Regenerated fiber manufacturing method

Abstract

The present invention relates to a method for producing recycled fibers, which includes the steps of: loading a pretreated fiber composite material into a cartridge; moving the cartridge containing the pretreated fiber composite material; exposing the cartridge to superheated steam and an oxidizing agent; removing matrix resin and char from the pretreated fiber composite material to produce recycled fibers; and moving the cartridge containing the recycled fibers and recovering the recycled fibers from the cartridge. This method can improve the decomposition rate of the fiber composite material while minimizing the decrease in tensile strength of the final recycled fiber.

Description

[Technical Field]

[0001] The present invention relates to a method for producing recycled fibers. [Background technology]

[0002] Fiber composites, typically composed of carbon or glass fibers mixed with thermosetting or thermoplastic resins (matrix resins), are widely used in aerospace, wind power generation, automotive, and other industrial applications due to their high strength, high elasticity, light weight, heat resistance, and chemical resistance. However, due to the strong bonding strength between the carbon and glass fibers and the resin, fiber composites are difficult to separate. Reuse is impossible, especially when made from thermosetting resins. Most fiber composites are discarded and incinerated or landfilled. Recently, waste disposal regulations for fiber composites, including carbon composites, have been tightening. In Europe, incineration is prohibited, and some countries have limited landfilling, but landfilling restrictions are gradually expanding. Therefore, technologies for recovering carbon and glass fibers from fiber composites can reduce environmentally problematic waste generation and are economically valuable from the perspective of reusing and recycling expensive carbon and glass fibers.

[0003] Currently, there are two main techniques for recovering carbon fiber from carbon fiber composites, a type of fiber composite material. Pyrolysis is the most widely used method due to its simple process. However, it has the disadvantage of generating resin residue (Char) on the surface of the recycled fiber after decomposition, which reduces the physical properties of the recovered carbon fiber (recycled fiber). Furthermore, a large amount of energy is required to heat a large-capacity heating furnace, and the decomposed resin is converted into gaseous substances and emitted, which can cause air pollution. Solvolysis is considered a more environmentally friendly method because the recovered carbon fiber (recycled fiber) has stable physical properties and does not generate exhaust gases. However, it has issues with the treatment and recovery of decomposition products, including solvents, which are discharged into wastewater. Furthermore, solvolysis requires a relatively long decomposition reaction time, and the decomposition conditions, such as the solvent, time, and temperature, must be tailored depending on the type and composition of the resin being decomposed. Finally, solvolysis requires pretreatment, decomposition reaction, washing, and drying, making the process complicated and time-consuming.

[0004] Therefore, the current direction of research and development is to develop a decomposition technology that combines an economical technology that can reduce the amount of energy used, which is a drawback of pyrolysis, and minimize the complicated process and long decomposition time, which are drawbacks of solvolysis, and an environmentally friendly technology that can reuse decomposition materials generated from resins in addition to carbon fibers. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, the inventors have conducted extensive research to solve the above problems, and as a result, have completed a method for producing recycled fibers that prevents the deterioration of the physical properties of recycled fibers such as carbon fibers recovered from fiber composite materials, while at the same time cooling and condensing superheated steam to convert it into water, which is recovered, and then separating and purifying it to reuse the decomposed resin.

[0006] Therefore, an object of the present invention is to provide an environmentally friendly method for producing regenerated fibers, which can obtain regenerated fibers with reduced deterioration in physical properties. [Means for solving the problem]

[0007] To achieve the above object, the present invention provides a method for producing recycled fibers, including the steps of: loading a pretreated fiber composite material into a cartridge; moving the cartridge containing the pretreated fiber composite material and exposing the cartridge to superheated steam and an oxidizing agent to remove matrix resin and char from the pretreated fiber composite material to produce recycled fibers; and moving the cartridge containing the recycled fibers and recovering the recycled fibers from the cartridge.

[0008] The step of exposing the cartridge to superheated steam and an oxidant may involve first exposing the cartridge containing the pretreated fiber composite material to superheated steam, and then moving the cartridge and exposing it to the oxidant.

[0009] The present invention may further include a step of first exposing the cartridge containing the pretreated fiber composite material to superheated steam, and then using cooling water to condense the gaseous matrix resin decomposed from the pretreated fiber composite material into a liquid state and removing the liquid before exposing the cartridge to an oxidizing agent.

[0010] The step of condensing the gaseous matrix resin decomposed from the pretreated fiber composite material into a liquid state and removing the liquid may include a step of causing the gaseous matrix resin decomposed from the pretreated fiber composite material by exposure to the superheated steam to escape from the cartridge, being separated from the cartridge, reacting with separately present cooling water, and becoming condensed water in a liquid state, which is then removed.

[0011] The oxidant may include air.

[0012] The fiber composite material may be a mixture of 'carbon fiber, glass fiber, or a mixture thereof' with a matrix resin.

[0013] The matrix resin may include an aromatic hydrocarbon compound.

[0014] The aromatic hydrocarbon compound may include a phenol compound.

[0015] The aromatic hydrocarbon compound may include bisphenol A, and the bisphenol A may be contained in an amount of 30% by weight or more based on the total amount of the aromatic hydrocarbon compound.

[0016] The pretreated fiber composite material may be a chopped or shredded fiber composite material.

[0017] The superheated steam may have a temperature range of 400°C to 900°C.

[0018] The cartridge containing the pretreated fiber composite material can be exposed to the superheated steam for 30 to 120 minutes.

[0019] The step of exposing to superheated steam includes a step of injecting the superheated steam into a cartridge containing the pretreated fiber composite material, and the superheated steam is injected into the cartridge at a flow rate of 10 kg / h to 30 kg / h.

[0020] The step of exposing to the oxidant includes the step of injecting the superheated steam into a cartridge containing the pretreated fiber composite material, and then injecting the oxidant into the cartridge, wherein the oxidant is injected into the cartridge at a flow rate of 5 L / min or more.

[0021] The present invention may further include a step of exposing the cartridge to nitrogen prior to exposing the cartridge to the superheated steam after the step of introducing the pretreated fiber composite material into the cartridge.

[0022] The present invention may further include a step of exposing the cartridge containing the recycled fibers to nitrogen before moving the cartridge after the step of producing the recycled fibers.

[0023] The char may be present on the surface of the recycled fibers from which the matrix resin has been removed. [Effects of the Invention]

[0024] The method for producing recycled fibers according to the present invention uses a pretreated fiber composite material, exposes the pretreated fiber composite material to superheated steam, and controls the temperature, exposure time, and flow rate of the superheated steam during the exposure. Furthermore, by adding an oxidant such as air, whose flow rate is separately controlled, in addition to the superheated steam, deterioration of the physical properties of the recovered recycled fiber is minimized. Furthermore, by using a cartridge system rather than a roller system, the process defect rate is significantly reduced, the process is simple, and the process time is significantly reduced. The matrix resin, one of the decomposition products, is converted into condensed water using cooling water instead of ambient air, allowing for easy reuse of the matrix resin. Furthermore, the rapid generation of condensed water significantly reduces energy consumption, significantly improving the economic efficiency and productivity of the recycled fiber production process compared to conventional pyrolysis methods. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a flowchart showing the sequence of a method for producing recycled fibers according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be described in more detail below.

[0027] The advantages and features of the technology described below, and the methods for achieving them, will become clearer with reference to the embodiments described in detail below. However, it can be said that the realized forms are not limited to the embodiments disclosed below. Unless otherwise defined, all terms (including technical and scientific terms) used in this specification should be used in the sense commonly understood by those having ordinary skill in the art. Furthermore, commonly used and predefined terms should not be interpreted ideally or excessively unless explicitly and specifically defined.

[0028] The terms used in the present invention are merely used to describe specific embodiments and are not intended to limit the present invention. Unless otherwise clearly indicated in the context, singular expressions include plural expressions.

[0029] In the present invention, the terms 'comprise' or 'have' and the like are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and should be understood not to preclude the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0030] Superheated steam is a high-temperature, dry steam created by heating vaporized water above its saturation temperature, and is a heat transfer medium that contains more heat than heated air. Superheated steam has a high heat transfer rate at the same pressure and a high heat density, allowing for rapid heating and shortening the heating time of the object being heated. Furthermore, since superheated steam is a gaseous substance consisting only of water molecules and lacks oxygen, it can maintain an inert state and has very high thermal efficiency due to heat transfer through multiple heat transfer mechanisms (convection, radiation, and condensation). Therefore, the technology of using superheated steam to recover recycled fibers such as carbon fiber has the advantage of being able to remove resins in a shorter time by directly spraying superheated steam onto the object to be decomposed.

[0031] However, the physical properties of recycled fibers such as recovered carbon fibers inevitably deteriorate, and if the deterioration in the physical properties of the recycled fibers is severe, they cannot be reused.In addition, the resin decomposed along with the recycled fibers may itself become an environmental pollution issue, so there has been a continuing need for more advanced technological improvements to the decomposition technology using superheated steam.

[0032] After accurately understanding the market needs, the inventors conducted extensive research and found that while conventional methods for producing recycled fibers using superheated steam injection involve moving a fiber composite material using rollers, by moving the fiber composite material in a cartridge rather than a roller, and by condensing the gaseous matrix resin decomposed by the injection of superheated steam using cooling water rather than ambient air, the inventors were able to dramatically improve the environmental friendliness, economy, and productivity of the recycled fiber production process. (In particular, while environmental issues such as the dispersion of fine dust have been a constant issue when using rollers, the use of cartridges eliminates such issues. Furthermore, while cartridges can be repeatedly used by cleaning, rollers require periodic replacement, making the use of cartridges far more advantageous in terms of environmental friendliness.) Furthermore, by pretreating a fiber composite material and exposing it to superheated steam, and controlling the temperature, exposure time, and flow rate of the superheated steam, it is possible to minimize the deterioration of the physical properties of the recovered recycled fiber, such as carbon fiber, thereby enabling the production of recycled fiber with properties far superior to those of conventional recycled fibers.

[0033] Referring to FIG. 1, the method for producing recycled fiber according to the present invention includes the steps of: loading pretreated fiber composite material into a cartridge (S100); moving the cartridge containing the pretreated fiber composite material (S200); exposing the cartridge to superheated steam and an oxidizing agent (S300); removing matrix resin and char from the pretreated fiber composite material to produce recycled fiber (S400); and moving the cartridge containing the recycled fiber and recovering the recycled fiber (S500).

[0034] That is, the pretreated fiber composite material is decomposed by superheated steam into recycled fibers and matrix resin, the recycled fibers are sequentially transported through the cartridge and recovered, and the matrix resin is converted from a gaseous state into liquid condensed water by cooling water as described below and transported to a condensed water tank, where it is then separated and purified for reuse. The recovered recycled fibers can be reused by chopping and milling.

[0035] In other words, according to the method for producing recycled fibers according to the present invention, recycled fibers with minimal deterioration in physical properties and reusable matrix resins can be easily obtained simultaneously from a fiber composite material through a series of continuous processes.

[0036] Specifically, the step of exposing the cartridge to the superheated steam and the oxidant may include first exposing the cartridge containing the pretreated fiber composite material to superheated steam, and then moving the cartridge and exposing it to the oxidant. Exposing the cartridge to superheated steam first may be more advantageous for removing matrix resin and char than exposing the cartridge to the oxidant first.

[0037] For example, the method for producing recycled fibers according to the present invention may further include exposing the cartridge containing the pretreated fiber composite material to superheated steam, and then using cooling water to condense the gaseous matrix resin decomposed from the pretreated fiber composite material into a liquid state and remove it before exposing it to an oxidizing agent. Condensing the matrix resin decomposed from the pretreated fiber composite material using cooling water rather than ambient air allows for much easier and more complete removal of the matrix resin. Specifically, the gaseous matrix resin decomposed from the pretreated fiber composite material by the exposure to superheated steam leaves the cartridge, separates from the cartridge, and reacts with separately present cooling water to become liquid condensed water, which is then transferred to a separate condensed water tank and finally removed.

[0038] Fiber composite materials that can be used in superheated steam cracking are broadly divided into carbon fiber composites (CFRP) and glass fiber composites (GFRP). They can be used for cracking regardless of structure, shape, or material type, and are typically mixed with a reinforcement material and a matrix resin. Examples of fibrous materials used as reinforcements include carbon fiber and glass fiber, while examples of matrix resins include thermosetting resins such as epoxy, phenol, unsaturated polyester, polyurethane, melamine, and urea, and thermoplastic resins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyamide, polycarbonate, and polyimide. Commonly used fiber composites are mixtures of the aforementioned reinforcements and matrix resins in a certain ratio, with the ratio of reinforcement to resin varying depending on the application.

[0039] For example, the matrix resin may include an aromatic hydrocarbon-based compound, and the aromatic hydrocarbon-based compound may include a phenolic compound, and the phenolic compound may include, but is not necessarily limited to, phenol, o-cresol, p-cresol, p-ethylphenol, p-isopropylphenol, p-isopropenylphenol, p-hydroxy-2,2-diphenylpropane, p-hydroxy-3-methyl-2,2-diphenylpropane, 2-(4-hydroxyphenyl)-2-(4'-methoxyphenyl)propane, bisphenol A, 2-(4-hydroxy-3-methylphenyl)-2-(4'-hydroxyphenyl)propane, 2-(benzofuran-5-yl)-2-(p-hydroxyphenyl)propane, or a combination thereof.

[0040] However, the aromatic hydrocarbon compound, specifically the phenolic compound, may include bisphenol A.

[0041] For example, bisphenol A may be contained in the largest amount among the aromatic hydrocarbon compounds (specifically, phenolic compounds), for example, 30 wt % or more, for example, 50 wt % or more, based on the total amount of the phenolic compounds. When the matrix resin containing aromatic hydrocarbon compounds (specifically, phenolic compounds) containing bisphenol A in the above content range has the above composition, it can be very easy to reuse it through separate recovery, separation, filtration, and purification.

[0042] For example, the pretreated fiber composite material may be a crushed or chopped fiber composite material. The fiber composite material used in the decomposition using superheated steam may be crushed or cut into a consistent size and shape for use in the process, which may be advantageous in terms of preventing deterioration in the physical properties of the resulting recycled fiber. For example, crushing methods such as shredders, choppers, cracker mills, and hammer mills can crush the fiber composite material into a consistent size range. However, crushed composite materials tend to be non-uniform in size, generating significant amounts of dust and powder, which may reduce the effectiveness of preventing deterioration in the quality and yield of the recovered carbon fiber and may also worsen the working environment. However, fiber composite materials produced using a cutting machine can be cut into consistent sizes, reducing the amount of dust and powder generated, increasing yield, and resulting in relatively uniform fiber lengths, such as recovered carbon fiber, resulting in recycled fiber with minimal deterioration in quality. That is, cutting, rather than crushing, may be more advantageous in terms of preventing deterioration in the physical properties of the recycled fiber.

[0043] The pretreated fiber composite material is loaded into a cartridge, and then automatically moved and exposed to superheated steam and an oxidant (specifically, the superheated steam and the oxidant are sequentially sprayed into the automatically moved cartridge), thereby causing decomposition of the pretreated fiber composite material.

[0044] For example, the method for producing recycled fibers according to the present invention provides an excellent decomposition rate of the fiber composite material. Here, the decomposition rate means the value obtained by the following mathematical formula 1.

[0045] [Formula 1] Decomposition rate (wt%)={(AB) / (A×C)}×100 In the above formula 1, A is the weight of the fiber composite material before decomposition (g), B is the weight of the fiber composite material after decomposition (g), C is the matrix resin content (wt%) in the fiber composite material based on the total amount of the fiber composite material before decomposition.

[0046] The superheated steam injected into the cartridge containing the pretreated fiber composite material is injected using a superheated steam generator, and can be superheated steam heated to a temperature of, for example, 400°C to 900°C, for example, 400°C to 800°C, for example, 500°C to 900°C, for example, 500°C to 800°C. If the temperature of the superheated steam is less than 400°C, a problem of a rapid decrease in decomposition rate may occur, and if the temperature of the superheated steam exceeds 900°C, the tensile strength of the recovered (manufactured) recycled fiber may be reduced, which is not preferable.

[0047] For example, superheated steam having the above temperature range is injected into the cartridge for 30 to 120 minutes, e.g., 30 to 110 minutes, e.g., 30 to 100 minutes, e.g., 30 to 90 minutes. If superheated steam having the above temperature range is injected into the cartridge for less than 30 minutes, a problem of a rapid decrease in the decomposition rate may occur, and if superheated steam having the above temperature range is injected into the cartridge for more than 120 minutes, the increase in the decomposition rate and the decrease in tensile strength are not so great, so it may be uneconomical to expose the pretreated fiber composite material to superheated steam having the above temperature range for more than 120 minutes.

[0048] For example, superheated steam within the above temperature range is injected into the cartridge at a flow rate of 10 kg / h to 30 kg / h, e.g., 10 kg / h to 25 kg / h, e.g., 10 kg / h to 20 kg / h, within the above time range. If the superheated steam flow rate is less than 10 kg / h or exceeds 30 kg / h, the tensile strength of the produced recycled fiber may be undesirably low.

[0049] Char, consisting of trace amounts of carbon derived from the matrix resin decomposed from the fiber composite material by exposure to the superheated steam, may remain on the surface of the reinforcement (carbon fiber and / or glass fiber). Char is generated at a ratio of approximately 5% to 10% by weight of the resin contained in the fiber composite material, and the char prevents the reinforcement from being separated into individual pieces and results in the production of a single mass. Reinforcement containing char has low flexibility and acts as an impurity in subsequent processes, so it must be removed. Char is a carbonaceous substance that is difficult to remove using only superheated steam in an inert atmosphere, but can be removed by adding an oxidizing agent. The oxidizing agent may be air or an active gas such as oxygen.

[0050] Specifically, the char-containing reinforcement material is transported in a cartridge, and then air is automatically injected into the cartridge containing the char-containing reinforcement material. Through this continuous process, i.e., by adding additional air, the char can be removed. High temperature and an appropriate air flow rate are required to remove the char. If the temperature is too low or the air flow rate is too low, the char will not be removed. If the temperature is too high or the air flow rate is too high, the char will be completely removed, but the reinforcement material may be damaged and its physical properties may deteriorate. Therefore, appropriate temperature, time, and air flow rate are important. To remove the char, the treatment can be performed at a temperature of 400°C to 900°C, for 10 to 90 minutes, with an air flow rate of 5 L / min or more. Preferably, the treatment is performed at a temperature of 500°C to 800°C, for 30 to 60 minutes, with an air flow rate of 5 L / min. In particular, even if the temperature and time range of the injected air are controlled within the above ranges, if the air flow rate is less than 5 L / min, the effect of improving the decomposition rate may be small.

[0051] If the char is not removed, it acts as an impurity and reduces the decomposition rate, so it is important to remove it. However, if the char is removed by injecting air as described above, the decomposition rate increases, but there is a problem that the tensile strength retention rate and elasticity retention rate of the finally recovered recycled fiber may be slightly reduced. To solve this problem, the flow rate of the injected air is controlled in the recycled fiber manufacturing method according to the present invention.

[0052] Furthermore, the method for producing recycled fibers according to the present invention may further include a step of exposing the cartridge to nitrogen after the step of introducing the pretreated fiber composite material into the cartridge and before exposing the cartridge to the superheated steam, or a step of exposing the cartridge containing the recycled fibers to nitrogen before moving the cartridge after the step of producing the recycled fibers. In this case, it may be more effective in preventing a decrease in the tensile strength retention rate and elasticity retention rate of the recovered recycled fibers.

[0053] The reinforcing material from which the char has been removed is automatically transported in the cartridge, and the reinforcing material (recycled fiber) can be recovered from the cartridge to produce recycled fiber. The weight of the recycled fiber recovered in this way is confirmed, and the decomposition rate and yield are finally calculated to confirm the physical properties of the recycled fiber.

[0054] The tensile strength of the recycled fiber (reinforcement) can be measured by the Single Fiber Method (ASTM C1557-03). The Single Fiber Method involves separating a single reinforcement strand of 25 mm or more and measuring it 30 times or more using a Universal Testing Machine (UTM) at a test speed of 1 mm / min, a grip spacing of 25 mm, and an initial load of 1 cN / tex, and then calculating the average value.

[0055] According to the recycled fiber manufacturing method of the present invention, i) a fiber composite material is pretreated before use, ii) it is clearly distinguishable from conventional roller processes in that it is a series of automated processes using a cartridge push method, iii) it is also distinguishable from conventional processes using outside air in that it uses cooling water to condense the gaseous matrix resin into a liquid state and remove it, iv) it controls the temperature, time, and flow rate of the superheated steam in the superheated steam exposure section, and v) it controls the temperature, time, and flow rate of the air in the resin removal section, so not only can recycled fibers be recovered with minimal deterioration in physical properties, but at the same time, the matrix resin can be easily obtained in the form of condensed water, making it environmentally friendly and significantly more efficient and economical than conventional recycled fiber recovery methods.

[0056] Preferred examples are presented below to aid in understanding the present invention. However, the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical idea of ​​the present invention. It is of course understood that such changes and modifications fall within the scope of the appended claims. [Example]

[0057] Test Example 1. Effect of superheated steam temperature 130 g of cut pieces of a hydrogen tank (50 x 100 mm) were placed in a cartridge in the inlet of a cartridge-push type automatic recycled fiber manufacturing device, and the cartridge was moved to be exposed to superheated steam. The decomposition rate and the physical properties of the final recovered carbon fiber were evaluated while varying the discharge temperature of the injected superheated steam as shown in Table 1 below, and the results are shown in Table 1 below. After the superheated steam injection, the cartridge was moved again and air was injected to expose the cartridge to air, with the air flow rate controlled at 5 L / min. After the superheated steam injection, cooling water was used before the air injection to condense and remove the decomposed matrix resin from the cut pieces of the hydrogen tank in the cartridge into which the superheated steam was injected. After the air injection, the cartridge was moved, and the carbon fiber was recovered from the cartridge.

[0058] [Table 1]

[0059] From Table 1, it can be seen that when the discharge temperature of the superheated steam is controlled to 400°C to 900°C, the decomposition rate and the tensile strength of the recovered regenerated fibers are both excellent.

[0060] 2. Effect of superheated steam flow rate The same procedure as in Test Example 1 was carried out except that the superheated steam flow rate was changed to that shown in Table 2 below instead of 20 kg / h, and the results are shown in Table 2 below.

[0061] [Table 2]

[0062] From Table 2 above, it can be seen that when the superheated steam flow rate is controlled to 10 kg / h to 30 kg / h, the decomposition rate and the tensile strength of the recovered regenerated fibers are both excellent.

[0063] 3. Effect of exposure time to superheated steam The same procedure as in Test Example 1 was carried out, except that the superheated steam exposure time was changed to the time shown in Table 3 below instead of 90 minutes, and the results are shown in Table 3 below.

[0064] [Table 3]

[0065] From Table 3 above, it can be seen that when the superheated steam exposure time is controlled to 30 to 120 minutes, the decomposition rate and the tensile strength of the recovered regenerated fibers are both excellent.

[0066] 4. Effect of air flow rate The same procedure as in Test Example 1 was carried out except that the air flow rate during air exposure was changed to that shown in Table 4 below instead of 5 L / min, and the results are shown in Table 4 below.

[0067] [Table 4]

[0068] From Table 4 above, it can be seen that when the temperature, time, and flow rate of the superheated steam in the superheated steam exposure section, as well as the air flow rate in the air injection section, are controlled within a certain range, the decomposition rate and the tensile strength of the recovered recycled fibers are all excellent.

[0069] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

Claims

1. loading the pretreated fiber composite material into a cartridge; moving the cartridge containing the pretreated fiber composite material; exposing the cartridge to superheated steam and an oxidant; Removing the matrix resin and char from the pretreated fiber composite material to produce recycled fibers; and moving a cartridge containing the recycled fibers and collecting the recycled fibers from the cartridge; A method for producing recycled fibers, comprising:

2. 2. The method for producing recycled fibers according to claim 1, wherein the step of exposing the cartridge to superheated steam and an oxidant is a step of first exposing the cartridge containing the pretreated fiber composite material to superheated steam, and then moving the cartridge and exposing it to the oxidant.

3. 3. The method for producing recycled fibers according to claim 2, further comprising the step of condensing the gaseous matrix resin decomposed from the pretreated fiber composite material into a liquid state using cooling water and removing it before first exposing the cartridge containing the pretreated fiber composite material to superheated steam and then exposing it to an oxidizing agent.

4. The step of condensing the decomposed gaseous matrix resin from the pretreated fiber composite material into a liquid state and removing the liquid matrix resin includes:

4. The method for producing recycled fibers according to claim 3, wherein the gaseous matrix resin decomposed from the pretreated fiber composite material by the exposure to the superheated steam escapes from the cartridge, is separated from the cartridge, reacts with separately present cooling water, and becomes liquid condensed water, which is then removed.

5. The method for producing recycled fibers according to claim 1 , wherein the oxidizing agent comprises air.

6. 2. The method for producing recycled fibers according to claim 1, wherein the fiber composite material is a mixture of 'carbon fiber, glass fiber, or a mixture thereof' with a matrix resin.

7. The method for producing recycled fibers according to claim 6 , wherein the matrix resin contains an aromatic hydrocarbon compound.

8. The method for producing regenerated fibers according to claim 7 , wherein the aromatic hydrocarbon compound includes a phenolic compound.

9. 8. The method for producing regenerated fibers according to claim 7, wherein the aromatic hydrocarbon compound contains bisphenol A, and the bisphenol A is contained in an amount of 30% by weight or more based on the total amount of the aromatic hydrocarbon compounds.

10. The method for producing recycled fibers according to claim 1 , wherein the pretreated fiber composite material is a crushed or cut fiber composite material.

11. The method for producing recycled fibers according to claim 1, wherein the superheated steam has a temperature range of 400°C to 900°C.

12. 2. The method for producing recycled fibers according to claim 1, wherein the cartridge containing the pretreated fiber composite material is exposed to the superheated steam for 30 to 120 minutes.

13. 2. The method for producing recycled fibers according to claim 1, wherein the step of exposing the pretreated fiber composite material to superheated steam includes a step of injecting the superheated steam into a cartridge containing the pretreated fiber composite material, and the superheated steam is injected into the cartridge at a flow rate of 10 kg / h to 30 kg / h.

14. 2. The method for producing recycled fibers according to claim 1, wherein the step of exposing to the oxidizing agent includes a step of injecting the superheated steam into a cartridge containing the pretreated fiber composite material, and then injecting the oxidizing agent into the cartridge, and the oxidizing agent is injected into the cartridge at a flow rate of 5 L / min or more.

15. The method for producing recycled fibers according to claim 1 , further comprising the step of exposing the cartridge to nitrogen before exposing the cartridge to the superheated steam after the step of introducing the pretreated fiber composite material into the cartridge.

16. The method for producing recycled fibers according to claim 1 , further comprising the step of exposing the cartridge containing the recycled fibers to nitrogen before moving the cartridge after the step of producing the recycled fibers.

17. The method for producing recycled fibers according to claim 1 , wherein the char is present on the surface of the recycled fibers from which the matrix resin has been removed.

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