Acrylonitrile terpolymer high-strength spinning solution and preparation method thereof

Abstract

The invention relates to a preparation method of a high-performance polyacrylonitrile-based carbon fiber precursor, which comprises the following steps: (1) by taking dimethyl sulfoxide or N, N-dimethyl formamide as a solvent and azodiisobutyronitrile as an initiator, initiating copolymerization of acrylonitrile, a second difunctional monomer 3-ammonium carboxylate methyl butyrate and a third monomer methyl acrylate at 50-70 DEG C; wherein the mass ratio of acrylonitrile to 3-ammonium carboxylate-3-methyl butyrate to methyl acrylate is (99-98.2): (0.2-1): 0.8, azodiisobutyronitrile accounts for 0.1-1.5 wt% of the total mass of the monomers, and the total concentration of the monomers is 16-30 wt%. And (2) defoaming and demonomerisation of the spinning solution prepared in the step (1), filtering to obtain a spinning stock solution, and then carrying out dry-jet wet spinning, stretching, oiling, drying and densifying, hot steam drafting and heat setting to obtain the carbon fiber precursor. According to the preparation method disclosed by the invention, the dual-functional-group comonomer 3-ammonium carboxylate-methyl butyrate is adopted, so that the dosage of the comonomer can be reduced, the production cost can be saved, meanwhile, the molecular weight and the structural regularity of polyacrylonitrile macromolecules can be improved, and the prepared carbon fiber precursor is uniform in structure, small in fineness and high in strength. The prepared polyacrylonitrile copolymer can effectively improve the thermal stability of the polyacrylonitrile copolymer in a pre-oxidation stage, and has a certain practical application prospect.

Description

Technical Field

[0001] The invention belongs to the field of preparation of copolymers for carbon fiber precursors, and particularly relates to a high-strength spinning stock solution of an acrylonitrile terpolymer and a preparation method thereof. Background Art

[0002] Carbon fiber has a series of superior physical, chemical and mechanical properties such as high specific strength, high specific modulus, heat and low temperature resistance, chemical corrosion resistance, friction resistance, thermal and electrical conductivity, radiation resistance, good damping and shock absorption, and is the most eye-catching new generation of reinforcement materials in the 21st century. At present, carbon fiber has been widely used in civil industries such as construction, transportation, energy, advanced sports goods, medical equipment, as well as cutting-edge fields such as aerospace, national defense and military.

[0003] The macromolecular chain structure of homopolymerized polyacrylonitrile is relatively regular and has high crystallinity. It reacts by free radical mechanism during pre-oxidation cyclization, which is difficult to control and cannot produce carbon fiber with good performance. When preparing polyacrylonitrile-based precursors for carbon fibers, the acrylonitrile content is generally required to be above 96%, and a small amount of vinyl monomer is usually added to copolymerize with acrylonitrile. The general requirements for the selection of copolymer components are: similar reactivity with acrylonitrile, easy polymerization, and the ability to form a stable spinning solution after polymerization with good spinnability; can promote the pre-oxidation reaction of the precursor, and the fiber structure is uniform after pre-oxidation; the structural defects are as few as possible during carbonization, and the carbon yield is high. Summary of the invention

[0004] The technical problem to be solved by the present invention is to propose a high-strength spinning solution of acrylonitrile terpolymer and a preparation method thereof. The present invention adopts a free radical solution polymerization method for polymerization, the polymerization reaction heat is easy to remove, the polymerization temperature is easy to control, and the relative molecular mass and distribution of the polymer are relatively uniform. The polyacrylonitrile-based carbon fiber precursor prepared by the present invention has a uniform structure, a small fineness, and a high strength, and is suitable for preparing high-performance carbon fibers.

[0005] The technical problem to be solved by the present invention is achieved through the following technical scheme: an acrylonitrile terpolymer high-strength spinning solution and a preparation method thereof.

[0006] The specific steps are as follows:

[0007] (1) Using one of dimethyl sulfoxide, N,N-dimethylformamide or N-vinyl pyrrolidone as solvent and azobisisobutyronitrile as initiator, acrylonitrile, a second bifunctional monomer 3-ammonium carboxylate-3-butyric acid methyl ester, and a third monomer methyl acrylate are copolymerized at 50-70° C., wherein the molar ratio of acrylonitrile / 3-ammonium carboxylate-3-butyric acid methyl ester / methyl acrylate is 99-98.2:0.2-1:0.8, the initiator azobisisobutyronitrile accounts for 0.1-1.5wt% of the total weight of the monomers, the total concentration of the monomers is 16-30wt%, and the polymerization reaction time is 8-12 hours.

[0008] (2) The spinning solution obtained in step (1) is subjected to dry-jet wet spinning, stretching, oiling, drying and densification, hot steam drawing, and heat setting to obtain carbon fiber precursor.

[0009] The molar ratio of acrylonitrile / monomer 3-carboxylic acid ammonium-3-butyric acid methyl ester / methyl acrylate described in step (1) is 99-98.2:0.2-1:0.8, and the total concentration of the monomers is 16-30wt%.

[0010] The initiator described in step (1) is azobisisobutyronitrile accounting for 0.1-1.5wt% of the total weight of the monomers, the reaction temperature is 50-70°C, and the reaction time is 8-12 hours.

[0011] The polymerization reaction temperature of step (1) is controlled as follows: the temperature is gradually increased from 30° C. to a polymerization reaction temperature of 50 to 75° C. in the first 6 hours, and then maintained at a constant temperature until the reaction is completed.

[0012] The solvent described in step (1) is one of dimethyl sulfoxide, N,N-dimethylformamide or N-vinyl pyrrolidone.

[0013] This patent uses 3-ammonium carboxylate-3-butyric acid methyl ester and methyl acrylate to copolymerize with acrylonitrile to prepare polyacrylonitrile copolymer, which improves the spinnability of polyacrylonitrile spinning solution and the density of filaments, while significantly improving its thermal stability and reducing the skin-core structure.

[0014] The introduction of the comonomer in the present invention can improve the spinnability of polyacrylonitrile spinning solution and the compactness of the filaments, accelerate the cyclization of linear polyacrylonitrile macromolecules, convert the free radical reaction of homopolymerized polyacrylonitrile in the pre-oxidation process into an ionic reaction, alleviate the violent exothermic reaction of the fiber during pre-oxidation, make the exothermic reaction easy to control, and provide a molecular-level channel for oxygen to diffuse and penetrate into the fiber core, greatly improve the pre-oxidation and carbonization speed, and improve the carbon fiber performance and carbonization yield. At the same time, the presence of the comonomer hinders the formation of hydrogen bonds between the polar group cyano group on the macromolecular chain and the adjacent carbon atom, reduces the flexibility of the polyacrylonitrile macromolecular chain, and improves the spinnability and stretchability of the polyacrylonitrile copolymer. In particular, the carboxyl group in the methyl acrylate molecule can initiate the pre-oxidation of the polyacrylonitrile precursor through an ionic mechanism, and the initiation efficiency is relatively high, which can significantly reduce the cyclization temperature, while widening the exothermic peak and reducing the heat release rate. The 3-carboxylic acid ammonium-3-methyl butyrate comonomer can reduce the melting point of the polymer and increase the decomposition temperature, thereby improving the spinnability of the stock solution.

[0015] Beneficial Effects

[0016] (1) The present invention uses a bifunctional monomer 3-ammonium carboxylate-3-methyl butyrate instead of itaconic acid, which reduces the chance of carboxyl group ionization during the polymerization process, is beneficial to increasing the molecular weight of acrylonitrile polymer and preparing high-performance carbon fiber precursor.

[0017] (2) The present invention adopts a free radical solution polymerization method for polymerization, the polymerization reaction heat is easy to remove, the polymerization temperature is easy to control, and the relative molecular mass and distribution of the polymer are relatively uniform.

[0018] (3) The initiator used in the present invention is azobisisobutyronitrile which does not contain metal ions. The obtained polyacrylonitrile has a high purity and does not need to be removed from impurities, thus reducing the production cost.

[0019] (4) The polyacrylonitrile polymer prepared by the present invention can effectively improve its thermal stability in the high-temperature pre-oxidation stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the DSC graph of the polymer in Example 1.

[0021] Figure 2 This is the FTIR spectrum of the polymer in Example 2. Specific implementation plan

[0022] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0023] Example 1

[0024] Acrylonitrile, 3-carboxylic acid ammonium-3-butyric acid methyl ester and methyl acrylate were mixed uniformly in a molar ratio of 99:0.2:0.8 and added to the reactor (the total concentration of the mixed monomers was 22%), followed by dimethyl sulfoxide, and finally azobisisobutyronitrile (accounting for 0.22% of the total mass of the mixed monomers). The mixture was reacted at 50-70°C for 8-12 hours to prepare polyacrylonitrile with a molecular weight of 1.7×10 5 g / mol, and the molecular weight distribution is 2.02. The above polymer solution is filtered through a 0.8 μm filter material, and the spinning solution is obtained by removing the monomers and degassing.

[0025] By the attached Figure 1 It can be seen that compared with polyacrylonitrile, the exothermic peak of the terpolymer prepared in Example 1 is broadened and the pre-oxidation starting temperature is reduced from 221.6°C to 206.6°C, which avoids concentrated heat release and promotes the pre-oxidation of carbon fiber precursors. In addition, the reduction in pre-oxidation temperature is beneficial to saving energy.

[0026] Example 2

[0027] Acrylonitrile, 3-carboxylic acid ammonium-3-butyric acid methyl ester and methyl acrylate were mixed uniformly in a molar ratio of 98.8:0.4:0.8 and added to the reactor (the total concentration of the mixed monomers was 22%), followed by dimethyl sulfoxide, and finally azobisisobutyronitrile (accounting for 0.22% of the total mass of the mixed monomers). The mixture was reacted at 50-70°C for 8-12 hours to prepare polyacrylonitrile with a molecular weight of 1.6×10 5 g / mol, and the molecular weight distribution is 2.36. The above polymer solution is filtered through a 0.8 μm filter material, and the spinning solution is obtained by removing single atoms and degassing.

[0028] Example 3

[0029] Acrylonitrile, 3-carboxylic acid ammonium-3-butyric acid methyl ester and methyl acrylate were mixed uniformly in a molar ratio of 98.6:0.6:0.8 and added to the reactor (the total concentration of the mixed monomers was 22%), followed by dimethyl sulfoxide, and finally azobisisobutyronitrile (accounting for 0.22% of the total mass of the mixed monomers). The mixture was reacted at 50-70°C for 8-12 hours to prepare polyacrylonitrile with a molecular weight of 1.4×10 5 g / mol, and the molecular weight distribution is 2.00. The above polymer solution is filtered through a 0.8 μm filter material, and the spinning solution is obtained by removing single atoms and degassing.

[0030] Example 4

[0031] Acrylonitrile, 3-carboxylic acid ammonium-3-butyric acid methyl ester and methyl acrylate were mixed uniformly in a molar ratio of 98.4:0.8:0.8 and added to the reactor (the total concentration of the mixed monomers was 22%), followed by dimethyl sulfoxide, and finally azobisisobutyronitrile (accounting for 0.22% of the total mass of the mixed monomers). The mixture was reacted at 50-70°C for 8-12 hours to prepare polyacrylonitrile with a molecular weight of 1.2×10 5 g / mol, and the molecular weight distribution is 2.15. The above polymer solution is filtered through a 0.8 μm filter material, and the spinning solution is obtained by removing single atoms and degassing.

[0032] Example 5

[0033] Acrylonitrile, 3-carboxylic acid ammonium-3-butyric acid methyl ester and methyl acrylate were mixed uniformly in a molar ratio of 98.2:1:0.8 and added to the reactor (the total concentration of the mixed monomers was 22%), followed by dimethyl sulfoxide, and finally azobisisobutyronitrile (accounting for 0.22% of the total mass of the mixed monomers). The mixture was reacted at 50-70°C for 8-12 hours to prepare polyacrylonitrile with a molecular weight of 1.1×10 5 g / mol, and the molecular weight distribution is 2.28. The above polymer solution is filtered through a 0.8 μm filter material, and the spinning solution is obtained by removing single atoms and degassing.

[0034] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

Claims

1. A method for preparing high-performance polyacrylonitrile-based carbon fiber precursor, characterized in that The following steps are involved: (1) Using one of dimethyl sulfoxide, N,N-dimethylformamide or N-vinyl pyrrolidone as a solvent and azobisisobutyronitrile as an initiator, acrylonitrile, a second bifunctional monomer 3-ammonium carboxylate-3-butyric acid methyl ester, and a third monomer methyl acrylate are copolymerized at 50-70° C., wherein the mass ratio of acrylonitrile / 3-ammonium carboxylate-3-butyric acid methyl ester / methyl acrylate is 99-98.2:0.2-1:0.8, the initiator azobisisobutyronitrile accounts for 0.1-1.5wt% of the total mass of the monomers, the total concentration of the monomers is 16-30wt%, and the polymerization reaction time is 8-12 hours. (2) The spinning solution obtained in step (1) is subjected to dry-jet wet spinning, stretching, oiling, drying and densification, hot steam drawing, and heat setting to obtain carbon fiber precursor.

2. The high-strength spinning solution of acrylonitrile terpolymer and the preparation method thereof as claimed in claim 1, characterized in that The mass ratio of acrylonitrile / monomer 3-carboxylic acid ammonium-3-butyric acid methyl ester / methyl acrylate described in step (1) is 99-98.2:0.2-1:0.8, and the total concentration of the monomers is 16-30wt%.

3. The high-strength spinning solution of acrylonitrile terpolymer and the preparation method thereof according to claim 1, characterized in that The initiator described in step (1) is azobisisobutyronitrile accounting for 0.1-1.2% of the total weight of the monomers, the reaction temperature is 50-70° C., and the reaction time is 8-12 hours.

4. The high-strength spinning solution of acrylonitrile terpolymer and the preparation method thereof as claimed in claim 1, characterized in that The polymerization reaction temperature is controlled as follows: the temperature is gradually increased from 30° C. to a polymerization reaction temperature of 50-75° C. in the first 6 hours, and then kept constant until the reaction is completed.

5. The high-strength spinning solution of acrylonitrile terpolymer and the preparation method thereof as claimed in claim 1, characterized in that The solvent described in step (1) is one of dimethyl sulfoxide, N,N-dimethylformamide or N-vinyl pyrrolidone.

Images