Preparation method of flame-retardant polyacrylonitrile fiber and flame-retardant polyacrylonitrile fiber

Abstract

The application belongs to the technical field of preparation of flame-retardant fibers, and discloses a preparation method of flame-retardant polyacrylonitrile fibers and the flame-retardant polyacrylonitrile fibers, the preparation method comprising the following steps: (1) adding a composite flame retardant powder and a polyacrylonitrile powder into dimethylacetamide, grinding and dispersing, and then filtering to obtain a flame-retardant slurry; (2) adding the polyacrylonitrile powder into dimethylacetamide, uniformly mixing, and heating to completely dissolve to obtain a polyacrylonitrile stock solution; (3) preparing a spinning stock solution: uniformly mixing the flame-retardant slurry and the polyacrylonitrile stock solution according to the mass ratio of the composite flame retardant to the polyacrylonitrile being 1:2.3-4.0 to obtain the spinning stock solution; and (4) spinning by using the spinning stock solution to prepare the flame-retardant polyacrylonitrile fibers. The application adds a certain amount of polyacrylonitrile in the flame-retardant slurry, which can more easily uniformly mix with the polyacrylonitrile stock solution, can increase the addition amount of the composite flame retardant in the fibers, and will not obviously affect the mechanical properties of the fibers.

Description

Technical Field

[0001] This invention belongs to the field of functional fiber preparation, specifically, it relates to a method for preparing flame-retardant polyacrylonitrile fiber and the flame-retardant polyacrylonitrile fiber. Background Technology

[0002] Polyacrylonitrile (PAC) fiber has properties very similar to wool, with good elasticity, a fluffy and soft texture, and better warmth retention than wool, earning it the nickname "synthetic wool." Depending on the application, PAC fiber can be spun purely or blended with natural fibers to produce textiles, which are widely used in clothing, architectural decoration, and other fields. However, conventional PAC fiber lacks flame-retardant properties, making its textiles flammable and posing certain safety hazards, thus limiting its application scenarios.

[0003] Introducing flame-retardant components into polyacrylonitrile fibers, thereby imparting flame-retardant properties to the fibers, can solve the aforementioned problems. Existing methods for preparing flame-retardant fibers or textiles can be mainly divided into the following two categories.

[0004] The first category is finishing methods, which involve applying a flame-retardant paste to the finished fibers or fabric through coating, impregnation, or other methods to form a flame-retardant outer layer. However, the bonding strength between the flame-retardant components added using finishing methods and the fibers is insufficient, and they will gradually fall off with prolonged use or repeated washing, resulting in the loss of flame-retardant properties. In addition, the flame-retardant outer layer attached to the outside of the fiber or fabric can also affect the soft and fluffy properties of the fiber.

[0005] The second type is blend spinning, where flame-retardant components are added to the spinning solution to produce flame-retardant fibers with the flame-retardant components dispersed within the fiber matrix. However, most existing flame-retardant components are in powder form. Adding them to the fiber alters its internal structure, thus affecting its mechanical properties. Therefore, this method has limitations on the amount of flame-retardant components added; otherwise, the fiber's mechanical properties may fail to meet requirements.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing flame-retardant polyacrylonitrile fiber using a blending spinning process, which can increase the amount of flame-retardant components added while ensuring the mechanical properties of the fiber.

[0008] Another aspect of the present invention provides a blended modified flame-retardant polyacrylonitrile fiber.

[0009] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows:

[0010] The first aspect of this invention provides a method for preparing flame-retardant polyacrylonitrile fibers, comprising the following steps:

[0011] (1) Add composite flame retardant powder and polyacrylonitrile powder to dimethylacetamide, grind and disperse, and then filter to obtain flame retardant slurry;

[0012] (2) Add polyacrylonitrile powder to dimethylacetamide, mix well, and heat until completely dissolved to obtain polyacrylonitrile stock solution;

[0013] (3) The flame retardant slurry and polyacrylonitrile stock solution are mixed evenly according to the mass ratio of composite flame retardant to polyacrylonitrile of 1:2.3 to 4.0 to obtain spinning stock solution;

[0014] (4) Spinning: The spinning solution is used to spin flame-retardant polyacrylonitrile fiber.

[0015] In this invention, composite flame retardant powder is blended with polyacrylonitrile to form a spinning solution, which is then spun into flame retardant polyacrylonitrile fiber. This allows the composite flame retardant to be firmly bound to the inside of the fiber and will not detach from the fiber during use. As a result, the flame retardant polyacrylonitrile fiber and its textiles can maintain good flame retardant effect after repeated washing.

[0016] In the preparation process, the composite flame retardant powder and a small amount of polyacrylonitrile powder are dispersed together in the solvent dimethylacetamide to form a flame retardant slurry. This slurry is then mixed with a polyacrylonitrile stock solution containing a larger amount of polyacrylonitrile to prepare a spinning stock solution. This process enables uniform mixing of the flame retardant slurry and the polyacrylonitrile stock solution, improving the uniformity of the dispersion of the composite flame retardant in the spinning stock solution. Consequently, flame retardant polyacrylonitrile fibers with the composite flame retardant components uniformly dispersed in the fibers can be obtained.

[0017] Through the above scheme, the mass ratio of composite flame retardant to polyacrylonitrile in the flame-retardant polyacrylonitrile fiber prepared by the present invention is 1:2.3 to 4.0, which is equivalent to the amount of composite flame retardant added to the fiber reaching 20wt% to 30wt%, which can significantly improve the flame retardant performance, while having little impact on the mechanical properties of the fiber.

[0018] In a preferred embodiment, the mass ratio of the composite flame retardant to polyacrylonitrile is 1:2.3 to 3.0, more preferably 1:3.0.

[0019] In a further embodiment, in step (1), the composite flame retardant accounts for 30% to 40% of the mass of the flame retardant slurry, and the polyacrylonitrile accounts for 3% to 9% of the mass of the flame retardant slurry.

[0020] In step (2), the mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution is 20.5% to 25.5%;

[0021] In step (3), the flame retardant slurry is mixed with polyacrylonitrile stock solution at a mass ratio of 1:3 to 10.

[0022] In a preferred embodiment, in step (1), the mass percentage of polyacrylonitrile in the flame retardant slurry is 5% to 9%, more preferably 7% to 9%.

[0023] In this invention, experiments have shown that by controlling the amount of polyacrylonitrile added to the flame-retardant slurry within the above-mentioned range, the composite flame retardant is more evenly dispersed in the prepared spinning solution, and the resulting flame-retardant polyacrylonitrile fiber can achieve a better level in terms of both flame retardant performance and mechanical properties.

[0024] In a further embodiment, in step (1), the rotational viscosity of the flame-retardant slurry at 90°C is 200–1700 mPa·s;

[0025] In step (2), the rotational viscosity of the polyacrylonitrile stock solution at 90°C is 2000-11000 mPa·s.

[0026] In a preferred embodiment, in step (1), the rotational viscosity of the flame-retardant slurry at 90°C is 1000–1700 mPa·s;

[0027] In step (2), the rotational viscosity of the polyacrylonitrile stock solution at 90°C is 6500-7600 mPa·s.

[0028] The viscosity of flame-retardant slurry and polyacrylonitrile stock solution is related to the amount of polyacrylonitrile added, while the amount of composite flame retardant added has a smaller effect on viscosity. In this invention, adding a certain amount of polyacrylonitrile to the flame-retardant slurry can appropriately increase the viscosity of the flame-retardant slurry and reduce the viscosity difference between the flame-retardant slurry and the polyacrylonitrile stock solution.

[0029] Thus, in the subsequent mixing process (3), it is beneficial to improve the mixing uniformity and obtain a spinning solution with more uniform dispersion of polyacrylonitrile and composite flame retardant. This can ensure the uniformity of the flame retardant properties of the fiber on the one hand, and avoid the adverse effects on the mechanical properties caused by the local concentrated distribution of composite flame retardant on the fiber on the other hand.

[0030] In this invention, experiments revealed that, with the same level of composite flame retardant added to the fiber, adding a small amount of polyacrylonitrile powder to the flame retardant slurry during preparation significantly improved the flame retardant properties of the resulting polyacrylonitrile fiber compared to a flame retardant slurry without polyacrylonitrile. This is presumably due to the reduced viscosity difference between the flame retardant slurry and the polyacrylonitrile solution, allowing the composite flame retardant to disperse more evenly when mixed to form the spinning solution, thus enhancing the flame retardant performance.

[0031] Furthermore, when mixing two systems with different viscosities, the smaller the viscosity difference, the lower the torque required during mixing, and consequently, the less wear on the mixing equipment. This invention appropriately increases the viscosity of the flame-retardant slurry by adding a certain amount of polyacrylonitrile, reducing the viscosity difference between the flame-retardant slurry and the polyacrylonitrile stock solution. This helps reduce wear on the mixing equipment used to mix the flame-retardant slurry and the polyacrylonitrile stock solution, thereby extending the service life of the mixing equipment.

[0032] In one specific implementation, in step (3), the flame retardant slurry and polyacrylonitrile stock solution are mixed and dispersed evenly through a static mixer to obtain the spinning stock solution for later use.

[0033] In a further embodiment, in steps (1) and (2), the temperature of dimethylacetamide is 0–10°C, preferably 0–4°C.

[0034] In the above scheme, polyacrylonitrile powder is added to dimethylacetamide (DMAC) at 0–10°C. Within this temperature range, the solubility of polyacrylonitrile is low, and it exists in DMAC as a solid powder. This weakens the interparticle interaction forces and reduces the likelihood of agglomeration, thus improving the uniformity of the mixture. Furthermore, at low temperatures, the viscosity of DMAC is relatively low, which further facilitates the uniform dispersion of the composite flame retardant powder and the polyacrylonitrile powder.

[0035] Specifically, in step (1), composite flame retardant powder and polyacrylonitrile powder are added to the low-temperature DMAC at 0-10°C. The two powders are not prone to agglomeration and can be uniformly mixed and dispersed in the solvent. In step (2), the polyacrylonitrile powder is added to the low-temperature DMAC for mixing, which can improve the mixing uniformity. As a result, in the subsequent heating process to prepare polyacrylonitrile stock solution, the polyacrylonitrile can be more fully dissolved.

[0036] In a further embodiment, in step (1), the composite flame retardant includes a brominated flame retardant and antimony trioxide; wherein the mass ratio of the brominated flame retardant to antimony trioxide is 1.8 to 3.5:1, preferably 2.3 to 3.0:1;

[0037] Preferably, the brominated flame retardant includes one or more of tetrabromobisphenol A-bis(2,3-dibromopropyl ether), decabromodiphenyl ethane, brominated polystyrene, ethylene bis(tetrabromophthalimide), pentabromobenzyl polyacrylate, and bromotriazine.

[0038] In the above scheme, the composite flame retardant uses an environmentally friendly brominated flame retardant combined with antimony trioxide, resulting in flame-retardant polyacrylonitrile fibers with low toxicity. Tests showed that controlling the ratio of the two to antimony trioxide at 1.8–3.5:1 further improved the flame-retardant properties of the fibers.

[0039] Among numerous brominated flame retardants with different compositions, experiments have shown that selecting one or more of tetrabromobisphenol A-bis(2,3-dibromopropyl ether), decabromodiphenyl ethane, brominated polystyrene, ethylene bis(tetrabromophthalimide), pentabromobenzyl polyacrylate, and bromotriazine, compared with other flame retardants, results in a smaller impact on fiber mechanical properties at the same level of flame retardant addition. It is speculated that specific groups in these components can form a certain binding interaction with polyacrylonitrile, thereby reducing the damage to the internal structure of the fiber caused by the addition of the flame retardant.

[0040] In a further step, in step (1), zirconia beads with a diameter of 0.4 to 2.0 mm are used for grinding in a sand mill;

[0041] Preferably, the grinding time is 2 to 8 hours.

[0042] In a further embodiment, in step (1), the filtration accuracy is 5 to 20 μm, preferably 5 to 10 μm.

[0043] In one specific implementation, the ground slurry is filtered using a filter cloth with a pore size of 5–20 μm to obtain a flame-retardant slurry for later use.

[0044] In a further embodiment, in step (2), the heating temperature is 85-95℃, preferably 90-95℃.

[0045] And / or, the molecular weight of polyacrylonitrile is 40,000 to 60,000.

[0046] In one specific implementation, in step (2), polyacrylonitrile powder is added to DMAC at 0-10°C, mixed evenly, and then heated to 85-95°C through a heat exchanger to completely dissolve the polyacrylonitrile.

[0047] As a specific implementation method, the flame retardant slurry obtained in step (1) is heated to 85-95°C by a heat exchanger and then mixed with polyacrylonitrile stock solution to form spinning stock solution.

[0048] In this invention, the flame-retardant slurry and polyacrylonitrile stock solution are mixed at a mass ratio of 1:3 to 10, with a relatively large amount of flame-retardant slurry added. Preheating the flame-retardant slurry to a temperature range close to that of the polyacrylonitrile stock solution before mixing avoids affecting the mixing effect and prevents the temperature of the resulting spinning solution from being too low.

[0049] In a further embodiment, in step (4), the temperature of the spinning solution is 50-90℃, the temperature of the coagulation bath is 40-60℃, the mass concentration of the coagulation bath is 40%-60%, the water washing temperature is 90-99℃, the spinning speed is 20-100m / min, and the total draw ratio is 5-8 times.

[0050] In one specific implementation, the coagulant in the coagulation bath is DMAC.

[0051] As a more specific approach, the spinning solution is heated to 50–90°C, spun out through a spinneret, and then solidified in a coagulation bath. After washing and drying, it is finally wound into a cylinder at a speed of 20–100 m / min to produce flame-retardant acrylic fibers.

[0052] In a more detailed scheme, after the spinning solution is solidified in the coagulation bath, it undergoes two water washing and stretching processes; wherein, the temperature of the first water washing is 98℃ and the stretching ratio is 2.5 to 3.5 times; the temperature of the second water washing is 98℃ and the stretching ratio is 1.8 to 2.3 times, preferably 2.0 to 2.3 times.

[0053] After the two washing and drawing processes described above, the yarn enters the drying process at a temperature of 140–150°C. During the drying process, three drawing processes are performed, with each drawing ratio controlled between 1.08 and 1.12 times. In one specific embodiment, the yarn bundle is sequentially dried through four drying rollers at a temperature controlled at 140–150°C. A drawing process is performed between each pair of adjacent drying rollers, and the single drawing ratio is controlled between 1.08 and 1.12 times by adjusting the rotational linear speed of the adjacent drying rollers.

[0054] In a preferred embodiment, the total draw ratio is 7 times, wherein the first wash draw ratio is 2.6 times, the second wash draw ratio is 2.1 times, and the draw ratios of the three washes during the drying process are 1.08 times, 1.08 times, and 1.10 times, respectively.

[0055] In another preferred embodiment, the total stretching ratio is 8 times, wherein the first wash stretches 2.7 times, the second wash stretches 2.7 times, and the stretching ratios of the three washes during the drying process are 1.10 times, 1.10 times, and 1.12 times, respectively.

[0056] In this invention, experiments have shown that achieving a higher draw ratio through multiple draw steps, especially further draw during the drying process, such as draw between drying rollers, can further improve the breaking strength of the resulting fibers compared to a single draw step.

[0057] A second aspect of the present invention provides a flame-retardant polyacrylonitrile fiber, comprising a polyacrylonitrile fiber matrix and a composite flame retardant doped in the polyacrylonitrile fiber matrix; the composite flame retardant comprises a brominated flame retardant and antimony trioxide, and the composite flame retardant accounts for 20% to 30% of the mass of the flame-retardant polyacrylonitrile fiber.

[0058] Preferably, the flame-retardant polyacrylonitrile fiber is prepared by the method for preparing flame-retardant polyacrylonitrile fiber provided in the first aspect above;

[0059] Preferably, the flame-retardant polyacrylonitrile fiber has a breaking strength of 2.0 to 3.2 cN / dtex and a limiting oxygen index of 26.5 to 32.0.

[0060] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0061] 1. When the composite flame retardant is added to the spinning solution and blended with polyacrylonitrile for spinning, the composite flame retardant component in the resulting flame-retardant polyacrylonitrile fiber will not separate with use, ensuring the long-lasting effectiveness of the flame retardant performance, and it can be repeatedly washed without losing its effectiveness.

[0062] 2. The addition of composite flame retardant is higher than that of existing technologies, which can improve flame retardant performance. The limiting oxygen index can reach 26.5-32.0, meeting the requirements of limiting oxygen index in application fields such as curtains, furniture and decorative fabrics. At the same time, it does not significantly affect the mechanical properties of the fiber. The fiber breaking strength can reach 2.0-3.2 cN / dtex. Therefore, the addition of composite flame retardant will not limit the application fields of the fiber. The resulting flame-retardant polyacrylonitrile fiber can be used to produce flame-retardant fabrics for use in building decoration, fireproof clothing and other fields, meeting the application requirements.

[0063] 3. The obtained flame-retardant acrylic fiber has the advantages of non-melting and low toxicity, and has low production cost, short production process and simple technology.

[0064] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0065] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings:

[0066] Figure 1 This is a process flow diagram of the flame-retardant polyacrylonitrile fiber preparation method in an embodiment of the present invention;

[0067] Figure 2 This is a schematic diagram of the structure of the flame-retardant polyacrylonitrile fiber spinning solution production system in an embodiment of the present invention.

[0068] In the diagram: 1. First mixing tank; 2. Second mixing tank; 3. Slurry transfer pump; 4. First filter; 5. First sand mill; 6. Second sand mill; 7. Slurry heat exchanger; 8. Slurry flow meter; 9. Static mixer; 10. First circulating pump; 11. Second circulating pump; 12. Mixing tank; 121. Jacket; 13. Slurry tank; 14. Slurry transfer pump; 15. Raw material heat exchanger; 16. Second filter; 17. Degassing tower; 18. Adhesive supply pump; 19. Raw material storage tank; 20. Raw material transfer pump; 21. 31. Raw material flow meter; 32. Solvent feed valve; 33. PAN feed valve; 34. Slurry discharge valve; 35. First circulation control valve; 36. First discharge control valve; 37. Second circulation control valve; 48. Slurry conveying pipeline; 49. Adhesive supply pipeline; 40. Raw material conveying pipeline; 41. First discharge pipeline; 42. First circulation pipeline; 43. Second discharge pipeline; 44. Second circulation pipeline; 45. Slurry conveying pipeline; 46. First feed pipe; 57. Second feed pipe.

[0069] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0071] In the description of this invention, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0072] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0073] like Figure 1As shown, an embodiment of the present invention provides a method for preparing flame-retardant polyacrylonitrile fiber, specifically including the following steps:

[0074] (1) Preparation of flame retardant slurry: Add composite flame retardant powder and polyacrylonitrile powder to DMAC at 0-10℃, grind in a sand mill with zirconia beads with a diameter of 0.4-2.0 mm for 2-8 hours, and filter with a filter cloth with a pore size of 5-20 μm to obtain flame retardant slurry; wherein, the mass ratio of composite flame retardant in the flame retardant slurry is 30%-40%, the mass ratio of polyacrylonitrile in the flame retardant slurry is 3%-9%, and the rotational viscosity of the flame retardant slurry at 90℃ is 200-1700 mpa.s;

[0075] (2) Preparation of polyacrylonitrile stock solution: Add polyacrylonitrile powder to DMAC at 0-10℃, mix evenly, and heat to 85-95℃ through a heat exchanger to completely dissolve the polyacrylonitrile to obtain polyacrylonitrile stock solution; wherein, the mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution is 20.5%-25.5%, and the rotational viscosity of the polyacrylonitrile stock solution at 90℃ is 2000-11000 mPa·s;

[0076] (3) Preparation of spinning solution: The flame retardant slurry and polyacrylonitrile stock solution are fed into a static mixer and mixed and dispersed evenly at a mass ratio of 1:3 to 10 to obtain the spinning solution; wherein, the mass ratio of composite flame retardant to polyacrylonitrile in the spinning solution is 1:2.3 to 4.0.

[0077] (4) Spinning: The spinning solution is used to spin flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 50-90℃, the temperature of the coagulation bath is 40-60℃, the coagulant in the coagulation bath is DMAC with a mass concentration of 40%-60%, the water washing temperature is 90-99℃, the spinning speed is 20-100m / min, and the draw ratio is 5-8 times.

[0078] It should be noted that in this invention, steps (1) and (2) above are not necessarily performed sequentially. They can be performed simultaneously, or step (2) can be performed first and then step (1).

[0079] To obtain spinning solution from production raw materials, the embodiments of the present invention employ the following methods: Figure 2 The flame-retardant polyacrylonitrile fiber spinning solution production system shown is used to prepare the spinning solution, that is, the production system is used to complete steps (1) to (3) in the above preparation method. The obtained spinning solution is then transported to conventional polyacrylonitrile spinning equipment to produce flame-retardant polyacrylonitrile fibers.

[0080] Specifically, the production system includes a flame-retardant slurry preparation unit, a polyacrylonitrile stock solution preparation unit, and a mixing unit.

[0081] In this process, composite flame retardant powder and solvent DMAC are added to the flame retardant slurry preparation unit, along with a certain amount of polyacrylonitrile powder. In the flame retardant slurry preparation unit, the composite flame retardant powder, polyacrylonitrile powder, and solvent are thoroughly mixed to form a flame retardant slurry. Solvent DMAC and polyacrylonitrile powder are then added to the polyacrylonitrile stock solution preparation unit, where they are thoroughly mixed to dissolve the polyacrylonitrile powder and form a polyacrylonitrile stock solution. The mixing unit is connected to both the flame retardant slurry preparation unit and the polyacrylonitrile stock solution preparation unit. The flame retardant slurry and polyacrylonitrile stock solution are thoroughly mixed in the mixing unit to obtain a spinning solution suitable for spinning.

[0082] In one specific embodiment, the flame-retardant slurry preparation unit has at least two dispersing devices, each of which is connected to the mixing unit.

[0083] The process of thoroughly mixing and dispersing composite flame retardant powder, polyacrylonitrile powder, and solvent to prepare a flame retardant slurry is usually discontinuous. That is, under normal circumstances, composite flame retardant powder, polyacrylonitrile powder, and solvent need to be added to the dispersion device in a certain proportion, then mixed and dispersed for a certain period of time before the prepared flame retardant slurry is discharged.

[0084] The operation of the aforementioned dispersion device can be defined as two stages: a preparation stage and a discharge stage. In the preparation stage, the composite flame retardant powder, polyacrylonitrile powder, and solvent are thoroughly mixed and dispersed in the dispersion device to form a flame-retardant slurry. In the discharge stage, the prepared flame-retardant slurry is discharged from the dispersion device and transported to the mixing unit.

[0085] By setting up two or more dispersing devices, during the operation of the production system, some dispersing devices can be in the preparation stage, preparing the flame-retardant slurry, while others are in the discharging stage, supplying the prepared flame-retardant slurry to the mixing unit. Thus, from an overall perspective, the flame-retardant slurry preparation unit can continuously supply flame-retardant slurry to the mixing unit, thereby achieving continuous production of spinning solution and improving production efficiency. This avoids the problem of the spinning solution production process being interrupted due to a lack of flame-retardant slurry being supplied to the mixing unit during the preparation process.

[0086] In a further embodiment, the flame-retardant slurry preparation unit is equipped with a valve assembly for controlling the connection between each dispersing device and the mixing unit. By setting the valve assembly, the dispersing device in the discharge stage can be connected to the mixing unit, while the connection between the dispersing device in the preparation stage and the mixing unit can be cut off, thus preventing insufficiently mixed and dispersed materials from entering the mixing unit.

[0087] In one specific implementation, the number of valve assemblies is the same as the number of dispersing devices, and the valve assemblies and dispersing devices are arranged in a one-to-one correspondence. Each valve assembly is used to control the on / off connection between the corresponding dispersing device and the mixing unit.

[0088] More specifically, each valve assembly independently controls the on / off connection between its corresponding dispersing device and the mixing unit.

[0089] In one specific embodiment, two dispersing devices are provided, including a first dispersing device and a second dispersing device. Two sets of valve assemblies are also provided, namely a first valve assembly and a second valve assembly. The first valve assembly is used to control whether the first dispersing device is connected to the mixing unit, and the second valve assembly is used to control whether the second dispersing device is connected to the mixing unit.

[0090] With the above structure, the production system can operate with the first and second dispersing devices alternating in the preparation of flame-retardant slurry. For example, when the first dispersing device is in the preparation stage, the second dispersing device is in the discharge stage. The second valve assembly controls its connection with the mixing unit, conveying the prepared flame-retardant slurry to the mixing unit. After the conveying is completed, the first dispersing device switches to the discharge stage, and the first valve assembly controls its connection with the mixing unit, conveying the flame-retardant slurry to the mixing unit. Simultaneously, the second dispersing device switches to the preparation stage, and the second valve assembly cuts off its connection with the mixing unit. This allows the second dispersing device to continue preparing flame-retardant slurry while the first dispersing device is conveying it to the mixing unit. At the mixing unit, the flame-retardant slurry can be continuously and uninterruptedly introduced, achieving continuous production of the spinning solution and improving production efficiency.

[0091] In a further embodiment, the specific structure of the dispersion device is described using the first dispersion device as an example. The first dispersion device includes a first stirring tank 1, a first sand mill 5, and a first circulating pump 10. The first sand mill 5 contains zirconium oxide beads with a diameter of 0.4 to 2.0 mm.

[0092] In this process, composite flame retardant powder, polyacrylonitrile powder, and solvent are added to the first mixing tank 1 and mixed. A first sand mill 5 is connected to the first mixing tank 1 via a first circulation pipeline 45, and a first circulation pump 10 is installed on the first circulation pipeline 45. The first circulation pump 10 drives the material to circulate along the first circulation pipeline 45 between the first mixing tank 1 and the first sand mill 5. As the material passes through the first sand mill 5, it is thoroughly ground and dispersed using zirconia beads, achieving a thorough and uniform dispersion of the composite flame retardant powder and polyacrylonitrile powder in the solvent, forming a flame-retardant slurry.

[0093] As a specific structure, the discharge port of the first mixing tank 1 is connected to a three-way structure. One outlet of the three-way structure is connected to the first circulation pipeline 45, and the other outlet is connected to the first discharge pipeline 44. The prepared flame-retardant slurry can be transported to the mixing unit along the first discharge pipeline 44.

[0094] The first valve assembly controls one of the first circulation pipeline 45 and the first discharge pipeline 44 to be connected to the discharge port of the first mixing tank 1. Specifically, when the first dispersion device is in the preparation stage, the first valve assembly controls the first circulation pipeline 45 to be connected to the discharge port of the first mixing tank 1, and at the same time, the first circulation pump 10 operates, driving the material to circulate through the first sand mill 5 to produce a flame-retardant slurry. When the first dispersion device is in the discharge stage, the first valve assembly controls the first discharge pipeline 44 to be connected to the discharge port of the first mixing tank 1, and the first circulation pump 10 is turned off, so that the prepared flame-retardant slurry can be discharged from the first mixing tank 1 and transported to the mixing unit along the first discharge pipeline 44.

[0095] In one specific embodiment, the first valve assembly includes a first three-way switching valve disposed at the aforementioned three-way structure position. The switching action of the first three-way switching valve can control the first circulation pipeline and the first discharge pipeline to be connected to the discharge port of the first mixing tank.

[0096] As another specific implementation method, such as Figure 2 As shown, the first valve assembly includes a first circulation control valve 34 and a first discharge control valve 35. The first circulation control valve 34 is located on the first circulation pipeline 45, and the first discharge control valve 35 is located on the first discharge pipeline 44. When the first dispersing device is in the preparation stage, the first circulation control valve 34 is open, the first circulation pump 10 operates, and the first discharge control valve 35 is closed. When the first dispersing device is in the discharge stage, the first circulation control valve 34 is closed, the first circulation pump 10 does not operate, and the first discharge control valve 35 is open.

[0097] Similar to the first dispersion device, the second dispersion device includes a second mixing tank 2, a second sand mill 6, and a second circulation pump 11. The second sand mill 6 contains zirconia beads with a diameter of 0.4–2.0 mm. The second sand mill 6 and the second circulation pump 11 are respectively installed on the second circulation pipeline 47. The outlet of the second mixing tank 2 is connected to the second circulation pipeline 47 and the second discharge pipeline 46 via a three-way connection. The second discharge pipeline 46 is connected to the mixing unit.

[0098] In one specific embodiment, the second valve assembly includes a second three-way switching valve located at the outlet of the second mixing tank, which controls one of the second circulation pipeline and the second discharge pipeline to be connected to the outlet of the second mixing tank through its switching action.

[0099] As another specific implementation method, such as Figure 2 As shown, the second valve assembly includes a second circulation control valve 36 and a second discharge control valve 37. The second circulation control valve 36 is located on the second circulation pipeline 47, and the second discharge control valve 37 is located on the second discharge pipeline 46. When the second dispersing device is in the preparation stage, the second circulation control valve 36 is open, the second circulation pump 11 operates, and the second discharge control valve 37 is closed. When the second dispersing device is in the discharge stage, the second circulation control valve 36 is closed, the second circulation pump 11 does not operate, and the second discharge control valve 37 is open.

[0100] In a further embodiment, the flame-retardant slurry preparation unit is equipped with a slurry delivery pump 3. The first mixing tank 1 and the second mixing tank 2 are both connected to the slurry delivery pump 3. The flame-retardant slurry prepared in the first mixing tank 1 and the second mixing tank 2 is delivered to the mixing unit by the driving force provided by the slurry delivery pump 3.

[0101] Specifically, the first discharge pipeline 44 and the second discharge pipeline 46 are respectively connected to the slurry conveying pump 3, and the outlet end of the slurry conveying pump 3 is connected to the mixing unit through the slurry conveying pipeline 48. When the slurry conveying pump 3 is running, it draws flame-retardant slurry from the first mixing tank 1 or the second mixing tank 2 and conveys it to the mixing unit along the slurry conveying pipeline 48.

[0102] In one specific embodiment, the mixing unit includes a static mixer 9, in which flame-retardant slurry and polyacrylonitrile stock solution are mixed evenly to form a spinning stock solution that can be used to produce flame-retardant polyacrylonitrile fibers.

[0103] In a further embodiment, a first filter 4 is provided on the slurry conveying pipeline 48. The flame-retardant slurry prepared by the dispersion device is first filtered through the first filter 4 and then enters the static mixer 9 to be mixed with the polyacrylonitrile stock solution.

[0104] The first filter 4 has a filtration accuracy of 5-20μm. By setting the first filter 4, large particles agglomerated in the flame retardant slurry can be filtered out, thus avoiding affecting the uniformity of the dispersion of the composite flame retardant powder in the spinning solution.

[0105] Furthermore, a heating device is also provided on the slurry conveying pipeline 48. The heating device is located downstream of the first filter 4 and can heat the filtered flame-retardant slurry.

[0106] After the flame-retardant slurry is heated to a certain temperature, it enters the static mixer 9 to mix with the polyacrylonitrile stock solution. On the one hand, the heated flame-retardant slurry and the polyacrylonitrile stock solution are closer in temperature, which is beneficial to improving the mixing effect. On the other hand, the spinning solution needs to reach a certain temperature range when used for spinning. Heating the flame-retardant slurry can prevent the temperature of the mixed spinning solution from being too low, thereby shortening the heating time of the spinning solution in subsequent spinning processes, and even allowing spinning to proceed directly without additional heating, thus improving production efficiency. The heating device is located downstream of the first filter 4 to prevent large particles from clogging the heating device.

[0107] In one specific implementation, the heating device is a slurry heat exchanger 7, which uses high-temperature steam to exchange heat with the relatively low-temperature flame-retardant slurry to achieve the heating purpose.

[0108] In a further embodiment, the polyacrylonitrile stock solution preparation unit includes a stock solution preparation device, a stock solution storage tank 19, and a stock solution transfer pump 20. Polyacrylonitrile powder and DMAC solvent at a temperature of 0–10°C are added to the stock solution preparation device, where they are mixed and heated to dissolve the polyacrylonitrile, thus preparing a polyacrylonitrile stock solution. The stock solution storage tank 19 is connected to the stock solution preparation device and is used to collect the prepared polyacrylonitrile stock solution. The stock solution transfer pump 20 is connected to the outlet of the stock solution storage tank 19 and is used to provide driving force to transport the polyacrylonitrile stock solution in the stock solution storage tank 19 to the static mixer 9 of the mixing unit.

[0109] As a specific structure, the outlet of the raw material storage tank 19 is connected to the raw material delivery pipeline 43, and the other end of the raw material delivery pipeline 43 is connected to the static mixer 9. The raw material delivery pump 20 is installed on the raw material delivery pipeline 43. When the raw material delivery pump 20 is running, it draws polyacrylonitrile raw material from the raw material storage tank 19 and delivers it to the static mixer 9 along the raw material delivery pipeline 43.

[0110] Using the above scheme, the polyacrylonitrile stock solution prepared by the stock solution preparation device is temporarily stored in the stock solution storage tank 19, and the stock solution transfer pump 20 directly draws the polyacrylonitrile stock solution from the stock solution storage tank 19 and delivers it to the static mixer 9. In this way, the process of preparing polyacrylonitrile stock solution by the stock solution preparation device can be a discontinuous production process, but the polyacrylonitrile stock solution can still be continuously delivered from the stock solution storage tank 19 to the static mixer 9, so as to achieve the purpose of continuous production of spinning stock solution.

[0111] In one specific embodiment, the stock solution preparation device includes a mixing tank 12, a slurry tank 13, and a degassing tower 17 arranged sequentially.

[0112] The mixing tank 12 is connected to a first feed pipe 49 and a second feed pipe 50. The first feed pipe 49 is equipped with a solvent feed valve 31, and the second feed pipe 50 is equipped with a PAN feed valve 32. Low-temperature DMAC and polyacrylonitrile are injected into the mixing tank 12 through the first feed pipe 49 and the second feed pipe 50, respectively, for stirring and mixing. After the polyacrylonitrile is fully dispersed, it is discharged through the outlet at the bottom of the mixing tank 12 and collected in the slurry tank 13.

[0113] The slurry tank 13 is connected to a slurry conveying pipeline 41, and a slurry conveying pump 14 is installed on the slurry conveying pipeline 41 to convey the polyacrylonitrile slurry collected in the slurry tank 13 to the downstream device.

[0114] Specifically, on the slurry conveying pipeline 41, downstream of the slurry conveying pump 14, a raw material heat exchanger 15 and a second filter 16 are sequentially installed. Steam is introduced into the raw material heat exchanger 15 to exchange heat with the passing polyacrylonitrile slurry, thereby heating the slurry and ensuring that the polyacrylonitrile is fully dissolved to form a polyacrylonitrile solution. The heated polyacrylonitrile solution then passes through the second filter 16, which removes undissolved large particles, preventing them from affecting the quality of the spinning solution.

[0115] The end of the slurry conveying pipeline 41 is connected to the degassing tower 17, which transports the polyacrylonitrile solution to the degassing tower 17 for degassing treatment. A vacuum system is connected to the top of the degassing tower 17, creating a negative pressure environment inside to achieve degassing treatment of the polyacrylonitrile solution. The outlet at the bottom of the degassing tower 17 is connected to the glue supply pipeline 42, the other end of which is connected to the raw material storage tank 19. A glue supply pump 18 is installed on the glue supply pipeline 42, which delivers the degassed polyacrylonitrile raw material into the raw material storage tank 19 for storage.

[0116] In the above scheme, the mixing and dissolution process of polyacrylonitrile and solvent can be discontinuous. Specifically, the discharge port at the bottom of the mixing tank 12 is connected to a slurry discharge valve 33. Initially, the slurry discharge valve 33 is closed, while the solvent inlet valve 31 and the PAN inlet valve 32 are opened respectively. Polyacrylonitrile and solvent are injected according to the ratio, and then the solvent inlet valve 31 and the PAN inlet valve 32 are closed, and stirring is started for mixing. The mixing tank 12 has a jacket 121 on the outside. By introducing warm water into the jacket 121, the material inside the mixing tank 12 is initially heated, and the polyacrylonitrile is dispersed and at least partially dissolved by stirring. After the polyacrylonitrile is fully dispersed, the slurry discharge valve 33 is opened, and the polyacrylonitrile slurry is injected into the slurry tank 13. After the polyacrylonitrile slurry is completely discharged, the slurry discharge valve 33 is closed, and the solvent inlet valve 31 and the PAN inlet valve 32 are reopened, so that polyacrylonitrile and solvent can be injected again for mixing and dispersion.

[0117] By collecting polyacrylonitrile slurry in slurry tank 13, polyacrylonitrile slurry can be continuously delivered to raw liquid heat exchanger 15 via slurry transfer pump 14, thereby allowing the polyacrylonitrile solution to be degassed to continuously enter degassing tower 17.

[0118] In a further embodiment, a slurry flow meter 8 is installed on the slurry conveying pipeline 48, and a raw liquid flow meter 21 is installed on the raw liquid conveying pipeline 43. Both the slurry flow meter 8 and the raw liquid flow meter 21 can be mass flow meters.

[0119] By setting up a slurry flow meter 8 and a raw liquid flow meter 21, the flow rates of flame retardant slurry and polyacrylonitrile raw liquid in the static mixer 9 of the mixing unit can be monitored in real time. This allows operators to understand the current mixing ratio of flame retardant slurry and polyacrylonitrile raw liquid and make timely adjustments when the mixing ratio deviates from the required ratio.

[0120] Furthermore, the slurry delivery pump 3 and the raw liquid delivery pump 20 are metering pumps, and the flow rates of the flame-retardant slurry and polyacrylonitrile raw liquid to the static mixer 9 can be adjusted by regulating the slurry delivery pump 3 and the raw liquid delivery pump 20, which facilitates control.

[0121] As a preferred embodiment, the slurry flow meter 8, the raw liquid flow meter 21, the slurry delivery pump 3, and the raw liquid delivery pump 20 are electrically connected to the controller of the production system. The controller can acquire the real-time monitoring results of the flow rates from the slurry flow meter 8 and the raw liquid flow meter 21, and automatically adjust the slurry delivery pump 3 and the raw liquid delivery pump 20 based on the real-time flow rates of the flame-retardant slurry and the polyacrylonitrile raw liquid, ensuring that the mixing ratio of the flame-retardant slurry and the polyacrylonitrile raw liquid meets the required ratio. This system allows for autonomous control and adjustment without the need for operator intervention, making it more intelligent.

[0122] In an embodiment of the present invention, the process of the production system producing spinning solution is as follows.

[0123] In the polymerization solution preparation unit, polyacrylonitrile powder and DMAC at 0-10°C are added to mixing tank 12, stirred and heated to fully disperse the polyacrylonitrile, and then the slurry discharge valve 33 is opened to discharge the polyacrylonitrile solution into slurry tank 13. After the slurry discharge valve 33 is closed, polyacrylonitrile powder and DMAC can be added to mixing tank 12 again.

[0124] The slurry transfer pump 14 operates, conveying the polyacrylonitrile slurry in the slurry tank 13 along the slurry transfer pipeline 41. After passing through the raw material heat exchanger 15, the slurry is heated to 85-95°C to fully dissolve the polyacrylonitrile. Then, it passes through the second filter 16 to remove undissolved large particles before entering the degassing tower 17 for degassing. The glue supply pump 18 operates, sending the degassed polyacrylonitrile raw material to the raw material storage tank 19. The raw material transfer pump 20 operates continuously during the operation of the production system, continuously conveying the polyacrylonitrile raw material from the raw material storage tank 19 to the static mixer 9.

[0125] In the flame-retardant slurry preparation unit, composite flame-retardant powder, polyacrylonitrile powder, and DMAC are added to the first mixing tank 1 and the second mixing tank 2 in a certain proportion, and the two tanks alternately stir and discharge the materials. Specifically, when the first dispersion device is in the preparation stage, the first circulation control valve 34 is open, the first discharge control valve 35 is closed, and the first circulation pump 10 is started to circulate the material between the first mixing tank 1 and the first sand mill 5. At the same time, when the second dispersion device is in the discharge stage, the second circulation control valve 36 is closed, the second circulation pump 11 is not running, and the second discharge control valve 37 is open to discharge the prepared flame-retardant slurry from the second mixing tank 2.

[0126] After a period of time, the first dispersion unit switches to the discharge stage, while the second dispersion unit switches to the preparation stage. Specifically, the second discharge control valve 37 closes, new material is added to the second mixing tank 2, the second circulation control valve 36 opens, and the second circulation pump 11 starts, driving the material to circulate between the second mixing tank 2 and the second sand mill 6. At the same time, the first circulation control valve 34 closes, the first circulation pump 10 stops running, and the first discharge control valve 35 opens, discharging the flame-retardant slurry from the first mixing tank 1.

[0127] During the above process, the slurry delivery pump 3 operates continuously, continuously conveying the flame-retardant slurry discharged from the first mixing tank 1 or the second mixing tank 2 to the static mixer 9. After being pumped out by the slurry delivery pump 3, the flame-retardant slurry flows along the slurry delivery pipeline 48, first passing through the first filter 4 to remove large agglomerated particles, then passing through the slurry heat exchanger 7 to be heated to 85-95°C, and finally entering the static mixer 9, where it is fully mixed with the polyacrylonitrile stock solution that is also conveyed to the static mixer 9, forming a spinning stock solution that can be used to prepare flame-retardant polyacrylonitrile fibers.

[0128] The following are specific examples of preparing spinning solution using the above-described production system and then producing flame-retardant polyacrylonitrile fibers.

[0129] Example 1

[0130] This embodiment uses the following preparation method to prepare flame-retardant polyacrylonitrile fibers, specifically including the following steps:

[0131] (1) Preparation of flame retardant slurry: Composite flame retardant powder and polyacrylonitrile powder were added to DMAC at 0℃, and the mixture was ground for 4 hours in a sand mill using zirconia beads with a diameter of 0.6-0.8 mm. The mixture was then filtered using a filter cloth with a pore size of 5 μm to obtain the flame retardant slurry. The composite flame retardant accounted for 35% of the mass of the flame retardant slurry, and the polyacrylonitrile accounted for 5% of the mass of the flame retardant slurry. The rotational viscosity of the flame retardant slurry at 90℃ was 660 mPa·s. The composite flame retardant included brominated polystyrene and antimony trioxide in a mass ratio of 3:1. The molecular weight of the polyacrylonitrile was 48,000.

[0132] (2) Preparation of polyacrylonitrile stock solution: Polyacrylonitrile powder was added to DMAC at 4°C and mixed evenly. The mixture was then heated to 90°C through a heat exchanger to completely dissolve the polyacrylonitrile and obtain a polyacrylonitrile stock solution. The mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution was 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90°C was 9000 mPa·s, and the molecular weight of polyacrylonitrile was 48000. The polyacrylonitrile stock solution was then filtered and degassed before use.

[0133] (3) Preparation of spinning solution: The flame retardant slurry is heated to 90°C through a heat exchanger, and the flame retardant slurry and polyacrylonitrile stock solution are fed into a static mixer at a mass ratio of 1:4 to mix and disperse evenly to obtain the spinning solution; wherein, the mass ratio of composite flame retardant to polyacrylonitrile in the spinning solution is 1:3, and the mass percentage of PAN in the spinning solution is 21%;

[0134] (4) Spinning: The spinning solution is used to spin flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90℃, the temperature of the coagulation bath is 55℃, the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, and after coagulation, it is washed twice with water at a temperature of 98℃. In the first water wash, it is stretched 6 times in one step, and no further stretching is performed. After washing, it is dried to obtain the product. The spinning speed is 85m / min.

[0135] In the flame-retardant polyacrylonitrile fiber prepared in this embodiment, the mass ratio of the composite flame retardant is 25%.

[0136] Example 2

[0137] This embodiment uses the following preparation method to prepare flame-retardant polyacrylonitrile fibers, specifically including the following steps:

[0138] (1) Preparation of flame retardant slurry: Composite flame retardant powder and polyacrylonitrile powder were added to DMAC at 0℃, and the mixture was ground for 4 hours in a sand mill using zirconia beads with a diameter of 0.6-0.8 mm. The mixture was then filtered using a filter cloth with a pore size of 5 μm to obtain the flame retardant slurry. The composite flame retardant accounted for 35% of the mass of the flame retardant slurry, and the polyacrylonitrile accounted for 7% of the mass of the flame retardant slurry. The rotational viscosity of the flame retardant slurry at 90℃ was 1000 mPa·s. The composite flame retardant included brominated polystyrene and antimony trioxide in a mass ratio of 3:1. The molecular weight of the polyacrylonitrile was 48000.

[0139] (2) Preparation of polyacrylonitrile stock solution: Polyacrylonitrile powder was added to DMAC at 4°C and mixed evenly. The mixture was then heated to 90°C through a heat exchanger to completely dissolve the polyacrylonitrile, thus obtaining a polyacrylonitrile stock solution. The mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution was 24.5%, the rotational viscosity of the polyacrylonitrile stock solution at 90°C was 7600 mPa·s, and the molecular weight of polyacrylonitrile was 48000. The polyacrylonitrile stock solution was then filtered and degassed before use.

[0140] (3) Preparation of spinning solution: The flame retardant slurry is heated to 90°C through a heat exchanger, and the flame retardant slurry and polyacrylonitrile stock solution are fed into a static mixer at a mass ratio of 1:4 to mix and disperse evenly to obtain the spinning solution; wherein, the mass ratio of composite flame retardant to polyacrylonitrile in the spinning solution is 1:3, and the mass percentage of PAN in the spinning solution is 21%;

[0141] (4) Spinning: The spinning solution is used to spin flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90℃, the coagulation bath temperature is 55℃, the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, the water washing temperature is 98℃, and the spinning speed is 97m / min; the total draw ratio is 8 times, wherein the first water washing draw ratio is 2.7 times, the second water washing draw ratio is 2.7 times, and three draw ratios are performed during the drying process, with draw ratios of 1.10 times, 1.10 times and 1.12 times respectively.

[0142] In the flame-retardant polyacrylonitrile fiber prepared in this embodiment, the mass ratio of the composite flame retardant is 25%.

[0143] Example 3

[0144] Based on Example 2 above, this embodiment adjusts the drawing process in step (4) to a one-step drawing process, while keeping other process steps and parameters unchanged.

[0145] Specifically, this embodiment employs a preparation method including the following steps to prepare flame-retardant polyacrylonitrile fibers:

[0146] (1) Preparation of flame retardant slurry: Composite flame retardant powder and polyacrylonitrile powder were added to DMAC at 0℃, and the mixture was ground for 4 hours in a sand mill using zirconia beads with a diameter of 0.6-0.8 mm. The mixture was then filtered using a filter cloth with a pore size of 5 μm to obtain the flame retardant slurry. The composite flame retardant accounted for 35% of the mass of the flame retardant slurry, and the polyacrylonitrile accounted for 7% of the mass of the flame retardant slurry. The rotational viscosity of the flame retardant slurry at 90℃ was 1000 mPa·s. The composite flame retardant included brominated polystyrene and antimony trioxide in a mass ratio of 3:1. The molecular weight of the polyacrylonitrile was 48000.

[0147] (2) Preparation of polyacrylonitrile stock solution: Polyacrylonitrile powder was added to DMAC at 4°C and mixed evenly. The mixture was then heated to 90°C through a heat exchanger to completely dissolve the polyacrylonitrile, thus obtaining a polyacrylonitrile stock solution. The mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution was 24.5%, the rotational viscosity of the polyacrylonitrile stock solution at 90°C was 7600 mPa·s, and the molecular weight of polyacrylonitrile was 48000. The polyacrylonitrile stock solution was then filtered and degassed before use.

[0148] (3) Preparation of spinning solution: The flame retardant slurry is heated to 90°C through a heat exchanger, and the flame retardant slurry and polyacrylonitrile stock solution are fed into a static mixer at a mass ratio of 1:4 to mix and disperse evenly to obtain the spinning solution; wherein, the mass ratio of composite flame retardant to polyacrylonitrile in the spinning solution is 1:3, and the mass percentage of PAN in the spinning solution is 21%;

[0149] (4) Spinning: The spinning solution is used to spin flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90℃, the temperature of the coagulation bath is 55℃, the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, and after coagulation, it is washed twice with water at a temperature of 98℃. In the first water wash, it is stretched 6 times in one step, and no further stretching is performed. After washing, it is dried to obtain the product. The spinning speed is 97m / min.

[0150] Example 4

[0151] This embodiment uses the following preparation method to prepare flame-retardant polyacrylonitrile fibers, specifically including the following steps:

[0152] (1) Preparation of flame retardant slurry: Composite flame retardant powder and polyacrylonitrile powder were added to DMAC at 0℃, and the mixture was ground for 4 hours in a sand mill using zirconia beads with a diameter of 0.6-0.8 mm. The mixture was then filtered using a filter cloth with a pore size of 5 μm to obtain the flame retardant slurry. The composite flame retardant accounted for 35% of the mass of the flame retardant slurry, and the polyacrylonitrile accounted for 5% of the mass of the flame retardant slurry. The rotational viscosity of the flame retardant slurry at 90℃ was 660 mPa·s. The composite flame retardant included decabromodiphenyl ethane and antimony trioxide in a mass ratio of 3:1. The molecular weight of the polyacrylonitrile was 48,000.

[0153] (2) Preparation of polyacrylonitrile stock solution: Polyacrylonitrile powder was added to DMAC at 4°C and mixed evenly. The mixture was then heated to 90°C through a heat exchanger to completely dissolve the polyacrylonitrile and obtain a polyacrylonitrile stock solution. The mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution was 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90°C was 9000 mPa·s, and the molecular weight of polyacrylonitrile was 48000. The polyacrylonitrile stock solution was then filtered and degassed before use.

[0154] (3) Preparation of spinning solution: The flame retardant slurry is heated to 90°C through a heat exchanger, and the flame retardant slurry and polyacrylonitrile stock solution are fed into a static mixer at a mass ratio of 1:4 to mix and disperse evenly to obtain the spinning solution; wherein, the mass ratio of composite flame retardant to polyacrylonitrile in the spinning solution is 1:3, and the mass percentage of PAN in the spinning solution is 21%;

[0155] (4) Spinning: The spinning solution is used to spin flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90℃, the temperature of the coagulation bath is 55℃, the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, the water washing temperature is 98℃, and the spinning speed is 85m / min; the total draw ratio is 7 times, wherein the first water washing draw ratio is 3.0 times, the second water washing draw ratio is 1.8 times, and three draw ratios are performed during the drying process, with draw ratios of 1.08 times, 1.09 times and 1.10 times respectively.

[0156] In the flame-retardant polyacrylonitrile fiber prepared in this embodiment, the mass ratio of the composite flame retardant is 25%.

[0157] Example 5

[0158] This embodiment uses the following preparation method to prepare flame-retardant polyacrylonitrile fibers, specifically including the following steps:

[0159] (1) Preparation of flame retardant slurry: Composite flame retardant powder and polyacrylonitrile powder were added to DMAC at 0℃, and the mixture was ground for 4 hours in a sand mill using zirconia beads with a diameter of 0.6-0.8 mm. The mixture was then filtered using a filter cloth with a pore size of 5 μm to obtain the flame retardant slurry. The composite flame retardant accounted for 35% of the mass of the flame retardant slurry, and the polyacrylonitrile accounted for 5% of the mass of the flame retardant slurry. The rotational viscosity of the flame retardant slurry at 90℃ was 660 mPa·s. The composite flame retardant included tetrabromobisphenol A-bis(2,3-dibromopropyl ether) and antimony trioxide in a mass ratio of 3:1. The molecular weight of the polyacrylonitrile was 48,000.

[0160] (2) Preparation of polyacrylonitrile stock solution: Polyacrylonitrile powder was added to DMAC at 4°C and mixed evenly. The mixture was then heated to 90°C through a heat exchanger to completely dissolve the polyacrylonitrile and obtain a polyacrylonitrile stock solution. The mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution was 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90°C was 9000 mPa·s, and the molecular weight of polyacrylonitrile was 48000. The polyacrylonitrile stock solution was then filtered and degassed before use.

[0161] (3) Preparation of spinning solution: The flame retardant slurry is heated to 90°C through a heat exchanger, and the flame retardant slurry and polyacrylonitrile stock solution are fed into a static mixer at a mass ratio of 1:4 to mix and disperse evenly to obtain the spinning solution; wherein, the mass ratio of composite flame retardant to polyacrylonitrile in the spinning solution is 1:3, and the mass percentage of PAN in the spinning solution is 21%;

[0162] (4) Spinning: The spinning solution is used to spin flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90℃, the temperature of the coagulation bath is 55℃, the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, the water washing temperature is 98℃, the spinning speed is 85m / min, and the total draw ratio is 7 times, wherein the first water washing draw ratio is 3.0 times, the second water washing draw ratio is 1.8 times, and three draw ratios are performed during the drying process, with draw ratios of 1.08 times, 1.09 times and 1.10 times respectively.

[0163] In the flame-retardant polyacrylonitrile fiber prepared in this embodiment, the mass ratio of the composite flame retardant is 25%.

[0164] Example 6

[0165] This embodiment uses the following preparation method to prepare flame-retardant polyacrylonitrile fibers, specifically including the following steps:

[0166] (1) Preparation of flame retardant slurry: Composite flame retardant powder and polyacrylonitrile powder were added to DMAC at 0℃, and the mixture was ground for 4 hours in a sand mill using zirconia beads with a diameter of 0.6-0.8 mm. The mixture was then filtered using a filter cloth with a pore size of 5 μm to obtain the flame retardant slurry. The composite flame retardant accounted for 35% of the mass of the flame retardant slurry, and the polyacrylonitrile accounted for 5% of the mass of the flame retardant slurry. The rotational viscosity of the flame retardant slurry at 90℃ was 660 mPa·s. The composite flame retardant included ethylene bis(tetrabromophthalimide) and antimony trioxide in a mass ratio of 3:1. The molecular weight of the polyacrylonitrile was 48,000.

[0167] (2) Preparation of polyacrylonitrile stock solution: Polyacrylonitrile powder was added to DMAC at 4°C and mixed evenly. The mixture was then heated to 90°C through a heat exchanger to completely dissolve the polyacrylonitrile and obtain a polyacrylonitrile stock solution. The mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution was 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90°C was 9000 mPa·s, and the molecular weight of polyacrylonitrile was 48000. The polyacrylonitrile stock solution was then filtered and degassed before use.

[0168] (3) Preparation of spinning solution: The flame retardant slurry is heated to 90°C through a heat exchanger, and the flame retardant slurry and polyacrylonitrile stock solution are fed into a static mixer at a mass ratio of 1:4 to mix and disperse evenly to obtain the spinning solution; wherein, the mass ratio of composite flame retardant to polyacrylonitrile in the spinning solution is 1:3, and the mass percentage of PAN in the spinning solution is 21%;

[0169] (4) Spinning: The spinning solution is used to spin flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90℃, the coagulation bath temperature is 55℃, the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, the water washing temperature is 98℃, and the spinning speed is 85m / min; the total draw ratio is 7 times, wherein the first water washing draw ratio is 2.6 times, the second water washing draw ratio is 2.1 times, and three draw ratios are performed during the drying process, with draw ratios of 1.08 times, 1.08 times and 1.10 times respectively.

[0170] In the flame-retardant polyacrylonitrile fiber prepared in this embodiment, the mass ratio of the composite flame retardant is 25%.

[0171] Example 7

[0172] This embodiment uses the following preparation method to prepare flame-retardant polyacrylonitrile fibers, specifically including the following steps:

[0173] (1) Preparation of flame retardant slurry: Composite flame retardant powder and polyacrylonitrile powder were added to DMAC at 0℃, and the mixture was ground for 4 hours in a sand mill using zirconia beads with a diameter of 0.6-0.8 mm. The mixture was then filtered using a filter cloth with a pore size of 5 μm to obtain the flame retardant slurry. The composite flame retardant accounted for 35% of the mass of the flame retardant slurry, and the polyacrylonitrile accounted for 5% of the mass of the flame retardant slurry. The rotational viscosity of the flame retardant slurry at 90℃ was 660 mPa·s. The composite flame retardant included polypentabromobenzyl acrylate and antimony trioxide in a mass ratio of 3:1. The molecular weight of the polyacrylonitrile was 48,000.

[0174] (2) Preparation of polyacrylonitrile stock solution: Polyacrylonitrile powder was added to DMAC at 4°C and mixed evenly. The mixture was then heated to 90°C through a heat exchanger to completely dissolve the polyacrylonitrile and obtain a polyacrylonitrile stock solution. The mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution was 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90°C was 9000 mPa·s, and the molecular weight of polyacrylonitrile was 48000. The polyacrylonitrile stock solution was then filtered and degassed before use.

[0175] (3) Preparation of spinning solution: The flame retardant slurry is heated to 90°C through a heat exchanger, and the flame retardant slurry and polyacrylonitrile stock solution are fed into a static mixer at a mass ratio of 1:4 to mix and disperse evenly to obtain the spinning solution; wherein, the mass ratio of composite flame retardant to polyacrylonitrile in the spinning solution is 1:3, and the mass percentage of PAN in the spinning solution is 21%;

[0176] (4) Spinning: The spinning solution is used to spin flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90℃, the coagulation bath temperature is 55℃, the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, the water washing temperature is 98℃, and the spinning speed is 85m / min; the total draw ratio is 7 times, wherein the first water washing draw ratio is 2.6 times, the second water washing draw ratio is 2.1 times, and three draw ratios are performed during the drying process, with draw ratios of 1.08 times, 1.08 times and 1.10 times respectively.

[0177] In the flame-retardant polyacrylonitrile fiber prepared in this embodiment, the mass ratio of the composite flame retardant is 25%.

[0178] Example 8

[0179] This embodiment uses the following preparation method to prepare flame-retardant polyacrylonitrile fibers, specifically including the following steps:

[0180] (1) Preparation of flame retardant slurry: Composite flame retardant powder and polyacrylonitrile powder were added to DMAC at 0℃, and the mixture was ground for 4 hours in a sand mill using zirconia beads with a diameter of 0.6-0.8 mm. The mixture was then filtered using a filter cloth with a pore size of 5 μm to obtain the flame retardant slurry. The composite flame retardant accounted for 35% of the mass of the flame retardant slurry, and the polyacrylonitrile accounted for 5% of the mass of the flame retardant slurry. The rotational viscosity of the flame retardant slurry at 90℃ was 660 mPa·s. The composite flame retardant included bromotriazine and antimony trioxide in a mass ratio of 3:1. The molecular weight of the polyacrylonitrile was 48,000.

[0181] (2) Preparation of polyacrylonitrile stock solution: Polyacrylonitrile powder was added to DMAC at 4°C and mixed evenly. The mixture was then heated to 90°C through a heat exchanger to completely dissolve the polyacrylonitrile and obtain a polyacrylonitrile stock solution. The mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution was 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90°C was 9000 mPa·s, and the molecular weight of polyacrylonitrile was 48000. The polyacrylonitrile stock solution was then filtered and degassed before use.

[0182] (3) Preparation of spinning solution: The flame retardant slurry is heated to 90°C through a heat exchanger, and the flame retardant slurry and polyacrylonitrile stock solution are fed into a static mixer at a mass ratio of 1:4 to mix and disperse evenly to obtain the spinning solution; wherein, the mass ratio of composite flame retardant to polyacrylonitrile in the spinning solution is 1:3, and the mass percentage of PAN in the spinning solution is 21%;

[0183] (4) Spinning: The spinning solution is used to spin flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90℃, the coagulation bath temperature is 55℃, the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, the water washing temperature is 98℃, and the spinning speed is 85m / min; the total draw ratio is 7 times, wherein the first water washing draw ratio is 2.6 times, the second water washing draw ratio is 2.1 times, and three draw ratios are performed during the drying process, with draw ratios of 1.08 times, 1.08 times and 1.10 times respectively.

[0184] In the flame-retardant polyacrylonitrile fiber prepared in this embodiment, the mass ratio of the composite flame retardant is 25%.

[0185] Comparative Example 1

[0186] This embodiment, based on Embodiment 1 above, prepares conventional polyacrylonitrile fibers without adding composite flame retardants, specifically including the following steps:

[0187] (1) Preparation of polyacrylonitrile spinning solution: Add polyacrylonitrile powder to DMAC at 4°C, mix evenly, and then heat to 90°C through a heat exchanger to completely dissolve the polyacrylonitrile to obtain a polyacrylonitrile stock solution; wherein, the mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution is 25%, the rotational viscosity of the polyacrylonitrile stock solution at 90°C is 9000 mPa·s, and the molecular weight of polyacrylonitrile is 48000; the polyacrylonitrile stock solution is filtered and degassed before use.

[0188] (2) Spinning: The spinning solution is used to spin conventional polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90℃, the temperature of the coagulation bath is 55℃, the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, after coagulation, two water washes are performed, both at a temperature of 98℃, and a one-step stretch of 6 times is performed in the first water wash, and after washing and drying, the fiber is obtained, and the spinning speed is 85m / min.

[0189] Comparative Example 2

[0190] This comparative example is based on Example 2, but without adding polyacrylonitrile powder to the flame-retardant slurry. Specifically, steps (1) and (2) are adjusted as follows:

[0191] (1) Preparation of flame retardant slurry: Add composite flame retardant powder to DMAC at 0℃, grind in a sand mill with zirconia beads of 0.6-0.8 mm in diameter for 5 hours, and filter with a filter cloth with 5 μm pore size to obtain flame retardant slurry; wherein, the composite flame retardant accounts for 35% by mass in the flame retardant slurry, and the 90℃ rotational viscosity of the flame retardant slurry is 200 mpa.s; the composite flame retardant includes brominated polystyrene and antimony trioxide in a mass ratio of 3:1;

[0192] (2) Preparation of polyacrylonitrile stock solution: Polyacrylonitrile powder was added to DMAC at 4°C and mixed evenly. The mixture was then heated to 90°C through a heat exchanger to completely dissolve the polyacrylonitrile, thus obtaining a polyacrylonitrile stock solution. The mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution was 26.25%, the rotational viscosity of the polyacrylonitrile stock solution at 90°C was 20,000 mPa·s, and the molecular weight of polyacrylonitrile was 48,000. The polyacrylonitrile stock solution was then filtered and degassed before use.

[0193] The operation and process parameters involved in steps (3) and (4) remain unchanged.

[0194] Comparative Example 3

[0195] The difference between this comparative example and Example 1 above is that the mass ratio of brominated polystyrene and antimony trioxide in step (1) is adjusted to 5:1, while other process steps and parameters remain unchanged.

[0196] Specifically, this comparative example uses the following preparation method, including the following steps, to prepare flame-retardant polyacrylonitrile fibers:

[0197] (1) Preparation of flame retardant slurry: Composite flame retardant powder and polyacrylonitrile powder were added to DMAC at 0℃, and the mixture was ground for 4 hours in a sand mill using zirconia beads with a diameter of 0.6-0.8 mm. The mixture was then filtered using a filter cloth with a pore size of 5 μm to obtain the flame retardant slurry. The composite flame retardant accounted for 35% of the mass of the flame retardant slurry, and the polyacrylonitrile accounted for 5% of the mass of the flame retardant slurry. The rotational viscosity of the flame retardant slurry at 90℃ was 660 mPa·s. The composite flame retardant included brominated polystyrene and antimony trioxide in a mass ratio of 5:1. The molecular weight of the polyacrylonitrile was 48,000.

[0198] (2) Preparation of polyacrylonitrile stock solution: Polyacrylonitrile powder was added to DMAC at 4°C and mixed evenly. The mixture was then heated to 90°C through a heat exchanger to completely dissolve the polyacrylonitrile and obtain a polyacrylonitrile stock solution. The mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution was 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90°C was 9000 mPa·s, and the molecular weight of polyacrylonitrile was 48000. The polyacrylonitrile stock solution was then filtered and degassed before use.

[0199] (3) Preparation of spinning solution: The flame retardant slurry is heated to 90°C through a heat exchanger, and the flame retardant slurry and polyacrylonitrile stock solution are fed into a static mixer at a mass ratio of 1:4 to mix and disperse evenly to obtain the spinning solution; wherein, the mass ratio of composite flame retardant to polyacrylonitrile in the spinning solution is 1:3, and the mass percentage of PAN in the spinning solution is 21%;

[0200] (4) Spinning: The spinning solution is used to spin flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90℃, the temperature of the coagulation bath is 55℃, the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, and after coagulation, it is washed twice with water at a temperature of 98℃. In the first water wash, it is stretched by 6 times in one step, and after washing, it is dried to obtain the product. The spinning speed is 85m / min.

[0201] In the flame-retardant polyacrylonitrile fiber prepared in this comparative example, the mass percentage of the composite flame retardant is 25%.

[0202] Experimental Example 1

[0203] This experimental example tested the mechanical and flame retardant properties of the polyacrylonitrile fibers obtained in the above examples and comparative examples. The specific test items and methods are as follows.

[0204] Tensile strength test: The tensile strength was determined according to the method provided in GB / T 16602-2008 Acrylic staple fiber and tow;

[0205] Limiting oxygen index test: The obtained polyacrylonitrile fibers are made into fabrics, and the limiting oxygen index is determined according to the method provided in "Textiles Combustion Performance Test Oxygen Index Method".

[0206] The test results in this experiment are shown in Table 1.

[0207] Table 1

[0208] Fracture strength (cN / dtex) Limiting oxygen index Example 1 2.3 29.1 Example 2 3.1 30.4 Example 3 2.7 30.4 Example 4 2.0 29.8 Example 5 2.1 28.4 Example 6 2.3 27.7 Example 7 2.5 28.1 Example 8 2.0 26.7 Comparative Example 1 3.2 18.8 Comparative Example 2 2.7 26.5 Comparative Example 3 2.4 26.6

[0209] Compared to Example 2, Example 3 uses a one-step drafting process, making it difficult for the total draft ratio to exceed 6 times. This indicates that the fiber prepared in Example 3 has a relatively low breaking strength. Therefore, in the preferred embodiment of this invention, a multi-step drafting process is used to achieve a relatively higher total draft ratio, which helps to further improve the mechanical properties of the fiber.

[0210] Compared to Example 1, Comparative Example 1, lacking the addition of a composite flame retardant, clearly lacks flame retardant properties. However, in terms of mechanical properties, the breaking performance of Example 1 only decreases slightly, indicating that the solution of this invention can achieve a high amount of composite flame retardant added, thereby imparting good flame retardant properties to the fiber. Simultaneously, the impact on the fiber's mechanical properties is within an acceptable range, and its application scope will not be limited due to insufficient mechanical properties.

[0211] In Comparative Example 2, no polyacrylonitrile was added to the flame-retardant slurry. Compared with Example 2, the tensile strength was slightly reduced and the limiting oxygen index was significantly lower. It can be seen that the present invention adds a certain amount of polyacrylonitrile to the flame-retardant slurry, which is beneficial to improving the flame-retardant properties of the fiber and also improves the mechanical properties.

[0212] Compared to Example 1, the scheme in Comparative Example 3 had a 5:1 mass ratio of brominated flame retardant to antimony trioxide in the composite flame retardant, which exceeded the range of this mass ratio in the present invention. The measured limiting oxygen index was significantly lower than that of Example 1. This demonstrates that when the proportion of antimony trioxide in the composite flame retardant is too low, it will affect the flame retardant properties of the resulting fibers.

[0213] Experimental Example 2

[0214] This experimental example is used to investigate the effect of the amount of polyacrylonitrile added in flame retardant slurry on fiber properties. Specifically, based on Example 2, the mass ratio of polyacrylonitrile in flame retardant slurry in step (1) is changed, and the mass ratio of polyacrylonitrile in polyacrylonitrile stock solution in step (2) is adjusted accordingly so that the mass ratio of composite flame retardant in fiber remains unchanged. Other process steps and parameters are the same as in Example 2.

[0215] A series of flame-retardant polyacrylonitrile fiber samples were prepared using the above method. Their flame-retardant and mechanical properties were tested using the same method as in Example 1. The results are shown in Table 2.

[0216] Table 2

[0217]

[0218] The experimental data above show that changes in the polyacrylonitrile content in the flame-retardant paste have little effect on the fiber breaking strength. However, as the polyacrylonitrile content in the flame-retardant paste increases, the limiting oxygen index (LOI) tends to rise within a certain range. When the mass percentage of polyacrylonitrile in the flame-retardant paste is controlled between 5% and 9%, an LIOI of not less than 29.5 can be achieved.

[0219] In a preferred embodiment of the present invention, when the mass percentage of polyacrylonitrile in the flame-retardant slurry is controlled at 7% to 9%, a limiting oxygen index higher than 30 can be achieved, resulting in excellent flame-retardant performance.

[0220] Once the mass percentage of polyacrylonitrile in the flame-retardant slurry exceeds 7%, further increasing this mass percentage does not produce a significant change in the limiting oxygen index. Therefore, in a more preferred embodiment of the present invention, the mass percentage of polyacrylonitrile in the flame-retardant slurry is controlled at 7%.

[0221] Experimental Example 3

[0222] This experimental example is used to investigate the effect of the compounding ratio of composite flame retardants on fiber properties. Specifically, based on Example 2, the mass ratio of brominated polystyrene and antimony trioxide in step (1) is changed (denoted as X:Y), and other process steps and parameters are the same as in Example 2.

[0223] A series of flame-retardant polyacrylonitrile fiber samples were prepared using the above method. Their flame-retardant and mechanical properties were tested using the same method as in Example 1. The results are shown in Table 3.

[0224] Table 3

[0225] X:Y Fracture strength (cN / dtex) Limiting oxygen index 1.5：1 2.2 24.1 1.8：1 2.5 26.5 2.3：1 2.7 30.5 3.0：1 3.1 30.4 3.5：1 3.1 27.2 4.0：1 3.2 25.6

[0226] As can be seen from the above experimental data, controlling the mass ratio of brominated flame retardant to antimony trioxide in the composite flame retardant at 1.8–3.5:1 yields flame-retardant polyacrylonitrile fibers with a breaking strength of not less than 2.5 cN / dtex and a limiting oxygen index of not less than 26.5. In a preferred embodiment, controlling the mass ratio at 2.3–3.0:1 results in a fiber breaking strength exceeding 2.7 cN / dtex and a limiting oxygen index exceeding 30. Even more preferred is a mass ratio of 3.0:1, which yields flame-retardant polyacrylonitrile fibers with a breaking strength of 3.1 cN / dtex and a limiting oxygen index of 30.4, achieving high levels of both flame retardant and mechanical properties.

[0227] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing flame-retardant polyacrylonitrile fiber, characterized in that, Includes the following steps: (1) Add composite flame retardant powder and polyacrylonitrile powder to dimethylacetamide at 0-10℃, grind and disperse, and then filter to obtain a flame retardant slurry; wherein the composite flame retardant accounts for 30%-40% of the mass of the flame retardant slurry, and the polyacrylonitrile accounts for 7%-9% of the mass of the flame retardant slurry; the rotational viscosity of the flame retardant slurry at 90℃ is 1000-1700 mPa·s; (2) Add polyacrylonitrile powder to dimethylacetamide, mix evenly, and heat until completely dissolved to obtain polyacrylonitrile stock solution; the rotational viscosity of the polyacrylonitrile stock solution at 90°C is 6500~7600mpa.s; (3) The flame retardant slurry and polyacrylonitrile stock solution are mixed evenly according to the mass ratio of composite flame retardant to polyacrylonitrile of 1:2.3 to 3.0 to obtain spinning stock solution; (4) The spinning solution is used to spin flame-retardant polyacrylonitrile fiber; In step (1), the composite flame retardant includes a brominated flame retardant and antimony trioxide; wherein the mass ratio of the brominated flame retardant to antimony trioxide is 2.3 to 3.0:1; the brominated flame retardant includes one or more of tetrabromobisphenol A-bis(2,3-dibromopropyl ether), decabromodiphenyl ethane, brominated polystyrene, and pentabromobenzyl polyacrylate; In step (4), after the spinning solution is solidified in the coagulation bath, it undergoes two water washing and stretching processes before entering the drying process. During the drying process, three stretching processes are performed, and the total stretching ratio in the water washing and drying processes is 7 to 8 times, producing flame-retardant polyacrylonitrile fiber. The first water washing temperature is 98℃, and the stretching ratio is 2.5 to 3.5 times; the second water washing temperature is 98℃, and the stretching ratio is 1.8 to 2.3 times; the drying temperature is 140 to 150℃, and the stretching ratio of each stretching process is controlled at 1.08 to 1.12 times.

2. The method for preparing flame-retardant polyacrylonitrile fiber according to claim 1, characterized in that, In step (2), the mass percentage of polyacrylonitrile in the polyacrylonitrile stock solution is 20.5% to 25.5%; In step (3), the flame retardant slurry is mixed with polyacrylonitrile stock solution at a mass ratio of 1:3 to 10.

3. The method for preparing flame-retardant polyacrylonitrile fiber according to claim 1, characterized in that, In step (2), the temperature of dimethylacetamide is 0 to 10°C.

4. The method for preparing flame-retardant polyacrylonitrile fiber according to claim 3, characterized in that, In steps (1) and (2), the temperature of dimethylacetamide is 0–4 °C.

5. The method for preparing flame-retardant polyacrylonitrile fiber according to any one of claims 1-4, characterized in that, In step (1), zirconia beads with a diameter of 0.4 to 2.0 mm are used for grinding in a sand mill.

6. The method for preparing flame-retardant polyacrylonitrile fiber according to claim 5, characterized in that, In step (1), the grinding time is 2 to 8 hours.

7. The method for preparing flame-retardant polyacrylonitrile fiber according to any one of claims 1-4, characterized in that, In step (1), the filtration accuracy is 5 to 20 μm.

8. The method for preparing flame-retardant polyacrylonitrile fiber according to claim 7, characterized in that, In step (1), the filtration accuracy is 5-10 μm.

9. The method for preparing flame-retardant polyacrylonitrile fiber according to any one of claims 1-4, characterized in that, In step (2), the heating temperature is 85–95°C; And / or, the molecular weight of polyacrylonitrile is 40,000 to 60,000.

10. The method for preparing flame-retardant polyacrylonitrile fiber according to claim 9, characterized in that, In step (2), the heating temperature is 90-95℃.

11. The method for preparing flame-retardant polyacrylonitrile fiber according to any one of claims 1-4, characterized in that, In step (4), the temperature of the spinning solution is 50-90℃, the temperature of the coagulation bath is 40-60℃, the mass concentration of the coagulation bath is 40%-60%, and the spinning speed is 20-100m / min.

12. A flame-retardant polyacrylonitrile fiber prepared by the method for preparing flame-retardant polyacrylonitrile fiber according to any one of claims 1-11, characterized in that, The product includes a polyacrylonitrile fiber matrix and a composite flame retardant incorporated into the polyacrylonitrile fiber matrix; the composite flame retardant includes a brominated flame retardant and antimony trioxide, and the composite flame retardant accounts for 25% to 30% of the mass of the flame-retardant polyacrylonitrile fiber.

13. The flame-retardant polyacrylonitrile fiber according to claim 12, characterized in that, The flame-retardant polyacrylonitrile fiber has a breaking strength of 2.0–3.2 cN / dtex and a limiting oxygen index of 26.5–32.0.

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