Ammoniation method of polyacrylonitrile powder

Abstract

The invention relates to the technical field of polyacrylonitrile-based carbon fibers, and provides an ammonification method of polyacrylonitrile powder. The preparation method comprises the following steps: demonomerisation is carried out on carboxyl-containing polyacrylonitrile feed liquid obtained by precipitation polymerization, and first drying is carried out to obtain carboxyl-containing polyacrylonitrile powder; the carboxyl-containing polyacrylonitrile powder is soaked in an ammoniation reagent aqueous solution for ammoniation; the ammoniation reagent is ammonium salt. Starting from the source of the spinning solution, the demonomerisation polyacrylonitrile powder is ammoniated before the spinning solution is prepared, the operation is simple, the ammoniation efficiency is high, and the hydrophilicity of polyacrylonitrile can be effectively improved; moreover, the ammoniation reagent adopted by the invention overcomes the defects of strong odor and high toxicity of common liquid amine and gaseous ammonia, and the ammoniated system is pure and environment-friendly; furthermore, the specific ammoniation reagent adopted by the invention does not introduce miscellaneous elements into the system, so that the influence on the performance of the final carbon fiber caused by impurities generated by pre-oxidation and carbonization in the later period is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of polyacrylonitrile-based carbon fibers, and in particular to a method for ammoniation of polyacrylonitrile powder. Background Art

[0002] With the development of aerospace, wind turbine blades, electric vehicles, pressure vessels and other fields, the need for lightweight, high-strength composite materials is becoming more and more urgent. Carbon fibers are often made into fiber-reinforced composite materials with plastics, metals, ceramics and other matrices to prepare high-strength structural materials. The method for preparing carbon fiber is: first, the precursor is spun into raw yarn, and then the carbon fiber is prepared by pre-oxidation and carbonization. The precursors used for spinning are mainly polyacrylonitrile (PAN), viscose fiber and asphalt. Among them, polyacrylonitrile-based carbon fiber has the advantages of excellent finished product quality, simple process and excellent mechanical properties, and has become the mainstream of carbon fiber production.

[0003] In the production process of polyacrylonitrile precursor, the coagulation of spinning solution is completed by double diffusion of solvent and precipitant and precipitation of polyacrylonitrile molecules. At present, the spinning method used in industry is mostly wet spinning. However, the coagulation double diffusion rate in the wet spinning process is relatively fast, which can easily cause defects such as large pores, skin-core structure and irregular fiber structure of polyacrylonitrile fiber, which will be inherited to polyacrylonitrile fiber and carbon fiber, seriously weakening the performance and application field of carbon fiber.

[0004] The process of coagulation double diffusion is closely related to the hydrophilicity of the spinning solution. Improving the hydrophilicity of the spinning solution can slow down the coagulation speed of the spinning solution and reduce defects such as macropores, skin-core structure and irregular fiber structure. Improving the hydrophilicity of the spinning solution by ammoniation is an effective means to avoid the above problems. At present, there are three mainstream ammoniation methods in the market, namely, adding ammonia before polymerization, adding ammonia before removing the single after polymerization (referred to as adding ammonia after polymerization), and adding ammonia in the coagulation bath. The above methods can improve the hydrophilicity of the spinning solution, but there are also some disadvantages, mainly as follows: 1. Adding ammonia before polymerization will hinder the polymerization reaction and have an adverse effect on mass transfer and heat transfer during the polymerization process. 2. Adding ammonia before removing the single after polymerization, the degree of ammonia is not easy to control. 3. Adding ammonia in the coagulation bath, the ammonia in the coagulation bath is not easy to mix and react evenly with the high-viscosity spinning solution, resulting in low ammonia efficiency. Summary of the invention

[0005] In view of this, the present invention provides a method for ammoniation of polyacrylonitrile powder. Starting from the source of spinning solution, the present invention effectively ammoniations the polyacrylonitrile powder after the single-molecule removal before preparing the spinning solution, which can effectively improve the hydrophilicity of polyacrylonitrile, and is simple to operate and environmentally friendly.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A method for ammoniation of polyacrylonitrile powder comprises the following steps:

[0008] The carboxyl-containing polyacrylonitrile liquid obtained by precipitation polymerization is first dried after being stripped of monomers to obtain a carboxyl-containing polyacrylonitrile powder;

[0009] The carboxyl-containing polyacrylonitrile powder is immersed in an aqueous solution of an aminating agent for amination; the aminating agent is an ammonium salt.

[0010] Preferably, the ammonium salt includes one or more of ammonium carbonate, ammonium acetate, ammonium formate and ammonium bicarbonate.

[0011] Preferably, the concentration of the aqueous solution of the aminating agent is 0.01 mol / L to 5 mol / L.

[0012] Preferably, the molar amount of amino groups of the ammonium salt in the aqueous solution of the aminating agent is greater than or equal to the molar amount of carboxyl groups in the aminated carboxyl-containing polyacrylonitrile powder.

[0013] Preferably, the molar ratio of the amino group in the ammonium salt to the carboxyl group in the carboxyl-containing polyacrylonitrile powder is 1 to 10:1; more preferably 1 to 5:1.

[0014] Preferably, the comonomer used in the precipitation polymerization is a carboxyl-containing comonomer, and the carboxyl-containing comonomer includes one or more of itaconic acid, acrylic acid, methacrylic acid, maleic acid, methylmaleic acid and fumaric acid.

[0015] Preferably, the temperature of the ammoniation is 30 to 100° C., and the time of the ammoniation is 0.5 to 48 hours.

[0016] Preferably, the method for removing the single monomers is: pouring the carboxyl-containing polyacrylonitrile solution into deionized water, and then filtering and rinsing.

[0017] Preferably, the first drying temperature is 40-80°C; more preferably 50-70°C.

[0018] Preferably, after the ammoniation, the obtained ammoniation product is washed and then subjected to a second drying; the temperature of the second drying is 40 to 80°C; more preferably 50 to 70°C.

[0019] The invention provides a method for ammoniation of polyacrylonitrile powder, comprising the following steps: removing the carboxyl-containing polyacrylonitrile liquid obtained by precipitation polymerization and then drying it to obtain the carboxyl-containing polyacrylonitrile powder; immersing the carboxyl-containing polyacrylonitrile powder in an ammoniation reagent aqueous solution for ammoniation; the ammoniation reagent is one or more of ammonium carbonate, ammonium acetate, ammonium formate and ammonium bicarbonate. The present invention starts from the source of spinning solution, and efficiently ammoniates the polyacrylonitrile powder after the single-molecule removal before preparing the spinning solution. The operation is simple, the ammoniation efficiency is high, and the hydrophilicity of polyacrylonitrile can be effectively improved. In addition, the current ammoniation method usually uses liquid amine or ammonia gas as an ammoniation agent, which has a large odor and toxicity. The ammoniation agent used in the present invention is ammonium salt or carbonamide, which overcomes the shortcomings of the commonly used liquid amine and gaseous ammonia, which have a large odor and high toxicity, and solves the difficulty that gaseous ammonia and most liquid amines are insoluble in the spinning solution solvent. The system after ammoniation is pure and environmentally friendly. Furthermore, the specific ammoniation agent used in the present invention will not introduce impurities other than carbon, hydrogen, oxygen and nitrogen into the system, thereby avoiding the generation of impurities by pre-oxidation and carbonization in the later stage to affect the performance of the final carbon fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the NMR spectrum of the carboxyl-containing polyacrylonitrile powder before amination in Example 1;

[0021] Figure 2 is the NMR spectrum of the polyacrylonitrile powder after ammoniation in Example 1;

[0022] Figure 3 The water contact angle test result of the carboxyl-containing polyacrylonitrile powder before ammoniation in Example 1;

[0023] Figure 4 The water contact angle test result of the polyacrylonitrile powder after ammoniation in Example 1;

[0024] Figure 5 These are the DSC test results of the polyacrylonitrile powder before and after ammoniation in Example 1. DETAILED DESCRIPTION

[0025] The present invention provides a method for ammoniation of polyacrylonitrile powder, comprising the following steps:

[0026] The carboxyl-containing polyacrylonitrile liquid obtained by precipitation polymerization is first dried after being stripped of monomers to obtain a carboxyl-containing polyacrylonitrile powder;

[0027] The carboxyl-containing polyacrylonitrile powder is immersed in an aqueous solution of an aminating agent for amination; the aminating agent is an ammonium salt.

[0028] The present invention removes the monomers from the carboxyl-containing polyacrylonitrile liquid obtained by precipitation polymerization and then first dries it to obtain a carboxyl-containing polyacrylonitrile powder. In the present invention, the carboxyl-containing polyacrylonitrile liquid is specifically a polymer slurry of carboxyl-containing polyacrylonitrile; the precipitation polymerization is specifically a precipitation polymerization reaction using acrylonitrile monomer and a comonomer. The present invention has no special requirements for the specific operation method of the precipitation polymerization, and a method well known to those skilled in the art can be used. In the present invention, the comonomer preferably includes a carboxyl-containing comonomer; the carboxyl-containing comonomer preferably includes one or more of itaconic acid, acrylic acid, methacrylic acid, maleic acid, methylmaleic acid and fumaric acid.

[0029] In the present invention, the method for removing monomers is preferably: pouring the carboxyl-containing polyacrylonitrile solution into deionized water, and then filtering and rinsing; the amount of deionized water used is based on the ability to terminate the precipitation polymerization reaction; the present invention has no special requirements for the number of filtering and rinsing, as long as the unreacted monomers can be removed.

[0030] In the present invention, the temperature of the first drying is preferably 40 to 80° C., more preferably 50 to 70° C.; the first drying is preferably vacuum drying.

[0031] After obtaining the carboxyl-containing polyacrylonitrile powder, the present invention soaks the carboxyl-containing polyacrylonitrile powder in an aqueous solution of an ammoniation agent for ammoniation; in the present invention, the ammoniation agent is an ammonium salt, and the ammonium salt preferably includes one or more of ammonium carbonate, ammonium acetate, ammonium formate and ammonium bicarbonate; the concentration of the aqueous solution of the ammoniation agent is preferably 0.01 mol / L to 5 mol / L, more preferably 0.1 to 0.5 mol / L; the molar amount of amino groups in the ammonium salt in the aqueous solution of the ammoniation agent is greater than or equal to the molar amount of carboxyl groups in the aminated carboxyl-containing polyacrylonitrile powder. Specifically, the molar ratio of amino groups in the ammonium salt to carboxyl groups in the carboxyl-containing polyacrylonitrile powder is 1 to 10:1, more preferably 1 to 5:1; further preferably 1 to 2:1; the mass ratio of the aqueous solution of the ammoniation agent to the carboxyl-containing polyacrylonitrile powder is preferably 1 to 50:1, specifically 10:1.

[0032] In the present invention, the temperature of the amination is preferably 30 to 100°C, specifically 40°C, 50°C, 55°C, 60°C, 65°C, 70°C, 80°C or 90°C; the time of the amination is preferably 0.5 to 48h, specifically 1h, 3h, 5h, 10h, 15h, 18h, 24h, 36h or 48h; the amination is preferably carried out under the condition of water bath heating; the present invention controls the temperature and time of the amination within the above range, so that the amination reagent and the carboxyl group in the carboxyl-containing polyacrylonitrile powder can fully react to achieve efficient amination.

[0033] In the present invention, after the ammoniation, the obtained aminated product is washed and then subjected to a second drying; the washing is preferably washed with deionized water, and the present invention removes the residual aminating agent in the aminated product by washing; the temperature of the second drying is preferably 40 to 80°C, specifically 50°C, 55°C, 60°C, 65°C or 70°C; the second drying is preferably vacuum drying.

[0034] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Example 1

[0036] The polymer slurry containing carboxyl polyacrylonitrile obtained by precipitation polymerization is poured into excess deionized water to terminate the polymerization and rinsed and filtered several times. After removing the unreacted monomers, the product is placed in a vacuum oven at 60°C and dried to constant weight, and finally a carboxyl polyacrylonitrile powder with a copolymer composition of 2 mol% acrylic acid, 1 mol% itaconic acid, and 97 mol% acrylonitrile is obtained. 10g of the obtained carboxyl polyacrylonitrile powder is placed in 100g of ammonium carbonate solution with a concentration of 0.5mol / L, and reacted for 1h at a water bath temperature of 50°C. After stopping the reaction, filter, rinse the aminated powder several times with ionized water to wash away the ammonium carbonate residue. Dry in a vacuum oven at 60°C to obtain the aminated polyacrylonitrile powder.

[0037] Example 2

[0038] The polymer slurry containing carboxyl polyacrylonitrile obtained by precipitation polymerization is poured into excess deionized water to terminate the polymerization and rinsed and filtered several times. After removing the unreacted monomer, the product is placed in a vacuum oven at 60°C and dried to constant weight, and finally a carboxyl polyacrylonitrile powder with a copolymer composition of 2 mol% acrylic acid, 1 mol% itaconic acid, and 97 mol% acrylonitrile is obtained. 10g of the obtained carboxyl polyacrylonitrile powder is placed in 100g of ammonium bicarbonate solution with a concentration of 0.5mol / L, and reacted for 1h at a water bath temperature of 50°C. After stopping the reaction, filter, rinse the aminated powder several times with ionized water to wash away the ammonium bicarbonate residue. Dry in a vacuum oven at 60°C to obtain the aminated polyacrylonitrile powder.

[0039] Example 3

[0040] The polymer slurry containing carboxyl polyacrylonitrile obtained by precipitation polymerization is poured into excess deionized water to terminate the polymerization and rinsed and filtered several times. After removing the unreacted monomers, the product is placed in a vacuum oven at 60°C and dried to constant weight, and finally a carboxyl polyacrylonitrile powder with a copolymer composition of 2 mol% acrylic acid, 1 mol% itaconic acid, and 97 mol% acrylonitrile is obtained. 10g of the obtained carboxyl polyacrylonitrile powder is placed in 100g of ammonium acetate solution with a concentration of 0.5mol / L, and reacted for 1h at a water bath temperature of 50°C. After stopping the reaction, filter, rinse the aminated powder several times with ionized water to wash away the ammonium acetate residue. Dry in a vacuum oven at 60°C to obtain the aminated polyacrylonitrile powder.

[0041] Example 4

[0042] The polymer slurry containing carboxyl polyacrylonitrile obtained by precipitation polymerization is poured into excess deionized water to terminate the polymerization and rinsed and filtered several times. After removing the unreacted monomers, the product is placed in a vacuum oven at 60°C and dried to constant weight, and finally a carboxyl polyacrylonitrile powder with a copolymer composition of 2 mol% acrylic acid, 1 mol% itaconic acid, and 97 mol% acrylonitrile is obtained. 10g of the obtained carboxyl polyacrylonitrile powder is placed in 100g of ammonium carbonate solution with a concentration of 1.5mol / L, and reacted for 1h at a water bath temperature of 50°C. After stopping the reaction, filter, rinse the aminated powder several times with ionized water to wash away the ammonium carbonate residue. Dry in a vacuum oven at 60°C to obtain the aminated polyacrylonitrile powder.

[0043] Example 5

[0044] The polymer slurry containing carboxyl polyacrylonitrile obtained by precipitation polymerization is poured into excess deionized water to terminate the polymerization and rinsed and filtered several times. After removing the unreacted monomers, the product is placed in a vacuum oven at 60°C and dried to constant weight, and finally a carboxyl polyacrylonitrile powder with a copolymer composition of 2 mol% acrylic acid, 1 mol% itaconic acid, and 97 mol% acrylonitrile is obtained. 10g of the obtained carboxyl polyacrylonitrile powder is placed in 100g of ammonium formate solution with a concentration of 0.5mol / L, and reacted for 1h at a water bath temperature of 50°C. After stopping the reaction, filter, rinse the aminated powder several times with ionized water to wash away the ammonium formate residue. Dry in a vacuum oven at 60°C to obtain the aminated polyacrylonitrile powder.

[0045] Example 6

[0046] The polymer slurry containing carboxyl polyacrylonitrile obtained by precipitation polymerization is poured into excess deionized water to terminate the polymerization and rinsed and filtered several times. After removing the unreacted monomers, the product is placed in a vacuum oven at 60°C and dried to constant weight, and finally a carboxyl polyacrylonitrile powder with a copolymer composition of 1 mol% acrylic acid, 1 mol% itaconic acid, and 98 mol% acrylonitrile is obtained. 10g of the obtained carboxyl polyacrylonitrile powder is placed in 100g of ammonium carbonate solution with a concentration of 0.5mol / L, and reacted for 1h at a water bath temperature of 50°C. After stopping the reaction, filter, rinse the aminated powder several times with ionized water to wash away the ammonium carbonate residue. Dry in a vacuum oven at 60°C to obtain the aminated polyacrylonitrile powder.

[0047] Performance Testing

[0048] The polyacrylonitrile powder before and after ammoniation in Example 1 was subjected to nuclear magnetic resonance testing, and the results were as follows: Figure 1 and Figure 2 As shown. Figure 1 and Figure 2 It can be seen that the ammonium salt aqueous solution effectively aminated the carboxyl groups in polyacrylonitrile.

[0049] The polyacrylonitrile powder before and after ammoniation in Example 1 was spread into films and the water contact angle test was performed. The results were as follows: Figure 3 and Figure 4 As shown. It can be seen that the hydrophilicity of polyacrylonitrile after amination has been greatly improved.

[0050] The polyacrylonitrile powder before and after ammoniation in Example 1 was subjected to DSC test, and the results are as follows: Figure 5 As shown. Figure 5 It can be seen that the concentrated heat release of the polyacrylonitrile powder after amination is further alleviated during the thermal stabilization process, which is conducive to the preparation of high-performance polyacrylonitrile carbon fibers.

[0051] The polyacrylonitrile powders before and after amination in Examples 2 to 6 were subjected to NMR, water contact angle and DSC tests. The results showed that effective amination was achieved and the hydrophilicity of polyacrylonitrile was greatly improved.

[0052] 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 method for ammoniation of polyacrylonitrile powder, characterized in that: The following steps are involved: The carboxyl-containing polyacrylonitrile liquid obtained by precipitation polymerization is first dried after being stripped of monomers to obtain a carboxyl-containing polyacrylonitrile powder; The carboxyl-containing polyacrylonitrile powder is immersed in an aqueous solution of an aminating agent for amination; the aminating agent is an ammonium salt.

2. The ammoniation method according to claim 1, characterized in that The ammonium salt includes one or more of ammonium carbonate, ammonium acetate, ammonium formate and ammonium bicarbonate.

3. The ammoniation method according to claim 1 or 2, characterized in that: The concentration of the aqueous solution of the aminating agent is 0.01 mol / L to 5 mol / L.

4. The ammoniation method according to claim 1 or 2, characterized in that: The molar amount of amino groups of the ammonium salt in the aqueous solution of the aminating agent is greater than or equal to the molar amount of carboxyl groups in the aminated carboxyl-containing polyacrylonitrile powder.

5. The ammoniation method according to claim 4, characterized in that The molar ratio of the amino group in the ammonium salt to the carboxyl group in the carboxyl-containing polyacrylonitrile powder is 1 to 10:

1.

6. The ammoniation method according to claim 1, characterized in that: The comonomer used in the precipitation polymerization is a carboxyl-containing comonomer; the carboxyl-containing comonomer includes one or more of itaconic acid, acrylic acid, methacrylic acid, maleic acid, methylmaleic acid and fumaric acid.

7. The ammoniation method according to claim 1, characterized in that: The temperature of the ammoniation is 30-100° C., and the time of the ammoniation is 0.5-48 hours.

8. The ammoniation method according to claim 1, characterized in that The method for removing the single monomers is as follows: pouring the carboxyl-containing polyacrylonitrile solution into deionized water, and then filtering and rinsing.

9. The ammoniation method according to claim 1, characterized in that: The first drying temperature is 40-80°C.

10. The ammoniation method according to claim 1, characterized in that: After the ammoniation, the method further includes washing the obtained ammoniation product and performing a second drying; the temperature of the second drying is 40 to 80°C.

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