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FAQ

General

Where can carbon fibers be obtained?

How do I go about exporting products using carbon fibers?

  • Carbon fiber products and technologies related to their design, manufacture and use may be subject to the Export Trade Control Order and Foreign Exchange Order or come under other goods and technologies specified by the government as subject to security export control.
    In order to export products or technologies that fall under the above or provide them to non-residents, it is necessary to obtain an export license from the Minister of Economy, Trade and Industry in accordance with the Foreign Exchange Law and other related laws and notifications or a service transaction permit, or complete other necessary procedures.
    For details, refer to the Ministry of Economy, Trade and Industry’s website: Export Control

    http://www.meti.go.jp/policy/anpo/

Are there any statistics for carbon fibers?

Are any carbon fiber market forecasts available?

  • Member companies may present market forecasts at the composite materials seminar held annually byJCMA. Please refer to them.

Can images on JCMA website be used elsewhere?

  • n principle, images onJCMA website may not be reproduced. However, some images for which member companies have copyrights may be used under a permissions system. Please consult us by clicking on the link below and inserting the purpose of use, desired image(s) and contact details for the posting location(s) in the “Contact us” field.

    http://www.carbonfiber.gr.jp/english/contact/index.html

技術編

Why are carbon fibers light and strong?

  • Carbon fibers are light because they consist of carbon atoms, which have a low atomic weight, they have a graphite crystal structure (stacked hexagonal mesh planes consisting of fused benzene rings) and there are large gaps between carbon atoms. The strength of carbon fibers stems from the strength in the direction of the mesh planes in the graphite crystal structure.

    ＜Reasons why carbon fibers are light＞
    The weight of a substance (g/cm3) is indicated by its density. The density of a substance is determined by the weight (atomic weight) of the atoms composing it and the way the atoms are arranged (crystal system). For example, the atomic weights of familiar metals are: aluminum 26.98, iron 55.85, gold 196.97. Whereas, the atomic weight of carbon is 12.01; 1/2 to less than 1/10 of that of the metal atoms.

    黒鉛の結晶構造
    Graphite crystal structure

    The density of materials consisting of the same carbon atoms varies with the crystal structure. The density of diamonds is 3.51 g/cm3 and that of graphite 2.26 g/cm3. The distance between carbon atoms differs with the way they are arranged and the gaps in crystals are larger in graphite than they are in diamonds. Carbon fibers are lighter than metals because carbon atoms have a low atomic weight and there are large gaps between them.

    ＜Reasons why carbon fibers are strong＞

    Graphite crystals have a structure in which hexagonal mesh planes consisting of fused benzene rings are stacked up. Binding in the stacking direction easily comes apart because of the very weak intermolecular forces.

    On the other hand, carbon atoms within hexagonal mesh planes have strong covalent bonds in 3 directions so the tensile strength in the mesh plane direction is extremely strong. (Diamonds are hard because all carbon atoms are linked by covalent bonds only)

Please explain the differences between carbon fibers and other carbon materials (charcoal, graphite).

  • Carbon fibers and charcoal belong to the same group of carbon materials. Both have the same hexagonal mesh plane crystal structure (graphite structure) but the structure differs greatly in regularity and atom arrangement. Carbon fibers have a mesh structure in which the atoms are regularly aligned in the fiber direction. Several layers of these graphite structure elements are stacked up and are interlinked. On the other hand, the graphite


    Source “Fundamentals of Carbonization Engineering”; Authors: Sugio Otani, Yuzo Sanada (published November 20 1980)


    low strength. Belonging to the same group of materials, graphite has a well-developed, regular graphite structure. As you know, it is soft and slippery. Natural graphite is obtainable from China, India and other countries.




    ※Click on the illustration to enlarge it.


    The illustration shows how the molecular structure of a single thread of carbon fiber is generated step by step in the carbonization and graphitization processes. It gives a clear idea of how carbon atoms become regularly aligned in the longitudinal direction of the graphite structure through high temperature treatment and stretching.
    (Source: A. R. Bunsell, Fibre Reinforcements for Composite Materials, Amsterdam, The Netherlands: Elsevier Science Publishers B.V., 1988, p. 120.)

What are carbon fibers made from?

  • They are made from materials like the acrylic fibers that are used in clothing and blankets, and coal tar obtained from the heavy fraction of oil or by distillation of coal.
    Please refer to “Manufacturing Process of Carbon Fibers” for further details.

Please explain the main difference of the properties and applications of PAN-based carbon fibers and pitch-based carbon fibers.

  • PAN-based carbon fibers are classified as regular tow (small tow) and large tow depending on the difference in the number of fibers bundled together. They are also classified into general purpose, medium elasticity, and high elasticity types depending on the tensile modulus.

  • Table  Classification of PAN-based carbon fibers by numbers of bundled fibers, and their features

      Number of fibers Density(g/cm3) diameter (μm) Features Main applications
    Regular tow
    (small tow)     		1-24K 1.74-1.95 5-7 High specific strength
    High specific elasticity     		Aircraft
    Sports, leisure
    Large tow 40Kor above Relatively low cost General areas of industry

    Table Classification of PAN-based carbon fibers according to tensile modulus

      Tensile modulus (GPa)
    General purpose type (HT) ≤240
    Medium elasticity type (IM) 241-300
    High elasticity type (HM) 350≤

    Pitch-based carbon-fibers comprise a continuous type and a discontinuous type. The type produced depends on the spinning process. Pitch-based carbon fibers are also classified as isotropic type (difficult to graphitize) and anisotropic type (easy to graphitize), depending on the pitch used as the raw material.
        Fiber diameter(µm) Density(g/cm3) Tensile strength(MPa) Tensile modulus(GPa) Features
    Isotropic Carbon details 12-18 1.63 720 32 Lightness, chemical resistance, heat resistance, ease of sliding.
    Graphite details 12-15 1.58 600 30


    Unlike PAN-based carbon fibers, the tensile modulus of anisotropic pitch-based carbon fibers, also called mesophase pitch-based carbon fibers, can be varied widely.

      No. of fibers Fiber diameter(µm) Density(g/cm3) Tensile strength(MPa) Tensile modulus(GPa) Main applications
    Anisotropic 1K、2K、3K、6K、12K、16K 7-10 1.7-2.2 3,600 6-935 Wide range in tensile modulus Industry, sports/leisure

    For details, refer to Types and Applications of Carbon Fibers (https://www.carbonfiber.gr.jp/english/material/usage.html）

Why are carbon fibers good conductors of electricity and heat?

  • Carbon fibers have a basic graphite crystal structure. Please look at the diagram of the graphite crystal structure for Q1. The electrons surrounding the six-membered ring (benzene nucleus) that composes aromatic compounds are called π electrons. The π electrons are not associated with any of the carbons that compose the benzene nucleus, they can move around freely. Since the benzene nucleuses are fused together in a hexagonal mesh plane, the π electrons can move anywhere within it. In other words, a potential difference applied to this structure will cause electrons to flow in the plane and produce an electric current. Thus, the more regular the graphite crystal structure, the better the conductor.

    On the other hand, heat is transmitted by the vibration of atoms (lattice) in the crystal. In an orderly structure such as that provided by the planes of the graphite crystal structure, vibrations are well transmitted in the direction of the plane. Carbon fibers are a good conductor of heat due to the vibration of the lattice in the direction of the planes of the graphite crystal structure. Lattice vibration in undeveloped crystals, such as those of charcoal, is weak and they also have many defects, which would inhibit the conduction of both electricity and heat.

Could you explain the various classification designations that are used for pitch-based carbon fibers?

  • Raw material pitch is divided into isotropic pitch, which is optically disordered and does not show deflection when observed under a polarizing microscope, and anisotropic pitch whose component molecules are arranged in a liquid crystal form and it shows optical anisotropy (mesophase pitch). For carbon fibers, with the graphite crystal structure formed from regularly stacked up carbon hexagonal mesh planes as the ideal, any disorderliness, voids or defects present in the structure will reduce the conduction of electricity and heat. This is also mentioned in the answer to another FAQ. With regard to achieving maximum benefit from the regularity of the structural arrangement of the raw material pitch, carbon fibers manufactured from anisotropic pitch have superior mechanical properties and higher electrical and heat conductivity than carbon fibers manufactured from isotropic pitch. Designations incorporating such differences in optical characteristics of raw material pitch are the most used in the classification of pitch-based carbon fibers. These and other designations are shown in the table below.

    Function Raw material derived from
    High performance HPCF
    High Performance Carbon Fiber     		Anisotropic pitch Mesophase pitch
    General purpose GPCF
    General Purpose Carbon Fiber     		Isotropic pitch Anisotropic pitch

As they are made from carbon, aren’t carbon fibers flammable?

  • Carbon fibers have a regular mesh structure, whereas the structure of charcoal is less regular, and interlinking is weaker so the structure is easily broken.
    Carbon reacts with oxygen to produce carbon dioxide. (C+O2->CO2) This chemical reaction is called an oxidation reaction. If a certain temperature (oxidation initiation temperature) is exceeded, the reaction proceeds rapidly. This reaction produces heat and if the temperature rises due to this heat, the oxidation reaction occurs even more readily. Combustion occurs when there is no break in the cycle of oxidation reaction->heat produced->temperature rise->stronger oxidation reaction, and powerful oxidation occurs.
    So the oxidation reaction depends on: (1) temperature (2) carbon supply and (3) air supply. An example of (1) is using water to extinguish a fire. Owing to the latent heat of water, the temperature drops to inhibit the oxidation reaction. An example of (3) is using a blanket or sheet as a means of extinguishing a fire. Cutting off the oxygen in air inhibits the oxidation reaction. We can explain (2) using differences in flammability due to crystal structure.

    As carbon fibers have a regularly arranged structure and strong bonding among carbon atoms, they do not burn easily but with an irregular structure with many gaps, which air comes into, charcoal burns relatively easily. Also in the case of carbon fibers, the more regular the structure, the more difficult it is for them to burn.

Could you tell us about the recycling activities of JCMA?

  • JCMA carried out recycling activities for carbon fibers from 2003-2012 but has now stopped.
    Regarding carbon fiber recycling activities, please contact the following.

    Corporate Communications Dept., Teijin Limited TEL 03-3506-4055
    Public Relations & Investor Relations Office, Mitsubishi Chemical Holdings Corporation TEL 03-6748-7140
    Corporate Communications Dept., Toray Industries, Inc. TEL 03-3245-5179

Safety

Could you explain the safety aspects of carbon fibers?

  • General points for attention regarding the properties and handling of carbon fibers are given in the following.
    For specific information regarding the handling of individual companies’ carbon fiber products, please contact them directly.

Properties of carbon fibers

  • (1) Physical and chemical properties
    External appearance, form, color, etc.
    Please refer to Technical Information Q&A 4 where this is explained in detail


    (2) Stability and Reactivity

    Flammability:   Carbon fibers are classified as non-combustible under the Fire Service Act. They do not ignite when exposed to the flame of a match or a gas burner. However, if treated at high temperatures (400℃≤) in air, the amount of oxidation steadily decreases. At high temperatures, they may become red hot. This is not natural.
    Explosiveness:     None
    Dust explosiveness:    No information available.
    Reactivity:    Oxidized by strong oxidizing agents but do not react with other agents.


    (3) Others:
    Conductivity: As carbon fibers conduct electricity, fly or waste yarn can cause short-circuits in electric power lines.
    Biocompatibility:As carbon has good compatibility with the human body, carbon fibers or fiber composites are used as artificial human body parts.

Precautions in handling

  • (1) Preventing fluff, dust and fly
    As carbon fibers are thin and have a low breaking elongation, when handled, fuzz, dust or fly are readily produced and dispersed in the air. This can be a cause of problems with the use of carbon fibers.
    As staple fiber carbon fiber products are prone to scattering, local ventilation is recommended when they are removed from the container or processed. Similar measures are advisable when cutting long continuous yarn to produce chopped fibers or when crushing it to produce milled fibers.
    When pulling long-fiber carbon fibers out from a bobbin, pulling strongly when using a guides will produce fluff and fly. Reducing the tension on the yarn, using less guides, and rotating guides are effective in preventing dust and fly. The making of woven textiles, braid, knit textiles, stitched preforms or punch-felts generates fuzz, dust or fly as the yarn is stripped off or scrubbed. Local ventilation and frequent cleaning are recommended.

    (2) Prevention of harm to human body

    Skin
    Since carbon fibers have a high modulus of elasticity and a small diameter, if fibers adhere to the skin or mucosa, they may cause irritation, itchiness or pain. Attention is needed; for example reducing skin exposure and measures to prevent dust, such as local ventilation.
    If fibers adhere to the skin, without rubbing, wash off with cold or warm water. Using an adhesive carpet cleaner or packing tape to remove them is also effective.
    Applying a protective cream to the skin before working is also effective. This is particularly effective when handling high elasticity modulus fibers.

    Eyes and throat
    Prevent adhesion or inhalation of dust or fly by wearing goggles and masks. Consult a specialist if you feel any discomfort in the eyes.

    (3) Problems with electrical equipment and electric shocks
    When airborne dust or fly gets into switches or control equipment, this may cause short circuits. We recommend purging electrical equipment using clean air and insulating connections (with paint or tape).
    When PCs or other electronic devices are brought into a working area where there is suspended dust or fibers, we recommend keeping them in plastic cases and blowing clean air into the cases.
    Waste yarn adhering to a plug may cause electric shocks or short-circuits when the plug is inserted into an electric outlet and result in injury Special care is needed with high voltages.

    (4) Cautions in disposal
    Carbon fiber and carbon fiber composite waste should be separated from general waste and treated as plastic waste under industrial waste.
    If a local government has its own regulations regarding disposal, please adhere to them.
    Do not incinerate in a regular incinerator. Carbon fibers are not completely combustible in regular incinerators and fly produced may cause short circuits in electrostatic precipitators.

    (5) Transportation cautions
    In addition to carefully packing carbon fiber products to prevent spillage, pay attention to preventing damage to packaging during transportation. If the case of spillage of chopped fibers, milled fibers and other types of staple fiber from packaging, sweep them up and treat as industrial waste. Sprinkling water on fibers will prevent scattering when sweeping them up.

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