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

Abstract

The invention 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 comprises the following steps that 1, composite flame retardant powder and polyacrylonitrile powder are added into dimethylacetamide, filtering is conducted after grinding and dispersing, and flame-retardant slurry is obtained; (2) adding polyacrylonitrile powder into dimethylacetamide, uniformly mixing, and heating until the polyacrylonitrile powder is completely dissolved to obtain a polyacrylonitrile stock solution; (3) preparing a spinning stock solution, namely uniformly mixing the flame-retardant slurry and a polyacrylonitrile stock solution according to the mass ratio of a composite flame retardant to polyacrylonitrile of 1: (2.3-4.0) to obtain the spinning stock solution; and (4) spinning by adopting the spinning solution to prepare the flame-retardant polyacrylonitrile fiber. A certain amount of polyacrylonitrile is added into the flame-retardant slurry, so that the flame-retardant slurry is more easily and uniformly mixed with the polyacrylonitrile stock solution, the addition amount of the composite flame retardant in the fiber can be increased, but the mechanical property of the fiber is not obviously influenced.

Description

Technical Field

[0001] The invention belongs to the field of functional fiber preparation, and in particular relates to a preparation method of flame-retardant polyacrylonitrile fiber and the flame-retardant polyacrylonitrile fiber. Background Art

[0002] The performance of polyacrylonitrile fiber is very similar to wool, with good elasticity, fluffy, curly and soft, and better warmth retention than wool, so it is known as synthetic wool. Polyacrylonitrile fiber can be spun pure or blended with natural fibers to make textiles according to the requirements of different uses. Its textiles are widely used in clothing, architectural decoration and other fields. However, conventional polyacrylonitrile fiber does not have flame retardant properties, and its textiles are easy to burn, which poses certain safety hazards, thus limiting the application scenarios of polyacrylonitrile fiber.

[0003] Introducing flame retardant components into polyacrylonitrile fibers to impart flame retardant properties to the fibers can solve the above problems. The methods for preparing flame retardant fibers or textiles in the prior art can be mainly divided into the following two categories.

[0004] The first type is the post-finishing method, which is to attach the slurry containing flame retardant ingredients to the finished fiber or fabric by coating, impregnation, etc. to form a flame retardant outer layer. However, the flame retardant ingredients added by the post-finishing method are not firmly bonded to the fiber, and will gradually fall off with the extension of the use process or multiple washings, resulting in the loss of flame retardant properties. In addition, the flame retardant outer layer attached to the outside of the fiber or fabric will also affect the soft and fluffy characteristics of the fiber.

[0005] The second type is co-spinning, where flame retardant components are added to the spinning solution, so that flame retardant fibers with flame retardant components dispersed inside the fiber matrix can be obtained. However, most existing flame retardant components are in powder form. Adding them inside the fiber will change the internal structure of the fiber and affect the mechanical properties of the fiber. Therefore, this method has certain restrictions on the amount of flame retardant components added, otherwise the mechanical properties of the fiber will not meet the requirements.

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

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and to provide a method for preparing flame-retardant polyacrylonitrile fiber using a blended 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 and modified flame-retardant polyacrylonitrile fiber.

[0009] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0010] A first aspect of the present invention provides a method for preparing a flame retardant polyacrylonitrile fiber, comprising the following steps:

[0011] (1) adding composite flame retardant powder and polyacrylonitrile powder to dimethylacetamide, grinding and dispersing, and then filtering to obtain a flame retardant slurry;

[0012] (2) adding polyacrylonitrile powder to dimethylacetamide, mixing evenly, and heating until completely dissolved to obtain a polyacrylonitrile stock solution;

[0013] (3) mixing the flame retardant slurry and the polyacrylonitrile stock solution uniformly according to a mass ratio of the composite flame retardant to polyacrylonitrile of 1:2.3-4.0 to obtain a spinning stock solution;

[0014] (4) Spinning: Spinning with the spinning solution to produce flame-retardant polyacrylonitrile fibers.

[0015] In the present invention, the composite flame retardant powder is blended with polyacrylonitrile to form a spinning solution, which is then spun into flame-retardant polyacrylonitrile fiber, so that the composite flame retardant is firmly combined inside the fiber and will not be separated from the fiber during use, so that the flame-retardant polyacrylonitrile fiber and its textiles can maintain good flame retardant effect after repeated washing.

[0016] During 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, which is then mixed with a polyacrylonitrile stock solution in which a larger amount of polyacrylonitrile is dissolved to prepare a spinning stock solution. This can achieve uniform mixing of the flame retardant slurry and the polyacrylonitrile stock solution, improve the dispersion uniformity of the composite flame retardant in the spinning stock solution, and thus obtain flame retardant polyacrylonitrile fibers in which the composite flame retardant components are uniformly dispersed in the fibers.

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

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

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

[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 in a mass ratio of 1:3 to 10.

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

[0023] In the present invention, experiments have found that by controlling the addition amount of polyacrylonitrile in the flame retardant slurry within the above range, the composite flame retardant is more evenly dispersed in the prepared spinning solution, and the flame retardant polyacrylonitrile fiber obtained can achieve better levels in flame retardancy and mechanical properties.

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

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

[0026] As a preferred embodiment, in step (1), the 90°C rotational viscosity of the flame retardant slurry 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 the flame retardant slurry and the polyacrylonitrile stock solution is related to the amount of polyacrylonitrile added therein, while the amount of the composite flame retardant added has little effect on the viscosity. In the present 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] In this way, in the mixing process of the subsequent step (3), it is beneficial to improve the mixing uniformity and obtain a spinning solution in which polyacrylonitrile and the composite flame retardant are more evenly dispersed, thereby ensuring the uniformity of the flame retardant properties of the fiber on the one hand, and avoiding the adverse effects of the composite flame retardant on the mechanical properties caused by the local concentrated distribution of the fiber on the other hand.

[0030] In the present invention, it is found through experiments that when the amount of the composite flame retardant added to the fiber is at the same level, a small amount of polyacrylonitrile powder is added to the flame retardant slurry during the preparation process, compared with the solution in which the flame retardant slurry does not contain polyacrylonitrile, the flame retardant performance of the flame retardant polyacrylonitrile fiber obtained is significantly improved. It is speculated that this may be due to the reduced viscosity difference between the flame retardant slurry and the polyacrylonitrile stock solution, and the composite flame retardant can be dispersed more evenly when mixed to form the spinning stock solution, thereby achieving the effect of improving the flame retardant performance.

[0031] In addition, when mixing two systems with different viscosities, the smaller the viscosity difference, the smaller the torque required during the mixing process, and the smaller the wear on the mixing equipment. The scheme of the present invention appropriately increases the viscosity of the flame retardant slurry by adding a certain amount of polyacrylonitrile to the flame retardant slurry, so that the viscosity difference between the flame retardant slurry and the polyacrylonitrile stock solution is reduced, which helps to reduce the wear on the mixing equipment used for mixing the flame retardant slurry and the polyacrylonitrile stock solution, thereby extending the service life of the mixing equipment.

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

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

[0034] In the above scheme, polyacrylonitrile powder is added to dimethylacetamide (DMAC) at 0-10°C. In this temperature range, the solubility of polyacrylonitrile is low, and it exists in DMAC in the form of solid powder, the interaction force between particles is weakened, and the possibility of agglomeration is low, which is conducive to improving the uniformity of mixing. In addition, at low temperatures, the viscosity of DMAC is relatively low, which is more conducive to the uniform dispersion of the composite flame retardant powder and the polyacrylonitrile powder.

[0035] Specifically, in step (1), the composite flame retardant powder and the polyacrylonitrile powder are added to the low-temperature DMAC at 0 to 10° C. The two powders are not easy to agglomerate 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, and then in the subsequent heating process to prepare the polyacrylonitrile stock solution, the polyacrylonitrile can be more fully dissolved.

[0036] In a further embodiment, in step (1), the composite flame retardant comprises 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), decabromodiphenylethane, brominated polystyrene, ethylenebistetrabromophthalimide, polypentabromobenzyl acrylate, and bromotriazine.

[0038] In the above scheme, the composite flame retardant uses environmentally friendly bromine flame retardant and antimony trioxide to make flame-retardant polyacrylonitrile fiber with low toxicity. After testing, the ratio of the two is controlled at 1.8 to 3.5:1, and the flame retardant performance of the fiber is better.

[0039] Among the many different components of brominated flame retardants, tests have found that the selection of one or more of tetrabromobisphenol A-bis (2,3-dibromopropyl ether), decabromodiphenylethane, brominated polystyrene and ethylene bis tetrabromophthalimide, polyacrylate pentabromobenzyl ester, and bromotriazine has less impact on the mechanical properties of the fiber at the same level of flame retardant addition compared to flame retardants of other components. It is speculated that the specific groups in the above components can produce a certain combination with polyacrylonitrile, thereby reducing the damage to the internal structure of the fiber by the addition of flame retardants.

[0040] In a further embodiment, in step (1), zirconia beads having 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] As a specific implementation manner, the ground slurry is filtered using a filter cloth with a pore size of 5 to 20 μm to obtain a flame retardant slurry for later use.

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

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

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

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

[0048] In the present invention, the flame retardant slurry is mixed with the polyacrylonitrile stock solution at a mass ratio of 1:3 to 10, and the amount of the flame retardant slurry added is relatively large. The flame retardant slurry is preheated to a temperature range close to that of the polyacrylonitrile stock solution before mixing, which can avoid affecting the mixing effect and will not make the temperature of the spinning stock solution obtained after mixing too low.

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

[0050] As a specific embodiment, the coagulant in the coagulation bath is DMAC.

[0051] As a more specific solution, the spinning solution is heated to 50-90°C, sprayed out through the spinneret assembly, and solidified in a coagulation bath. It is then washed and dried, and finally wound into a tube at a speed of 20-100 m / min to make flame-retardant acrylic fiber.

[0052] In a more detailed scheme, after the spinning solution is coagulated in the coagulation bath, it undergoes two water washing and stretching steps; wherein, the first water washing temperature is 98°C, and the stretching multiple is 2.5 to 3.5 times; the second water washing temperature is 98°C, and the stretching multiple is 1.8 to 2.3 times, preferably 2.0 to 2.3 times.

[0053] After the above two washing and drawing steps, the tow enters the drying process, the drying temperature is 140-150°C, three drawing steps are performed during the drying process, and the drawing multiples of each drawing step are controlled at 1.08-1.12 times. In a specific embodiment, the tow is dried by four drying rollers in sequence, the temperature of the drying rollers is controlled at 140-150°C, and one drawing step is performed between two adjacent drying rollers. By controlling the rotational linear speed of the two adjacent drying rollers, the single drawing multiple is controlled at 1.08-1.12 times.

[0054] In a preferred embodiment, the total stretching multiple is 7 times, wherein the first water washing stretching is 2.6 times, the second water washing stretching is 2.1 times, and the stretching multiples of the three stretching processes during the drying process are 1.08 times, 1.08 times and 1.10 times respectively.

[0055] In another preferred embodiment, the total stretching multiple is 8 times, wherein the first water washing stretching is 2.7 times, the second water washing stretching is 2.7 times, and the stretching multiples of the three stretching processes during the drying process are 1.10 times, 1.10 times and 1.12 times respectively.

[0056] In the present invention, it has been found through experiments that a higher stretching multiple is achieved through multiple stretching steps, especially further stretching during the drying process, such as stretching between drying rollers, can further improve the breaking strength of the obtained fiber compared to a one-step stretching method.

[0057] The 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 bromine flame retardant and antimony trioxide, and the mass proportion of the composite flame retardant in the flame-retardant polyacrylonitrile fiber is 20% to 30%;

[0058] Preferably, the flame retardant polyacrylonitrile fiber is prepared by the method for preparing the 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] After adopting the above technical scheme, the present invention has the following beneficial effects compared with the prior art.

[0061] 1. The composite flame retardant is added to the spinning solution and blended with polyacrylonitrile for spinning. The composite flame retardant component in the flame-retardant polyacrylonitrile fiber will not separate with use, ensuring the long-lasting and effective flame retardant performance, which can be repeatedly washed without failure.

[0062] 2. The added content of the composite flame retardant is higher than that of the existing technology, which can improve the flame retardant performance. The limiting oxygen index can reach 26.5-32.0, which meets the requirements of the limiting oxygen index in application fields such as curtains, curtains, and decorative fabrics for furniture products. At the same time, it has no obvious effect on the mechanical properties of the fiber. The fiber breaking strength can reach 2.0-3.2 cN / dtex. Therefore, the application field of the fiber will not be limited by the addition of the composite flame retardant. The obtained flame-retardant polyacrylonitrile fiber can be used to produce flame-retardant fabrics used in architectural decoration, fire-resistant clothing and other fields to meet the use needs.

[0063] 3. The flame-retardant acrylic fiber produced has the advantages of no melting droplets and low toxicity, and has low production cost, short production process and simple process.

[0064] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the drawings described below are only some embodiments. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the accompanying drawings:

[0066] Figure 1 is a process flow chart of a method for preparing flame-retardant polyacrylonitrile fiber in an embodiment of the present invention;

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

[0068] In the figure: 1, first stirring tank; 2, second stirring tank; 3, slurry delivery 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 circulation pump; 11, second circulation pump; 12, mixing tank; 121, jacket; 13, slurry tank; 14, slurry delivery pump; 15, raw liquid heat exchanger; 16, second filter; 17, degassing tower; 18, glue supply pump; 19, raw liquid storage tank; 20, raw liquid delivery pump; 21 , raw liquid flow meter; 31, solvent feed valve; 32, PAN feed valve; 33, slurry discharge valve; 34, first circulation control valve; 35, first discharge control valve; 36, second circulation control valve; 37, second discharge control valve; 41, slurry conveying pipeline; 42, rubber supply pipeline; 43, raw liquid conveying pipeline; 44, first discharge pipeline; 45, first circulation pipeline; 46, second discharge pipeline; 47, second circulation pipeline; 48, slurry conveying pipeline; 49, first feed pipe; 50, second feed pipe.

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

[0070] In order to make the purpose, 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 in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0071] In the description of the present invention, it should be noted that the directions or positional relationships indicated by terms such as “upper”, “lower”, “front”, “back”, “left”, “right”, “vertical”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0072] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

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

[0074] (1) Preparation of flame retardant slurry: adding composite flame retardant powder and polyacrylonitrile powder to DMAC at 0-10°C, grinding for 2-8 hours using zirconium oxide beads with a diameter of 0.4-2.0 mm in a sand mill, and filtering using a filter cloth with a pore size of 5-20 μm to obtain a flame retardant slurry; wherein the mass proportion of the composite flame retardant in the flame retardant slurry is 30%-40%, the mass proportion of polyacrylonitrile in the flame retardant slurry is 3%-9%, and the rotational viscosity of the flame retardant slurry at 90°C is 200-1700 mPa.s;

[0075] (2) Preparation of polyacrylonitrile stock solution: adding polyacrylonitrile powder to DMAC at 0 to 10° C., mixing evenly, and heating to 85 to 95° C. by a heat exchanger to completely dissolve the polyacrylonitrile to obtain a polyacrylonitrile stock solution; wherein the mass proportion of polyacrylonitrile in the polyacrylonitrile stock solution is 20.5% to 25.5%, and the rotational viscosity of the polyacrylonitrile stock solution at 90° C. is 2000 to 11000 mPa.s;

[0076] (3) preparing a spinning solution: feeding the flame retardant slurry and the polyacrylonitrile solution into a static mixer in a mass ratio of 1:3 to 10 to mix and disperse them evenly to obtain a spinning solution; wherein the mass ratio of the composite flame retardant to the polyacrylonitrile in the spinning solution is 1:2.3 to 4.0;

[0077] (4) Spinning: Spinning the spinning solution to produce flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 50-90° C., the temperature of the coagulation bath is 40-60° C., the coagulant in the coagulation bath is DMAC, the mass concentration is 40%-60%, the washing temperature is 90-99° C., the spinning speed is 20-100 m / min, and the drafting multiple is 5-8 times.

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

[0079] In order to obtain the spinning solution from the production raw materials, the following method is used in the embodiment of the present invention: Figure 2 The flame retardant polyacrylonitrile fiber spinning solution production system is used to prepare 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 a conventional polyacrylonitrile spinning device to produce flame retardant polyacrylonitrile fiber.

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

[0081] The composite flame retardant powder and the solvent DMAC are added to the flame retardant slurry preparation unit respectively, and a certain amount of polyacrylonitrile powder is also added. In the flame retardant slurry preparation unit, the composite flame retardant powder, the polyacrylonitrile powder and the solvent are fully mixed to prepare the flame retardant slurry. The solvent DMAC and the polyacrylonitrile powder are added to the polyacrylonitrile stock solution preparation unit respectively, and are fully mixed therein to dissolve the polyacrylonitrile powder to prepare the polyacrylonitrile stock solution. The mixing unit is connected to the flame retardant slurry preparation unit and the polyacrylonitrile stock solution preparation unit respectively, and the flame retardant slurry and the polyacrylonitrile stock solution are fully mixed in the mixing unit to obtain a spinning stock solution that can be used for spinning.

[0082] As a specific implementation, the flame retardant slurry preparation unit has at least two dispersing devices, and each dispersing device is connected to the mixing unit respectively.

[0083] The process of fully mixing and dispersing the composite flame retardant powder, polyacrylonitrile powder and solvent to form a flame retardant slurry is usually discontinuous. That is, under normal circumstances, it is necessary to add the composite flame retardant powder, polyacrylonitrile powder and solvent to the dispersion device in a certain proportion, and then mix and disperse for a certain period of time, and then discharge the prepared flame retardant slurry.

[0084] The working process of the above-mentioned dispersing device can be defined as two working stages, namely, the preparation stage and the discharging stage. In the preparation stage, the composite flame retardant powder, polyacrylonitrile powder and solvent are fully mixed and dispersed in the dispersing device to form a flame retardant slurry. In the discharging stage, the prepared flame retardant slurry is discharged from the dispersing device and transported to the mixing unit.

[0085] By setting two or more dispersing devices, when the production system is working, part of the dispersing devices can be in the preparation stage to prepare the flame-retardant slurry, while the other part of the dispersing devices can be in the discharge stage to transport the prepared flame-retardant slurry to the mixing unit. In this way, from the overall point of view, the flame-retardant slurry preparation unit can continuously transport the flame-retardant slurry to the mixing unit, thereby achieving the purpose of continuous production of spinning solution and improving production efficiency. There will be no problem that during the preparation of the flame-retardant slurry, the flame-retardant slurry is not transported to the mixing unit, resulting in the suspension of the production process of the spinning solution.

[0086] In a further solution, the flame retardant slurry preparation unit is provided with a valve assembly for controlling the connection and disconnection between each dispersing device and the mixing unit. By providing the valve assembly, the dispersing device in the discharging 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, thereby preventing insufficiently mixed and dispersed materials from entering the mixing unit.

[0087] As a specific implementation, the number of the valve assemblies is the same as the number of the dispersion devices, the valve assemblies and the dispersion devices are arranged one-to-one, and each of the valve assemblies is used to control the on-off between the corresponding dispersion device and the mixing unit.

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

[0089] In a specific solution, two dispersing devices are provided, including a first dispersing device and a second dispersing device. Two 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, when the production system is working, the first dispersing device and the second dispersing device can alternately prepare the flame-retardant slurry. For example, when the first dispersing device is in the preparation stage, the second dispersing device is in the discharge stage, and the second valve assembly controls it to be connected with the mixing unit to transport the prepared flame-retardant slurry to the mixing unit. After the transportation is completed, the first dispersing device switches to the discharge stage, and the first valve assembly controls it to be connected with the mixing unit to transport the flame-retardant slurry to the mixing unit. At the same time, the second dispersing device switches to the preparation stage, and the second valve assembly cuts off the connection between it and the mixing unit, so that the flame-retardant slurry can be continuously prepared by the second dispersing device while the flame-retardant slurry is transported to the mixing unit by the first dispersing device. At the mixing unit, the flame-retardant slurry can enter continuously and uninterruptedly, realizing the continuous production of spinning solution and improving production efficiency.

[0091] In a further solution, the specific structure of the dispersing device is described by taking the first dispersing device as an example. The first dispersing device includes a first stirring tank 1, a first sand mill 5 and a first circulation pump 10. The first sand mill 5 has zirconium oxide beads with a diameter of 0.4 to 2.0 mm.

[0092] The composite flame retardant powder, polyacrylonitrile powder and solvent are added to the first stirring tank 1 and stirred and mixed. The first sand mill 5 is connected to the first stirring tank 1 through the first circulation pipeline 45, and the first circulation pump 10 is arranged 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 stirring tank 1 and the first sand mill 5. When the material passes through the first sand mill 5, the zirconium oxide beads are used to fully grind and disperse the material, so that the composite flame retardant powder and the polyacrylonitrile powder are fully and evenly dispersed in the solvent to form a flame retardant slurry.

[0093] As a specific structure, the discharge port of the first stirring 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 the first circulation pipeline 45 and the first discharge pipeline 44 to be connected to the discharge port of the first stirring tank 1. Specifically, when the first dispersing 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 stirring tank 1, and at the same time, the first circulation pump 10 is running to drive the material to circulate through the first sand mill 5 to make a flame retardant slurry. When the first dispersing 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 stirring tank 1, and the first circulation pump 10 is closed, so that the prepared flame retardant slurry can be discharged from the first stirring tank 1 and transported to the mixing unit along the first discharge pipeline 44.

[0095] As a specific embodiment, the first valve assembly includes a first three-way switching valve arranged at the above-mentioned three-way structure position, and 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 stirring tank.

[0096] As another specific implementation, 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 arranged on the first circulation pipeline 45, and the first discharge control valve 35 is arranged on the first discharge pipeline 44. When the first dispersing device is in the preparation stage, the first circulation control valve 34 is opened, the first circulation pump 10 is running, 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 is not running, and the first discharge control valve 35 is opened.

[0097] Similar to the first dispersing device, the second dispersing device includes a second stirring tank 2, a second sand mill 6, and a second circulating pump 11, wherein the second sand mill 6 has zirconium oxide beads with a diameter of 0.4 to 2.0 mm. The second sand mill 6 and the second circulating pump 11 are respectively arranged on the second circulating pipeline 47. The discharge port of the second stirring tank 2 is connected to the second circulating pipeline 47 and the second discharge pipeline 46 through a three-way structure, and the second discharge pipeline 46 is connected to the mixing unit.

[0098] As a specific embodiment, the second valve assembly includes a second three-way switching valve arranged at the three-way structure position at the discharge port of the second stirring tank, and through its switching action, controls the second circulation pipeline and the second discharge pipeline to select one of them to be connected to the discharge port of the second stirring tank.

[0099] As another specific implementation, 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 arranged on the second circulation pipeline 47, and the second discharge control valve 37 is arranged on the second discharge pipeline 46. When the second dispersing device is in the preparation stage, the second circulation control valve 36 is opened, the second circulation pump 11 is running, 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 is not running, and the second discharge control valve 37 is opened.

[0100] In a further scheme of this embodiment, the flame retardant slurry configuration unit is provided with a slurry delivery pump 3, and the first stirring tank 1 and the second stirring tank 2 are both connected to the slurry delivery pump 3, and the driving force provided by the slurry delivery pump 3 is utilized to deliver the prepared flame retardant slurry in the first stirring tank 1 and the second stirring tank 2 to the mixing unit.

[0101] Specifically, the first discharge pipeline 44 and the second discharge pipeline 46 are respectively connected to the slurry delivery pump 3, and the outlet end of the slurry delivery pump 3 is connected to the mixing unit through the slurry delivery pipeline 48. The slurry delivery pump 3 is running to extract the flame retardant slurry from the first stirring tank 1 or the second stirring tank 2, and deliver it to the mixing unit along the slurry delivery pipeline 48.

[0102] As a specific implementation, the mixing unit includes a static mixer 9, and the flame retardant slurry and the polyacrylonitrile stock solution are evenly mixed in the static mixer 9 to form a spinning stock solution that can be used to make flame retardant polyacrylonitrile fibers.

[0103] In a further solution, a first filter 4 is provided on the slurry conveying pipeline 48, and 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 filtering accuracy of the first filter 4 is 5-20 μm. By providing the first filter 4, large particles agglomerated in the flame retardant slurry can be filtered out to avoid affecting the dispersion uniformity of the composite flame retardant powder in the spinning solution.

[0105] Furthermore, a heating device is provided on the slurry conveying pipeline 48 , and the heating device is arranged downstream of the first filter 4 , so as to heat the flame retardant slurry after filtering.

[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 temperature of the heated flame retardant slurry is closer to that of the polyacrylonitrile stock solution, which is conducive to improving the mixing effect. On the other hand, the prepared spinning solution needs to reach a certain temperature range when used for spinning. Heating the flame retardant slurry can avoid the temperature of the mixed spinning solution being too low, thereby shortening the heating time of the spinning solution in the subsequent spinning process, and even directly spinning without additional heating, thereby improving production efficiency. The heating device is arranged downstream of the first filter 4 to prevent large agglomerated particles from clogging the heating device.

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

[0108] In a further embodiment, the polyacrylonitrile stock solution preparation unit comprises a stock solution preparation device, a stock solution storage tank 19 and a stock solution delivery pump 20. Polyacrylonitrile powder and a solvent DMAC at a temperature of 0 to 10°C are added to the stock solution preparation device, where they are mixed and heated to dissolve the polyacrylonitrile to prepare a polyacrylonitrile stock solution. The stock solution storage tank 19 is connected to the stock solution preparation device to collect the prepared polyacrylonitrile stock solution. The stock solution delivery pump 20 is connected to the discharge port of the stock solution storage tank 19 to provide a driving force to deliver 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 discharge port of the stock liquid storage tank 19 is connected to the stock liquid delivery pipeline 43, and the other end of the stock liquid delivery pipeline 43 is connected to the static mixer 9. The stock liquid delivery pump 20 is arranged on the stock liquid delivery pipeline 43. When the stock liquid delivery pump 20 is in operation, the polyacrylonitrile stock liquid is extracted from the stock liquid storage tank 19 and delivered to the static mixer 9 along the stock liquid delivery pipeline 43.

[0110] By adopting the above scheme, the polyacrylonitrile stock solution prepared by the stock solution preparation device is transported to the stock solution storage tank 19 for temporary storage, and the stock solution delivery pump 20 directly extracts 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 the 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 continuously producing the spinning stock solution.

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

[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 provided with a solvent feed valve 31, and the second feed pipe 50 is provided with a PAN feed valve 32. Low-temperature DMAC and polyacrylonitrile are respectively injected into the mixing tank 12 through the first feed pipe 49 and the second feed pipe 50 for stirring and mixing. After the polyacrylonitrile is fully dispersed, it is discharged through the discharge port 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 delivery pipeline 41 , and a slurry delivery pump 14 is provided on the slurry delivery pipeline 41 to deliver the polyacrylonitrile slurry collected in the slurry tank 13 to a downstream device.

[0114] Specifically, on the slurry delivery pipeline 41, located in the downstream area of ​​the slurry delivery pump 14, a stock solution heat exchanger 15 and a second filter 16 are sequentially provided. Steam is introduced into the stock solution heat exchanger 15 to exchange heat with the passing polyacrylonitrile slurry, so as to achieve the purpose of heating the polyacrylonitrile slurry, so that the polyacrylonitrile therein is fully dissolved to form a polyacrylonitrile solution. The heated polyacrylonitrile solution passes through the second filter 16, which can filter out large particles that cannot be dissolved to avoid affecting the quality of the spinning stock solution.

[0115] The end of the slurry conveying pipeline 41 is connected to the degassing tower 17, and the polyacrylonitrile solution is conveyed to the degassing tower 17 for degassing. The top of the degassing tower 17 is connected to a vacuum system, and a negative pressure environment is formed inside the degassing tower 17 to achieve degassing of the polyacrylonitrile solution. The discharge port at the bottom of the degassing tower 17 is connected to the glue supply pipeline 42, and the other end of the glue supply pipeline 42 is connected to the stock solution storage tank 19. The glue supply pipeline 42 is provided with a glue supply pump 18, which can deliver the polyacrylonitrile stock solution obtained after the degassing treatment into the stock solution storage tank 19 for storage.

[0116] In the above scheme, the mixed dissolution process of polyacrylonitrile and solvent can be discontinuous. Specifically, the discharge port at the bottom of the mixing tank 12 is connected to the slurry discharge valve 33. In the initial state, the slurry discharge valve 33 is closed, the solvent feed valve 31 and the PAN feed valve 32 are opened respectively, and polyacrylonitrile and solvent are injected according to the ratio, and then the solvent feed valve 31 and the PAN feed valve 32 are closed, and stirring is started for mixing. The outer side of the mixing tank 12 is provided with a jacket 121. By passing warm water into the jacket 121, the material inside the mixing tank 12 is preliminarily heated, and the polyacrylonitrile is dispersed and at least partially dissolved by stirring the material. 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 feed valve 31 and the PAN feed valve 32 are reopened, and the polyacrylonitrile and the solvent can be injected again for mixing and dispersion.

[0117] By using the slurry tank 13 to collect the polyacrylonitrile slurry, the polyacrylonitrile slurry can be continuously transported to the raw liquid heat exchanger 15 through the slurry transport pump 14, and then the polyacrylonitrile solution to be degassed continuously enters the degassing tower 17.

[0118] In a further solution, a slurry flowmeter 8 is provided on the slurry delivery pipeline 48, and a raw liquid flowmeter 21 is provided on the raw liquid delivery pipeline 43. The slurry flowmeter 8 and the raw liquid flowmeter 21 can both be mass flowmeters.

[0119] By setting up the slurry flowmeter 8 and the raw liquid flowmeter 21, the flow of the flame retardant slurry and the polyacrylonitrile raw liquid in the static mixer 9 delivered to the mixing unit can be monitored in real time, so that the operator can understand the current mixing ratio of the flame retardant slurry and the 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 stock solution delivery pump 20 are metering pumps respectively, and the delivery flow rates of the flame retardant slurry and the polyacrylonitrile stock solution to the static mixer 9 can be adjusted by adjusting the slurry delivery pump 3 and the stock solution delivery pump 20, so as to facilitate control.

[0121] As a preferred solution, the slurry flow meter 8, the stock liquid flow meter 21, the slurry delivery pump 3 and the stock liquid delivery pump 20 are electrically connected to the controller of the production system respectively, and the controller can obtain the real-time monitoring results of the flow rate of the slurry flow meter 8 and the stock liquid flow meter 21, and automatically adjust the slurry delivery pump 3 and the stock liquid delivery pump 20 according to the real-time flow rate of the flame retardant slurry and the polyacrylonitrile stock solution, so that the mixing ratio of the flame retardant slurry and the polyacrylonitrile stock solution meets the required ratio. Autonomous control and adjustment can be achieved without active intervention by the operator, which is more intelligent.

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

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

[0124] The slurry delivery pump 14 is in operation to deliver the polyacrylonitrile slurry in the slurry tank 13 along the slurry delivery pipeline 41, and is heated to 85-95°C by the stock solution heat exchanger 15 to fully dissolve the polyacrylonitrile, and then filtered by the second filter 16 to remove the undissolved large particles, and then enter the degassing tower 17 for degassing. The glue supply pump 18 is in operation to deliver the polyacrylonitrile stock solution obtained after degassing into the stock solution storage tank 19. The stock solution delivery pump 20 is continuously in operation when the production system is working, and continuously delivers the polyacrylonitrile stock solution in the stock solution storage tank 19 to the static mixer 9.

[0125] In the flame retardant slurry preparation unit, the composite flame retardant powder, polyacrylonitrile powder and DMAC are added to the first stirring tank 1 and the second stirring tank 2 in a certain proportion, and the two alternately perform the process of stirring and discharging the materials. Specifically, when the first dispersing device is in the preparation stage, the first circulation control valve 34 is opened, the first discharge control valve 35 is closed, and the first circulation pump 10 is started to circulate the material between the first stirring tank 1 and the first sand mill 5. At the same time, the second dispersing 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 opened to discharge the flame retardant slurry prepared in the second stirring tank 2.

[0126] After a period of time, the first dispersing device switches to the discharging stage, and the second dispersing device switches to the preparation stage. Specifically, the second discharging control valve 37 is closed, new materials are added to the second mixing tank 2, the second circulation control valve 36 is opened, and the second circulation pump 11 is started to drive the materials to circulate between the second mixing tank 2 and the second sand mill 6. At the same time, the first circulation control valve 34 is closed, the first circulation pump 10 stops running, and the first discharging control valve 35 is opened to discharge the flame retardant slurry in the first mixing tank 1.

[0127] In the above process, the slurry delivery pump 3 is continuously operated, and the flame retardant slurry discharged from the first stirring tank 1 or the second stirring tank 2 can be continuously delivered 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 passes through the first filter 4 to filter out large agglomerated particles, then passes through the slurry heat exchanger 7, is heated to 85-95° C., and finally enters the static mixer 9, and is fully mixed with the polyacrylonitrile stock solution also delivered to the static mixer 9 to form a spinning stock solution that can be used to prepare flame retardant polyacrylonitrile fibers.

[0128] The following is a specific example of using the above production system to prepare spinning solution and then make flame-retardant polyacrylonitrile fiber.

[0129] Example 1

[0130] This embodiment adopts the following preparation method to prepare flame-retardant polyacrylonitrile fiber, which specifically includes the following steps:

[0131] (1) Preparation of flame retardant slurry: Add composite flame retardant powder and polyacrylonitrile powder to DMAC at 0°C, grind for 4 hours in a sand mill using zirconium oxide beads with a diameter of 0.6-0.8 mm, and filter using a filter cloth with a pore size of 5 μm to obtain a flame retardant slurry; wherein the mass proportion of the composite flame retardant in the flame retardant slurry is 35%, the mass proportion of polyacrylonitrile in the flame retardant slurry is 5%, and the rotational viscosity of the flame retardant slurry at 90°C is 660 mPa.s; the composite flame retardant comprises brominated polystyrene and antimony trioxide in a mass ratio of 3:1; the molecular weight of polyacrylonitrile is 48,000;

[0132] (2) Preparation of polyacrylonitrile stock solution: Add polyacrylonitrile powder to DMAC at 4° C., mix well, and heat to 90° C. through a heat exchanger to completely dissolve the polyacrylonitrile to obtain a polyacrylonitrile stock solution; wherein the mass proportion of polyacrylonitrile in the polyacrylonitrile stock solution is 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90° C. is 9000 mPa.s; the molecular weight of the polyacrylonitrile is 48,000; the polyacrylonitrile stock solution is filtered and degassed for later use;

[0133] (3) preparing spinning solution: the flame retardant slurry is heated to 90° C. by a heat exchanger, and the flame retardant slurry and polyacrylonitrile solution are sent to a static mixer in a mass ratio of 1:4 to be mixed and dispersed uniformly to obtain a spinning solution; wherein the mass ratio of the 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 fibers; wherein the temperature of the spinning solution is 90° C., the temperature of the coagulation bath is 55° C., the coagulant in the coagulation bath is DMAC, and the mass concentration is 50%. After coagulation, two water washes are performed, and the water washing temperature is 98° C. In the first water wash, a one-step stretching of 6 times is performed, and no subsequent stretching is performed. After water washing, the fibers are dried to obtain the fibers, and the spinning speed is 85 m / min.

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

[0136] Example 2

[0137] This embodiment adopts the following preparation method to prepare flame-retardant polyacrylonitrile fiber, which specifically includes the following steps:

[0138] (1) Preparation of flame retardant slurry: Add composite flame retardant powder and polyacrylonitrile powder to DMAC at 0°C, grind for 4 hours in a sand mill using zirconium oxide beads with a diameter of 0.6-0.8 mm, and filter using a filter cloth with a pore size of 5 μm to obtain a flame retardant slurry; wherein the mass proportion of the composite flame retardant in the flame retardant slurry is 35%, the mass proportion of polyacrylonitrile in the flame retardant slurry is 7%, and the rotational viscosity of the flame retardant slurry at 90°C is 1000 mPa.s; the composite flame retardant comprises brominated polystyrene and antimony trioxide in a mass ratio of 3:1; the molecular weight of polyacrylonitrile is 48000;

[0139] (2) Preparation of polyacrylonitrile stock solution: Add polyacrylonitrile powder to DMAC at 4° C., mix well, and heat to 90° C. through a heat exchanger to completely dissolve the polyacrylonitrile to obtain a polyacrylonitrile stock solution; wherein the mass proportion of polyacrylonitrile in the polyacrylonitrile stock solution is 24.5%, the rotational viscosity of the polyacrylonitrile stock solution at 90° C. is 7600 mPa.s; the molecular weight of polyacrylonitrile is 48000; the polyacrylonitrile stock solution is filtered and degassed for later use;

[0140] (3) preparing spinning solution: the flame retardant slurry is heated to 90° C. by a heat exchanger, and the flame retardant slurry and polyacrylonitrile solution are sent to a static mixer in a mass ratio of 1:4 to be mixed and dispersed uniformly to obtain a spinning solution; wherein the mass ratio of the 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: Spinning the spinning solution to prepare flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90° C., the temperature of the coagulation bath is 55° C., the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, the water washing temperature is 98° C., and the spinning speed is 97 m / min; the total drafting multiple is 8 times, wherein the first water washing drafting is 2.7 times, the second water washing drafting is 2.7 times, and three draftings are performed during the drying process, and the drafting multiples are 1.10 times, 1.10 times and 1.12 times, respectively.

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

[0143] Example 3

[0144] In this embodiment, based on the above-mentioned embodiment 2, the stretching process in step (4) is adjusted to a one-step stretching, and other process steps and parameters remain unchanged.

[0145] Specifically, this embodiment adopts a preparation method comprising the following steps to prepare flame-retardant polyacrylonitrile fiber:

[0146] (1) Preparation of flame retardant slurry: Add composite flame retardant powder and polyacrylonitrile powder to DMAC at 0°C, grind for 4 hours in a sand mill using zirconium oxide beads with a diameter of 0.6-0.8 mm, and filter using a filter cloth with a pore size of 5 μm to obtain a flame retardant slurry; wherein the mass proportion of the composite flame retardant in the flame retardant slurry is 35%, the mass proportion of polyacrylonitrile in the flame retardant slurry is 7%, and the rotational viscosity of the flame retardant slurry at 90°C is 1000 mPa.s; the composite flame retardant comprises brominated polystyrene and antimony trioxide in a mass ratio of 3:1; the molecular weight of polyacrylonitrile is 48000;

[0147] (2) Preparation of polyacrylonitrile stock solution: Add polyacrylonitrile powder to DMAC at 4° C., mix well, and heat to 90° C. through a heat exchanger to completely dissolve the polyacrylonitrile to obtain a polyacrylonitrile stock solution; wherein the mass proportion of polyacrylonitrile in the polyacrylonitrile stock solution is 24.5%, the rotational viscosity of the polyacrylonitrile stock solution at 90° C. is 7600 mPa.s; the molecular weight of polyacrylonitrile is 48000; the polyacrylonitrile stock solution is filtered and degassed for later use;

[0148] (3) preparing spinning solution: the flame retardant slurry is heated to 90° C. by a heat exchanger, and the flame retardant slurry and polyacrylonitrile solution are sent to a static mixer in a mass ratio of 1:4 to be mixed and dispersed uniformly to obtain a spinning solution; wherein the mass ratio of the 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 fibers; wherein the temperature of the spinning solution is 90° C., the temperature of the coagulation bath is 55° C., the coagulant in the coagulation bath is DMAC, and the mass concentration is 50%. After coagulation, two water washes are performed, and the water washing temperature is 98° C., and a one-step stretching of 6 times is performed in the first water wash, and no subsequent stretching is performed. After water washing, the fibers are dried to obtain the fibers, and the spinning speed is 97 m / min.

[0150] Example 4

[0151] This embodiment adopts the following preparation method to prepare flame-retardant polyacrylonitrile fiber, which specifically includes the following steps:

[0152] (1) Preparation of flame retardant slurry: Add composite flame retardant powder and polyacrylonitrile powder to DMAC at 0°C, grind for 4 hours in a sand mill using zirconium oxide beads with a diameter of 0.6-0.8 mm, and filter using a filter cloth with a pore size of 5 μm to obtain a flame retardant slurry; wherein the mass proportion of the composite flame retardant in the flame retardant slurry is 35%, the mass proportion of polyacrylonitrile in the flame retardant slurry is 5%, and the rotational viscosity of the flame retardant slurry at 90°C is 660 mPa.s; the composite flame retardant comprises decabromodiphenylethane and antimony trioxide in a mass ratio of 3:1; the molecular weight of polyacrylonitrile is 48,000;

[0153] (2) Preparation of polyacrylonitrile stock solution: Add polyacrylonitrile powder to DMAC at 4° C., mix well, and heat to 90° C. through a heat exchanger to completely dissolve the polyacrylonitrile to obtain a polyacrylonitrile stock solution; wherein the mass proportion of polyacrylonitrile in the polyacrylonitrile stock solution is 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90° C. is 9000 mPa.s; the molecular weight of the polyacrylonitrile is 48,000; the polyacrylonitrile stock solution is filtered and degassed for later use;

[0154] (3) preparing spinning solution: the flame retardant slurry is heated to 90° C. by a heat exchanger, and the flame retardant slurry and polyacrylonitrile solution are sent to a static mixer in a mass ratio of 1:4 to be mixed and dispersed uniformly to obtain a spinning solution; wherein the mass ratio of the 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: Spinning the spinning solution to prepare flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90° C., the temperature of the coagulation bath is 55° C., the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, the water washing temperature is 98° C., and the spinning speed is 85 m / min; the total drafting multiple is 7 times, wherein the first water washing drafting is 3.0 times, the second water washing drafting is 1.8 times, and three draftings are performed during the drying process, and the drafting multiples are 1.08 times, 1.09 times and 1.10 times, respectively.

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

[0157] Example 5

[0158] This embodiment adopts the following preparation method to prepare flame-retardant polyacrylonitrile fiber, which specifically includes the following steps:

[0159] (1) Preparation of flame retardant slurry: Add composite flame retardant powder and polyacrylonitrile powder to DMAC at 0°C, grind for 4 hours in a sand mill using zirconium oxide beads with a diameter of 0.6-0.8 mm, and filter using a filter cloth with a pore size of 5 μm to obtain a flame retardant slurry; wherein the mass proportion of the composite flame retardant in the flame retardant slurry is 35%, the mass proportion of polyacrylonitrile in the flame retardant slurry is 5%, and the rotational viscosity of the flame retardant slurry at 90°C is 660 mPa.s; the composite flame retardant comprises tetrabromobisphenol A-bis(2,3-dibromopropyl ether) and antimony trioxide in a mass ratio of 3:1; the molecular weight of polyacrylonitrile is 48,000;

[0160] (2) Preparation of polyacrylonitrile stock solution: Add polyacrylonitrile powder to DMAC at 4° C., mix well, and heat to 90° C. through a heat exchanger to completely dissolve the polyacrylonitrile to obtain a polyacrylonitrile stock solution; wherein the mass proportion of polyacrylonitrile in the polyacrylonitrile stock solution is 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90° C. is 9000 mPa.s; the molecular weight of the polyacrylonitrile is 48,000; the polyacrylonitrile stock solution is filtered and degassed for later use;

[0161] (3) preparing spinning solution: the flame retardant slurry is heated to 90° C. by a heat exchanger, and the flame retardant slurry and polyacrylonitrile solution are sent to a static mixer in a mass ratio of 1:4 to be mixed and dispersed uniformly to obtain a spinning solution; wherein the mass ratio of the 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: Spinning the spinning solution to prepare flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90° C., the temperature of the coagulation bath is 55° C., the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, the water washing temperature is 98° C., the spinning speed is 85 m / min, and the total drafting multiple is 7 times, wherein the first water washing drafting is 3.0 times, the second water washing drafting is 1.8 times, and three draftings are performed during the drying process, and the drafting multiples are 1.08 times, 1.09 times and 1.10 times, respectively.

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

[0164] Example 6

[0165] This embodiment adopts the following preparation method to prepare flame-retardant polyacrylonitrile fiber, which specifically includes the following steps:

[0166] (1) Preparation of flame retardant slurry: Add composite flame retardant powder and polyacrylonitrile powder to DMAC at 0°C, grind for 4 hours in a sand mill using zirconium oxide beads with a diameter of 0.6-0.8 mm, and filter using a filter cloth with a pore size of 5 μm to obtain a flame retardant slurry; wherein the mass proportion of the composite flame retardant in the flame retardant slurry is 35%, the mass proportion of polyacrylonitrile in the flame retardant slurry is 5%, and the rotational viscosity of the flame retardant slurry at 90°C is 660 mPa.s; the composite flame retardant comprises ethylenebistetrabromophthalimide and antimony trioxide in a mass ratio of 3:1; the molecular weight of polyacrylonitrile is 48,000;

[0167] (2) Preparation of polyacrylonitrile stock solution: Add polyacrylonitrile powder to DMAC at 4° C., mix well, and heat to 90° C. through a heat exchanger to completely dissolve the polyacrylonitrile to obtain a polyacrylonitrile stock solution; wherein the mass proportion of polyacrylonitrile in the polyacrylonitrile stock solution is 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90° C. is 9000 mPa.s; the molecular weight of the polyacrylonitrile is 48,000; the polyacrylonitrile stock solution is filtered and degassed for later use;

[0168] (3) preparing spinning solution: the flame retardant slurry is heated to 90° C. by a heat exchanger, and the flame retardant slurry and polyacrylonitrile solution are sent to a static mixer in a mass ratio of 1:4 to be mixed and dispersed uniformly to obtain a spinning solution; wherein the mass ratio of the 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: Spinning the spinning solution to prepare flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90° C., the temperature of the coagulation bath is 55° C., the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, the water washing temperature is 98° C., and the spinning speed is 85 m / min; the total drafting multiple is 7 times, wherein the first water washing drafting is 2.6 times, the second water washing drafting is 2.1 times, and three draftings are performed during the drying process, and the drafting multiples are 1.08 times, 1.08 times and 1.10 times, respectively.

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

[0171] Example 7

[0172] This embodiment adopts the following preparation method to prepare flame-retardant polyacrylonitrile fiber, which specifically includes the following steps:

[0173] (1) Preparation of flame retardant slurry: Add composite flame retardant powder and polyacrylonitrile powder to DMAC at 0°C, grind for 4 hours in a sand mill using zirconium oxide beads with a diameter of 0.6-0.8 mm, and filter using a filter cloth with a pore size of 5 μm to obtain a flame retardant slurry; wherein the mass proportion of the composite flame retardant in the flame retardant slurry is 35%, the mass proportion of polyacrylonitrile in the flame retardant slurry is 5%, and the rotational viscosity of the flame retardant slurry at 90°C is 660 mPa.s; the composite flame retardant comprises pentabromobenzyl polyacrylate and antimony trioxide in a mass ratio of 3:1; the molecular weight of polyacrylonitrile is 48,000;

[0174] (2) Preparation of polyacrylonitrile stock solution: Add polyacrylonitrile powder to DMAC at 4° C., mix well, and heat to 90° C. through a heat exchanger to completely dissolve the polyacrylonitrile to obtain a polyacrylonitrile stock solution; wherein the mass proportion of polyacrylonitrile in the polyacrylonitrile stock solution is 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90° C. is 9000 mPa.s; the molecular weight of the polyacrylonitrile is 48,000; the polyacrylonitrile stock solution is filtered and degassed for later use;

[0175] (3) preparing spinning solution: the flame retardant slurry is heated to 90° C. by a heat exchanger, and the flame retardant slurry and polyacrylonitrile solution are sent to a static mixer in a mass ratio of 1:4 to be mixed and dispersed uniformly to obtain a spinning solution; wherein the mass ratio of the 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: Spinning the spinning solution to prepare flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90° C., the temperature of the coagulation bath is 55° C., the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, the water washing temperature is 98° C., and the spinning speed is 85 m / min; the total drafting multiple is 7 times, wherein the first water washing drafting is 2.6 times, the second water washing drafting is 2.1 times, and three draftings are performed during the drying process, and the drafting multiples are 1.08 times, 1.08 times and 1.10 times, respectively.

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

[0178] Example 8

[0179] This embodiment adopts the following preparation method to prepare flame-retardant polyacrylonitrile fiber, which specifically includes the following steps:

[0180] (1) Preparation of flame retardant slurry: Add composite flame retardant powder and polyacrylonitrile powder to DMAC at 0°C, grind for 4 hours in a sand mill using zirconium oxide beads with a diameter of 0.6-0.8 mm, and filter using a filter cloth with a pore size of 5 μm to obtain a flame retardant slurry; wherein the mass proportion of the composite flame retardant in the flame retardant slurry is 35%, the mass proportion of polyacrylonitrile in the flame retardant slurry is 5%, and the rotational viscosity of the flame retardant slurry at 90°C is 660 mPa.s; the composite flame retardant comprises bromotriazine and antimony trioxide in a mass ratio of 3:1; the molecular weight of polyacrylonitrile is 48,000;

[0181] (2) Preparation of polyacrylonitrile stock solution: Add polyacrylonitrile powder to DMAC at 4° C., mix well, and heat to 90° C. through a heat exchanger to completely dissolve the polyacrylonitrile to obtain a polyacrylonitrile stock solution; wherein the mass proportion of polyacrylonitrile in the polyacrylonitrile stock solution is 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90° C. is 9000 mPa.s; the molecular weight of the polyacrylonitrile is 48,000; the polyacrylonitrile stock solution is filtered and degassed for later use;

[0182] (3) preparing spinning solution: the flame retardant slurry is heated to 90° C. by a heat exchanger, and the flame retardant slurry and polyacrylonitrile solution are sent to a static mixer in a mass ratio of 1:4 to be mixed and dispersed uniformly to obtain a spinning solution; wherein the mass ratio of the 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: Spinning the spinning solution to prepare flame-retardant polyacrylonitrile fiber; wherein the temperature of the spinning solution is 90° C., the temperature of the coagulation bath is 55° C., the coagulant in the coagulation bath is DMAC with a mass concentration of 50%, the water washing temperature is 98° C., and the spinning speed is 85 m / min; the total drafting multiple is 7 times, wherein the first water washing drafting is 2.6 times, the second water washing drafting is 2.1 times, and three draftings are performed during the drying process, and the drafting multiples are 1.08 times, 1.08 times and 1.10 times, respectively.

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

[0185] Comparative Example 1

[0186] Based on the above-mentioned Example 1, this example does not add a composite flame retardant to prepare conventional polyacrylonitrile fiber, and specifically includes the following steps:

[0187] (1) preparing polyacrylonitrile spinning stock solution: adding polyacrylonitrile powder to DMAC at 4° C., mixing evenly, heating to 90° C. by a heat exchanger to completely dissolve the polyacrylonitrile, and obtaining a polyacrylonitrile stock solution; wherein the mass proportion of polyacrylonitrile in the polyacrylonitrile stock solution is 25%, the rotational viscosity of the polyacrylonitrile stock solution at 90° C. is 9000 mPa.s; the molecular weight of the polyacrylonitrile is 48000; the polyacrylonitrile stock solution is filtered and degassed for later use;

[0188] (2) Spinning: The spinning solution is used to spin conventional polyacrylonitrile fibers; wherein the temperature of the spinning solution is 90°C, the temperature of the coagulation bath is 55°C, the coagulant in the coagulation bath is DMAC, and the mass concentration is 50%. After coagulation, two water washes are performed, and the water wash temperature is 98°C. In the first water wash, a one-step stretching of 6 times is performed, and the fibers are dried after water washing. The spinning speed is 85 m / min.

[0189] Comparative Example 2

[0190] This comparative example is based on Example 2, except that polyacrylonitrile powder is not added to the flame retardant slurry. Specifically, the adjustment steps (1) and (2) are as follows:

[0191] (1) Preparation of flame retardant slurry: adding composite flame retardant powder to DMAC at 0°C, grinding for 5 hours using zirconium oxide beads with a diameter of 0.6 to 0.8 mm in a sand mill, filtering using a filter cloth with a pore size of 5 μm to obtain a flame retardant slurry; wherein the composite flame retardant accounts for 35% by weight of the flame retardant slurry, and the rotational viscosity of the flame retardant slurry at 90°C is 200 mPa.s; the composite flame retardant comprises brominated polystyrene and antimony trioxide in a mass ratio of 3:1;

[0192] (2) Preparation of polyacrylonitrile stock solution: Add polyacrylonitrile powder to DMAC at 4° C., mix well, and heat to 90° C. through a heat exchanger to completely dissolve the polyacrylonitrile to obtain a polyacrylonitrile stock solution; wherein the mass proportion of polyacrylonitrile in the polyacrylonitrile stock solution is 26.25%, the rotational viscosity of the polyacrylonitrile stock solution at 90° C. is 20,000 mPa.s; the molecular weight of polyacrylonitrile is 48,000; the polyacrylonitrile stock solution is filtered and degassed for later use;

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

[0194] Comparative Example 3

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

[0196] Specifically, this comparative example adopts the following preparation method comprising the following steps to prepare the flame retardant polyacrylonitrile fiber:

[0197] (1) Preparation of flame retardant slurry: Add composite flame retardant powder and polyacrylonitrile powder to DMAC at 0°C, grind for 4 hours in a sand mill using zirconium oxide beads with a diameter of 0.6-0.8 mm, and filter using a filter cloth with a pore size of 5 μm to obtain a flame retardant slurry; wherein the mass proportion of the composite flame retardant in the flame retardant slurry is 35%, the mass proportion of polyacrylonitrile in the flame retardant slurry is 5%, and the rotational viscosity of the flame retardant slurry at 90°C is 660 mPa.s; the composite flame retardant comprises brominated polystyrene and antimony trioxide in a mass ratio of 5:1; the molecular weight of polyacrylonitrile is 48,000;

[0198] (2) Preparation of polyacrylonitrile stock solution: Add polyacrylonitrile powder to DMAC at 4° C., mix well, and heat to 90° C. through a heat exchanger to completely dissolve the polyacrylonitrile to obtain a polyacrylonitrile stock solution; wherein the mass proportion of polyacrylonitrile in the polyacrylonitrile stock solution is 25.0%, the rotational viscosity of the polyacrylonitrile stock solution at 90° C. is 9000 mPa.s; the molecular weight of the polyacrylonitrile is 48,000; the polyacrylonitrile stock solution is filtered and degassed for later use;

[0199] (3) preparing spinning solution: the flame retardant slurry is heated to 90° C. by a heat exchanger, and the flame retardant slurry and polyacrylonitrile solution are sent to a static mixer in a mass ratio of 1:4 to be mixed and dispersed uniformly to obtain a spinning solution; wherein the mass ratio of the 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 fibers; wherein the temperature of the spinning solution is 90°C, the temperature of the coagulation bath is 55°C, the coagulant in the coagulation bath is DMAC, and the mass concentration is 50%. After coagulation, two water washes are performed, and the water washing temperature is 98°C. In the first water wash, a one-step stretching of 6 times is performed, and the fibers are dried after water washing. The spinning speed is 85 m / min.

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

[0202] Test Example 1

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

[0204] Breaking strength test: Determine the breaking strength according to the method provided in GB / T 16602-2008 Acrylic staple fibers and tows;

[0205] Limiting oxygen index test: The obtained polyacrylonitrile fiber is made into a fabric, and the limiting oxygen index is determined by referring to the method provided in "GBT 5454-1997 Textile Combustion Performance Test Oxygen Index Method".

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

[0207] Table 1

[0208] Breaking 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 with Example 2, the spinning process of Example 3 adopts a one-step drafting scheme, and the total drafting multiple is not easy to exceed 6 times. It can be seen that the breaking strength of the fiber prepared in Example 3 is relatively low. Therefore, in the preferred embodiment of the present invention, a multiple-step drafting scheme is adopted to achieve a relatively higher total drafting multiple, which helps to further improve the mechanical properties of the fiber.

[0210] Compared with Example 1, the scheme of Comparative Example 1 obviously does not have flame retardant properties because no composite flame retardant is added. In terms of mechanical properties, the fracture performance of Example 1 only slightly decreases, indicating that the scheme of the present invention can achieve a higher amount of composite flame retardant addition, thereby giving the fiber good flame retardant properties. At the same time, the impact on the mechanical properties of the fiber is within an acceptable range, and its application range will not be limited due to insufficient mechanical properties.

[0211] In the scheme of Comparative Example 2, polyacrylonitrile was not added to the flame retardant slurry. Compared with Example 2, the breaking strength was slightly decreased and the limiting oxygen index was significantly reduced. It can be seen that the scheme of 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 with Example 1, the mass ratio of the bromine flame retardant to antimony trioxide in the composite flame retardant of Comparative Example 3 is 5:1, which exceeds the range of the mass ratio in the scheme of the present invention, and the measured limiting oxygen index is significantly lower than that in Example 1. It can be seen that when the proportion of antimony trioxide in the composite flame retardant is too small, the flame retardant properties of the obtained fiber will be affected.

[0213] Test Example 2

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

[0215] A series of flame retardant polyacrylonitrile fiber samples were prepared in the above manner, and their flame retardant properties and mechanical properties were tested. The testing method was the same as that in Example 1. The results are shown in Table 2.

[0216] Table 2

[0217]

[0218] From the above test data, it can be seen that the change of polyacrylonitrile content in the flame retardant slurry has little effect on the fiber breaking strength, but with the increase of polyacrylonitrile content in the flame retardant slurry, the limiting oxygen index shows an upward trend within a certain range. When the mass proportion of polyacrylonitrile in the flame retardant slurry is controlled at 5% to 9%, the limiting oxygen index can reach no less than 29.5.

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

[0220] After the mass proportion of polyacrylonitrile in the flame retardant slurry exceeds 7%, the limiting oxygen index does not change significantly if the mass proportion is further increased. Therefore, in a more preferred embodiment of the present invention, the mass proportion of polyacrylonitrile in the flame retardant slurry is controlled at 7%.

[0221] Test Example 3

[0222] This test example is used to investigate the effect of the compounding ratio of the composite flame retardant on the 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 the other process steps and parameters are the same as those in Example 2.

[0223] A series of flame retardant polyacrylonitrile fiber samples were prepared in the above manner, and their flame retardant properties and mechanical properties were tested. The testing method was the same as that in Example 1. The results are shown in Table 3.

[0224] Table 3

[0225] X:Y Breaking 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] It can be seen from the above test data that by controlling the mass ratio of the brominated flame retardant to antimony trioxide in the composite flame retardant to 1.8-3.5:1, a flame-retardant polyacrylonitrile fiber with a breaking strength of not less than 2.5 cN / dtex and a limiting oxygen index of not less than 26.5 can be obtained. In the preferred scheme, the above mass ratio is controlled at 2.3-3.0:1, the breaking strength of the fiber can reach more than 2.7 cN / dtex, and the limiting oxygen index can reach more than 30. In the more preferred scheme, the above mass ratio is controlled to 3.0:1, and a flame-retardant polyacrylonitrile fiber with a breaking strength of 3.1 cN / dtex and a limiting oxygen index of 30.4 can be obtained, and its flame retardant properties and mechanical properties can reach a high level.

[0227] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment, it is not used to limit the present invention. Any technician familiar with this patent can make some changes or modify the technical contents suggested above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the solution of the present invention.

Claims

1. A method for preparing flame-retardant polyacrylonitrile fiber, characterized in that: The following steps are involved: (1) adding composite flame retardant powder and polyacrylonitrile powder to dimethylacetamide, grinding and dispersing, and then filtering to obtain a flame retardant slurry; (2) adding polyacrylonitrile powder to dimethylacetamide, mixing evenly, and heating until completely dissolved to obtain a polyacrylonitrile stock solution; (3) mixing the flame retardant slurry and the polyacrylonitrile stock solution uniformly according to a mass ratio of the composite flame retardant to polyacrylonitrile of 1:2.3-4.0 to obtain a spinning stock solution; (4) The spinning solution is used to spin flame-retardant polyacrylonitrile fibers.

2. The method for preparing the flame-retardant polyacrylonitrile fiber according to claim 1, characterized in that: In step (1), the mass proportion of the composite flame retardant in the flame retardant slurry is 30% to 40%, and the mass proportion of polyacrylonitrile in the flame retardant slurry is 3% to 9%; 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 in a mass ratio of 1:3 to 10.

3. The method for preparing the flame-retardant polyacrylonitrile fiber according to claim 1 or 2, characterized in that: In step (1), the 90°C rotational viscosity of the flame retardant slurry is 200 to 1700 mPa.s; In step (2), the rotational viscosity of the polyacrylonitrile stock solution at 90°C is 2000 to 11000 mPa.s.

4. The method for preparing the flame-retardant polyacrylonitrile fiber according to any one of claims 1 to 3, characterized in that: In steps (1) and (2), the temperature of dimethylacetamide is 0 to 10°C, preferably 0 to 4°C.

5. The method for preparing the flame-retardant polyacrylonitrile fiber according to any one of claims 1 to 4, characterized in that: In step (1), the composite flame retardant comprises 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; Preferably, the brominated flame retardant includes one or more of tetrabromobisphenol A-bis(2,3-dibromopropyl ether), decabromodiphenylethane, brominated polystyrene, ethylenebistetrabromophthalimide, polypentabromobenzyl acrylate, and bromotriazine.

6. The method for preparing the flame-retardant polyacrylonitrile fiber according to any one of claims 1 to 5, characterized in that: In step (1), zirconia beads having a diameter of 0.4 to 2.0 mm are used for grinding in a sand mill; Preferably, the grinding time is 2 to 8 hours.

7. The method for preparing the flame-retardant polyacrylonitrile fiber according to any one of claims 1 to 6, characterized in that: In step (1), the filtration accuracy is 5 to 20 μm, preferably 5 to 10 μm.

8. The method for preparing the flame-retardant polyacrylonitrile fiber according to any one of claims 1 to 7, characterized in that: In step (2), the heating temperature is 85 to 95° C., preferably 90 to 95° C.; And / or, the molecular weight of polyacrylonitrile is 40,000 to 60,000.

9. The method for preparing the flame-retardant polyacrylonitrile fiber according to any one of claims 1 to 8, characterized in that: In step (4), the temperature of the spinning solution is 50-90°C, the temperature of the coagulation bath is 40-60°C, the mass concentration of the coagulation bath is 40%-60%, the water washing temperature is 90-99°C, the spinning speed is 20-100 m / min, and the total drafting multiple is 5-8 times.

10. A flame retardant polyacrylonitrile fiber, characterized in that: It comprises 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 mass proportion of the composite flame retardant in the flame-retardant polyacrylonitrile fiber is 20% to 30%; Preferably, the flame retardant polyacrylonitrile fiber is prepared by the method for preparing the flame retardant polyacrylonitrile fiber according to any one of claims 1 to 9; 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.

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