A method for improving the crystallinity, homogenization and densification degree of PAN nascent fibers

Abstract

The present invention belongs to the field of manufacturing high-performance carbon fiber precursor filaments, and provides a method for improving the crystallinity, homogenization and densification degree of polyacrylonitrile nascent fibers, including: copolymerizing acrylonitrile and comonomers by dissolving them in a solvent respectively, and then removing monomers and degassing to obtain a polymer spinning dope; extruding the polymer spinning dope through a spinneret, passing through an air layer, and entering a coagulation bath composed of a mixed solution of a solvent and a coagulant (triethylene glycol, triethanolamine or ethyl carbamate) for coagulation molding, and then performing drawing to obtain PAN nascent fibers. Replacing the precipitant-water in the coagulation bath with triethylene glycol or triethanolamine or ethyl carbamate can improve the crystallinity and the degree of densification and homogenization of the nascent fibers without affecting the double-diffusion rate. Alleviating the formation of the skin-core structure is an important direction for improving carbon fiber products.

Description

Technical Field

[0001] The present invention belongs to the technical field of manufacturing high-performance carbon fiber precursor, and particularly relates to a method for improving the crystallinity, densification degree and homogenization degree of polyacrylonitrile nascent fibers. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the understanding of the overall background of the present invention, and it is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Carbon fiber is an inorganic fiber with a carbon content of 90% or more, and has the advantages of light weight, high axial modulus, corrosion resistance, creep resistance, etc. Therefore, carbon fiber composites are widely used in aerospace, new energy, construction, weaponry and other fields. Compared with other spinning raw material systems, polyacrylonitrile-based carbon fiber has simple manufacturing process and excellent performance.

[0004] The quality of carbon fiber precursor largely determines the mechanical properties of carbon fiber, and the key indicators such as the structure and crystallinity of the fiber depend on the forming method of the spinning dope stream in the coagulation bath. In the dry-jet wet spinning or wet spinning process, when the polyacrylonitrile spinning dope stream enters the coagulation bath, double diffusion occurs, which causes the rapid precipitation of polyacrylonitrile molecular chains, resulting in a skin-core structure in the nascent fiber.

[0005] In Patent ZL200610117242.4, step 6 is "After the spinning dope removes bubbles, it is spun, and then solidified into nascent fibers through a coagulation bath. The coagulation bath is an aqueous solution of the solvent used in the spinning dope, the concentration of the coagulation bath is 55-80 wt%, and the temperature of the coagulation bath is 20-55 °C". This method has a fast solidification rate and is easy to form a skin layer structure. Although a high coagulation bath concentration or a low temperature can alleviate the skin-core structure, it is recorded in CN102677209A that a high coagulation bath concentration and a low temperature can slow down the double diffusion rate, but also increase the residence time of the dope in the coagulation bath.

[0006] In view of this, in order to overcome the skin-core structure generated in the process of producing precursor in the prior art, it is particularly crucial to find a method for preparing a nascent fiber with improved crystallinity, homogenization and densification degree.

[0007] Patent ZL 201510340513.1 discloses a method for improving the crystallinity of polyacrylonitrile nascent fibers. By adjusting the viscosity of the polymer solution, the entanglement state between polymer molecules before solidification is regulated, thereby changing the nucleation and growth processes of polymer molecules during the formation of the crystalline structure, and ultimately improving the crystallinity of polyacrylonitrile nascent fibers. However, the inventors found that this method requires the nascent fibers to be placed in a solution with the same composition as the coagulation bath and left standing for 24 hours. The reaction time is relatively long, the production efficiency is low, and the crystallinity of polyacrylonitrile nascent fibers also needs to be improved. Summary of the Invention

[0008] In order to solve the above problems, the present invention provides a method for improving the crystallinity, homogenization and densification degree of nascent fibers. The inventors of the present invention found that replacing the precipitant - water in the coagulation bath with triethylene glycol, triethanolamine or ethyl carbamate can improve the crystallinity and dense homogenization degree of nascent fibers without affecting the double diffusion rate. Alleviating the formation of the skin - core structure is an important direction for improving carbon fiber products.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] In the first aspect of the present invention, a method for improving the crystallinity, homogenization and densification degree of polyacrylonitrile nascent fibers is provided, including:

[0011] Dissolving acrylonitrile and comonomers in a solvent respectively for copolymerization, and then removing monomers and degassing to obtain a polymer spinning dope;

[0012] After extruding the polymer spinning dope through a spinneret, passing through an air layer, and entering a coagulation bath composed of a mixed solution of a solvent and a coagulant for solidification molding, and then performing stretching to obtain PAN nascent fibers;

[0013] Wherein, the coagulant is triethylene glycol, triethanolamine or ethyl carbamate;

[0014] The proportion of the coagulant is 10 - 90%.

[0015] In the second aspect of the present invention, PAN nascent fibers prepared by the above method are provided.

[0016] In the third aspect of the present invention, the application of triethylene glycol, triethanolamine or ethyl carbamate in improving the crystallinity, porosity and breaking strength of PAN nascent fibers is provided.

[0017] Advantages of the Present Invention

[0018] (1) In the present invention, triethylene glycol, triethanolamine or ethyl carbamate is used as a coagulant. The nascent fiber obtained after the fine stream of the spinning solution passes through the coagulation bath has improved densification and homogenization degrees, and the crystallinity of the nascent fiber is greatly enhanced. Triethylene glycol is a linear molecule with hydroxyl groups at both ends and contains two ether groups in the molecular chain. On the one hand, compared with water, triethylene glycol has a longer molecular chain and weaker polarity, so the interaction force with the polyacrylonitrile molecular chain is weak, which thus inhibits the stretching and free movement of the polyacrylonitrile chain to a lesser extent. This allows the molecular chain to have sufficient time and a more stretched state to stack and crystallize while also alleviating the formation of the skin-core structure and increasing the homogenization degree of the fiber. On the other hand, the linear-structured triethylene glycol is easily inserted between the molecular chains in the amorphous region of the polyacrylonitrile nascent fiber. During the stretching process in the coagulation bath, the double ether bonds in triethylene glycol rotate freely, which is beneficial to the stretching in the coagulation bath, reduces the breakage of molecular chains, and improves the densification and crystallinity of the nascent fiber. For the specific mechanism, refer to Figure 1 . Triethanolamine has three hydroxyl groups and one amino group. The rich polar groups endow triethanolamine with the coagulation ability for the PAN molecular chain. In addition, the hydroxyl and amino groups in triethanolamine can form multiple interaction forces with the PAN molecular chain, thus effectively shielding the strong interaction forces between the PAN molecular chains, which is beneficial to the stretching in the coagulation bath, making the nascent fiber have a high crystallinity and a uniform and dense structure. The amino group in ethyl carbamate has polarity, endowing it with the coagulation ability for the PAN molecular chain. In addition, in the coagulation bath, the amino group in ethyl carbamate can shield the strong interaction forces between the PAN molecular chains, and the large-volume methyl group can also reduce the mutual interaction forces between the PAN molecular chains, which is beneficial to the stretching in the coagulation bath.

[0019] (2) The preparation method of the present invention is simple, highly practical, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The attached drawings forming a part of this specification are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0021] Figure 1 is a schematic diagram of dry-jet wet spinning for preparing nascent fibers with high densification, high homogenization degree and high crystallinity according to an embodiment of the present invention.

[0022] Figure 2 is a schematic diagram of the device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains.

[0024] A method for improving the crystallinity, homogenization and densification degree of polyacrylonitrile nascent fibers, comprising:

[0025] Dissolving acrylonitrile and comonomers in a solvent respectively for copolymerization, and then performing monomer removal and degassing to obtain a polymer spinning dope;

[0026] After extruding the polymer spinning dope through a spinneret, passing through an air layer, and entering a coagulation bath composed of a mixed solution of a solvent and a coagulant for coagulation molding, and then performing drawing to obtain PAN nascent fibers;

[0027] Wherein, the coagulant is triethylene glycol, triethanolamine or ethyl carbamate;

[0028] The proportion of the coagulant is 10-90%.

[0029] Wherein, triethylene glycol as the coagulant has a relatively lower polarity than water; the molecular chain of triethylene glycol has two ether bonds that can rotate freely; the coagulant can be miscible with the solvent in the coagulation bath.

[0030] In some embodiments, the solvent is selected from one or more mixtures of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, acetone.

[0031] In some embodiments, the temperature of the coagulation bath is 10-70°C.

[0032] In some embodiments, the draw ratio is 5%-200%.

[0033] In some embodiments, the linear velocity of the polymer liquid in the spinneret holes is 5-50 m / min.

[0034] In some embodiments, the residence time of the nascent fibers in the coagulation bath is 3-20 s.

[0035] The present invention also provides a method for the crystallinity, homogenization and densification degree of high polyacrylonitrile nascent fibers, specifically comprising:

[0036] The step of obtaining a polyacrylonitrile spinning dope by polymerizing acrylonitrile monomers with a copolymer, and then, through the dry-jet wet spinning technique, passing through an air layer and entering a coagulation bath for coagulation, and finally obtaining a nascent fiber after stretching; Triethylene glycol, used as a coagulant, has a relatively lower polarity than water; The molecular chain of triethylene glycol has two ether bonds that can rotate freely; Triethanolamine has three ethoxy groups and one amino group, making it have both the properties of an alcohol and an amine; Ethyl carbamate has one amino group and one methyl group; The coagulant described above can be miscible with the solvent in the coagulation bath.

[0037] In some embodiments, the comonomers include itaconic acid, sodium acrylate, sodium methacrylate, methyl acrylate, methyl methacrylate, methacrylic acid, and acrylamide;

[0038] In some embodiments, the proportion of the comonomers is 0.1% - 10%, more preferably 1%;

[0039] In some embodiments, the molecular weight of the acrylonitrile polymer in the polymer spinning dope is 50,000 - 500,000.

[0040] In some embodiments, the distance of the air layer is 5 - 200 mm.

[0041] The following further describes the present invention in detail with reference to specific embodiments. It should be noted that the specific embodiments are interpretations of the present invention rather than limitations.

[0042] Example 1

[0043] A coagulation molding method for improving the crystallinity, homogenization, and densification degree of PAN nascent fibers, and its preparation steps are as follows:

[0044] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained, and the ratio of the comonomers was 99:1. After 12 h of monomer removal and degassing, dry-jet wet spinning could be carried out. The linear velocity of the polymer through the spinneret was 25 m / min. The coagulation bath was a mixed solution of dimethyl sulfoxide and triethylene glycol (mass ratio 3.5:6.5), the draw ratio of the coagulation bath was 25%, the residence time of the nascent fiber in the coagulation bath was 6 s, and the temperature of the coagulation bath was maintained at 30 °C. The breaking strength of the nascent fiber obtained was 0.41 cN / Dtex. The porosity of the nascent fiber was 10.1% obtained by BET specific surface area and pore size measurement. The dried nascent fiber was cut into pieces and ground into powder, and the powder was tested by a D / max-rc type X-ray diffractometer. The scanning range was 5-50°, the scanning rate was 4° / min, and the crystallinity C was calculated by the Hinrichen method. The formula was C = Ac / (Ac + Aa), where Ac was the area of the diffraction peak of the crystalline region at 2θ≈17°, and Aa was the area of the diffraction peak of the amorphous region. The calculated crystallinity was 43.5%.

[0045] Example 2

[0046] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained, and the ratio of the comonomers was 99:1. The polymerization process was as in Example 1. The draw ratio of the coagulation bath was adjusted to 50%, and the other process parameters and steps were the same as in Example 1. The calculated porosity of the nascent fiber was 6.4%, the calculated breaking strength of the nascent fiber was 0.53 cN / Dtex, and the calculated crystallinity of the nascent fiber was 47.1%.

[0047] Example 3

[0048] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained, and the ratio of the comonomers was 99:1. The polymerization process was as in Example 1. The draw ratio of the coagulation bath was adjusted to 80%, and the other process parameters and steps were the same as in Example 1. The calculated porosity of the nascent fiber was 3.2%, the calculated breaking strength of the nascent fiber was 0.65 cN / Dtex, and the calculated crystallinity of the nascent fiber was 52.7%.

[0049] Example 4

[0050] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. The draw ratio of the coagulation bath was adjusted to 100%, and the other process parameters and steps were the same as in Example 1. The porosity of the as-spun fiber was calculated to be 1.8%, the breaking strength of the as-spun fiber was calculated to be 0.71 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 54.5%.

[0051] Example 5

[0052] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. The draw ratio of the coagulation bath was adjusted to 120%, and the other process parameters and steps were the same as in Example 1. The porosity of the as-spun fiber was calculated to be 2.0%, the breaking strength of the as-spun fiber was calculated to be 0.66 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 55.3%.

[0053] Example 6

[0054] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. The mass ratio of the coagulation bath was adjusted to 4:6, and the other process parameters were as in Example 4. The porosity of the as-spun fiber was calculated to be 1.6%, the breaking strength of the as-spun fiber was calculated to be 0.73 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 55.8%.

[0055] Example 7

[0056] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. A mixed solution of dimethyl sulfoxide and triethanolamine (mass ratio 3.5:6.5) was used, the draw ratio of the coagulation bath was adjusted to 100%, and the other process parameters and steps were the same as in Example 4. The porosity of the as-spun fiber was calculated to be 2.1%, the breaking strength of the as-spun fiber was calculated to be 0.67 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 53.1%.

[0057] Example 8

[0058] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. A mixed solution of dimethyl sulfoxide and triethanolamine (mass ratio 3.5:6.5) was used, and the coagulation bath draw ratio was adjusted to 120%. The remaining process parameters and steps were the same as in Example 5. The porosity of the as-spun fiber was calculated to be 2.4%, the breaking strength of the as-spun fiber was calculated to be 0.65 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 54.2%.

[0059] Example 9

[0060] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. The coagulation bath used a mixed solution of dimethyl sulfoxide and triethanolamine, and the mass ratio of the coagulation bath was 4:6. The remaining process parameters were as in Example 6. The porosity of the as-spun fiber was calculated to be 1.9%, the breaking strength of the as-spun fiber was calculated to be 0.70 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 54.5%.

[0061] Example 10

[0062] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. A mixed solution of dimethyl sulfoxide and ethyl carbamate (mass ratio 3.5:6.5) was used, and the coagulation bath draw ratio was adjusted to 100%. The remaining process parameters and steps were the same as in Example 4. The porosity of the as-spun fiber was calculated to be 2.5%, the breaking strength of the as-spun fiber was calculated to be 0.62 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 50.2%.

[0063] Example 11

[0064] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. A mixed solution of dimethyl sulfoxide and ethyl carbamate (mass ratio 3.5:6.5) was used as the coagulation bath, and the coagulation bath draw ratio was adjusted to 120%. The other process parameters and steps were the same as in Example 5. The porosity of the as-spun fiber was calculated to be 2.0%, the porosity of the as-spun fiber was calculated to be 3%, the breaking strength of the as-spun fiber was calculated to be 0.58 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 50.8%.

[0065] Example 12

[0066] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. The coagulation bath used a mixed solution of dimethyl sulfoxide and triethanolamine, and the mass ratio of the coagulation bath was 4:6. The other process parameters were as in Example 6. The porosity of the as-spun fiber was calculated to be 2.2%, the breaking strength of the as-spun fiber was calculated to be 0.65 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 51.2%.

[0067] Comparative Example 1

[0068] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. The coagulation bath used a mixed solution of dimethyl sulfoxide and water (mass ratio 3.5:6.5). The other process parameters and steps were the same as in Example 1. The porosity of the as-spun fiber was calculated to be 16.3%, the breaking strength of the as-spun fiber was calculated to be 0.14 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 39.2%.

[0069] Comparative Example 2

[0070] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. The composition of the coagulation bath was as in Comparative Example 1, and the remaining process parameters and steps were the same as in Example 2. The porosity of the as-spun fiber was calculated to be 14.2%, the breaking strength of the as-spun fiber was calculated to be 0.19 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 40.3%.

[0071] Comparative Example 3

[0072] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. The composition of the coagulation bath was as in Comparative Example 1, and the remaining process parameters were as in Example 3. The porosity of the as-spun fiber was calculated to be 13.1%, the breaking strength of the as-spun fiber was calculated to be 0.32 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 42.4%.

[0073] Comparative Example 4

[0074] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. The composition of the coagulation bath was as in Comparative Example 1, and the remaining process parameters were as in Example 4. The porosity of the as-spun fiber was calculated to be 7.2%, the breaking strength of the as-spun fiber was calculated to be 0.46 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 43.6%.

[0075] Comparative Example 5

[0076] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained. The ratio of the comonomers was 99:1, and the polymerization process was as in Example 1. The composition of the coagulation bath was as in Comparative Example 1, and the remaining process parameters were as in Example 5. The porosity of the as-spun fiber was calculated to be 7.8%, the breaking strength of the as-spun fiber was calculated to be 0.41 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 45.1%.

[0077] Comparative Example 6

[0078] The PAN copolymer was obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out at 60 °C. Finally, an acrylonitrile-itaconic acid binary copolymer was obtained, and the ratio of the comonomers was 99:1. The polymerization process was as in Example 1. The coagulation bath used a mixed solution of dimethyl sulfoxide and water (mass ratio 4:6), and the other process parameters were as in Example 6. The porosity of the as-spun fiber was calculated to be 6.2%, the breaking strength of the as-spun fiber was calculated to be 0.51 cN / Dtex, and the crystallinity of the as-spun fiber was calculated to be 45.7%.

[0079] Table 1: Breaking strength, porosity, and crystallinity of the PAN as-spun fibers prepared in the examples and comparative examples.

[0080]

[0081]

[0082] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for improving the crystallinity, homogenization and densification degree of polyacrylonitrile nascent fibers, characterized in that, Comprising: Acrylonitrile and a comonomer are respectively dissolved in a solvent for copolymerization, and then degassed and de-bubbled to obtain a polymer spinning dope; The polymer spinning dope is extruded through a spinneret, passes through an air layer, and enters a coagulation bath composed of a mixed solution of a solvent and a coagulant for coagulation molding, and is drawn in the coagulation bath to obtain PAN nascent fibers; Wherein, the coagulant is triethylene glycol; The proportion of the coagulant is 10-90%; The temperature of the coagulation bath is 10-70°C; The draw ratio is 80%-200%.

2. The method for increasing the crystallinity, homogenization and densification degree of the polyacrylonitrile nascent fiber according to claim 1, characterized in that, The solvent is selected from one or more mixtures of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and acetone.

3. The method for increasing the crystallinity, homogenization and densification degree of the polyacrylonitrile nascent fiber as described in claim 1, characterized in that, The linear velocity of the polymer solution in the spinneret hole is 5-50 m / min.

4. The method for improving the crystallinity, homogenization and densification degree of polyacrylonitrile nascent fibers according to claim 1, characterized in that, The residence time of the nascent fibers in the coagulation bath is 3-20 s.

5. The method for increasing the crystallinity, homogenization and densification degree of the polyacrylonitrile nascent fiber as described in claim 1, characterized in that, The comonomer includes itaconic acid, sodium acrylate sulfonate, sodium methacrylate sulfonate, methyl acrylate, methyl methacrylate, methacrylic acid, and acrylamide; Or, the proportion of the comonomer is 0.1%-10%; Or, the molecular weight of the acrylonitrile polymer in the polymer spinning dope is 50,000-500,000.

6. The method for increasing the crystallinity, homogenization and densification degree of the polyacrylonitrile nascent fiber according to claim 1, characterized in that, The distance of the air layer is 5-200 mm.

7. PAN nascent fibers prepared by the method according to any one of claims 1-6.

8. The PAN nascent fiber according to claim 7, characterized in that, Application of triethylene glycol in improving the crystallinity, porosity, and breaking strength of PAN nascent fibers.

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