METHOD FOR MANUFACTURING CARBON FIBER AND CARBON FIBER COMPOSITE BOTTLE

Abstract

A method for manufacturing carbon fiber, the method includes: placing a carbon fiber as an anode in an electrolyte, wherein the electrolyte is nitric acid, sulfuric acid, phosphoric acid, acetic acid, ammonium bicarbonate, sodium hydroxide, or potassium nitrate; and performing a surface treatment, wherein a surface of the carbon fiber is oxidized by active oxygen generated by anodic electrolysis, and thereby oxygen-containing functional groups are introduced to the surface. The disclosure also provides a carbon fiber composite bottle, which includes a bottle body and a carbon fiber. The bottle body is a type III bottle or a type IV bottle. The carbon fiber surrounds the bottle body, the surface oxygen concentration of the carbon fiber is 5-35%, and the surface roughness of the carbon fiber is 5-25 nm.

Claims

1. A method for manufacturing carbon fiber, comprising: placing a carbon fiber as an anode in an electrolyte, wherein the electrolyte is nitric acid, sulfuric acid, phosphoric acid, acetic acid, ammonium bicarbonate, sodium hydroxide, or potassium nitrate; and performing a surface treatment, wherein a surface of the carbon fiber is oxidized by active oxygen generated by anodic electrolysis, and thereby oxygen-containing functional groups are introduced to the surface.

2. The method for manufacturing the carbon fiber of claim 1, wherein the carbon fiber is rayon base fiber, asphalt base fiber, or polyacrylonitrile fiber.

3. The method for manufacturing the carbon fiber of claim 1, wherein a conductivity value of the electrolyte is from 200 ms/cm to 3,000 ms/cm.

4. The method for manufacturing the carbon fiber of claim 1, wherein temperature of the electrolyte is controlled at 15-40° C.

5. The method for manufacturing the carbon fiber of claim 1, wherein the perfoming the surface treatment comprises controlling voltage at 5-40 V.

6. The method for manufacturing the carbon fiber of claim 1, wherein an electricity amount supplied in the surface treatment is 3-40 coulombs/gram.

7. The method for manufacturing the carbon fiber of claim 1, wherein a time for the surface treatment is 5-90 seconds.

8. The method for manufacturing the carbon fiber of claim 1, wherein the electrolyte is the sulfuric acid, the ammonium bicarbonate, or the phosphoric acid, a conductivity value of the electrolyte is 250-700 ms/cm, and an electricity amount supplied in the surface treatment is 15-25 coulombs/gram.

9. A carbon fiber composite bottle, comprising: a bottle body, wherein the bottle body is a type III bottle or a type IV bottle; and a carbon fiber, covering the bottle body, wherein a surface oxygen concentration of the carbon fiber is 5-35%, and a surface roughness of the carbon fiber is 5-25 nm.

10. The carbon fiber composite bottle of claim 9, wherein a tensile strength of the carbon fiber is greater than 5,100 MPa.

11. A method for manufacturing carbon fiber, comprising: providing a carbon fiber, wherein the carbon fibers contain an oil agent, and an amount of the oil agent is 0.5-3.0% by weight of the carbon fiber; performing a oxidation of the carbon fiber at 200-300° C. in air or oxygen; performing a first carbonization of the carbon fiber at 400-800° C.; perfoming a second carbonization of the carbon fiber at 900-2,000° C.; placing the carbon fiber as an anode in an electrolyte, wherein the electrolyte is nitric acid, sulfuric acid, phosphoric acid, acetic acid, ammonium bicarbonate, sodium hydroxide, or potassium nitrate; and performing a surface treatment, wherein a surface of the carbon fiber is oxidized by active oxygen generated by anodic electrolysis, and thereby oxygen-containing functional groups are introduced to the surface.

12. The method for manufacturing the carbon fiber of claim 11, wherein the perfoming the surface treatment comprises controlling voltage at 5-40 V, and an electricity amount supplied in the surface treatment is 3-40 coulombs/gram.

13. The method for manufacturing the carbon fiber of claim 11, wherein a conductivity value of the electrolyte is from 200 ms/cm to 700 ms/cm.

14. The method for manufacturing the carbon fiber of claim 11, wherein temperature of the electrolyte is controlled at 15-40° C.

15. The method for manufacturing the carbon fiber of claim 11, wherein the performing the surface treatment comprises controlling voltage at 5-20 V.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows:

[0017] FIG. 1 illustrates a flowchart of a method for manufacturing carbon fiber according to some embodiments of the present disclosure.

[0018] FIG. 2 shows a schematic diagram of an electrolysis apparatus according to some embodiments of the present disclosure.

[0019] FIG. 3 illustrates the surface roughness of the carbon fiber according to some embodiments of the present disclosure.

[0020] FIG. 4 illustrates a flowchart of a method for manufacturing a carbon fiber composite bottle according to some embodiments of the present disclosure.

[0021] FIG. 5A illustrates a type III bottle of the carbon fiber composite bottle according to some embodiments of the present disclosure.

[0022] FIG. 5B illustrates a type IV bottle of the carbon fiber composite bottle according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

[0023] It can be understood that different embodiments or examples provided by the following contents can be used to implement different features of the subject matter of this disclosure. The specific components and arrangements of the examples are intended to simplify the disclosure and not to limit the disclosure. Of course, these are only examples and are not intended to be limiting. For example, the following description in which a first feature is formed on or over a second feature includes direct contact between the two features, or an additional feature between the two features. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

[0024] Terms used in this specification generally have ordinary meanings in this field and the context in which they are used. The embodiments in this specification, including the examples of any terms discussed herein, are only illustrative, and do not limit the scope and meaning of this disclosure or any exemplary terms. Similarly, the present disclosure is not limited to the embodiments provided in this specification.

[0025] It will be understood that although the terms first, second, etc., can be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another. For example, without departing from the scope of this embodiment, the first element may be called the second element, and similarly, the second element may be called the first element.

[0026] As used herein, the term “and/or” includes any and all combinations of one or more associated listed items.

[0027] As used herein, the terms “comprise”, “include”, and “have” should be understood as open terms, that is, they mean including but not limited to.

[0028] When a material contains more than 90% of carbon fiber, due to the low activity of the carbon fiber surface itself, if the material is directly applied as an intermediate product or a composite material for a processing process without special treatment, the performance of the product is insufficient. Generally, after carbon fiber is carbonized at high temperature, the carbon fiber usually undergoes a surface treatment procedure to improve the surface reactivity of the carbon fiber. The disclosure provides a carbon fiber having an activated surface and the carbon fiber can be used to produce carbon fiber composite bottles, such as type III bottles or type IV bottles.

[0029] Carbonized fiber has a strong chemical inertness because its surface is basically composed of carbon atoms. However, the carbon fiber needs to be compounded with resin and other base materials, and surface of the carbon fiber is desired to have appropriate activity. Therefore, the number of oxygen-containing active functional groups on the carbon fiber surface should be increased through a surface oxidation treatment. There are several oxidation methods, and electrochemical oxidation is mainly used in industry. Electrochemical oxidation treatment takes advantage of the conductivity of carbon fiber. Carbon fiber is placed in an electrolyte solution as an anode, and active oxygen generated by an anodic electrolysis oxidizes the surface of the carbon fiber, thus oxygen-containing functional groups are introduced to improve the interface bonding performance of the composite materials having carbon fiber.

[0030] FIG. 1 illustrates a flowchart of a method for manufacturing carbon fiber according to some embodiments. First, in step 110 of the method 100 for manufacturing carbon fiber, a raw carbon fiber (which is also called carbon fiber precursor) is provided.

[0031] In some embodiments, the carbon fiber is rayon base fiber, asphalt base fiber, or polyacrylonitrile fiber, especially polyacrylonitrile fiber is most suitable for producing carbon fiber precursor. In some embodiments, the carbon fiber precursor is polyacrylonitrile fiber, and the production process for polyacrylonitrile fiber produces high performance raw carbon fiber made from wet spinning and dry jet spinning.

[0032] In some embodiments, it is preferable to control the adhesion amount of an oil agent on the raw carbon fiber in the range of 0.5-3.0% by weight, and in the range of 0.8-2.0% by weight is most suitable. If the adhesion amount of the oil agent is less than 0.5% by weight, the carbon fiber itself is too loose, and the operability of the carbon fiber firing process decreases. If the adhesion amount of the oil agent is higher than 3.0% by weight, the oil agent will easily produce chemical cross-linking reaction in the oxidation stage of the carbon fiber firing process, which will cause local defects in the high-temperature carbonization stage, resulting in hairiness in the finished carbon fiber products.

[0033] Next, step 120 of the method 100 for manufacturing carbon fiber is an oxidation stage of the carbon fiber firing process, and the oxidation stage is carried out at 200-300° C. in air or oxygen environment. In some embodiments, when the production cost is a main consideration, air is used.

[0034] In some embodiments, in the oxidation stage, the oxidation density is preferably controlled at 1.30-1.42 g/cm.sup.3, and 1.33-1.39 g/cm.sup.3 is the most suitable range.

[0035] After the carbon fiber passes through the oxidation stage, in step 130 of the method 100 for manufacturing carbon fiber, the carbon fiber is carbonized at 400-800° C. through a lower-temperature carbonization stage, and the reaction environment is filled with inert gas. In some embodiments, when the production cost is a main consideration, nitrogen gas is used. In some embodiments, when the compactness and the defect reduction of the carbon fiber are considered, the heating rate of the low-temperature carbonization is preferably below 600° C./min, and the most suitable range is controlled below 400° C./min, which can avoid an excessive carbonization reaction leading the performance degradation of the carbon fiber.

[0036] In some embodiments, in the low-temperature carbonization stage, the carbonization density is preferably controlled at 1.50-1.62 g/cm.sup.3, and 1.53-159 g/cm.sup.3 is the most suitable range.

[0037] Next, step 140 of the method 100 for manufacturing carbon fiber is a high-temperature carbonization stage. In some embodiments, when the production cost is a main consideration in the high-temperature carbonization, nitrogen gas is used. In some embodiments, the temperature range of the high-temperature carbonization stage is 900-2,000° C. From the viewpoint of the performance of carbon fiber, the maximum temperature of carbonization is preferably higher than 1,200° C., and it is most suitable to control the temperature in the range of 1,300-1,400° C.

[0038] In some embodiments, when the compactness and the defect reduction of the carbon fiber are considered, the heating rate of the high-temperature carbonization is preferably below 600° C./min, and the most suitable range is controlled below 400° C./min, which can avoid an excessive reaction in carbonization stage, and the resulting carbon fiber will have high performance.

[0039] Next, in step 150 of the method 100 for manufacturing carbon fiber, a surface treatment is performed to introduce functional groups through surface oxidation. The steps of the surface treatment are described in detail below.

[0040] After the surface treatment, in step 160 of the method 100 for manufacturing carbon fiber, the carbon fiber passes through a sizing agent immersion tank (i.e., a sizing treatment) and then a drying oven. Then, in step 170 of the method 100 for manufacturing carbon fiber, the finished carbon fiber is collected by reeling.

[0041] In some embodiment, in order to satisfy that compatibility of a composite resin in a downstream process, epoxy resin is mainly used for the sizing agent, and the adhesion amount of the sizing agent is preferably controlled in the range of 0.5-3.0%, and 0.8-2.0% is most suitable. If the adhesion amount of the sizing agent is less than 0.5%, the carbon fiber itself is too loose, and the downstream composite material is easy to produce hairiness. If the adhesion amount of the sizing agent is higher than 3.0%, the bundle property of the carbon fiber will become better, but the fiber opening property will become worse in the downstream processing of the composite material.

[0042] The surface treatment of step 150 of the method 10 for manufacturing carbon fiber is described in detail below. The degree of surface oxidation of carbon fiber can be controlled by changing the reaction temperature, the electrolyte concentration, the treatment time, and the electricity amount of the reaction.

[0043] FIG. 2 illustrates a surface treatment apparatus for a surface treatment of the carbon fiber according to some embodiments. A surface treatment apparatus 200 is a single-stage surface treatment apparatus. The surface treatment apparatus 200 includes a treatment tank 210, an anode roller 220 above a first side 212 of the treatment tank 210, a first immersion roller 230 near the first side 212 in the treatment tank 210, a second immersion roller 232 near a second side 214 in the treatment tank 210, a guide roller 240 above the second side 214 of the treatment tank 210, and a cathode plate 250 in the treatment tank 210. The electrolyte 260 is in the treatment tank 210, wherein the electrolyte 260 partially submerges the first immersion roller 230 and the second immersion roller 232, and the electrolyte 260 completely submerges the cathode plate 250.

[0044] As shown in FIG. 2, the carbon fiber 270 is placed above the first side 212 of the treatment tank 210, enters the treatment tank 210 through the anode roller 220, is immersed in the electrolyte 260 through the first immersion roller 230, then leaves the electrolyte 260 through the second immersion roller 232, and then leaves the surface treatment apparatus 200 through the guide roller 240 above the second side 214 of the treatment tank 210.

[0045] In some embodiments, the carbon fiber can be treated by single-stage or multi-stage surface treatment apparatus, and the concentration of the functional oxygen groups on the carbon fiber surface can be increased by matching the treatment time and electricity amount.

[0046] In some embodiments, the electrolyte used for the surface treatment is nitric acid, sulfuric acid, phosphoric acid, acetic acid, ammonium bicarbonate, sodium hydroxide, potassium nitrate, or the like. It is better to control the electrolyte with the conductivity value of 200-3,000 ms/cm. When the subsequent washing efficiency and the service life of electrolysis apparatus are considered, the most suitable range of the conductivity value is 300-2,500 ms/cm.

[0047] In some embodiments, sulfuric acid, phosphoric acid or ammonium bicarbonate is used as an electrolyte for the surface treatment of carbon fiber, the electrolyte has good production operability and can be used to produce carbon fiber with better performance.

[0048] The higher the temperature of the electrolyte, the higher the electron conduction efficiency; thus the electrolytic treatment efficiency is improved. In some embodiments, the electrolyte temperature is preferably controlled at 15-40° C., especially at 20-30° C. When the temperature of the electrolyte is higher than 40° C., the water content in the electrolyte is easily evaporated and the electrolyte is concentrated, which makes it difficult to maintain the uniformity of the electrolyte. After the carbon fiber passes through the surface treatment apparatus, the quality of the carbon fiber becomes extremely unstable.

[0049] In some embodiments, the voltage for the surface treatment is preferably controlled at 5˜40 V. If the voltage is too high in the production process, it will affect the operation and safety of personnel, so it is best to control the voltage at a lower voltage of 5-20 V.

[0050] In some embodiments, the electricity amount supplied to the surface treatment of carbon fiber is preferably in the range of 3-40 coulombs/gram, especially in the range of 10-30 coulombs/gram. If the supplied electricity amount is less than 3 coulombs/gram, the surface oxygen concentration of the carbon fiber is obviously insufficient, which is unfavorable for bonding with the base resin at the interface, and a test result shows that the bursting strength of a composite bottle wrapped with the carbon fiber is low. If the supplied electricity amount is higher than 40 coulomb/gram, the electrolytic intensity is too high, which will easily damage the fiber, resulting in the problems of exposed internal holes and excessive surface roughness of the carbon fiber, and the increase of the surface defects of the carbon fiber will lead to strength reduction of the carbon fiber.

[0051] In some embodiments, when the production operability is considered, it is preferable to control the surface treatment time of the carbon fiber for 5-90 seconds, especially for 10-50 seconds. If the treatment time is less than 5 seconds, the surface oxygen content of the fiber carbon is obviously insufficient, which is unfavorable for bonding with the base resin at the interface, and the bursting strength of a composite bottle wrapped with the carbon fiber is low. If the treatment time is more than 90 seconds, the electrolysis efficiency is too high, which will easily damage the carbon fiber, the internal defects of the carbon fiber will be exposed and the surface roughness will be too large, and the strength of the carbon fiber will be reduced due to the increase of the surface defects.

[0052] In some embodiments, after the surface treatment, the physical properties of the carbon fiber, the surface functional oxygen concentration of the carbon fiber (i.e., O.sub.1S/C.sub.1S), and the surface roughness Ra of the carbon fiber are measured.

[0053] In some embodiments, according to Japanese JIS R-7608 standard, the tensile strength and the tensile modulus of the carbon fiber are continuously measured for 6 times or more and averaged.

[0054] In some embodiments, after the surface treatment, the tensile strength of the carbon fiber is preferably at least greater than 5,100 MPa; the tensile strength over 5,300 MPa is most suitable. The coefficient of variation of the tensile strength should be at least controlled at 5.0% or below.

[0055] In some embodiments, the surface functional oxygen concentration of carbon fiber is referred to as O.sub.1S/C.sub.1S (hereinafter referred to as the surface oxygen concentration), which is measured by an X-ray photoelectron spectrometer, model ESCALAB, 220i XL. The carbon fiber is placed on a tooling table and fixed, and the measurement is performed according to normal operating procedures. The O.sub.1S peak area was integrated from the bond energy of 528 eV to 540 eV, and the C.sub.1S peak area was integrated from the bond energy of 282 eV to 292 eV. The surface functional oxygen concentration of carbon fiber was determined from the O.sub.1S/C.sub.1S ratio, which is measured continuously for 6 times or more and averaged.

[0056] In some embodiments, after the surface treatment, the surface oxygen concentration of the carbon fiber is preferably controlled at 5-45%; the range of 10-35% is most suitable when the chemical bonding force of the interface with the base resin is considered. If the surface oxygen concentration of the carbon fiber is lower than 5%, it is unfavorable for the carbon fiber to bond with the base resin at the interface, and the bursting strength of the composite bottle wrapped with the carbon fiber is low. If the surface oxygen concentration is higher than 45%, the chemical bonding force between the carbon fiber and the base resin is too strong, which leads to easily produce local stress concentration points, resulting in overall performance degradation.

[0057] In some embodiments, an atomic force microscope (AFM) is used to observe the surface morphology and to analyze the roughness of the micron-sized carbon fibers. This method adopts Bruker Dimension ICON model to analyze the microstructure and the surface topography of the sample, and the application mode is Tapping mode. FIG. 3 shows the surface of the carbon fiber, and the surface roughness Ra is as shown in FIG. 3. In some embodiments, the surface roughness is defined as the average roughness of the center line within a reference length L, which is measured by the instrument for 6 times or more and averaged.

[0058] In some embodiments, after the surface treatment, the surface roughness Ra of the carbon fiber is preferably controlled at 5-35 nm; when the physical bonding force with the base resin at the interface is considered, it is best to control the surface roughness Ra in the range of 7-30 nm, especially in the range of 10-25 nm is best. If the surface roughness of the carbon fiber is less than 5 nm, it is unfavorable to bond with the base resin at the interface, and the bursting strength of the composite bottle wrapped with the carbon fiber is low. If the surface roughness is greater than 35 nm, the physical bonding force between the carbon fiber and the base resin is too strong, but the carbon fiber will be poorly opened when the resin is impregnated in the later stages of the production and processing for the composite material, and the bursting strength variation of the composite bottle wrapped with the carbon fiber will be increased.

[0059] FIG. 4 illustrates a flowchart of a method for making a carbon fiber composite bottle according to some embodiments. First, in step 410 of the method 400 for making the carbon fiber composite bottle, the surface-treated carbon fiber is provided.

[0060] Next, in step 420, the carbon fiber undergoes a resin impregnation process.

[0061] Next, in step 430, the carbon fiber is placed in a carbon fiber wrapping machine for gas bottles to produce a semi-finished gas bottle.

[0062] Next, in step 440, the semi-finished product is hardened.

[0063] Next, in step 450, a finished carbon fiber composite bottle, such as a gas bottle, is produced.

[0064] The resulting carbon fiber composite bottle is then subjected to a quality inspection in step 460 and a bursting test in step 470.

[0065] In some embodiments, the carbon fiber yarn is dipped in a resin tank and undergoes a wrapping machine to produce a semi-finished gas bottle. After the semi-finished gas bottle is hardened, the finished product is pressurized and repeatedly subjected to bursting tests for 6 times or more, and the average value is obtained.

[0066] Generally, there are four types of bottles: type I bottles with no outer coating, type II bottles with an outer coating of glass fiber, type III bottles and type IV bottles with an outer coating of carbon fiber. The classification of these four types of bottles is shown in Table 1 below.

TABLE-US-00001 TABLE 1 Type Type I bottle Type II bottle Type III bottle Type IV bottle Weight 1.35 1.05 0.43 0.35 (kg/liter) Use period 15 15 30 30 (year) Description Material of the Material of the Material of the The material of inner tank is steel inner tank is steel inner tank is the inner tank is aluminum general purpose plastic The outer layer is The outer layer is The outer layer is The outer layer is not covered with coated with glass coated with coated with carbon fiber fiber, and the carbon fiber, and carbon fiber, and inner tank is the inner tank is the inner tank is wrapped with the wrapped with the wrapped with the glass fiber only in carbon fiber in carbon fiber in annular way. annual way and in annual way and in spiral way spiral way

[0067] In some embodiments, the types of the carbon fiber composite bottle include all type III bottles and type IV bottles, such as: paint bomb bottle for recreation, oxygen bottle for medical use, gas bottle for fire fighting equipment, or fuel bottle for transportation.

[0068] FIG. 5A shows a schematic diagram of a type III bottle. A carbon fiber composite bottle 510 includes a bottle body 512 and carbon fiber 514. The material of the bottle body 512 is aluminum. The carbon fiber 514 is wound around the bottle body 512 in annular way and in spiral way.

[0069] FIG. 5B shows a schematic diagram of a type IV bottle. A carbon fiber composite bottle 520 includes a bottle body 522 and carbon fibers 524. The material of the bottle body 522 is high-density polyparaene (HDPE) in one example. The carbon fiber 524 is wound around the bottle body 522 in annular way and in spiral way.

[0070] Table 2 below shows the comparisons of the different surface treatment conditions for treating carbon fiber, the operability of the various processes, and the surface oxygen concentrations, the surface roughnesses, the carbon fiber strengths, and the bursting strengths of the carbon fiber composite bottles having the resulting carbon fibers.

TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Comparative Comparative Example 1 example 1 Example 2 Example 2 Example 3 Example 4 Example 5 Example 3 Electrolyte Sulfuric Sulfuric Sulfuric Ammonium Ammonium Ammonium Ammonium Phosphoric acid acid acid bicarbonate bicarbonate bicarbonate bicarbonate acid Conductivity 250 300 500 500 500 700 2600 700 (ms/cm) Electricity 15 50 40 20 5 45 10 25 amount (coulomb/ gram) operability ∘ ∘ ∘ ∘ ∘ ∘ Δ ∘ of the process Surface 15 40 35 20 10 36 — 22 oxygen concentration Surface 18 28 25 16 14.5 18.5 — 19.2 roughness (nm) Carbon 5,225 4,650 5,120 5,410 5,385 5,180 — 5,430 fiber strength (Mpa) Bursting 1,060 852 950 1,200 765 800 — 1,210 strength of the carbon fiber composite bottle Symbols for process operability: ∘ Excellent; Δ Unable to operate normally.

[0071] In this test, each of the carbon fiber composite bottles has a volume of 2 liters and can be used for a medical gas bottle.

[0072] In Examples 1, 2 and 3, sulfuric acid, ammonium bicarbonate, and phosphoric acid were used as the electrolytes for the surface treatments of the carbon fibers. When the carbon fibers passed through the surface treatment apparatus, the conductivities of the apparatus were adjusted to 250˜700 ms/cm, the supplied electricity amounts were 15˜25 coulombs/g, and the surface functional oxidation concentrations of the carbon fibers were 15˜22%, which provided sufficient oxygen concentrations to strengthen the chemical bonding force with base resin. In addition, the measurement values of the surface roughness of the carbon fibers were 16˜19.2 nm, the surface defects were small; and the strengths of the carbon fibers were as high as 5,225 MPa or above. The carbon fiber composite bottles were made for blasting test, and the blasting strengths were higher than the design standard of 1,000 bar.

[0073] In Comparative Examples 1, 2, and 4, sulfuric acid and ammonium bicarbonate electrolyte were used as electrolytes, the excessive conductivities and the treatment electricity amounts resulted in the excessive concentrations of the surface functional oxygen concentrations and the large roughnesses of the surface of the carbon fibers, which reduced the performances of the carbon fibers.

[0074] In Comparative Example 3, ammonium bicarbonate electrolyte was used as an electrolyte, the supplied electricity amount was too low, which resulted in the insufficient concentrations of the surface functional oxygen of the carbon fiber. The carbon fiber composite bottle of the comparative example 3 had low burst strengths, which cannot reach the design standard of 1,000 bars.

[0075] In Comparative Example 5, ammonium bicarbonate was used as an electrolyte, the conductivity was as high as 2,600 ms/cm, but this leaded the problem of volatile organic compounds (VOC) in the surrounding environment of surface treatment apparatus. Although an exhaust hood is disposed above the electrolytic tank, the odor still escaped to the outside, and the operability of the process was not good.

[0076] The present disclosure provides a method for manufacturing carbon fiber.

[0077] After the surface treatment and the activation, the resulting carbon fiber can be used to produce carbon fiber composite bottles. The composite bottles have the advantages of light weight, long service life, good corrosion resistance, and no pollution to filling media. The composite bottles can be widely used in type III bottles or type IV bottles, such as paint bomb bottles for leisure and entertainment, oxygen bottles for medical use, gas bottles for fire fighting equipment, or fuel bottles for transportation.

[0078] Although the present disclosure has been described in detail according to some embodiments, other embodiments are also possible. Therefore, the spirit and scope of the appended claims should not be limited to the embodiments described herein.