Carbon Fiber Processing Technology

 

1. Performance

Carbon fiber is made of organic matrix fiber (such as viscose, polyacrylonitrile or asphalt) by high temperature decomposition method under inert gas at 1000-3000 degrees. As a result, all elements except carbon are removed.

 

Carbon fiber is black, hard, and has the characteristics of high strength and light weight. It is a new material with excellent mechanical properties. Its specific gravity is less than 1/4 of steel. The tensile strength of carbon fiber resin composite material is generally above 3500Mpa, which is 7-9 times that of steel. The tensile elastic modulus is 23000-43000Mpa, which is also higher than steel.

 

Therefore, the specific strength of CFRP, that is, the ratio of the strength of the material to its density, can reach more than 2000Mpa/(g/cm3), while the specific strength of A3 steel is only about 59Mpa/(g/cm3), and its specific modulus is also higher than that of steel. The higher the specific strength of the material, the smaller the self-weight of the component, and the higher the specific modulus, the greater the stiffness of the component. In this sense, it has predicted the broad application prospects of carbon fiber in engineering.

 

4. Price

The price of carbon fiber is the main factor restricting the development of carbon fiber. Carbon fiber production companies around the world are committed to reducing the price of carbon fiber. The Rocky Mountain Institute of the United States has conducted research and analysis on carbon fiber used in the automotive industry and concluded that: “When the price of carbon fiber drops below $16.5 per kilogram, carbon fiber will be competitive with steel.”

 

The price of carbon fiber from Zoltek of the United States is currently the cheapest in the world. Zoltek is still making further efforts, and its goal is to reduce the price of carbon fiber to about $11 per kilogram by 2000. The main measure taken by Zoltek of the United States to reduce the price of carbon fiber is to reduce the cost of the precursor used for carbon fiber. The company has mastered the technology of producing carbon fiber using acrylonitrile precursor used in general textiles, which has created conditions for the widespread application of carbon fiber and laid the foundation for the rapid development of carbon fiber.

 

In my country, the current price of carbon fiber precursor is 40 to 50 yuan per kilogram, carbon fiber is 200 yuan per kilogram, and prepreg is 500 yuan per kilogram. Each level of deep processing has a high degree of added value.

 

5. Classification

There are many ways to classify carbon fiber, which can be classified according to raw materials, characteristics, processing temperature and shape.

 

5.1 Classification by Raw Materials

Based on raw materials, it can be divided into six types: rayon and lignin of cellulose fiber series; polyacrylonitrile series; pitch series; phenol resin series and gas phase carbon fiber series.

 

5.1.1 Rayon Cellulose Fiber

Rayon cellulose fiber will not melt when heated. If it is heated in an inert gas in an oxygen-free state, it is very easy to obtain carbon fiber.

 

5.1.2 Polyacrylonitrile (PAN) Carbon Fiber

The manufacturing process of polyacrylonitrile (PAN) carbon fiber can be roughly divided into five procedures: preparation of polyacrylonitrile fiber; stabilization process (anti-inflammatory); carbonization process; surface treatment and sizing process; graphitization process.

 

5.1.3 Pitch-based Carbon Fiber

The residue after crude oil is refined at a high temperature of more than 900℃ contains about 95wt% carbon. If the sulfuric acid is removed by electrolysis and then washed with water, a very pure pitch (Pitch) can be obtained.

 

5.1.4 Gas-phase Growth Carbon Fiber

Gas-phase growth carbon fiber has two types: substrate growth method and fluidized catalyst growth method. Metal particles (M) such as iron, cobalt, and nickel are heated to 1100℃, and acetylene (C2H2) is thermally decomposed and dehydrogenated to form carbon deposition and growth under the metal particles to form carbon fiber. This is a schematic diagram of the substrate growth method, which shows that hydrogen (H2) gas and benzene (C6H6) gas must be fed in during the process.

 

5.2 Classification by Characteristics

Based on the characteristics, it is divided into three types: ordinary carbon fiber; high-strength and high-modulus carbon fiber and activated carbon fiber. Ordinary carbon fiber is called when the strength is below 120㎏/㎜2 and the Young’s modulus is below 10000㎏/㎜2; high-strength and high-modulus carbon fiber is called when the strength is above 150㎏/㎜2 and the modulus is above 17000㎏/㎜2.

 

5.2.1 Activated Carbon Fiber

Currently, commercial activated carbon has three forms: powder, granular and fibrous. Powdered Activated Carbon (PAC) is mostly made of sawdust, with an average size of about 15-25μm; Granular Activated Carbon (GAC) is roughly made of coal and asphalt powder, with an average size of about 4-6mm; Fiber Activated Carbon Fiber (ACF) is mostly made of PAN, Rayon, Pitch and Phenolic Resin fibers, with an average diameter of about 7-15μm.

 

Adsorption of Activated Carbon Fiber: Its adsorption varies depending on the raw materials. Among them, the Phenolic Resin system developed by Japan and other countries has a better effect. In the process of solvent adsorption, the first is surface mass transfer, then diffusion in the pores, followed by active true adsorption and multi-layer adsorption, and finally capillary condensation. Therefore, activated carbon fiber is an excellent solvent adsorption material, and can even be recycled. At the same time, it can be widely used for air purification, decolorization, deodorization, medical hygiene, gas masks/respirators, electronic materials and various pollution prevention filter materials.

 

 

 

5.3 Classification by Processing Temperature

If classified by processing temperature, it can be divided into three types: flame-resistant, carbon fiber and graphite. The processing heating temperature of flame-resistant carbon fiber is 200-350℃, which can be used as an electrical insulator; the processing heating temperature of carbon fiber is 500-1500℃, which can be used as an electrical conductive material; the processing heating temperature of graphite carbon fiber is above 2000℃, in addition to improving heat resistance and electrical conductivity, it also has self-lubricating properties.

 

5.4 Classification by the Shape of Carbon Fiber Products

If classified by the shape of carbon fiber products, it can be divided into cotton-like short fibers; filamentary continuous fibers; fiber bundles (Tow); fabrics; felt carpets and woven long objects, etc.

 

6 Applications

The main use of carbon fiber is to utilize its “light and strong” and “light and hard” mechanical properties, and it is widely used in structural materials such as aviation, aerospace, military industry, sports and leisure; using its dimensional stability, it is used in space machinery, radio telescopes and various molded products; using its fatigue resistance, it is used in helicopter blades; using its vibration attenuation, it is used in audio equipment; using its high temperature resistance, it is used in aircraft brake pads and insulation materials; using its chemical resistance, it is used in sealing fillers and filter materials; using its electrical properties, it is used in electrode materials, electromagnetic wave shielding materials, antistatic materials; using its bioadaptability, it is used in artificial bones and ligaments; using its X-ray transmittance, it is used in X-ray bed boards, etc.

 

 

In addition, it can be activated into activated carbon fiber and applied in various adsorption fields. Specific applications include:

① The annual output of fishing rods is about 12 million, and the annual carbon fiber consumption is 1200t;

② With the requirements of lightweight and long size, golf clubs now account for 50% of the use of carbon fiber sports products, and the annual carbon fiber consumption is 2000t;

③ The annual market size of tennis rackets is about 4.5 million, and the annual carbon fiber consumption is about 500t;

④ In terms of aircraft, the use of composite materials in small business jets and helicopters has accounted for 70%-80%, military aircraft 30%-40%, and large passenger aircraft 15%-20%;

⑥ High modulus carbon fiber is used for artificial satellite structures, solar panels and antennas, and 800H and advanced launch vehicles and missile shells, launch tubes, etc. are used. T300 carbon fiber, etc.;

 

⑥ In the field of civil engineering and construction, it has been used for repair and processing sheets, building components, steel bar substitutes, roof frame materials, etc.;

⑦ In the field of energy, it has been used in automobile compressed natural gas tanks and windmill blades (up to 30-40m), submarine oil field pipelines, elevators, etc.;

⑧ In the field of transportation, it has been used in racing cars, automobile drive shafts, large truck bodies, etc.;

⑨ In the field of electronics and electrical appliances, it has been used to reinforce thermoplastic resin extrusion products, such as antistatic IC disks and laptop computer chassis, which have electromagnetic wave shielding effects;

⑩ Others include X-ray boxes, medical bed boards, various rollers for printing, film making, papermaking, etc., pressure vessels for air or oxygen breathing, etc.

 

 

Before the mid-1990s, the military industry, aerospace and aviation industry, and sports and leisure industry were the main markets for CT carbon fiber. Since the United States successfully industrialized LT carbon fiber in 1996, the competition between CT carbon fiber and LT carbon fiber has been very fierce.

 

At present, PAN-based carbon fiber is in a period of rapid growth in the world: product performance tends to be high-performance, T700S is rapidly replacing T300 as general-grade carbon fiber; production has increased rapidly, increasing by 48.1% from 1996 to 2000; the use in aerospace and sports goods has increased steadily, and the increase in civil industry has been larger, exceeding the former two, especially with the large-scale production of large-tow carbon fiber and the reduction in prices, the demand for civil industry has increased rapidly.