What Is Carbon Fiber Manufacturing?

High-strength, high-modulus fibers with a carbon content of more than 90%. High temperature resistance ranks first among all chemical fibers. It uses acrylic fiber and viscose fiber as raw materials and is carbonized by high temperature oxidation. It is an excellent material for manufacturing high-tech equipment such as aerospace. ^[1]

A special fiber made of carbon. It has the characteristics of high temperature resistance, friction resistance, electrical conductivity, thermal conductivity, and corrosion resistance. The appearance is fibrous, soft, and can be processed into various fabrics. Because its graphite microcrystalline structure is preferentially oriented along the fiber axis, it has a high Strength and modulus. The density of carbon fibers is small, so the specific strength and specific modulus are high. The main use of carbon fiber is as a reinforcing material and resin, metal, ceramics and charcoal composite, manufacturing advanced composite materials. Carbon fiber reinforced epoxy resin composite materials have the highest specific strength and specific modulus among existing engineering materials.

In 1879, Edison used cellulose fibers, such as bamboo, linen, or cotton yarns as raw materials, and first produced carbon fibers and obtained patents. However, the mechanical properties of the fibers produced at that time were very low, and the process could not be industrialized and failed to develop.

In the early 1950s, due to the development of cutting-edge technologies such as rockets, aerospace and aviation, new materials with high specific strength, specific modulus and high temperature resistance were urgently needed. On the other hand, precursor fibers can be obtained through heat treatment process Carbon fiber continuous filament, this process lays the foundation for the industrialization of carbon fiber. The major technological advances that carbon fibers have experienced over the past 40 years are as follows:

In the early 1950s, the Wright-Patterson Air Force Base in the United States used viscose fibers as raw materials and successfully produced carbon fibers. The products were used as ablative materials for rocket nozzles and nose cones, and the effect was very good. In 1956, United Carbide Co., Ltd. successfully trial-produced high modulus viscose-based carbon fibers. The brand name "Thornel-25" was put on the market. At the same time, the technology of stress graphitization was developed to increase the strength and modulus of carbon fibers.

In the early 1960s, Akio Shinto of Japan invented a method for preparing carbon fiber using polyacrylonitrile (PAN) fiber as a raw material, and obtained a patent. In 1963, Japan Carbon Company and Tokai Electrode Company used Jinto's patent to develop polyacrylonitrile-based carbon fibers. In 1965, Japan Carbon Company successfully produced ordinary polyacrylonitrile-based carbon fibers. In 1964, the Royal Aeronautical Research Centre (RAE) trial-produced high-performance polyacrylonitrile-based carbon fibers by adding tension during pre-oxidation. Courteulds, Hercules and Rolls-Royce use RAE technology for industrial production.

In 1965, Japan's Otani Sugirou first made polyvinyl chloride pitch-based carbon fibers and published a pioneering research report on pitch-based carbon fibers.

In 1969, Japan Carbon Company succeeded in developing high-performance polyacrylonitrile-based carbon fibers. In 1970, Toray Textile Inc. of Japan relied on advanced polyacrylonitrile precursor technology and exchanged carbonization technology with United Carbide Corporation to develop high-performance polyacrylonitrile-based carbon fibers. In 1971 Toray launched the high-performance polyacrylonitrile-based carbon fiber product (Torayca) on the market. Subsequently, the performance, variety and output of the product continued to develop, and it is still a world leader. Since then, Japan's Toho, Asahi Kasei, Mitsubishi Rayon, and Sumitomo Corporation have successively invested in the production of polyacrylonitrile-based carbon fibers. (See Polyacrylonitrile-based carbon fiber)

In 1970, Japan's Wu Yu Chemical Industry Co., Ltd. adopted Otani Sugirou's patent and first built a 120 t / a general-purpose (GPCF) pitch-based carbon fiber production plant. In 1978, the output increased to 240 t. After the product was used as a cement reinforcing material, it was found to be very effective. The output increased to 400 t in 1984 and again to 900 t in 1986. In 1976, United Carbide Company of the United States successfully produced high-performance mesophase pitch-based carbon fiber (HPCF), with an annual output of 113 tons, which increased to 230 tons in 1982 and 311 tons in 1985.

Since 1982, Toray Japan, Toho, Japan Carbon, Hercules, Celanese, and Courtaulds have produced high-strength, ultra-high-strength, high-modulus, ultra-high-modulus, high-strength medium-mode, and high-strength high-mode Other types of high-performance products, carbon fiber tensile strength increased from 3.5 GPa to 5.5 GPa, small-scale products reached 7.0 GPa. The increase in modulus from 230 GPa to 600 GPa is a major breakthrough in carbon fiber process technology, which has brought application development into a new high-level stage.

Since 1981, significant progress has been made in asphalt science, and several new processes for the preparation of mesophase pitch have been developed, such as the pre-mesophase method of the Kyushu Industrial Laboratory in Japan, the new mesophase method of the EXXON company in the United States, and the potential mesophase developed by Gunma University in Japan Phase method has promoted the development of high-performance pitch-based carbon fibers. Subsequently, Japan's Mitsubishi Chemical Corporation, Osaka Gas Company, and Nippon Steel Corporation successively built a number of high-performance carbon fiber production plants with different specifications. It is characterized by an increase in modulus and an increase in strength. The 1980s was a period of prosperity for pitch-based carbon fibers.

Viscose-based carbon fiber has not been developed since the mid-1960s, and only a small number of products have been produced for use by the military and special sectors.

The modern industrialization of carbon fiber is a precursor fiber carbonization process. The composition and carbon content of the three raw fiber materials are shown in the table.

Name of raw fiber used for making carbon fiber Chemical content Carbon content /% Carbon fiber yield /% Viscose fiber (C6H10O5) n4521 35 Polyacrylonitrile fiber (C3H3N) n6840 55 Asphalt fiber C, H9580 90

The process of making carbon fibers using these three types of fibrils includes: stabilization treatment (air at 200-400 ° C, or chemical treatment with flame-resistant reagents), carbonization (400-1400 ° C, nitrogen), and graphitization (above 1800 ° C) , Under an argon atmosphere). In order to improve the bonding performance of the carbon fiber and the composite material matrix, surface treatment, sizing, and drying processes are required.

Another method of making carbon fibers is the vapor phase growth method. Discontinuous chopped carbon fibers can be prepared by reacting a mixed gas of methane and hydrogen at a high temperature of 1000 ° C in the presence of a catalyst, with a maximum length of 50 cm. Its structure is different from polyacrylonitrile-based or pitch-based carbon fiber, which is easy to graphitize, has good mechanical properties, high electrical conductivity, and is easy to form interlayer compounds. (See Vapor Growth Carbon Fiber)

Classification and naming

Now the main products of carbon fiber are polyacrylonitrile-based, pitch-based and viscose-based. Each type of product is divided into many varieties due to different types of fibrils, processes and properties of the final carbon fiber. The term "carbon fiber" is actually a general term for a variety of carbon fibers, so classification and nomenclature are important.

In the late 1970s, the International Union of Theoretical and Applied Chemistry (IUPAC) made provisions for the classification and naming of carbon fibers. First use PAN (polyacrylonitrile), MP (mesophase pitch) and VS (viscose) to indicate the type of carbon fiber, and then use lowercase English letters to indicate the heat treatment temperature, such as lht (for heat treatment temperature, below 1400 ° C), hht ( The heat treatment temperature is above 2000 ), and then the symbols representing performance (such as HT for high strength, HM high mode, SHT ultra high strength, HTHS high strength and high strain, IM medium mode and UHM ultra high mode, etc.) are added. It is also pointed out that polyacrylonitrile-based, viscose-based and ordinary pitch-based carbon fibers are all difficult to graphitize polymer carbons, while mesophase pitch-based carbon fibers and vapor-grown carbon fibers are easily graphitizable carbons.

At the Third International Carbon Fiber Conference (London, 1985). It has been suggested that carbon fibers be classified into the following 5 grades according to mechanical properties.

Ultra High Modulus (UHM): Modulus above 395 GPa;

High modulus (HM): The modulus is between 310 and 395 GPa;

Medium Modulus (IM): The modulus is between 255 and 310 GPa;

Ultra High Strength (UHT): Above 3.5 GPa

The modulus is below 255 GPa;

High-strength grade (HT): Strength up to 3.5 GPa.

Both of these grading methods have disadvantages. At present, the classification of high-performance carbon fiber products is specified by the manufacturer: the types of fibrils, the number of monofilament holes, the diameter, the arrangement (such as parallel, tangled, twisted, etc.), whether surface treatment (and types), and Sizing (and types of sizing agents). Some important high-performance trade names and properties can be seen in polyacrylonitrile-based carbon fibers and pitch-based carbon fibers.

Development outlook

In the early 1990s, high-performance and ultra-high-performance carbon fibers have been introduced. It is expected that in the future, work will be devoted to perfecting processes, expanding production, reducing costs, and developing applications. Some special carbon fibers, such as antioxidant carbon fibers (to increase the temperature of the composite material), low-density carbon fibers (for 0.035 mm ultra-thin prepreg tape), high thermal conductivity and low resistance carbon fibers (to meet electromagnetic and RF shielding For interference, and can dissipate excess thermal energy), low thermal expansion coefficient carbon fiber (for satellite antenna systems, reflectors, etc.), hollow carbon fiber (for aircraft manufacturing industry, improve the impact toughness of composite materials, high temperature filtration in nuclear reactors) Media, media for the separation of biomolecules, serum and plasma) and activated carbon fibers, will develop greatly with the development of science and engineering. Vapor-grown carbon fiber has a stable process in the near future, and there will be significant progress in continuous production. The date of industrial production is not expected to be too far away. ^[3]