CN112708969A - Preparation method of polyacrylonitrile pre-oxidized fiber - Google Patents
Preparation method of polyacrylonitrile pre-oxidized fiber Download PDFInfo
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- CN112708969A CN112708969A CN201911019198.7A CN201911019198A CN112708969A CN 112708969 A CN112708969 A CN 112708969A CN 201911019198 A CN201911019198 A CN 201911019198A CN 112708969 A CN112708969 A CN 112708969A
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
- D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
- D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
- D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
- D01F9/20—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products
- D01F9/21—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D01F9/22—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyacrylonitriles
- D01F9/225—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyacrylonitriles from stabilised polyacrylonitriles
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Abstract
The invention relates to a preparation method of polyacrylonitrile pre-oxidized fiber, which mainly solves the problems of easy strand burnout, unstable preparation process and large bulk density fluctuation in the prior art. The method comprises the steps of sequentially carrying out pretreatment, multi-section high-temperature air treatment and post-treatment on polyacrylonitrile tows to prepare polyacrylonitrile pre-oxidized fibers; the method for multi-stage high-temperature air treatment comprises the following steps: heating the pretreated polyacrylonitrile tow in at least 3 temperature zones; after pretreatment, the increase percentage of the bulk density of the fibers in the polyacrylonitrile tow is less than or equal to 0.5 percent; after multi-section high-temperature air treatment, the bulk density of the obtained fiber in each temperature zone meets the following requirements: [ (rho) is more than or equal to 0.85N/ρN+1)/(ρN+1/ρN+2)]21.18 or less, wherein rhoN、ρN+1、ρN+2Respectively the bulk density of the fiber obtained after the fiber passes through N, N +1 and N +2 temperature zones, wherein N is a positive integer. The method has the advantages of difficult strand burnout, stable preparation process, small fiber density fluctuation and good economy, and is suitable for gatheringIn the industrial production of pre-oxidized acrylonitrile fiber.
Description
Technical Field
The invention belongs to the technical field of preparation of pre-oxidized fibers, and particularly relates to a preparation method of polyacrylonitrile pre-oxidized fibers, and more particularly relates to a method for preparing polyacrylonitrile pre-oxidized fibers by taking polyacrylonitrile copolymer fibers prepared by dry spinning as a raw material.
Background
The Polyacrylonitrile (PAN) pre-oxidized fiber has the characteristics of extremely high heat resistance, flame retardance, corrosion resistance, infusibility and no softening, and simultaneously has sufficient strength and extensibility and excellent processability. Compared with asbestos and glass fiber, the asbestos fiber has good draping feeling, has the characteristics of low density and high water content, and can be used as clothing material. Meanwhile, the heat-insulating material has the characteristics of good heat-insulating property and electrical insulating property, and can be used as a raw material of a fire-resistant filler, an insulating work garment, a fire-fighting garment and a welding work garment.
At high temperature, polyacrylonitrile protofilament is subjected to a series of chemical and physical changes in the air atmosphere to form polyacrylonitrile pre-oxidized fiber. In the process, the linear molecular chain of the PAN protofilament is converted into a heat-resistant ladder-shaped structure, so that the PAN protofilament has the properties of no melting, no softening, high temperature resistance and the like.
The preparation method of the polyacrylonitrile protofilament can be divided into wet spinning, dry-jet wet spinning and melt spinning according to the different spinning methods of the nascent fiber, and the polyacrylonitrile protofilament prepared by different spinning methods can be used for preparing the pre-oxidized fiber. However, the spinning method can cause the prepared polyacrylonitrile protofilament to have different surface appearance, fiber compactness, internal pore structure, crystallinity, orientation degree, oil content and the like, so that the subsequent polyacrylonitrile pre-oxidized fiber has obvious difference.
The dry spinning of polyacrylonitrile protofilament is to dissolve polyacrylonitrile copolymer in solvents such as dimethyl formamide, extrude polyacrylonitrile copolymer solution from spinneret capillary hole, enter spinning channel, inject high-temperature inert gas into the channel, the solvent volatilizes from polyacrylonitrile copolymer solution fast under high temperature, the volatilized solvent is taken away by high-temperature inert gas, while removing the solvent gradually, the stock solution trickle is drawn by high power and stretched into filament, thus form the nascent fiber; and (3) carrying out subsequent processes of secondary drafting, washing, oiling and shaping on the nascent fiber to form polyacrylonitrile protofilament.
The process for preparing the polyacrylonitrile protofilament by the dry spinning has the advantages of high solid content, high spinning speed and the like, and the prepared polyacrylonitrile protofilament has the characteristics of high fiber compactness, high mechanical strength and the like. Meanwhile, the cross section of the protofilament presents a dumbbell shape, so that the protofilament has different wearing touch feeling and clothes style from the conventional circular cross section or flat cross section prepared by other spinning methods when being used as clothes fiber.
The preparation process of the polyacrylonitrile pre-oxidized fiber comprises the processes of tow spreading, pre-drying, secondary spreading, multi-section high-temperature air treatment, sizing, post-drying, filament winding and the like, wherein the high-temperature treatment process is an important process for preparing the pre-oxidized fiber, a series of chemical and physical changes mainly occur in the process, a large amount of heat is generated in the process, and improper treatment processes can cause the heat release of the tows to be concentrated to cause the tows to be heated and broken. Patents CN109440230A and CN109537106A disclose methods for preparing polyacrylonitrile precursor, pre-oxidized fiber or carbon fiber, but the disclosed method for spinning polyacrylonitrile precursor is wet spinning or dry-jet wet spinning, and does not disclose flow and process for preparing pre-oxidized fiber, nor process control parameters for preparing pre-oxidized fiber. Patent CN104662214B discloses a preparation method of polyacrylonitrile preoxidized fiber with kidney-shaped section, the fiber section in the patent presents kidney-shaped section peculiar to wet spinning, and is obviously different from dumbbell-shaped section of dry spinning, and the fiber is used as intermediate fiber in the preparation process of carbon fiber.
In view of the defects of easy strand burnout, unstable preparation process and large bulk density fluctuation existing in the process of preparing carbon fibers by using the existing dry spinning polyacrylonitrile fibers as preoxidation precursors, and the influence on the service performance of products due to the close relationship between the bulk density and the flame retardant coefficient, the method for preparing the polyacrylonitrile preoxidation fibers by using the polyacrylonitrile copolymer fibers prepared by the dry spinning as raw materials, which is difficult to strand burnout, stable in preparation process and small in bulk density fluctuation, is urgently needed to be researched and developed.
Disclosure of Invention
The invention aims to solve the technical problem of providing a preparation method of polyacrylonitrile pre-oxidized fiber aiming at the defects of the prior art. The method better solves the problems of easy burnout of the wire harness, unstable preparation process and large bulk density fluctuation, and has the advantages of difficult burnout of the filament bundle in the spinning process, stable preparation process and small bulk density fluctuation.
In order to solve the technical problems, the invention provides a preparation method of polyacrylonitrile pre-oxidized fiber, which comprises the following steps: sequentially carrying out pretreatment, multi-section high-temperature air treatment and post-treatment on polyacrylonitrile tows to prepare polyacrylonitrile preoxidized fiber; the method for multi-stage high-temperature air treatment comprises the following steps: heating the pretreated polyacrylonitrile tow in at least 3 temperature zones, preferably 3 to 5 temperature zones;
after the pretreatment, the increase percentage of the bulk density of the fibers in the polyacrylonitrile tow is less than or equal to 0.5 percent;
after the multi-section high-temperature air treatment, the bulk density of the obtained fiber in each temperature area meets the following conditions: [ (rho) is more than or equal to 0.85N/ρN+1)/(ρN+1/ρN+2)]21.18 or less, wherein rhoN、ρN+1、ρN+2Respectively the bulk density of the fiber obtained after the fiber passes through N, N +1 and N +2 temperature zones, wherein N is a positive integer.
In the invention, the effect of small fluctuation of the bulk density of the obtained polyacrylonitrile preoxidized fiber is realized by controlling the relationship among the bulk densities of the fibers obtained in each temperature zone.
In the process of the multi-section high-temperature air treatment, the formation of a pre-oxidized fiber structure is difficult to achieve only through 1 or 2 temperature zones with gradually rising temperature, and generally longer oxidation time is needed, the energy consumption is higher, and the economy is poor. In the invention, 3-5 high-temperature treatment temperature zones are preferably adopted to ensure that the fiber structure is slowly changed, and the stable structure of the pre-oxidized fiber is slowly formed by controlling a proper fiber body density increasing value. From the viewpoint of equipment investment and running cost, the more the number of temperature zones is, the better, and when more than 6 temperature zones are employed, the economical efficiency becomes poor. Through setting up multistage high temperature air treatment of 3 at least temperature zones for the silk bundle is difficult for burning out, and the preparation process is stable.
In the technical scheme, in the process of the multi-section high-temperature air treatment, the flow direction of the adopted hot air flow is reverse to the running direction of the polyacrylonitrile tows.
In the invention, the multi-section high-temperature air treatment can adopt a tubular furnace or a box furnace, preferably adopts the tubular furnace, because the tows usually return and run in a high-temperature section, the blowing direction and the tow direction can be ensured to be opposite by adopting the tubular furnace, the tow running direction and the hot air direction can not be ensured to be opposite by adopting the box furnace, and the tow running direction and the hot air direction are inevitably in the same direction.
In the technical scheme, in the process of the multi-section high-temperature air treatment, the drafting ratio of the fibers in the polyacrylonitrile tows is gradually reduced. In order to avoid the fiber from freely shrinking to form a large number of defects in the pre-oxidized fiber in the multi-stage high-temperature air treatment process, a certain drawing ratio is usually required to be applied in the fiber treatment process. In the process of multi-section high-temperature air treatment, a fiber cyclization structure is formed, the interaction between molecular chains is changed, and the mechanical strength is reduced, so that the fiber drafting ratio of the polyacrylonitrile filament bundle is gradually reduced. In the invention, the drafting ratio of the fiber in the polyacrylonitrile tow of each temperature zone is controlled to be less than or equal to 1.05 times.
In the invention, the multi-stage high-temperature air treatment temperature is not too low, the temperature is too low, longer treatment time is needed, and the treatment economy is poor. Therefore, the minimum temperature of the multi-stage high-temperature air treatment is more than or equal to 250 ℃. Furthermore, the temperature of each temperature zone included in the multi-stage high-temperature air treatment is gradually increased along the running direction of the polyacrylonitrile filament bundle to give higher energy for the next reaction.
In the above technical scheme, the polyacrylonitrile filament bundle is polyacrylonitrile fiber (i.e., polyacrylonitrile precursor) prepared by a dry spinning method. The protofilament can adopt the mode of case dress or package, preferably adopts the mode of case dress, and it has the advantage that connects few, reduces frequent grafting and leads to stopping. The cross section of the fiber is dumbbell-shaped, and the linear density of the fiber is 1.5-2.0detx according to the application of the dumbbell-shaped pre-oxidized fiber. In order to improve the economical efficiency of the preparation process, the number of the polyacrylonitrile tows (single-strand fibers) is 30000-300000. When the number of the fibers exceeds 300000, the preparation process has poor adjustability; if the number of the catalyst particles is less than 30000, the economic efficiency is deteriorated. In order to reduce the electrostatic enhancement of the fiber caused by the water volatilization of the precursor in the storage process and reduce the production cost during the precursor, the water content of the precursor can be properly increased, and the water content of the polyacrylonitrile filament bundle is preferably less than or equal to 5 wt%. When the moisture content of the polyacrylonitrile tow is more than 5 wt%, excessive shrinkage of the fiber during pre-drying is caused, so that the tow is more likely to be fluffed.
In the technical scheme, the initial bulk density of the fibers in the polyacrylonitrile tow is 1.18-1.195g/cm3The bulk density of the obtained polyacrylonitrile pre-oxidized fiber (final product) is 1.36-1.38g/cm3. In the invention, the bulk density of the obtained polyacrylonitrile pre-oxidized fiber is the bulk density of the pre-oxidized fiber obtained in the last temperature zone of the multi-section high-temperature air treatment.
In the technical scheme, in order to ensure that the high-temperature polyacrylonitrile protofilament subjected to multi-section high-temperature air treatment has a proper width, the polyacrylonitrile filament bundle needs to be pretreated. The pretreatment comprises a primary spreading treatment, a pre-drying treatment and a secondary spreading treatment. The spreading treatment and the pre-drying treatment of the polyacrylonitrile filament bundle are used for ensuring that the filament bundle has a proper width before entering the multi-section high-temperature air treatment furnace.
In the technical scheme, the spreading treatment adopts a method of flattening by a rubber pressing roller, so that the width of the fiber with certain water content is gradually widened. Preferably, the pressure of the rubber compression roller is less than or equal to 0.2 MPa. The compression roller is preferably made of butyronitrile, ethylene propylene rubber or silicon rubber, the Shore A hardness of the compression roller is preferably 50-70, the damage to the tows is increased when the hardness is too high, and the tows are not flattened when the hardness is too low.
Among the above-mentioned technical scheme, in the predrying process, the tension between high temperature air and the drive roller in the predrying furnace makes the silk bundle further widen and make the fibre blow away, does benefit to the fibre and has the same water content and the quicker discharge preoxidation heat before getting into multistage high temperature air treatment stove. The fiber glass transition temperature is reduced due to a certain amount of moisture contained in the filament bundle, so the temperature of the pre-drying treatment is not high, and the temperature of the pre-drying treatment is preferably less than or equal to 130 ℃. In the preliminary drying process, moisture is mainly volatilized between fibers or inside the fibers, and a gas may be used, and nitrogen is preferable, but air is preferable from the viewpoint of economy. The pre-drying medium of the pre-drying process is therefore preferably a stream of hot air, the direction of flow of which is counter to the direction of travel of the polyacrylonitrile tow. In order to reduce the damage of microscopic particle impurities in the air to the fiber tows, the air needs to be filtered, and the air is preferably filtered by a non-woven fabric folded filter element from the aspects of economy and fiber mechanical property, and the filtering precision is preferably 0.5-5 μm, and more preferably 1-2 μm.
In the present invention, the pre-drying treatment will increase the bulk density of the fiber, and can be controlled by the pre-drying temperature and time, but it is generally not desirable to increase the bulk density too high. When the bulk density of the fiber is increased too high, or it will result in densification of the surface structure of the fiber, it is detrimental to the diffusion of oxygen into the fiber interior during subsequent high temperature processes.
In the technical scheme, the post-treatment comprises sizing treatment, post-drying treatment and silk collecting treatment. After multi-stage high-temperature air treatment, in order to increase the subsequent processability of the fibers, the fibers need to be subjected to sizing treatment. After the sizing treatment, post-drying treatment is needed, wherein the temperature of the post-drying treatment is less than or equal to 120 ℃, so that the bonding between fibers caused by too high temperature and too fast volatilization of a sizing agent is avoided.
In the present invention, the composition of the polyacrylonitrile-based copolymer is not particularly limited, for example, but not limited thereto, the polyacrylonitrile-based comonomer is a vinyl-containing monomer, and preferably, the comonomer is one or more of acrylates, vinyl esters, acrylamides, sulfonates, and ammonium salts.
The substances (e.g., sizing agent, etc.) used in the present invention are those commonly used in the art, unless otherwise specified.
Compared with the prior art, the invention has the following beneficial effects:
the preparation method of the polyacrylonitrile pre-oxidized fiber provided by the invention can use dry spinning to prepare the polyacrylonitrile copolymer fiber as a raw material, stably prepare the polyacrylonitrile pre-oxidized fiber, avoid the problems of overheating fracture of polyacrylonitrile protofilament of a larger tow and large fluctuation of bulk density of the fiber in the oxidation treatment process, and simultaneously has the advantage of good economy.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings.
FIG. 1 shows an optical microscope photograph of a polyacrylonitrile pre-oxidized fiber prepared according to the method of the present invention.
Detailed Description
In order that the present invention may be more readily understood, the following detailed description of the invention is given by way of example only, and is not intended to limit the scope of the invention.
The measurement method provided by the invention comprises the following steps:
(1) the method for measuring the water content of the polyacrylonitrile tows comprises the following steps: randomly taking 10m long tows, and measuring the weight W of the tows0The tow was placed in a vacuum oven at 80 ℃ under an absolute pressure of 1KPa for 10 hours, and the weight W of the tow was measured1The water content of the tow is%0-W1)/W0×100％。
(2) Method for measuring linear density of fiber: the GB/T14343-2008 method is adopted.
(3) Method for measuring density of fiber body: the density gradient column method is adopted for measurement.
(4) CV value (reflecting the size of bulk density fluctuation) measurement method of the fiber bulk density: randomly taking 20 samples for testing, and obtaining the product after mathematical analysis.
Examples
Example 1
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.5%. The multi-section high-temperature air treatment adopts a tubular furnace for heating, and is divided into three temperature zones, wherein the temperature of the three temperature zones is 250 ℃, 260 ℃ and 267 ℃ respectively along the running direction of the polyacrylonitrile filament bundle. The fiber draft ratios of the three temperature zones are respectively 1, 0.99 and 0.98 times. After the treatment of three temperature zones, the bulk density of the fiber obtained in each temperature zone is 1.2100g/cm3、1.2800g/cm3、1.3640g/cm3. After high-temperature air treatment, the tows are subjected to sizing treatment by a sizing agent with the solid content of 3 wt%, and then are dried at 120 ℃ and then are wound to obtain the preoxidized fiber continuous tows. The preparation process is stable, and the obtained fiber has a CV value of bulk density of 5.2%.
Example 2
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.5%. The multi-section high-temperature air treatment adopts a tubular furnace for heating, and is divided into three temperature zones, wherein the temperature of the three temperature zones is 255 ℃, 258 ℃ and 267 ℃ respectively along the running direction of the polyacrylonitrile filament bundle. The fiber draft ratios of the three temperature zones are respectively 1, 0.99 and 0.98 times. After the treatment of three temperature zones, the bulk density of the fiber obtained in each temperature zone is 1.2499g/cm3、1.2587g/cm3、1.3742g/cm3. After high-temperature air treatment, the tows are subjected to sizing treatment by a sizing agent with the solid content of 3 wt%, and then are dried at 120 ℃ and then are wound to obtain the preoxidized fiber continuous tows. The preparation process is stable, and the obtained fiber has a bulk density CV value of 4.3%.
Example 3
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.5%. The multi-section high-temperature air treatment adopts a tubular furnace for heating, and is divided into three temperature zones, wherein the temperature of the three temperature zones is 250 ℃, 257 ℃ and 270 ℃ respectively along the running direction of the polyacrylonitrile filament bundle. The fiber draft ratios of the three temperature zones are respectively 1, 0.99 and 0.98 times. After the treatment of three temperature zones, the bulk density of the fiber obtained in each temperature zone is 1.2103g/cm3、1.2696g/cm3、1.3800g/cm3. After high-temperature air treatment, the tows are subjected to sizing treatment by a sizing agent with the solid content of 3 wt%, and then are dried at 120 ℃ and then are wound to obtain the preoxidized fiber continuous tows. The preparation process is stable, and the obtained fiber has a CV value of bulk density of 5.3%.
Example 4
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.5%. The multi-section high-temperature air treatment adopts a tubular furnace for heating, and is divided into four temperature zones, and the temperatures of the four temperature zones are 250 ℃, 257 ℃, 259 ℃ and 265 ℃ respectively along the running direction of the polyacrylonitrile filament bundle. The fiber draft ratios of the four temperature zones are respectively 1, 0.99, 0.98 and 0.97 times. After four temperature zones, the bulk density of the fiber obtained in each temperature zone is 1.2103g/cm3、1.2696g/cm3、1.3243g/cm3、1.3797g/cm3. After high-temperature air treatment, the tows are subjected to sizing treatment by a sizing agent with the solid content of 3 wt%, and then are dried at 120 ℃ and then are wound to obtain the preoxidized fiber continuous tows. TheThe preparation process is stable, and the obtained fiber has a bulk density CV value of 3.8 percent.
Example 5
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.5%. The multi-section high-temperature air treatment adopts a tubular furnace for heating, and is divided into four temperature zones, and the four temperature zones have the temperatures of 250 ℃, 254 ℃, 257 ℃ and 265 ℃ along the running direction of the polyacrylonitrile filament bundle. The fiber draft ratios of the four temperature zones are respectively 1, 0.99, 0.98 and 0.97 times. After four temperature zones, the bulk density of the fiber obtained in each temperature zone is 1.2102g/cm3、1.2202g/cm3、1.3224g/cm3、1.3795g/cm3. After high-temperature air treatment, the tows are subjected to sizing treatment by a sizing agent with the solid content of 3 wt%, and then are dried at 120 ℃ and then are wound to obtain the preoxidized fiber continuous tows. The preparation process is stable, and the obtained fiber has a bulk density CV value of 3.3%.
Example 6
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.5%. The multi-section high-temperature air treatment adopts a tube furnace for heating, and is divided into five temperature zones, and the temperature of the five temperature zones is 250 ℃, 254 ℃, 257 ℃, 260 ℃ and 262 ℃ respectively along the running direction of the polyacrylonitrile filament bundle. The fiber draft ratios of the five temperature zones are respectively 1, 0.99, 0.98, 0.97 and 0.96 times. After five temperature zones, the bulk density of the fiber obtained in each temperature zone is 1.2102g/cm3、1.2203g/cm3、1.2504g/cm3、1.3108g/cm3、1.3602g/cm3. After high-temperature air treatment, the tows are subjected to sizing treatment by a sizing agent with the solid content of 3 wt%, and then are dried at 120 ℃ and then are wound to obtain the preoxidized fiber continuous tows. The preparation process is stable, and the obtained fiber has a bulk density CV value of 4.3%.
Example 7
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.5%. The multistage high-temperature air treatment adopts a tubular furnace for heating, and is divided into three temperature zones, wherein the temperature of the three temperature zones is 250 ℃, 263 ℃ and 268 ℃ respectively along the running direction of the polyacrylonitrile filament bundle. The fiber draft ratios of the three temperature zones are respectively 1, 0.99 and 0.98 times. After the treatment of three temperature zones, the bulk density of the fiber obtained in each temperature zone is 1.2106g/cm3、1.3395g/cm3、1.3665g/cm3. After high-temperature air treatment, the tows are subjected to sizing treatment by a sizing agent with the solid content of 3 wt%, and then are dried at 120 ℃ and then are wound to obtain the preoxidized fiber continuous tows. The preparation process is stable, and the obtained fiber has a bulk density CV value of 6.0%.
Comparative example 1
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.5%. The multistage high-temperature air treatment adopts a tubular furnace for heating, and is divided into two temperature zones, wherein the temperature of the two temperature zones is 250 ℃ and 270 ℃ respectively along the running direction of the polyacrylonitrile filament bundle. The fiber draft ratios of the two temperature zones are 1 and 0.99 times respectively. After the treatment of two temperature zones, the bulk density of the obtained fiber in each temperature zone is 1.2104g/cm3、1.3612g/cm3. The stability is poor in the fiber preparation process, and the phenomenon of fiber burning-out can occur.
Comparative example 2
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.52%. The multistage high-temperature air treatment adopts a tubular furnace for heating, and is divided into three temperature zones, wherein the temperature of the three temperature zones is 250 ℃, 260 ℃ and 269 ℃ respectively along the running direction of the polyacrylonitrile filament bundle. The fiber draft ratios of the three temperature zones are respectively 1, 0.99 and 0.98 times. After the treatment of three temperature zones, the bulk density of the fiber obtained in each temperature zone is 1.211g/cm3、1.282g/cm3、1.365g/cm3. After high-temperature air treatment, the tows are subjected to sizing treatment by a sizing agent with the solid content of 3 wt%, and then are dried at 120 ℃ and then are wound to obtain the preoxidized fiber continuous tows. The preparation process is stable, and the obtained fiber has a bulk density CV value of 7.2%.
Comparative example 3
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.5%. The multi-section high-temperature air treatment adopts a tubular furnace for heating, and is divided into six temperature zones, and the temperature of the six temperature zones is 250 ℃, 253 ℃, 255 ℃, 258 ℃, 265 ℃ and 267 ℃ along the running direction of the polyacrylonitrile filament bundle. The fiber draft ratios of the six temperature zones are respectively 1, 0.99, 0.98, 0.97, 0.96 and 0.95 times. After six temperature zones, the bulk density of the fiber obtained in each temperature zone is 1.2102g/cm3、1.2203g/cm3、1.2504g/cm3、1.2881g/cm3、1.3108g/cm3、1.3608g/cm3. After high-temperature air treatment, the tows are subjected to sizing treatment by a sizing agent with the solid content of 3 wt%, and then are dried at 120 ℃ and then are wound to obtain the preoxidized fiber continuous tows. The preparation process is stable, the CV value of the bulk density of the obtained fiber is 4.3%, and the energy consumption of equipment is increased by 20% compared with that of a five-temperature zone.
Comparative example 4
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.5%. The multistage high-temperature air treatment adopts a tubular furnace for heating, and is divided into three temperature zones, wherein the temperature of the three temperature zones is 254 ℃, 258 ℃ and 264 ℃ respectively along the running direction of the polyacrylonitrile filament bundle. The fiber draft ratios of the three temperature zones are respectively 1, 0.99 and 0.98 times. After the treatment of three temperature zones, the bulk density of the fiber obtained in each temperature zone is 1.2499g/cm3、1.2520g/cm3、1.364g/cm3. After high-temperature air treatment, the tows are subjected to sizing treatment by a sizing agent with the solid content of 3 wt%, and then are dried at 120 ℃ and then are wound to obtain the preoxidized fiber continuous tows. The preparation process is stable, and the obtained fiber has a CV value of bulk density of 9.3%.
Comparative example 5
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.5%. The multistage high-temperature air treatment adopts a tubular furnace for heating, and is divided into three temperature zones, wherein the temperature of the three temperature zones is 254 ℃, 258 ℃ and 268 ℃ respectively along the running direction of the polyacrylonitrile filament bundle. Fiber of three temperature zonesThe draft ratios were 1, 0.99, and 0.98 times, respectively. After the treatment of three temperature zones, the bulk density of the fiber obtained in each temperature zone is 1.2499g/cm3、1.2520g/cm3、1.37g/cm3. After high-temperature air treatment, the tows are subjected to sizing treatment by a sizing agent with the solid content of 3 wt%, and then are dried at 120 ℃ and then are wound to obtain the preoxidized fiber continuous tows. The preparation process is stable, and the obtained fiber has a bulk density CV value of 11.3%.
Comparative example 6
At a bulk density of 1.192g/cm3And the linear density is 1.5dtex, the dry spinning is carried out to prepare the polyacrylonitrile filament bundle, the number of filament bundle fibers is 300000, and the water content of the fibers is 5wt percent. The polyacrylonitrile filament bundle is flattened under a 0.2MPa ethylene propylene rubber compression roller, air is used as a heating medium for pre-drying, the flow direction of hot air is reverse to the running direction of the filament bundle, the pre-drying temperature is 130 ℃, and the bulk density of the fiber after pre-drying treatment is increased by 0.5%. The multi-section high-temperature air treatment adopts a tubular furnace for heating, and is divided into three temperature zones, wherein the temperature of the three temperature zones is 253 ℃, 262 ℃ and 264 ℃ respectively along the running direction of the polyacrylonitrile filament bundle. The fiber draft ratios of the three temperature zones are respectively 1, 0.99 and 0.98 times. After the treatment of three temperature zones, the bulk density of the fiber obtained in each temperature zone is 1.2105g/cm3、1.343g/cm3、1.3604g/cm3. After high-temperature air treatment, the tows are subjected to sizing treatment by a sizing agent with the solid content of 3 wt%, and then are dried at 120 ℃ and then are wound to obtain the preoxidized fiber continuous tows. The preparation process is stable, and the obtained fiber has a bulk density CV value of 14.1%.
As can be seen from the above examples and comparative examples, the preparation method of the polyacrylonitrile pre-oxidized fiber provided by the invention can stably prepare the polyacrylonitrile pre-oxidized fiber by using the polyacrylonitrile copolymer fiber prepared by dry spinning as a raw material. As can be seen from FIG. 1, the interface of the obtained fiber is in a special dumbbell shape, which is different from a general round structure, and the oxidation preparation process is different from the round structure. In addition, in the oxidation preparation process, the polyacrylonitrile protofilament is not easy to burn off, the obtained fiber has small bulk density fluctuation and good economical efficiency, and better effect is obtained.
It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The present invention has been described with reference to exemplary embodiments, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.
Claims (10)
1. A method for preparing a polyacrylonitrile pre-oxidized fiber, comprising: sequentially carrying out pretreatment, multi-section high-temperature air treatment and post-treatment on polyacrylonitrile tows to prepare polyacrylonitrile preoxidized fiber;
the method for multi-stage high-temperature air treatment comprises the following steps: heating the pretreated polyacrylonitrile tow in at least 3 temperature zones, preferably 3 to 5 temperature zones;
after the pretreatment, the increase percentage of the bulk density of the fibers in the polyacrylonitrile tow is less than or equal to 0.5 percent;
after the multi-section high-temperature air treatment, the bulk density of the obtained fiber in each temperature area meets the following conditions: [ (rho) is more than or equal to 0.85N/ρN+1)/(ρN+1/ρN+2)]21.18 or less, wherein rhoN、ρN+1、ρN+2Respectively the bulk density of the fiber obtained after the fiber passes through N, N +1 and N +2 temperature zones, wherein N is a positive integer.
2. The method as claimed in claim 1, wherein the hot air flow is in a direction opposite to the direction of the polyacrylonitrile filament bundle during the multi-stage high temperature air treatment.
3. The preparation method according to claim 1 or 2, characterized in that in the multi-stage high-temperature air treatment process, the draft ratio of the fibers in the polyacrylonitrile tow is gradually reduced, and the draft ratio of the fibers in the polyacrylonitrile tow in each temperature zone is less than or equal to 1.05 times.
4. The method according to any one of claims 1 to 3, wherein the minimum temperature of the multi-stage high temperature air treatment is not less than 250 ℃.
5. The production method according to any one of claims 1 to 4, wherein the polyacrylonitrile tow is a fiber produced by a dry spinning method; the cross section of the fiber is dumbbell-shaped, and the linear density of the fiber is 1.5-2.0 detx;
the number of the fibers of the polyacrylonitrile fiber bundle is 30000-300000; the water content of the polyacrylonitrile tows is less than or equal to 5 wt%.
6. The method according to any one of claims 1 to 5, wherein the initial bulk density of the fibers in the polyacrylonitrile tow is 1.18 to 1.195g/cm3The bulk density of the obtained polyacrylonitrile pre-oxidized fiber is 1.36-1.38g/cm3。
7. The production method according to any one of claims 1 to 6, wherein the pretreatment includes a primary spreading treatment, a pre-drying treatment, and a secondary spreading treatment.
8. The production method according to claim 7, wherein the spreading process is a method of flattening with a rubber roller; preferably, the pressure of the rubber compression roller is less than or equal to 0.2 MPa.
9. The preparation method according to claim 7, wherein the temperature of the pre-drying treatment is no more than 130 ℃; the pre-drying medium for the pre-drying treatment is hot air flow, and the flow direction of the hot air flow is opposite to the running direction of the polyacrylonitrile tows.
10. The production method according to any one of claims 1 to 9, wherein the post-treatment comprises a sizing treatment, a post-drying treatment, and a filament winding treatment; wherein the temperature of the post-drying treatment is less than or equal to 120 ℃.
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