KR20170033708A - Preparing method for carbon fiber using sulfuric acid crosslinking and carbon fiber - Google Patents
Preparing method for carbon fiber using sulfuric acid crosslinking and carbon fiber Download PDFInfo
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- KR20170033708A KR20170033708A KR1020150131829A KR20150131829A KR20170033708A KR 20170033708 A KR20170033708 A KR 20170033708A KR 1020150131829 A KR1020150131829 A KR 1020150131829A KR 20150131829 A KR20150131829 A KR 20150131829A KR 20170033708 A KR20170033708 A KR 20170033708A
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Abstract
(1) a step of adding sulfuric acid to the polyolefin fibers and supporting the polyolefin fibers on sulfuric acid; (2) charging the polyolefin fibers supported on the sulfuric acid into a furnace filled with an inert gas; (3) a heating rate adjusting step of heating the furnace at a heating rate of 1 to 5 캜 / min; (4) maintaining the furnace at a temperature of 150 to 180 DEG C for 10 minutes to 1 hour to crosslink the polyolefin fibers; (5) a washing step of neutralizing the polyolefin fiber crosslinked with the sulfuric acid; And (6) a carbonization step of carbonizing the neutralized polyolefin fibers at a temperature of 600 to 1,200 ° C in a carbonization furnace, which is an inert atmosphere, after drying the neutralized polyolefin fibers. The carbon fiber manufacturing method of the present invention is characterized in that sulfuric acid The carbon fiber is produced by cyclizing the chain structure of the polyolefin to improve the thermal properties. Thus, the carbon fiber having a lower unit cost than the conventional carbon fiber can be produced, and the carbon fiber has a low unit cost And thus can be usefully used as various reinforcing agents such as reinforcing agents for various carbon fiber reinforced plastics.
Description
The present invention relates to a method for producing carbon fibers using sulfuric acid crosslinking, more specifically, by producing a carbon fiber having improved thermal properties by cyclizing a polyolefin chain structure by sulfuric acid, And a method for manufacturing the fiber.
BACKGROUND OF THE INVENTION [0002] Carbon fibers are extremely superior in terms of mechanical strength, electrical conductivity, thermal conductivity, and the like compared to glass fibers and the like, and thus are used in a wide variety of applications such as plastic reinforced materials, gas storage materials, and electrode materials.
Today, the use of carbon fiber, which is a high strength and high-elasticity material, is becoming popular, but due to the high production cost of carbon fiber, it is difficult to supply it.
Examples of the method for producing carbon fibers include a method of carbonizing organic fibers such as synthetic fibers and petroleum pitch fibers and a method of producing carbon fibers by pyrolyzing hydrocarbons such as benzene or methane in the presence of a catalyst ) Is well known.
Among them, the method of carbonizing organic fibers such as synthetic fibers and petroleum pitch fibers is mostly made from petroleum-based precursors such as polyacrylonitrile and pitch. In the method using polyacrylonitrile, A carbon fiber is produced by carbonizing after oxidizing stabilization process using air or an oxidizing gas or a mixed gas thereof in an appropriate ratio, and a method using pitch is a method of melt spinning the pitch, An oxidizing gas such as sulfuric acid, nitrogen oxide (NOx), or the like, or a mixed gas obtained by mixing them in an appropriate ratio is used for oxidation stabilization and then carbonized to produce carbon fibers. However, since the method of carbonizing organic fibers such as synthetic fibers and petroleum pitch fibers uses a petroleum-based precursor, a high precursor unit cost and a high processing cost arising from the stabilization step peculiar to the petroleum-based precursor, There is a problem that the production unit cost increases.
Therefore, by using a low cost precursor instead of the existing expensive petroleum precursor, the cost of the precursor in the production of carbon fibers can be lowered and the stabilization step can be omitted. Development is required.
A problem to be solved by the present invention is to provide a method of producing a carbon fiber using a polyolefin, which can produce a carbon fiber having a lower unit cost than conventional carbon fibers.
Another object of the present invention is to provide a carbon fiber produced using a polyolefin.
In order to solve the above problems,
(1) a step of adding sulfuric acid to the polyolefin fibers to carry the polyolefin fibers onto the sulfuric acid;
(2) charging the polyolefin fibers supported on the sulfuric acid into a furnace filled with an inert gas;
(3) a heating rate adjusting step of heating the furnace at a heating rate of 1 to 5 캜 / min;
(4) maintaining the furnace at a temperature of 150 to 180 DEG C for 10 minutes to 1 hour to crosslink the polyolefin fibers;
(5) a washing step of neutralizing the polyolefin fiber crosslinked with the sulfuric acid; And
(6) A method of manufacturing a carbon fiber comprising the step of carbonizing the washed polyolefin fibers and then carbonizing the fibers at a temperature of 600 to 1,200 ° C in an inert atmosphere carbonization furnace.
In addition, in order to solve the above-mentioned problem, the present invention is characterized in that the polyolefin fibers supported on sulfuric acid are heated at a temperature raising rate of 1 to 5 ° C / min and maintained at a temperature of 150 to 180 ° C for 10 minutes to 1 hour , And carbonization at a temperature of 600 to 1,200 ° C.
The carbon fiber manufacturing method of the present invention produces carbon fiber by a method of improving the thermal property by cyclizing the chain structure through cross-linking of polyolefin using sulfuric acid. Therefore, carbon fiber having lower unit cost than conventional carbon fiber Since the carbon fibers have a low unit cost, they can be usefully used as reinforcing agents for various carbon fiber reinforced plastics.
Fig. 1 is an electron microscope (SEM) photograph of the polyolefin fiber produced in Example 3 and having been cyclized. Fig.
2 is an electron micrograph (SEM) photograph of the carbon fiber (b) of Example 15 produced by carbonization of the polyolefin fiber produced in Example 3.
Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.
The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.
The method for producing carbon fibers of the present invention comprises the steps of: (1) a step of adding sulfuric acid to polyolefin fibers to carry the polyolefin fibers onto sulfuric acid; (2) charging the polyolefin fibers supported on the sulfuric acid into a furnace filled with an inert gas; (3) a heating rate adjusting step of heating the furnace at a heating rate of 1 to 5 캜 / min; (4) maintaining the furnace at a temperature of 150 to 180 DEG C for 10 minutes to 1 hour to crosslink the polyolefin fibers; (5) a washing step of neutralizing the polyolefin fiber crosslinked with the sulfuric acid; And (6) drying the washed polyolefin fibers, followed by carbonization at a temperature of 600 to 1200 ° C in an inert atmosphere carbonization furnace.
Hereinafter, the carbon fiber manufacturing method of the present invention will be described in detail for each step.
(1) a step of adding sulfuric acid to the polyolefin fibers to carry the polyolefin fibers onto the sulfuric acid
In the step (1), sulfuric acid is added to the polyolefin fibers to support the polyolefin fibers on the sulfuric acid. The sulfuric acid may be concentrated sulfuric acid, and when the concentrated sulfuric acid is used, the crosslinking reaction of the polyolefin fibers can proceed more smoothly.
The polyolefin fiber may be a polyolefin based fiber and may be at least one selected from the group consisting of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene and polyisobutylene have.
The polyolefin fibers may have a weight average molecular weight of 150,000 g / mol or more, specifically 150,000 to 500,000 g / mol. When the molecular weight of the polyolefin fiber is 150,000 g / mol or more, it has appropriate mechanical properties. Therefore, it is possible to prevent the fiber state from being damaged or the strength to be lowered after the carbonization step, and thus the carbon fiber can be suitably produced.
The polyolefin fibers may be supported by placing the polyolefin fibers in a suitable container and then adding sulfuric acid thereto. For example, the polyolefin fibers may be placed in a crucible, and sulfuric acid may be added to the polyolefin fibers to completely support the polyolefin fibers.
(2) a charging step in which the polyolefin fiber to which sulfuric acid is added is placed in a furnace filled with an inert gas;
Then, in step (2), the polyolefin fiber to which the sulfuric acid has been added is charged into a furnace filled with an inert gas.
As the furnace, it is preferable to use a furnace capable of precisely controlling the temperature to control the crosslinking reaction of the polyolefin fibers with sulfuric acid according to the temperature.
The furnace may be equipped with a heating means so as to control the temperature of the furnace, and the heating means can preferably be used to precisely control the heating rate and the temperature of the furnace.
The heating means may include a heating element, and the polyolefin fiber to which the sulfuric acid has been added is placed in a tube and the tube is charged into a furnace, and then the tube is heated using the heating body. .
The tube may be made of various materials such as iron, steel, copper, nickel, stainless steel, aluminum or alumina, and may be corroded by the sulfuric acid in step (1) It may be coated with Teflon.
The heating element may be positioned above or below the tube. When the heating element is located on both the top and bottom of the tube, the heating rate and the temperature of the furnace can be precisely controlled.
The tube may be filled with an inert gas to prevent the polyolefin fibers supported on the sulfuric acid from reacting with other materials. In particular, when the polyolefin fibers are crosslinked with concentrated sulfuric acid having a characteristic of absorbing moisture, It is necessary to remove all of the oxygen.
Accordingly, in the step (2), the tube may be stabilized by filling it with an inert gas for a certain period of time, and the charging time of the inert gas may be 10 minutes to 3 hours, preferably 20 minutes to 2 hours , More preferably from 30 minutes to 1 hour.
After the stabilization, the polyolefin fibers to which the sulfuric acid has been added are introduced into the tube, and then a further inert gas charging process can be performed. The polyolefin fibers to which the sulfuric acid has been added are introduced into the tube through the additional inert gas charging process to remove water and oxygen that may be introduced into the furnace and the additional inert gas charging process is performed for 5 to 30 minutes, For 10 to 20 minutes.
The inert gas may be helium, neon, argon, krypton, xenon, radon, nitrogen, or the like, specifically, helium in the process of filling the inert gas with the inert gas and stabilizing the inert gas.
(3) heating rate control step of heating the furnace at a heating rate of 1 to 5 DEG C / min
Subsequently, in step (3), the furnace charged with the polyolefin fibers carried on the sulfuric acid is heated.
At this time, the heating may be performed at a heating rate in a constant range of 1 to 5 ° C / min, preferably at a heating rate of 1 to 3 ° C / min.
When the heating rate is less than 1 ° C / min, crosslinking degree of the polyolefin fibers is insufficient and the degree of crosslinking of the polyolefin fibers is insufficient, If the rate of temperature rise exceeds 5 DEG C / min, the crosslinking reaction of the polyolefin fibers occurs rapidly, cracks are generated on the surface of the fibers, and the conditions necessary for crosslinking the polyolefin fibers are not satisfied .
At this time, the heating of the furnace can be performed through the heating element which can be positioned on the upper and lower sides of the tube.
(4) maintaining the furnace at a temperature of 150 to 180 ° C for 10 minutes to 1 hour to carry out a temperature holding step of crosslinking the polyolefin fibers
Then, in step (4), the temperature of the furnace heated at a constant heating rate is maintained for a predetermined time so that the polyolefin fibers are crosslinked by sulfuric acid.
In step (4), the dehydrogenation reaction of the polyolefin fibers by the sulfuric acid added to the polyolefin fibers and the crosslinking reaction therebetween are carried out, and the polyolefin chain structure is cyclized through the crosslinking reaction, And the thermal characteristics are improved.
The dehydrogenation reaction of the polyolefin fibers can be represented by the following reaction formula (1). [Reaction Scheme 1]
As shown in Reaction Scheme 1, in the molecular chain structure of the polyolefin fiber produced by the dehydrogenation reaction, the pi (pi) bond of the terminal double bond is opened, and the double bond of the neighboring molecular chain can be connected and crosslinked. The crosslinking of the polyolefin chain structure occurs in the crosslinking process, which is considered to be caused by forming a polygonal structure when the molecular chains of the polyolefin fibers are connected to each other. According to the production method of the present invention, by the cyclization of the polyolefin chain structure, the fiber holding state of the carbon fiber to be produced can be improved and the thermal property can be improved. At this time, the ring may be a hexagonal ring.
The suitable temperature of the furnace may be 150 to 180 캜, preferably 160 to 170 캜.
When the temperature of the furnace is lower than the proper temperature, the degree of crosslinking of the polyolefin fibers becomes insufficient, which is not suitable for the progress of subsequent carbonization. When the temperature of the furnace exceeds the proper temperature, the polyolefin fibers are seriously damaged, So that it is difficult to maintain the shape.
The temperature holding time of the furnace may be 10 minutes to 1 hour, preferably 10 to 30 minutes.
When the temperature holding time of the furnace is less than 10 minutes, the degree of crosslinking of the polyolefin fibers becomes insufficient and the polyolefin fibers are damaged when the temperature holding time of the furnace exceeds 1 hour There arises a problem that it is difficult to maintain the fiber form.
(5) washing step of neutralizing polyolefin fibers crosslinked with sulfuric acid
Subsequently, in step (5), a washing step of neutralizing the polyolefin fibers crosslinked with the sulfuric acid is carried out.
The neutralization may be carried out by using distilled water to wash all the sulfuric acid components, and the washing may be performed until the polyolefin fiber crosslinked with the sulfuric acid shows a pH of 7.
(6) Carbonization step of carbonizing the neutralized polyolefin fiber at a temperature of 600 to 1,200 ° C in an inert atmosphere carbonization furnace
Subsequently, in step (6), the neutralized polyolefin fibers are dried and then carbonized in an inert atmosphere carbonization furnace.
The carbonization may be performed in an inert atmosphere, wherein the inert atmosphere is filled with a gas such as helium, neon, argon, krypton, xenon, or radon, or an inert gas (N 2 ) , And the inert gas may preferably be nitrogen.
The carbonization may be performed at a temperature of 600 to 1,200 ° C, preferably 700 to 1,100 ° C, more preferably 800 to 1,000 ° C.
If the carbonization temperature is lower than the proper temperature, other elements constituting the polyolefin fiber may remain, which may result in an unsatisfactory quality. If the carbonization temperature exceeds the proper temperature, unstable ring chains may not maintain a hexagonal ring shape when carbonization proceeds Can be decomposed.
The carbonization may be performed for 1 to 10 minutes, and more specifically for 1 to 5 minutes.
If the carbonization time is less than the proper time, other elements constituting the polyolefin fiber may remain and may not have proper quality. If the carbonization temperature exceeds the appropriate time, unstable ring chains may not maintain a hexagonal ring shape when carbonization proceeds Can be decomposed.
The carbon fiber can be produced through the manufacturing method of the present invention as described above. Accordingly, the present invention provides the carbon fiber produced according to the above production method.
That is, in the carbon fiber of the present invention, the polyolefin fiber supported on sulfuric acid is heated at a temperature raising rate of 1 to 5 ° C / min, held at a temperature of 150 to 180 ° C for 10 minutes to 1 hour, As shown in Fig.
The polyolefin fibers supported by the sulfuric acid are heated at a heating rate of 1 to 5 / min, preferably a heating rate of 1 to 3 / min, at a temperature of 150 to 180 ° C, preferably 160 to 170 ° C , For 10 minutes to 1 hour, preferably 10 to 30 minutes.
At this time, the polyolefin fibers supported by the sulfuric acid may be heated in a furnace filled with an inert gas.
The inert atmosphere may be an inert gas such as helium, neon, argon, krypton, xenon, or radon, or a nitrogen (N 2 ) atmosphere, and the inert gas is preferably nitrogen Lt; / RTI >
The carbonization may be performed at a temperature of 600 to 1,200 ° C, preferably 700 to 1,100 ° C, more preferably 800 to 1,000 ° C.
The integrated pyrolysis in progress temperature (IPDT) of the carbon fiber according to an exemplary embodiment of the present invention may be 500 ° C or higher, preferably 1,000 to 3,000 ° C, and more preferably 1,000 to 2,200 ° C.
Example
Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples, but the present invention is not limited by these Examples and Experimental Examples. The embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.
Example 1
Low density polyethylene (LDPE) fibers (LUTENE MB9205, manufactured by LG Chemie) having a weight average molecular weight of 150,000 g / mol were carried in concentrated sulfuric acid (98%) and then charged into a stainless steel tube coated with Teflon and charged into a furnace . The furnace was heated to a temperature of 150 ° C at a heating rate of 1 ° C / min and maintained for 20 minutes to cause a cyclization reaction. The resultant was neutralized by washing with distilled water to a pH of 7, And dried at a temperature of 60 캜 for 24 hours to prepare a polyolefin fiber having a cyclic structure.
Example 2
A polyolefin fiber having been cyclized was produced in the same manner as in Example 1, except that the temperature for raising the temperature in Example 1 was changed to 160 ° C instead of 150 ° C.
Example 3
A polyolefin fiber having been cyclized was produced in the same manner as in Example 1, except that the temperature of elevation was changed to 170 ° C instead of 150 ° C in Example 1. An electron microscope (SEM) photograph of the prepared polyolefin fiber Is shown in Fig.
Example 4
A polyolefin fiber having been cyclized was prepared in the same manner as in Example 1, except that the heating temperature was changed from 180 ° C to 150 ° C instead of 150 ° C.
Example 5
The polyolefin fibers having been subjected to the cyclization were produced in the same manner as in Example 1, except that the temperature raising rate in Example 1 was set at 3 ° C / min instead of 1 ° C / min.
Example 6
A polyolefin fiber having been subjected to cyclization was produced in the same manner as in Example 2, except that the temperature raising rate in Example 2 was set at 3 ° C / min instead of 1 ° C / min.
Example 7
A polyolefin fiber having been subjected to cyclization was produced in the same manner as in Example 3, except that the temperature-raising rate in Example 3 was changed from 3 ° C / min to 1 ° C / min.
Example 8
The polyolefin fiber subjected to the cyclization was produced in the same manner as in Example 4, except that the heating rate in Example 4 was set at 3 ° C / min instead of 1 ° C / min.
Example 9
The polyolefin fibers having been subjected to the cyclization were produced in the same manner as in Example 1, except that the heating rate in Example 1 was changed from 5 ° C / min to 1 ° C / min.
Example 10
A polyolefin fiber having been cyclized was produced in the same manner as in Example 2, except that the temperature raising rate in Example 2 was set at 5 ° C / min instead of 1 ° C / min.
Example 11
A polyolefin fiber having been cyclized was produced in the same manner as in Example 3, except that the heating rate was changed from 5 ° C / min to 1 ° C / min.
Example 12
The polyolefin fiber subjected to the cyclization was produced in the same manner as in Example 4, except that the heating rate in Example 4 was set at 5 ° C / min instead of 1 ° C / min.
Comparative Example 1
Low density polyethylene (LDPE) fibers (LUTENE MB9205, manufactured by LG Chemie) having a weight average molecular weight of 150,000 g / mol were used.
Examples 13 to 24 and Comparative Example 2: Production of carbon fiber
The carbonized fiber samples were prepared by carbonizing the cyclized polyolefin fibers prepared in Examples 1 to 12 and the polyolefin fibers prepared in Comparative Examples in a vertical furnace in a nitrogen (N 2 ) atmosphere at a carbonization temperature of 900 for 3 minutes . FIG. 2 is an electron microscope (SEM) photograph of the carbon fiber prepared in Example 15. FIG.
Experimental Example 1: Calorimetric measurement of sulfuric acid-crosslinked polyolefin-based fibers
The calorific value of the polyolefin fibers produced in Examples 1 to 12 and the polyolefin fibers of Comparative Examples were measured. The calorific value was measured by differential scanning calorimetry (DSC-60, manufactured by Shimadzu Corporation) using differential scanning calorimetry (DSC) to expose the sample to a nitrogen (N 2 ) atmosphere at a temperature within 400 ° C. . Table 1 below shows the calorific values of the polyolefin fibers produced in Examples 1 to 10 and the polyolefin fibers of the comparative examples.
As can be seen from the above Table 1, the polyolefin fibers produced by the cyclization in Examples 1 to 12 exhibited a smaller heat absorbing amount and calorific value than the comparative example, and the cyclization produced in Examples 1 to 12 It was confirmed that the polyolefin fibers were smoothly crosslinked.
From the results of Examples 1 to 4, Examples 5 to 8, and Examples 9 to 12, it can be seen that the higher the heating temperature, the greater the degree of crosslinking and the smaller the heat absorption amount and the calorific value. 5, 9, Examples 2, 6, 10, Examples 3, 7, 11, and Examples 4, 8, 12. When the heating rate was the same but the heating rate was the same, it was confirmed that the higher the heating rate, the larger the degree of crosslinking and the smaller the heat absorption amount and the heating value.
Experimental Example 2: Measurement of carbonization yield of sulfuric acid-crosslinked polyolefin-based fibers
The fiber state of each of the carbon fiber samples prepared in Examples 13 to 24 and Comparative Example 2 was observed and the yield of carbon fibers at the time of producing the carbon fiber was measured with a thermogravimetric analyzer (TGA-50, manufactured by Shimadzu) Table 2 shows the results.
(%)
(° C)
(?,?, X)
?: A state in which a slight breakage or surface damage has occurred to the fiber
X: The state of the fiber collapsed due to the dynamic repulsion phenomenon
As shown in Table 2, it was confirmed that the polyolefin fibers (Examples 1, 5 and 9) in which cyclic sulfuric acid crosslinking was carried out at a relatively low temperature of 150 ° C were relatively unstable in fiber shape 13, 17, 21), which is judged to be due to the instability of the crosslink density. On the contrary, the polyolefin fibers (Examples 4, 8 and 12) in which sulfuric acid crosslinking was carried out at a relatively high temperature of 180 ° C (Examples 4, 8 and 12) were found to have undergone cross-linking as a whole due to the high sulfuric acid crosslinking temperature, (Examples 16, 20 and 24).
On the other hand, the intrinsic thermal decomposition progress temperature (IPDT), which is the theoretical temperature at which complete pyrolysis of the material can occur, tends to increase as the heating temperature of the sulfuric acid crosslinking increases. Also, in Examples 1, 5, 9, (Examples 13, 17, 21, 14, 18, 22, Examples 15, 19, 23, and 12) Through the Examples 16, 20 and 24, it was confirmed that the integral thermal decomposition progress temperature (IPDT) was high when the heating temperature was relatively high when the heating rate was relatively high.
Claims (16)
(2) charging the polyolefin fibers supported on the sulfuric acid into a furnace filled with an inert gas;
(3) a heating rate adjusting step of heating the furnace at a heating rate of 1 to 5 캜 / min;
(4) maintaining the furnace at a temperature of 150 to 180 DEG C for 10 minutes to 1 hour to crosslink the polyolefin fibers;
(5) a washing step of neutralizing the polyolefin fiber crosslinked with the sulfuric acid; And
(6) carbonizing the neutralized polyolefin fibers, followed by carbonization at a temperature of 600 to 1,200 ° C in an inert atmosphere carbonization furnace.
Wherein the polyolefin fibers have a molecular weight of at least 150,000 g / mol.
Wherein the polyolefin is at least one selected from the group consisting of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene and polyisobutylene.
And the charging time of the inert gas in the step (2) is 10 minutes to 3 hours.
Wherein the inert gas is helium, neon, argon, krypton, xenon, radon or nitrogen.
Wherein the heating rate in step (3) is 1 to 3 占 폚 / min.
Wherein the temperature of the furnace of step (4) is 160 to 170 占 폚.
And the temperature holding time in the step (4) is 10 to 30 minutes.
Wherein the neutralization of step (5) comprises removing residual sulfuric acid using distilled water.
Wherein the carbonization of step (6) is carried out at a temperature of 700-1,100 占 폚.
And carbonization of the step (6) is performed for 1 to 10 minutes.
Wherein the polyolefin is at least one selected from the group consisting of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene and polyisobutylene.
Wherein the heating rate is 1 to 3 占 폚 / min.
Wherein the carbon fibers are heated by heating the polyolefin fibers supported on the sulfuric acid, maintained at 160 to 170 캜 for 10 to 30 minutes, and then carbonized at a temperature of 700 to 1,100 캜.
Wherein the integral thermal decomposition progress temperature (IPDT) of the carbon fiber is 500 DEG C or higher.
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