Method of Manufacturing Carbon Fiber and Carbon Fiber Manufactured Thereby

This application claims, under 35 U.S.C. § 119 (a), the benefit of priority from Korean Patent Application No. 10-2024-0052224, filed on Apr. 18, 2024, the entire contents of which are incorporated herein by reference.

The present disclosure relates to a method of manufacturing carbon fiber and carbon fiber manufactured thereby.

Carbon fiber has excellent properties such as light weight, high strength, high durability, and high temperature resistance, and is widely used in various fields. However, conventional processes of manufacturing carbon fiber have several problems.

A process of manufacturing polyacrylonitrile (PAN)-based carbon fiber requires a lot of energy and high production costs due to heat treatment under conditions of inevitably long time and high temperature in an oxidation stabilization process and a carbonization process of PAN, as well as high precursor cost.

In addition, there is a limit to precursors needed for PAN-based carbon fiber production, and there is a possibility of additional cost increases due to unstable supply.

A process of manufacturing polyvinyl chloride (PVC)-based carbon fiber has low precursor cost, but the carbon yield is not high, so improvement thereof is needed.

The present disclosure has been made keeping in mind the problems encountered in the related art, and an object of the present disclosure is to provide a novel method of manufacturing carbon fiber capable of increasing the carbon yield when manufacturing carbon fiber from a raw material containing a chlorine group in the side chain, such as PVC, etc., among compounds having a carbon skeleton.

Another object of the present disclosure is to provide carbon fiber manufactured thereby and having high crystallinity and good properties.

The objects of the present disclosure are not limited to the foregoing. The objects of the present disclosure will be able to be clearly understood through the following description and to be realized by the means described in the claims and combinations thereof.

An aspect of the present disclosure provides a method of manufacturing carbon fiber, including (a) preparing a solution by mixing a raw material containing at least one chlorine group in a side chain of a repeat unit with a solvent, (b) forming a fibrous material by spinning the solution, (c) forming a ladder-like chemical ring structure in the fibrous material by hydrothermally treating the fibrous material with a hydrochloric acid solution at a predetermined temperature for a predetermined time, and (d) carbonizing a result of step (c).

Another aspect of the present disclosure provides carbon fiber obtained by carbonizing a fibrous material having a ladder-like chemical structure, in which the fibrous material is prepared by spinning of a raw material containing at least one chlorine group in a side chain of a repeat unit and hydrothermal treatment with a hydrochloric acid solution.

The above and other objects, features and advantages of the present disclosure will be more clearly understood from the following preferred embodiments taken in conjunction with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed herein, and may be modified into different forms. These embodiments are provided to thoroughly explain the disclosure and to sufficiently transfer the spirit of the present disclosure to those skilled in the art.

Throughout the drawings, the same reference numerals will refer to the same or like elements. For the sake of clarity of the present disclosure, the dimensions of structures are depicted as being larger than the actual sizes thereof. It will be understood that, although terms such as “first”, “second”, etc. may be used herein to describe various elements, these elements are not to be limited by these terms. These terms are only used to distinguish one element from another element. For instance, a “first” element discussed below could be termed a “second” element without departing from the scope of the present disclosure. Similarly, the “second” element could also be termed a “first” element. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It will be further understood that the terms “comprise”, “include”, “have”, etc., when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. Also, it will be understood that when an element such as a layer, film, area, or sheet is referred to as being “on” another element, it may be directly on the other element, or intervening elements may be present therebetween. Similarly, when an element such as a layer, film, area, or sheet is referred to as being “under” another element, it may be directly under the other element, or intervening elements may be present therebetween.

Unless otherwise specified, all numbers, values, and/or representations that express the amounts of components, reaction conditions, polymer compositions, and mixtures used herein are to be taken as approximations including various uncertainties affecting measurement that inherently occur in obtaining these values, among others, and thus should be understood to be modified by the term “about” in all cases. Furthermore, when a numerical range is disclosed in this specification, the range is continuous, and includes all values from the minimum value of said range to the maximum value thereof, unless otherwise indicated. Moreover, when such a range pertains to integer values, all integers including the minimum value to the maximum value are included, unless otherwise indicated.

Referring to, a method of manufacturing carbon fiber according to an aspect of the present disclosure includes:

The raw material in step (a) (S) may be a material containing a carbon main chain and at least one chlorine group in the side chain, and may be a polymer, an oligomer, or a low-molecular-weight material.

The weight average molecular weight (Mw) of the raw material in step (a) (S) is not particularly limited, but may be, for example, 2,000 g/mol to 500,000 g/mol.

The raw material in step (a) (S) may include any one selected from the group consisting of polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), copolymers of vinyl chloride and with other monomers, and combinations thereof, and may include, for example, polyvinyl chloride.

When the raw material in step (a) (S) is a copolymer of vinyl chloride and another monomer, the other monomer may include an ethylenically unsaturated compound. Examples of the copolymer may include vinyl chloride (chloroethylene)-ethylene copolymer, chloroethylene-dichloroethylene copolymer, and the like.

The concentration of the raw material of the solution in step (a) (S) may be 1 wt % to 25 wt %. Here, a fibrous material may be stably formed by subsequent spinning of the solution having the above concentration.

The solvent of the solution in step (a) (S) may be used without limitation so long as it is able to effectively dissolve the raw material, and may include acetone, N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), dimethylformamide (DMF), dimethylacetamide (DMAc), nitrobenzene, cyclohexane, chloroform, methyl isobutyl ketone, etc., and may include, for example, dimethylacetamide (DMAc).

The spinning in step (b) (S) may be performed so that a spinning material is discharged into a medium as shown in, and may be conducted by wet spinning. The medium may include a material in which the raw material is insoluble or poorly soluble, may correspond to a so-called coagulation bath, and may include, for example, water.

The spinning in step (b) (S) may be performed so that the temperature of the solution is 35° C. to 45° C. If the temperature of the solution is less than 35° C., the cross-section of the formed fibrous material may be flat rather than round, and it may be difficult to evenly distribute tensile stress throughout the fiber, deteriorating mechanical strength of carbon fiber that is subsequently manufactured. On the other hand, if the temperature of the solution exceeds 45° C., a fibrous material having high porosity may be formed due to fast exchange between the medium and the solution, the density of carbon fiber that is subsequently manufactured may be lowered, and the properties thereof may deteriorate.

The spinning in step (b) (S) may be performed at a discharge rate of 0.5 ml/h to 8 ml/h. When spinning is performed at this discharge rate, a fibrous material may be stably formed.

The spun fibrous material in step (b) (S) may be continuously wound by a winder such as a roller, etc., and may be wound to have a predetermined spinning draw ratio. The spinning draw ratio may correspond to the (linear speed when winding the fibrous material)/(discharge linear speed when forming the fibrous material), and the draw ratio may be 1.2-6.

The spinning in step (b) (S) may be performed using a wet spinning machine with a spinneret diameter of 50 μm to 200 μm.

The hydrothermal treatment in step (c) (S) is a stabilization process to minimize decomposition of the fibrous material formed in step (b) (S) during subsequent carbonization and to obtain high carbon yield.

The hydrothermal treatment in step (c) (S) may be performed with an aqueous hydrochloric acid solution having a hydrochloric acid concentration of 0.1 wt % to 40 wt % in a closed container. For example, the concentration of the aqueous hydrochloric acid solution may be 25 wt % to 40 wt %. When hydrochloric acid having the above concentration is further included during hydrothermal treatment, a stable ladder-like ring structure may be formed while accelerating the separation of chlorine group from the fibrous material.

The hydrothermal treatment in step (c) (S) may be performed with an aqueous solution, and may be conducted at a predetermined pressure, for example, a pressure ranging from the vapor pressure of the aqueous solution to 30 bar.

The hydrothermal treatment in step (c) (S) may be performed at a temperature of 200° C. to 300° C. If the temperature is less than 200° C., the fibrous material may not be sufficiently stabilized, whereas if the temperature exceeds 300° C., thermal decomposition of the fibrous material may occur.

The hydrothermal treatment in step (c) (S) may be performed for 20 hours or more, preferably for 24 to 48 hours. If the hydrothermal treatment time is less than 20 hours, formation of the ladder-like chemical ring structure may not be complete, and thermal decomposition may occur rapidly in the subsequent carbonization process, which may lower yield, resulting in carbon fiber having high porosity. On the other hand, if the hydrothermal treatment time exceeds 48 hours, an improvement in yield may be insignificant and energy may be wasted.

The hydrothermal treatment in step (c) (S) may be performed to reach the above temperature at a heating rate of 5° C./min to 12° C./min.

When the hydrothermal treatment in step (c) (S) is performed in this way, a ladder-like chemical ring structure may be formed in the fibrous material, and an O—C—O structure, C═O bond, C═C bond, —OH group (hydroxyl group), etc. may be included and detected. The ladder-like ring structure may include consecutive ring structures linked by sharing carbon-carbon bonds, and may contain substantially no nitrogen or may contain nitrogen below the detection limit. The ladder-like structure may include a structure in which each 4-12 membered ring shares a specific atom-atom (e.g., carbon-carbon) bond with an adjacent 4-12 membered ring and is continuously connected linearly or curvedly. The ladder-like structure may include fused polycyclic ring structure, and each ring except the end ring may be connected to 2 to 3 rings. The ladder-like ring structure may, for example, include a structure similar to the oxidation and cyclization steps during carbonization of linear low-density polyethylene (LLDPE), and may further include an O—C—O structure.

The carbonization in step (d) (S) may be performed at a temperature of 800° C. to 2,000° C. in an inert gas atmosphere. Carbonization may proceed stably in the above temperature range and the desired yield may be obtained. The inert gas may include helium, argon, neon, etc.

The carbonization in step (d) (S) may be performed to reach the above temperature at a heating rate of 5.5° C./min or less, for example, at a heating rate of 0.5° C./min to 5° C./min. If the heating rate exceeds 5.5° C./min, the hydrothermally treated fibrous material may undergo thermal decomposition rapidly, and a large number of pores may be formed, which may deteriorate the properties of the manufactured carbon fiber.

The carbonization in step (d) (S) may be performed by maintaining the above temperature for 0.5 to 3 hours.

Carbon fiber manufactured in steps (a) to (d) (Sto S) may have high crystallinity, low porosity, and good mechanical properties, and manufacturing costs may be significantly reduced.

The yield of carbon fiber manufactured by the above method may be 50 wt % or more, 60 wt % or more, or 65 wt % or more, and 90 wt % or less. The yield may be calculated as (carbon weight of manufactured carbon fiber/carbon weight of raw material)*100%.

Carbon fiber according to another aspect of the present disclosure may be obtained by carbonizing a fibrous material having a ladder-like chemical structure, in which the fibrous material may be prepared by spinning of a raw material containing at least one chlorine group in the side chain of a repeat unit and hydrothermal treatment with a hydrochloric acid solution.

The fibrous material having the ladder-type chemical structure, raw material, spinning, and hydrothermal treatment are substantially the same as described above, and thus a redundant description thereof will be omitted.

The carbon fiber may have longitudinal tensile strength of 600 MPa to 1,500 MPa.

The carbon fiber may have a thickness (maximum length of the fiber cross-section perpendicular to the longitudinal direction) of 20 μm to 70 μm.

The carbon fiber may have a density of 1.02 g/cmto 1.25 g/cm.

Since the carbon fiber is not derived from polyacrylonitrile (PAN), it may contain substantially no nitrogen or may contain nitrogen below the detection limit.

A better understanding of the present disclosure may be obtained through the following examples and comparative examples. However, these examples are not to be construed as limiting the technical spirit of the present disclosure.

(a) A spinning solution having a concentration of 17 wt % was prepared by mixing polyvinyl chloride (PVC) with dimethylacetamide (DMAc).

(b) The spinning solution was spun into a coagulation bath containing water using a wet spinning machine, and the fibrous material was wound by a roller. Here, the temperature of the spinning solution was 40° C., the spinneret diameter was 160 μm, the discharge rate was 2 ml/h, and the draw ratio was 5.

(c) The fibrous material was placed in a hydrothermal treatment machine and hydrothermally treated with a 37 wt % aqueous hydrochloric acid solution under conditions of a temperature of 250° C., a heating rate of 10° C./min, a pressure equal to or greater than vapor pressure of the aqueous solution, and a total of 24 hours, forming a ladder-like chemical ring structure in the fibrous material.

(d) Carbon fiber was manufactured by carbonizing the hydrothermally treated fibrous material in an argon gas atmosphere under conditions of a heating rate of 5° C./min, a temperature of 900° C., and a temperature maintenance time of 1 hour.