Spinning material composition, precursor and method for its production and pre-oxidation method, pre-oxidized fiber

Abstract

The present application relates to the field of spinning, in particular to a kind of spinning raw material composition, protofilament and its preparation method and pre-oxidation method, pre-oxidized fiber.The composition includes: acrylonitrile, itaconic acid, acrylate compound, double cyanide compound containing alkenyl or polycyanide compound containing alkenyl, initiator and solvent.Pre-oxidized fiber is prepared by using the composition formula of the present application, and the breaking elongation, oxygen index, oxygen content and breaking strength of pre-oxidized fiber can be ensured at a high level.

Description

Technical Field

[0001] This invention relates to the field of spinning, specifically to a spinning raw material composition, raw yarn and its preparation method and pre-oxidation method, and pre-oxidized fiber. Background Technology

[0002] Polyacrylonitrile (PAN) fiber pre-oxidized yarns can be used in flame retardancy, fireproofing, and sealing applications. Needle-punched felts made from chopped PAN fibers, after carbonization, are also used in C / C composite materials or as insulation felt for high-temperature furnaces. In recent years, the photovoltaic industry has developed rapidly, leading to an increasing demand for high-temperature furnaces and consequently, a significant increase in the demand for PAN pre-oxidized yarns. However, most pre-oxidized yarns currently on the market are transitional yarns from carbon fiber production or PAN precursor yarns intended for carbon fiber production that have undergone pre-oxidation. There are no PAN precursor yarns specifically prepared for the production of pre-oxidized yarns. Due to the formulation and spinning process, the pre-oxidation time required for precursor fibers intended for carbon fiber manufacturing is relatively long, mostly between 40 and 60 minutes. This results in higher costs for PAN fiber pre-oxidized fibers. Furthermore, based on existing PAN fiber formulations, a high draw ratio is required during the preparation of PAN precursor fibers, leading to lower elongation at break and insufficient deformation in the prepared pre-oxidized fibers. Even when the draw ratio is adjusted to a lower level, the breaking strength of the prepared pre-oxidized fibers will still be low, failing to simultaneously meet the requirements of high elongation at break and high breaking strength. This is detrimental to the smooth progress of the subsequent needle-punching felting process of chopped fibers.

[0003] In recent years, several institutions have developed low-cost carbon fibers through different approaches, and theoretically, their related technologies can also help reduce the cost of PAN fiber pre-oxidized fibers. CN115369521A points out that a high-oxygen atmosphere can be used in the oxidation furnace to replace air for the oxidation reaction. This measure can effectively reduce the oxidation time and improve the fiber's core-sheath structure, but using an oxygen-rich atmosphere increases the risk of fire in the oxidation furnace, affecting production safety. CN114427128A uses civilian-grade acrylic fiber as raw material to prepare flame-retardant pre-oxidized fibers. Oak Ridge National Laboratory in the United States has also conducted similar research. Although using civilian-grade acrylic fiber can reduce the cost of the precursor fiber, the high K-number of civilian-grade acrylic fiber makes heat transfer difficult during the oxidation process, resulting in an oxidation time of over 120 minutes. Overall, the cost of pre-oxidized fibers is not low. In addition, there are studies using high-energy electron radiation, microwave heating, and other technologies to replace traditional oxidation furnaces for pre-oxidation, but large-scale application has not yet been achieved. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of long pre-oxidation time and high pre-oxidation cost of the raw yarn in the prior art, and the inability to guarantee high breaking elongation and breaking strength of the prepared pre-oxidized yarn at the same time, as well as insufficient deformation. The invention provides a spinning raw material composition, raw yarn, preparation method and pre-oxidation method, and pre-oxidized fiber. The raw yarn obtained by this spinning raw material composition has the characteristics of short pre-oxidation time and low pre-oxidation cost, and the pre-oxidized yarn prepared has high breaking strength and breaking elongation.

[0005] To achieve the above objectives, a first aspect of the present invention provides a spinning raw material composition comprising: acrylonitrile, itaconic acid, acrylate compounds, a dicyandiamide compound containing an alkenyl group or a polycyandiamide compound containing an alkenyl group, an initiator, and a solvent.

[0006] A second aspect of the present invention provides a method for preparing raw silk, wherein the method uses the spinning raw material composition described in the first aspect as raw material and obtains raw silk by wet spinning.

[0007] The third aspect of the present invention provides a precursor fiber prepared by the preparation method described in the second aspect.

[0008] The fourth aspect of the present invention provides a pre-oxidation method for the precursor fiber described in the third aspect, the pre-oxidation method comprising the following steps: S1. Under an inert atmosphere, the precursor fiber is subjected to a first heat treatment to obtain a cyclized fiber; S2. Under an oxygen-containing atmosphere, the cyclized fiber is subjected to a second heat treatment.

[0009] The fifth aspect of the present invention provides a pre-oxidized fiber prepared by the pre-oxidation method described in the fourth aspect.

[0010] Through the above technical solution, the present invention has the following beneficial effects:

[0011] By using the composition formulation of the present invention to prepare pre-oxidized fibers, it is possible to ensure that the elongation at break, oxygen index, oxygen content and breaking strength of the pre-oxidized fibers are all at a high level.

[0012] The pre-oxidation method for the precursor fibers prepared by the composition of this invention combines two-step heat treatment, namely cyclization followed by oxidation, which can reduce the heat of reaction, solve the problem of concentrated heat release in fibers during high-temperature and rapid oxidation, and resolve the contradiction between oxygen diffusion, heat release and residence time during pre-oxidation. While significantly shortening the processing time, it ensures that the fiber oxygen content and limiting oxygen index meet the requirements for use, and significantly reduces production costs.

[0013] The pre-oxidized fiber prepared by this invention has an oxygen content of not less than 10%, a fineness of not less than 1.3 dtex, a breaking strength of not less than 2.8 cN / dtex, a breaking elongation of not less than 14%, a limiting oxygen index of not less than 35%, a bulk density of not less than 1.34, and good processability. Attached Figure Description

[0014] Figure 1 These are cross-sectional morphology photographs of the pre-oxidized fibers prepared in Examples 1, 2, 1, and 2, observed using an ultramicrotome and an optical microscope. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] The present invention provides a spinning raw material composition comprising: acrylonitrile, itaconic acid, acrylate compound, alkenyl dicyano compound or alkenyl polycyano compound, initiator and solvent.

[0017] The polycyano compounds described in this invention refer to compounds containing two or more cyano groups.

[0018] By using the composition formulation of the present invention to prepare pre-oxidized fibers, it is possible to ensure that the elongation at break, oxygen index, oxygen content and breaking strength of the pre-oxidized fibers are all at a high level.

[0019] The composition formulation of this invention lacks fumaric acid for intermolecular cyclization and crosslinking, resulting in a product with very low tensile strength. Furthermore, if the formulation does not contain acrylates with large side groups, the core-skin phenomenon will be severe during the rapid oxidation process of this invention, leading to low oxygen content and limiting oxygen index. The formulation of this invention yields a product with suitable elongation at break, oxygen index, and oxygen content, while also exhibiting high tensile strength.

[0020] According to a preferred embodiment of the present invention, the alkenyl-containing dicyano compound or alkenyl-containing polycyano compound has 4-6 carbon atoms. By adopting the aforementioned preferred embodiment, the performance of the prepared product can be further improved.

[0021] According to a preferred embodiment of the present invention, the alkenyl-containing dicyandiamide compound is fumarate. By adopting the aforementioned preferred embodiment, the performance of the product prepared from the composition can be further improved.

[0022] According to a preferred embodiment of the present invention, the acrylate compound is a C4-C8 alkyl methacrylate, preferably a C4-C6 alkyl methacrylate, more preferably isoamyl methacrylate and / or isobutyl methacrylate. By adopting the aforementioned preferred embodiment, the performance of the prepared product can be further improved.

[0023] In this invention, there are no particular requirements for the content of each component in the composition. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the total content of acrylonitrile, itaconic acid, an alkenyl-containing dicyano compound or an alkenyl-containing polycyano compound and an acrylate compound in the composition is 18-20 wt%, and the solvent content is 80-82 wt%. By adopting the aforementioned preferred embodiment, the performance of the prepared product can be further improved.

[0024] According to a preferred embodiment of the present invention, the mass ratio of the alkenyl-containing dicyano compound or the alkenyl-containing polycyano compound to acrylonitrile is 0.3-0.5:100. By adopting the aforementioned preferred embodiment, the performance of the prepared product can be further improved.

[0025] According to a preferred embodiment of the present invention, the mass ratio of itaconic acid to acrylonitrile is 0.3-0.5:100. By adopting the aforementioned preferred embodiment, the performance of the prepared product can be further improved.

[0026] According to a preferred embodiment of the present invention, the mass ratio of acrylate compound to acrylonitrile is 1-4:100; preferably 2-4:100. By adopting the aforementioned preferred embodiment, the performance of the prepared product can be further improved.

[0027] According to a preferred embodiment of the present invention, the mass ratio of initiator to acrylonitrile is 0.1-1.0:100. By adopting the aforementioned preferred embodiment, the performance of the prepared product can be further improved.

[0028] In this invention, the solvent can be a conventional choice in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the solvent is selected from dimethyl sulfoxide and / or dimethylformamide.

[0029] In this invention, the type of initiator can be a conventional choice in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the initiator is selected from azobisisobutyronitrile and / or azobisisoheptanenitrile.

[0030] The present invention provides a method for preparing raw yarn, which uses the aforementioned spinning raw material composition as raw material to obtain raw yarn through wet spinning.

[0031] According to a preferred embodiment of the present invention, the wet spinning includes the following steps:

[0032] a. The spinning raw material composition undergoes a polymerization reaction to obtain a spinning solution;

[0033] b. The spinning solution is spun and solidified to obtain nascent fibers;

[0034] c. Nascent fibers are subjected to hot water stretching;

[0035] In the wet spinning process, the total draw ratio is 6.5-7.5 times. The total draw ratio is the ratio of the final winding speed to the speed of the first roller, i.e., the negative draw during solidification is not taken into account. At this draw ratio, it can be ensured that the raw yarn obtained can be used to prepare pre-oxidized yarn with a high breaking elongation. Moreover, due to the interaction of the formulation of the present invention, the breaking strength of the product will not be low. That is, the method of the present invention can prepare products with both high breaking strength and breaking elongation.

[0036] When the composition of the present invention is used in the preparation of precursor fiber, and the precursor fiber is used in the preparation of pre-oxidized fiber, the role of the alkenyl dicyano compound or the alkenyl polycyano compound such as fumaric acid can carry out intermolecular cyclization reaction, maintain high mechanical properties while significantly reducing heat treatment time, and significantly improve the performance of pre-oxidized fiber when combined with specific drawing conditions.

[0037] It should be noted that steam drafting is not used in the wet spinning process of this invention. The wet spinning process, after hot water drafting, also includes oiling, drying and densification, and heat setting. The total draft ratio of the wet spinning is controlled to be 6.5-7.5 times (excluding the negative drafting in the solidification stage). By adopting the aforementioned preferred scheme, the performance of the prepared product can be further improved.

[0038] In this invention, the polymerization reaction conditions are not particularly required, as long as the materials can be polymerized. According to a preferred embodiment of the invention, the polymerization reaction conditions include: a polymerization temperature of 45-65°C and a polymerization time of 8-12 hours. By adopting the aforementioned preferred scheme, the performance of the prepared product can be further improved.

[0039] In this invention, there is no particular limitation on the total draw ratio of solidification in step b. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the solidification in step b is multi-stage solidification, and the total draw ratio of solidification is 1.2-3.0 times, preferably 2-2.6 times. The total draw ratio of the solidification stage does not include the negative draw ratio of the first solidification bath. By adopting the aforementioned preferred scheme, the performance of the prepared product can be further improved, while reducing production costs.

[0040] In this invention, the solidification method includes three-stage solidification, wherein the first-stage solidification bath concentration is 65-77%, the temperature is 25-50℃, and the negative draw is 30-50%; the second-stage solidification bath concentration is 30-55%, the temperature is 50-70℃, and the draw is 1-1.5 times; and the third-stage solidification bath concentration is 10-25%, the temperature is 70-85℃, and the draw is 1.5-2 times. By adopting the aforementioned preferred scheme, the performance of the prepared product can be further improved.

[0041] In this invention, there is no particular limitation on the hot water stretching ratio in step c. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the total stretching ratio of the hot water stretching in step c is 2-3.5 times, preferably 3-3.5 times. By adopting the aforementioned preferred scheme, the performance of the prepared product can be further improved, while reducing production costs.

[0042] In this invention, the hot water stretching method includes performing 4-6 stages of hot water stretching at a temperature of 80-95℃.

[0043] In this invention, there are certain requirements for the specific feeding method for the preparation of precursor fibers. Due to the competitive polymerization rate of alkenyl dicyano compounds or alkenyl polycyano compounds such as fumaric acid, a stepwise feeding method must be adopted. Therefore, step a includes the following steps: (1) mixing acrylonitrile, itaconic acid, a portion of alkenyl dicyano compounds or alkenyl polycyano compounds, acrylate compounds, initiators, and solvents to initiate polymerization; (2) adding another portion of alkenyl dicyano compounds within a period of 2-5 hours after the start of polymerization. Alternatively, a polycyano compound containing an alkenyl group may be added; preferably, the other portion of the alkenyl-containing dicyano compound or polycyano compound is added in 2-7 portions, with an interval of 0.5-3 hours between each addition; more preferably, the other portion of the alkenyl-containing dicyano compound or polycyano compound is added in 2-4 portions, with an interval of 1-3 hours between each addition; wherein the mass ratio of the portion of the alkenyl-containing dicyano compound or polycyano compound to the other portion of the alkenyl-containing dicyano compound or polycyano compound is 1:1-4. By adopting the aforementioned preferred scheme, the alkenyl-containing dicyano compound or polycyano compound can be more evenly distributed in the polymer molecular chain, thereby improving product performance.

[0044] This invention provides a precursor fiber prepared by the aforementioned method. The precursor fiber of this invention is adaptable to rapid pre-oxidation processes, and is particularly suitable for the pre-oxidation process of this invention.

[0045] This invention provides a pre-oxidation method for the precursor fiber prepared by the aforementioned preparation method, the pre-oxidation method comprising the following steps:

[0046] S1. Under an inert atmosphere, the raw yarn undergoes a first heat treatment to obtain cyclized yarn;

[0047] S2. Under an oxygen-containing atmosphere, the cyclic filament undergoes a second heat treatment.

[0048] The pre-oxidation method for the precursor fibers prepared by the composition of this invention, combined with two-step heat treatment, can promote the oxidation reaction and reduce the heat of reaction, solve the problem of concentrated heat release of fibers during high-temperature and rapid oxidation, and resolve the contradiction between oxygen diffusion, heat release and residence time during pre-oxidation. While significantly shortening the processing time, it ensures that the fiber oxygen content and limiting oxygen index meet the requirements for use, and significantly reduces production costs.

[0049] According to a preferred embodiment of the present invention, the temperature of the first heat treatment is 30-50°C higher than the initial (first temperature zone) temperature of the second heat treatment. By adopting the aforementioned preferred solution, the performance of the pre-oxidized fiber can be further improved, while reducing production costs.

[0050] In this invention, the temperature conditions for the first heat treatment can be selected over a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the first heat treatment include a temperature of 285-300°C.

[0051] In this invention, the time conditions for the first heat treatment can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the first heat treatment include: a time of 1-2 minutes.

[0052] In this invention, the stretching conditions for the first heat treatment can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the first heat treatment include a stretching ratio of 1.08-1.10.

[0053] By employing the aforementioned conditions for the first heat treatment, the performance of the prepared product can be further improved.

[0054] In this invention, the temperature conditions for the second heat treatment can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the second heat treatment include a temperature of 250-280°C.

[0055] In this invention, the time conditions for the second heat treatment can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the second heat treatment include a time of 10-14 minutes.

[0056] In this invention, the range of selectable stretching ratio conditions for the second heat treatment is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the second heat treatment include: a total stretching ratio of 0.9-0.95.

[0057] By employing the aforementioned second heat treatment conditions, the performance of the prepared product can be further improved.

[0058] In this invention, the second heat treatment method can be a conventional choice in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the second heat treatment is divided into 2-6 temperature zones, with the temperature increasing sequentially along the direction of the filament bundle, and the temperature difference between adjacent temperature zones is 5-15°C. By adopting the aforementioned preferred scheme, the performance of the prepared product can be further improved.

[0059] The present invention provides a pre-oxidized fiber prepared by the aforementioned pre-oxidation method.

[0060] This invention, through a specific polymerization formulation, special spinning parameter control, and pre-oxidation heat treatment process, can reduce costs by shortening the heat treatment time while maintaining high tensile strength in the product. The pre-oxidized fiber prepared by this invention has an oxygen content of not less than 10%, a fineness of not less than 1.3 dtex, a tensile strength of not less than 2.8 cN / dtex, a tensile elongation of not less than 14%, a limiting oxygen index of not less than 35%, a bulk density of not less than 1.34, and good processability.

[0061] The present invention will be described in detail below through embodiments.

[0062] Example 1

[0063] (1) Polymerization and Degassing: Acrylonitrile (AN), itaconic acid (IA), a portion of fumaric acid (FN), i-BMA and azobisisobutyronitrile were added to dimethyl sulfoxide (DMSO) to obtain a spinning raw material composition of 100 kg, wherein AN accounted for 18% of the total mass of the system, IA accounted for 0.4% of the mass of AN, FN accounted for 0.1% of the mass of AN, i-BMA accounted for 3% of the mass of AN, and the amount of azobisisobutyronitrile was 0.45% of the mass of AN. The polymerization temperature was 63℃. After 2 hours of polymerization, 0.1% of the mass of AN was added to FN. After another 2 hours of polymerization, 0.1% of the mass of AN was added to FN. After a total of 12 hours of polymerization, residual monomers and bubbles were removed to obtain the spinning solution.

[0064] (2) Spinning: The spinning solution is used to prepare the precursor yarn by wet spinning. Three-stage coagulation is adopted. The first stage coagulation bath concentration is 70%, temperature is 45℃, and negative draw is 30%. The second stage coagulation bath concentration is 50%, temperature is 60℃, and draw is 1.4 times. The third stage coagulation bath concentration is 20%, temperature is 85℃, and draw is 1.6 times. The subsequent five-stage hot water draw is at 95℃, and the total hot water draw ratio is 3.1 times. After oiling, drying and densification, and heat setting, the finished precursor yarn is obtained. The total draw in the spinning stage is 6.9 times.

[0065] (3) The raw yarn was circumcised at 290℃, stretched by 1.1 times, and held for 1.5 minutes. Then it was subjected to continuous oxidation treatment in four temperature zones at 253 / 261 / 270 / 278℃, with a holding time of 2.5 minutes in each zone and stretch ratios of 0.995 / 0.99 / 0.985 / 0.98 respectively. After being impregnated with an antistatic agent and dried, it was wound up to obtain the finished PAN pre-oxidized fiber 1.

[0066] Example 2

[0067] (1) Polymerization and Degassing: Acrylonitrile (AN), itaconic acid (IA), fumaric acid (FN), isoamyl methacrylate (i-PMA), and azobisisobutyronitrile were added to dimethylformamide to obtain a spinning raw material composition of 100 kg. AN accounted for 19% of the total mass of the system, IA accounted for 0.3% of the mass of AN, FN accounted for 0.1% of the mass of AN, i-PMA accounted for 2% of the mass of AN, and azobisisobutyronitrile accounted for 0.45% of the mass of AN. The polymerization temperature was 63℃. 0.1% of the mass of AN and FN were added 2 hours after the start of polymerization. Subsequently, 0.1% of the mass of AN and FN were added every 0.5 hours. That is, 4 additions were made 2 hours after the start of polymerization. After a total of 12 hours of polymerization, the residual monomers and bubbles were removed to obtain the spinning solution.

[0068] (2) Spinning: The spinning solution is used to prepare the precursor yarn by wet spinning. Three-stage coagulation is adopted. The first stage coagulation bath concentration is 70%, temperature is 45℃, and negative draw is 40%. The second stage coagulation bath concentration is 50%, temperature is 60℃, and draw is 1.5 times. The third stage coagulation bath concentration is 20%, temperature is 85℃, and draw is 1.72 times. The subsequent five-stage hot water draw is at 95℃, and the total hot water draw ratio is 2.6 times. After oiling, drying and densification, and heat setting, the finished precursor yarn is obtained. The total draw in the spinning stage is 6.7 times.

[0069] (3) The raw yarn was circumcised at 285℃, stretched by 1.08 times, and held for 2 minutes. Then it was subjected to continuous oxidation treatment in four temperature zones at 255 / 261 / 272 / 279℃, with a holding time of 2.5 minutes in each zone and a stretch ratio of 0.995 / 0.99 / 0.98 / 0.98 respectively. After being impregnated with an antistatic agent and dried, it was wound up to obtain the finished PAN pre-oxidized fiber 2.

[0070] Example 3

[0071] (1) Polymerization and Degassing: Acrylonitrile (AN), itaconic acid (IA), fumaric acid (FN), i-BMA and azobisisobutyronitrile were added to dimethyl sulfoxide (DMSO) to obtain a spinning raw material composition of 100 kg, wherein AN accounted for 18% of the total mass of the system, IA accounted for 0.5% of the mass of AN, FN accounted for 0.1% of the mass of AN, i-BMA accounted for 4% of the mass of AN, and azobisisobutyronitrile accounted for 0.45% of the mass of AN. The polymerization temperature was 63℃. After 2 hours of polymerization (including the 2nd hour), 0.1% of the mass of AN was added every hour for a total of 3 times. After a total of 12 hours of polymerization, the residual monomers and bubbles were removed to obtain the spinning solution.

[0072] (2) Spinning: The spinning solution is used to prepare the precursor yarn by wet spinning. Three-stage coagulation is adopted. The first stage coagulation bath concentration is 70%, temperature is 45℃, and negative draw is 25%. The second stage coagulation bath concentration is 50%, temperature is 60℃, and draw is 1.5 times. The third stage coagulation bath concentration is 20%, temperature is 85℃, and draw is 1.5 times. The subsequent five-stage hot water draw is at 95℃, and the total hot water draw ratio is 3.33 times. After oiling, drying and densification, and heat setting, the finished precursor yarn is obtained. The total draw in the spinning stage is 7.5 times.

[0073] (3) The raw yarn is circumcised at 300℃, stretched by 1.09 times, and held for 1 minute. Then it is subjected to continuous oxidation treatment in four temperature zones at 253 / 261 / 270 / 278℃, with a holding time of 2.5 minutes in each zone and a stretch ratio of 0.995 / 0.99 / 0.985 / 0.98 respectively. After being impregnated with an antistatic agent and dried, it is wound up to obtain the finished PAN pre-oxidized fiber 3.

[0074] Example 4

[0075] Similar to Example 1, except that the mass of i-BMA was adjusted to 6% of the mass of AN, and the mass of acrylonitrile was reduced accordingly to obtain PAN pre-oxidized fiber 4. During the process, it was found that the polymerization conversion rate was reduced in step (1), and cracking was prone to occur during the pre-oxidation process in step (3), which reduced the product yield and quality.

[0076] Example 5

[0077] Same as Example 1, except that i-BMA is replaced with n-BMA to obtain pre-oxidized fiber 5.

[0078] Example 6

[0079] Similar to Example 3, except that the total mass of fumaric acid was adjusted to 0.8% of the mass of AN, and the corresponding mass of acrylonitrile was reduced, that is, FN was divided into 4 equal parts, and 0.2% of the mass of AN was added each time to obtain PAN pre-oxidized fiber 6.

[0080] Example 7

[0081] Similar to Example 1, the difference lies in step (3), where the raw yarn is cyclized at 260°C (due to the low temperature of the first treatment, the cyclization is insufficient, so the starting temperature of the second treatment needs to be lowered and the residence time is increased to ensure stable operation, which increases energy consumption), stretched by 1.06 times, and the residence time is 3 minutes. Then, it undergoes continuous oxidation treatment in four temperature zones at 235 / 250 / 260 / 270°C, with a residence time of 4 minutes in each zone and a stretch ratio of 0.995 / 0.99 / 0.985 / 0.98, respectively, to obtain PAN pre-oxidized fiber 7.

[0082] Example 8

[0083] Similar to Example 1, except that the spinning solution prepared in Example 1 was used to prepare the precursor yarn using a wet spinning process. A three-stage coagulation process was adopted: the first stage coagulation bath concentration was 70%, the temperature was 45°C, and the negative draw ratio was 30%; the second stage coagulation bath concentration was 50%, the temperature was 60°C, and the draw ratio was 1.2 times; the third stage coagulation bath concentration was 20%, the temperature was 85°C, and the draw ratio was 1.4 times; followed by a five-stage hot water draw at 95°C with a hot water draw ratio of 4.1 times. After oiling, drying and densification, it was steam-drawn 2.4 times, and then oiled, dried and densified, and heat-set to obtain the finished precursor yarn. The total draw ratio during the spinning stage was 6.9 times.

[0084] Thus, the finished PAN pre-oxidized fiber 8 is obtained.

[0085] Example 9

[0086] Similar to Example 1, except that in step (3): the raw yarn is circumcised at 285°C, stretched by 1.1 times, and held for 1.5 minutes. Then, it is subjected to continuous oxidation treatment in three temperature zones at 265 / 270 / 278°C, with a holding time of 3.5 minutes in each zone and a stretch ratio of 0.995 / 0.99 / 0.98. After being impregnated with an antistatic agent and dried, it is wound up to obtain the finished PAN pre-oxidized fiber 9.

[0087] Comparative Example 1

[0088] Same as Example 1, except that i-BMA was replaced with an equal amount of acrylonitrile to obtain PAN pre-oxidized fiber 10.

[0089] Comparative Example 2

[0090] Same as Example 1, except that FN is replaced with an equal amount of acrylonitrile to obtain the finished PAN pre-oxidized fiber 11.

[0091] Comparative Example 3

[0092] The precursor fibers prepared in Example 1 were directly fed into an oxidation furnace at 253°C without undergoing cyclization treatment, resulting in large-scale fiber breakage and preventing smooth operation.

[0093] Test case

[0094] The PAN pre-oxidized fibers prepared in the examples and comparative examples were subjected to the following tests according to national standards: fineness, breaking strength, and elongation of the fibers were tested according to GB / T1437-2008; bulk density of the fibers was tested according to GB / T30019-2013; oxygen content of the fibers was determined using an elemental analyzer in oxygen mode; and limiting oxygen index of the fibers was tested according to GB / T5454-1997. All test data are shown in Table 1.

[0095] Table 1

[0096]

[0097] The cross-sectional morphology of the pre-oxidized fibers was observed using an ultramicrotome and an optical microscope. (See images below.) Figure 1 From Table 1 and Figure 1 It can be seen that adding the FN component to the system results in pre-oxidized fibers with better strength. Further addition of methacrylate copolymer components with large-volume side groups to the polymerization system leads to a more moderate core-sheath structure in the pre-oxidized fibers, with higher oxygen content and oxygen index. Controlling the draw ratio during spinning allows the finished PAN pre-oxidized fibers to achieve a breaking elongation of over 14%, while maintaining a breaking strength of around 3 cN / dtex. Without cyclization, direct oxidation at high temperatures results in direct fiber burn-out, making production impossible. In summary, this method significantly shortens the pre-oxidation time and reduces production costs while maintaining a certain oxygen content, a high limiting oxygen index, high strength, and high breaking elongation.

[0098] 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 inventive concept, 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 considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A spinning raw material composition, characterized in that, The composition includes: acrylonitrile, itaconic acid, acrylate compounds, alkenyl-containing dicyano compounds or alkenyl-containing polycyano compounds, an initiator, and a solvent.

2. The spinning raw material composition according to claim 1, wherein, The alkenyl-containing dicyano compound or alkenyl-containing polycyano compound has 4-6 carbon atoms, preferably fumaric acid dicyano compound; and / or The acrylate compound is a C4-C8 alkyl methacrylate, preferably a C4-C6 alkyl methacrylate, and more preferably isoamyl methacrylate and / or isobutyl methacrylate.

3. The spinning raw material composition according to claim 1 or 2, wherein, Based on the total mass of the composition, the composition contains, The total content of acrylonitrile, itaconic acid, alkenyl-containing dicyano compounds or alkenyl-containing polycyano compounds, and acrylate compounds is 18-20 wt%, and the solvent content is 80-82 wt%; and / or The mass ratio of an alkenyl-containing dicyano compound or an alkenyl-containing polycyano compound to acrylonitrile is 0.3-0.5:100; and / or The mass ratio of itaconic acid to acrylonitrile is 0.3-0.5:100; and / or The mass ratio of acrylate compound to acrylonitrile is 1-4:100; preferably 2-4:100; and / or The mass ratio of initiator to acrylonitrile is 0.1-1.0:

100.

4. The spinning raw material composition according to any one of claims 1-3, wherein, The solvent is selected from dimethyl sulfoxide and / or dimethylformamide; and / or The initiator is selected from azobisisobutyronitrile and / or azobisisoheptanenitrile.

5. A method for preparing raw silk, characterized in that, The preparation method uses the spinning raw material composition according to any one of claims 1-4 as raw material, and obtains the precursor yarn through wet spinning. Preferably, The wet spinning process includes the following steps: a. The spinning raw material composition according to any one of claims 1-4 undergoes a polymerization reaction to obtain a spinning solution; b. The spinning solution is spun and solidified to obtain nascent fibers; c. Nascent fibers are subjected to hot water stretching; The total draw ratio during the wet spinning process is 6.5-7.5 times.

6. The preparation method according to claim 5, wherein, The total draw ratio of solidification in step b is 1.2-3.0 times; and / or In step c, the total draw ratio of hot water stretching is 2-3.5 times.

7. The preparation method according to claim 5 or 6, wherein, Step a includes the following steps: (1) Initiate polymerization by mixing acrylonitrile, itaconic acid, a portion of a dicyandiamide compound containing an alkenyl group or a polycyandiamide compound containing an alkenyl group, an acrylate compound, an initiator and a solvent; (2) Add another portion of alkenyl-containing dicyano compound or alkenyl-containing polycyano compound within a time period of 2-5 hours after the start of polymerization; preferably, the other portion of alkenyl-containing dicyano compound or alkenyl-containing polycyano compound is added in 2-7 portions, with an interval of 0.5-3 hours between each addition; more preferably, the other portion of alkenyl-containing dicyano compound or alkenyl-containing polycyano compound is added in 2-4 portions, with an interval of 1-3 hours between each addition; The mass ratio of one portion of the alkenyl-containing dicyandiamide compound or alkenyl-containing polycyandiamide compound to the other portion of the alkenyl-containing dicyandiamide compound or alkenyl-containing polycyandiamide compound is 1:1-4.

8. The precursor fiber prepared by the preparation method according to any one of claims 5-7.

9. The pre-oxidation method for raw fibers according to claim 8, characterized in that, The pre-oxidation method includes the following steps: S1. Under an inert atmosphere, the raw yarn undergoes a first heat treatment to obtain cyclized yarn; S2. The cyclic filaments undergo a second heat treatment under an oxygen-containing atmosphere; Preferably, The temperature of the first heat treatment is 30-50°C higher than the initial temperature of the second heat treatment; and / or The conditions for the first heat treatment include: a temperature of 285-300℃, and / or a time of 1-2 minutes, and / or an elongation of 1.08-1.10; and / or The conditions for the second heat treatment include: a temperature of 250-280°C, and / or a time of 10-14 minutes, and / or a draw ratio of 0.9-0.95; and / or More preferably, The second heat treatment is divided into 2-6 temperature zones, with the temperature increasing sequentially along the direction of the filament bundle, and the temperature difference between adjacent temperature zones is 5-15℃.

10. The pre-oxidized fiber prepared by the pre-oxidation method according to claim 9.

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