low, which is an important factor restricting the preparation of high-performance PAN precursor filaments. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems existing in the prior art, such as low solid content of polyacrylonitrile spinning solution and easy occurrence of gelation during the dissolution process, and to provide a method for increasing the solid content of polyacrylonitrile spinning solution. This method can increase the solid content of polyacrylonitrile spinning dope and has the advantages of environmental protection, controllable reaction, and reduction of chemical reagent use.

[0005] To achieve the above purpose, the present invention provides a method for increasing the solid content of polyacrylonitrile spinning solution, which includes:

[0006] A mixture containing a solvent and polyacrylonitrile is heated in a CO 2 gas atmosphere, pressurized to make CO 2 in a supercritical state for reaction, and after the reaction is completed, it is cooled and depressurized to obtain a polyacrylonitrile spinning solution.

[0007] The present invention uses supercritical carbon dioxide as a medium to dissolve polyacrylonitrile in a solvent (such as an aqueous solution of sodium thiocyanate). Supercritical carbon dioxide has a plasticizing and swelling effect. By using its swelling effect, the action of strong polar functional groups (such as cyano functional groups) is weakened, and at the same time, the entanglement of polyacrylonitrile macromolecular chains is weakened, thereby increasing the solubility of polyacrylonitrile in the solvent and thus increasing the solid content of the polyacrylonitrile spinning solution. The preparation method described in the present invention uses supercritical carbon dioxide-assisted treatment to increase the solubility of polyacrylonitrile in the solvent, especially to increase the solubility of polyacrylonitrile in inorganic solvents (such as aqueous solutions of sodium thiocyanate and zinc chloride). This preparation method has the advantages of environmental protection, controllable reaction, and reduction in the use of chemical reagents. The polyacrylonitrile spinning solution described in the present invention has great industrial application value. Detailed implementation mode

[0008] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0009] The present invention provides a method for increasing the solid content of a polyacrylonitrile sodium thiocyanate spinning solution, and the method includes:

[0010] A mixture containing a solvent and polyacrylonitrile is heated in a CO 2 gas atmosphere and pressurized to make CO 2 in a supercritical state for reaction. After the reaction is completed, it is cooled and depressurized to obtain a polyacrylonitrile spinning solution. Supercritical carbon dioxide is used as a medium to dissolve polyacrylonitrile in the solvent. Supercritical carbon dioxide has a plasticizing and swelling effect. By using its swelling effect, the action of strong polar functional groups (such as cyano functional groups) is weakened, and at the same time, the entanglement of polyacrylonitrile macromolecular chains is weakened, thereby increasing the solubility of polyacrylonitrile in the solvent and increasing the solid content of the polyacrylonitrile spinning solution.

[0011] According to the present invention, when supercritical carbon dioxide is used as a medium to dissolve polyacrylonitrile in a solvent, as long as the temperature is raised and / or the pressure is increased to make CO 2 in a supercritical state, for the present invention, preferably, CO 2 The temperature of the supercritical state is 60 - 90 °C, more preferably 60 - 85 °C, which is beneficial to increasing the solubility of polyacrylonitrile in the solvent and increasing the solid content of the polyacrylonitrile spinning solution.

[0012] According to the present invention, when supercritical carbon dioxide is used as a medium to dissolve polyacrylonitrile in a solvent, as long as the temperature is raised and / or the pressure is increased to make CO 2It is only necessary to be in the supercritical state. For the present invention, preferably, CO 2 The pressure in the supercritical state is 8 - 16 MPa, more preferably 8 - 15 MPa, which is beneficial to increasing the solubility of polyacrylonitrile in the solvent and increasing the solid content of the polyacrylonitrile spinning solution.

[0013] According to the present invention, the reaction of polyacrylonitrile with the solvent in a supercritical carbon dioxide medium can increase the solubility of polyacrylonitrile in the solvent. For the present invention, the preferred reaction time is 8 - 40 min; more preferably, the reaction is carried out for 8 - 40 min at a stirring speed of 100 - 1500 r / min, which is beneficial to increasing the solubility of polyacrylonitrile in the solvent and increasing the solid content of the polyacrylonitrile spinning solution.

[0014] According to the present invention, after the reaction is completed, the temperature is lowered and the pressure is released. Preferably, the temperature is lowered to 25 - 30 °C.

[0015] According to the present invention, after the reaction is completed, the temperature is lowered and the pressure is released. Preferably, the pressure release time is 2 - 6 min.

[0016] According to a preferred embodiment of the present invention, the molecular weight of the polyacrylonitrile is 20,000 - 100,000, preferably 30,000 - 80,000, which is beneficial to increasing the solubility of polyacrylonitrile in the solvent and increasing the solid content of the polyacrylonitrile spinning solution.

[0017] According to a preferred embodiment of the present invention, the solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, ethylene carbonate, aqueous ethylene carbonate solution, propylene carbonate, aqueous propylene carbonate solution, aqueous sodium thiocyanate solution, aqueous zinc chloride solution, and N-methylpyrrolidone; preferably at least one of aqueous sodium thiocyanate solution and aqueous zinc chloride solution; since the dissolution ability of inorganic solvents for polyacrylonitrile is poor, resulting in a low solid content, using supercritical carbon dioxide-assisted treatment is beneficial to increasing the solubility of polyacrylonitrile in the aqueous sodium thiocyanate solution and increasing the solid content of the polyacrylonitrile spinning solution.

[0018] According to the present invention, when the solvent is an aqueous sodium thiocyanate solution, the mass concentration of the aqueous sodium thiocyanate solution is 50 - 54 wt%, which is beneficial to increasing the solubility of polyacrylonitrile in the aqueous sodium thiocyanate solution and increasing the solid content of the polyacrylonitrile spinning solution.

[0019] According to a preferred embodiment of the present invention, when the solvent is an aqueous sodium thiocyanate solution or an aqueous zinc chloride solution, by mass fraction, the polyacrylonitrile content in the polyacrylonitrile spinning solution is 11 - 17 wt%.

[0020] When the solvent is an aqueous sodium thiocyanate solution or an aqueous zinc chloride solution, the mass ratio of polyacrylonitrile to the solvent is 1:8 - 4, preferably 1:7.4 - 4.8.

[0021] According to the present invention, by filtering the aforementioned polyacrylonitrile spinning solution, particles that affect spinning are removed. Preferably, a filtering device with a pore size of 1 - 7 μm is used to filter the polyacrylonitrile spinning solution obtained by cooling and depressurizing; the present invention has no special requirements for the filtering device, as long as it can remove particles that affect spinning. Preferably, the filtering device is selected from at least one of a filter mesh, a filter cloth, and a sintered metal mesh.

[0022] According to a preferred embodiment of the present invention, the method for increasing the solid content of the polyacrylonitrile spinning solution is carried out in a supercritical reaction kettle, and includes the following steps:

[0023] Place the solvent in the supercritical reaction kettle, remove the air in the reaction kettle, and make the inside of the reaction kettle in a CO 2 atmosphere, and add polyacrylonitrile (PAN) powder; heat up and pressurize to make CO 2 in a supercritical state, stir and react for a certain period of time. After the reaction ends, cool down, depressurize, and take out the spinning solution in the supercritical reaction kettle, and filter the spinning solution through a filter mesh with a pore size of 0.5 - 5 μm to obtain the polyacrylonitrile spinning solution.

[0024] According to the present invention, according to actual needs, CO can be charged repeatedly 2 to remove the air, so that the inside of the reaction kettle is in a CO 2 atmosphere. For example, CO is charged 2 - 6 times 2 to remove the air, so that the inside of the reaction kettle is in a CO 2 atmosphere

[0025] According to the present invention, according to actual needs, the air in the reaction kettle can be removed by evacuating - charging carbon dioxide once or multiple times. For example, the air in the reaction kettle is removed by evacuating - charging carbon dioxide 2 - 6 times, so that the inside of the reaction kettle is in a CO 2 atmosphere.

[0026] According to the present invention, for the pressurization, carbon dioxide can be charged into the supercritical reaction kettle to pressurize and make CO 2 in a supercritical state.

[0027] In the present invention, the solid content of the polyacrylonitrile sodium thiocyanate spinning solution refers to the mass content of polyacrylonitrile in the polyacrylonitrile sodium thiocyanate spinning solution.

[0028] The present invention will be described in detail below through examples. In the following examples, the sodium thiocyanate raw material is a commercially available product from Aladdin Reagent (Shanghai) Co., Ltd. with a CAS number of 540 - 72 - 7.

[0029] Example 1

[0030] (1) Place 870 g of an aqueous sodium thiocyanate solution with a concentration of 50.57% in a supercritical reaction kettle, evacuate and refill with CO three times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 130 g of PAN powder with a molecular weight of 100,000 to the reaction kettle. At 80 °C, further introduce CO into the reaction kettle 2 until the pressure reaches 8 MPa to form a supercritical state in the reaction kettle. Set the stirring rate of the reaction kettle to 800 r / min. After reacting for 15 min, slowly release the pressure for 2 min; Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reaction kettle, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 1 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 12.967%.

[0031] Example 2

[0032] Place 860 g of an aqueous sodium thiocyanate solution with a concentration of 51.16% in a supercritical reaction kettle, evacuate and refill with CO three times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 140 g of PAN powder with a molecular weight of 100,000 to the reaction kettle. At 80 °C, further introduce CO into the reaction kettle 2 until the pressure reaches 8 MPa to form a supercritical state in the reaction kettle; Set the stirring rate of the reaction kettle to 800 r / min. After reacting for 15 min, slowly release the pressure for 2 min, take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reaction kettle, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 1 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 13.941%.

[0033] Example 3

[0034] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a reaction kettle, evacuate and refill with CO three times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 150 g of PAN powder with a molecular weight of 100,000 to the reaction kettle. At 80 °C, further introduce CO into the reaction kettle 2 until the pressure reaches 8 MPa to form a supercritical state in the reaction kettle; Set the stirring rate of the reaction kettle to 800 r / min. After reacting for 15 min, slowly release the pressure for 2 min, take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reaction kettle, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 1 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.928%.

[0035] Example 4

[0036] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a supercritical reactor, evacuate and refill with CO three times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 150 g of PAN powder with a molecular weight of 100,000 to the reactor. At 80 °C, further introduce CO into the reactor 2 until the pressure reaches 8 MPa to form a supercritical state in the reactor; set the stirring rate of the reactor to 800 r / min. After reacting for 15 min, slowly release the pressure for 2 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reactor, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 2 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.955%.

[0037] Example 5

[0038] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a supercritical reactor, evacuate and refill with CO three times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 150 g of PAN powder with a molecular weight of 100,000 to the reactor. At 80 °C, further introduce CO into the reactor 2 until the pressure reaches 8 MPa to form a supercritical state in the reactor. Set the stirring rate of the reactor to 800 r / min. After reacting for 15 min, slowly release the pressure for 2 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reactor, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.980%.

[0039] Example 6

[0040] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a supercritical reactor, evacuate and refill with CO five times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 150 g of PAN powder with a molecular weight of 100,000 to the reactor. At 80 °C, further introduce CO into the reactor 2 until the pressure reaches 8 MPa to form a supercritical state in the reactor; set the stirring rate of the reactor to 800 r / min. After reacting for 15 min, slowly release the pressure for 2 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reactor, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.983%.

[0041] Example 7

[0042] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a supercritical reactor, evacuate and fill with CO 5 times 2 to completely displace the air, and maintain a CO 2 atmosphere. Add 150 g of PAN powder with a molecular weight of 40,000 to the reactor, and then introduce CO into the reactor at 80 °C 2 until the pressure reaches 8 MPa to form a supercritical state in the reactor; set the stirring rate of the reactor to 100 r / min. After reacting for 15 min, slowly relieve the pressure for 2 min, take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reactor, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.989%.

[0043] Example 8

[0044] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a supercritical reactor, evacuate and fill with CO 5 times 2 to completely displace the air, and maintain a CO 2 atmosphere. Add 150 g of PAN powder with a molecular weight of 20,000 to the reactor, and then introduce CO into the reactor at 80 °C 2 until the pressure reaches 8 MPa to form a supercritical state in the reactor; set the stirring rate of the reactor to 800 r / min. After reacting for 15 min, slowly relieve the pressure for 2 min, take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reactor, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.991%.

[0045] Example 9

[0046] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a supercritical reactor, evacuate and fill with CO 5 times 2 to completely displace the air, add 150 g of PAN powder with a molecular weight of 20,000 to the reactor, and then introduce CO into the reactor at 80 °C 2 until the pressure reaches 8 MPa to form a supercritical state in the reactor; set the stirring rate of the reactor to 800 r / min. After reacting for 5 min, slowly relieve the pressure for 2 min, take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reactor, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.979%.

[0047] Example 10

[0048] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a supercritical reactor, evacuate and refill with CO 5 times 2 to completely displace the air, and maintain a CO 2 atmosphere. Add 150 g of PAN powder with a molecular weight of 20,000 to the reactor. When the temperature reaches 80 °C, introduce CO into the reactor again 2 until the pressure reaches 12 MPa to form a supercritical state in the reactor; set the stirring rate of the reactor to 800 r / min. After reacting for 15 min, slowly release the pressure for 2 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reactor, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.993%.

[0049] Example 11

[0050] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a supercritical reactor, evacuate and refill with CO 5 times 2 to completely displace the air, and maintain a CO 2 atmosphere. Add 150 g of PAN powder with a molecular weight of 20,000 to the reactor. When the temperature reaches 80 °C, introduce CO into the reactor again 2 until the pressure reaches 12 MPa to form a supercritical state in the reactor; set the stirring rate of the reactor to 1500 r / min. After reacting for 15 min, slowly release the pressure for 2 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reactor, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.996%.

[0051] Example 12

[0052] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a supercritical reactor, evacuate and refill with CO 5 times 2 to completely displace the air, and maintain a CO 2 atmosphere. Add 150 g of PAN powder with a molecular weight of 20,000 to the reactor. When the temperature reaches 80 °C, introduce CO into the reactor again 2 until the pressure reaches 12 MPa to form a supercritical state in the reactor; set the stirring rate of the reactor to 100 r / min. After reacting for 15 min, slowly release the pressure for 2 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reactor, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.978%.

[0053] Example 13

[0054] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a supercritical reactor, evacuate and fill with CO 5 times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 150 g of PAN powder with a molecular weight of 20,000 to the reactor. Then, at 90 °C, introduce CO into the reactor 2 until the pressure reaches 12 MPa to form a supercritical state in the reactor. Set the stirring rate of the reactor to 100 r / min. After reacting for 15 min, slowly release the pressure for 2 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reactor, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.988%.

[0055] Example 14

[0056] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a reactor, evacuate and fill with CO 5 times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 150 g of PAN powder with a molecular weight of 20,000 to the reactor. Then, at 50 °C, introduce CO into the reactor 2 until the pressure reaches 12 MPa to form a supercritical state in the reactor. Set the stirring rate of the reactor to 100 r / min. After reacting for 15 min, slowly release the pressure for 2 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reactor, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.969%.

[0057] Example 15

[0058] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a supercritical reactor, evacuate and fill with CO 5 times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 150 g of PAN powder with a molecular weight of 20,000 to the reactor. Then, at 50 °C, introduce CO into the reactor 2 until the pressure reaches 12 MPa to form a supercritical state in the reactor. Set the stirring rate of the reactor to 100 r / min. After reacting for 15 min, slowly release the pressure for 4 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reactor, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.973%.

[0059] Example 16

[0060] Place 840 g of an aqueous sodium thiocyanate solution with a concentration of 52.38% in a supercritical reaction kettle, evacuate and fill with CO 5 times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 160 g of PAN powder with a molecular weight of 20,000 to the reaction kettle. At 50 °C, further introduce CO into the reaction kettle 2 until the pressure reaches 12 MPa to form a supercritical state in the reaction kettle; set the stirring rate of the reaction kettle to 100 r / min. After reacting for 15 min, slowly release the pressure for 4 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reaction kettle, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 15.969%.

[0061] Example 17

[0062] Place 830 g of an aqueous sodium thiocyanate solution with a concentration of 53.01% in a supercritical reaction kettle, evacuate and fill with CO 5 times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 170 g of PAN powder with a molecular weight of 20,000 to the reaction kettle. At 50 °C, further introduce CO into the reaction kettle 2 until the pressure reaches 12 MPa to form a supercritical state in the reaction kettle; set the stirring rate of the reaction kettle to 100 r / min. After reacting for 15 min, slowly release the pressure for 4 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reaction kettle, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 16.951%.

[0063] Example 18

[0064] Place 830 g of an aqueous zinc chloride solution with a concentration of 72.29% in a supercritical reaction kettle, evacuate and fill with CO 5 times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 170 g of PAN powder with a molecular weight of 20,000 to the reaction kettle. At 50 °C, further introduce CO into the reaction kettle 2 until the pressure reaches 12 MPa to form a supercritical state in the reaction kettle; set the stirring rate of the reaction kettle to 100 r / min. After reacting for 15 min, slowly release the pressure for 4 min. Take out the polyacrylonitrile zinc chloride spinning solution in the supercritical reaction kettle, and pass the polyacrylonitrile zinc chloride spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 15.726%.

[0065] Example 19

[0066] Place 820 g of an aqueous sodium thiocyanate solution with a concentration of 53.01% in a supercritical reaction kettle, evacuate and fill with CO 5 times 2 to completely displace the air and maintain a CO 2 atmosphere. Add 180 g of PAN powder with a molecular weight of 20,000 to the reaction kettle. Then, at 50 °C, introduce CO into the reaction kettle 2 until the pressure reaches 12 MPa to form a supercritical state in the reaction kettle. Set the stirring rate of the reaction kettle to 100 r / min. After reacting for 15 min, slowly release the pressure for 4 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reaction kettle, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 4 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 16.950%.

[0067] Comparative Example 1

[0068] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a reaction kettle, add 150 g of PAN powder with a molecular weight of 100,000, and then introduce air into the reaction kettle at 80 °C until the pressure reaches 8 MPa. Set the stirring rate of the reaction kettle to 800 r / min. After reacting for 15 min, slowly release the pressure for 2 min. Take out the polyacrylonitrile sodium thiocyanate spinning solution in the supercritical reaction kettle, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 1 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 14.011%.

[0069] Comparative Example 2

[0070] Place 850 g of an aqueous sodium thiocyanate solution with a concentration of 51.76% in a beaker, add 150 g of PAN powder with a molecular weight of 100,000. Set the stirring rate of the external stirrer to 800 r / min. After reacting for 15 min, take out the polyacrylonitrile sodium thiocyanate spinning solution, and pass the polyacrylonitrile sodium thiocyanate spinning solution through a filter screen with a pore diameter of 1 μm to obtain a spinning dope. The solid content of the spinning dope is measured to be 13.264%.

[0071] It can be seen from Comparative Example 1 and Comparative Example 2 that the method for increasing the solid content of the polyacrylonitrile spinning solution described in the present invention can significantly increase the solid content of the polyacrylonitrile spinning solution.

[0072] It can be seen from Example 19 that the polyacrylonitrile feed ratio is 18 wt%, and the solid content of the spinning dope is 16.950%, which is basically the same as the solid content of the spinning dope in Example 17. The part of polyacrylonitrile exceeding 17 wt% is also difficult to dissolve in the sodium thiocyanate solution. Therefore, according to the preferred implementation mode of the present invention, the mass ratio of polyacrylonitrile to the solvent is 1:8 - 4, preferably 1:7.4 - 4.8.

[0073] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for increasing the solid content of a polyacrylonitrile spinning solution, characterized in that, the method comprises: A mixture containing a solvent and polyacrylonitrile is heated in a CO 2 gas atmosphere, pressurized so that the CO 2 is in a supercritical state for reaction. After the reaction, the temperature is lowered and the pressure is released to obtain a polyacrylonitrile spinning solution; CO 2 The supercritical state temperature is 60 - 90 °C, and CO 2 The supercritical state pressure is 8 - 16 MPa, and the reaction time is 8 - 40 min; the molecular weight of the polyacrylonitrile is 20,000 - 100,000; the solvent is at least one of an aqueous sodium thiocyanate solution and an aqueous zinc chloride solution; the mass ratio of polyacrylonitrile to the solvent is 1:8 - 4.

2. The method according to claim 1, wherein, CO 2 The supercritical state temperature is 65 - 85 °C; and / or CO 2 The pressure in the supercritical state is 8 - 15 MPa.

3. The method according to claim 1 or 2, wherein, react for 8 - 40 min at a stirring speed of 100 - 1500 r / min.

4. The method according to claim 1 or 2, wherein, cool down to 25 - 30 °C; and / or the pressure relief time is 2 - 6 min.

5. The method according to claim 1 or 2, wherein, the molecular weight of the polyacrylonitrile is 30,000 - 80,000.

6. The method according to claim 1 or 2, wherein, the solvent is selected from at least one of N,N - dimethylformamide, N,N - dimethylacetamide, dimethyl sulfoxide, ethylene carbonate, ethylene carbonate aqueous solution, propylene carbonate, propylene carbonate aqueous solution, sodium thiocyanate aqueous solution, zinc chloride aqueous solution, and N - methylpyrrolidone.

7. The method according to claim 1, wherein, the mass concentration of the sodium thiocyanate aqueous solution is 50 - 54 wt%.

8. The method according to claim 1, wherein, the mass ratio of polyacrylonitrile to the solvent is 1:7.4 - 4.

8.

9. The method according to claim 1 or 2, wherein, filter the polyacrylonitrile spinning solution obtained by cooling and pressure relief using a filtering device with a pore size of 1 - 7 μm.

10. The method according to claim 9, wherein, the filtering device is selected from at least one of a filter mesh, a filter cloth, and a sintered metal mesh.

11. The method according to claim 1, wherein, by mass fraction, the polyacrylonitrile content in the polyacrylonitrile spinning solution is 11 - 17 wt%.