Among glasses made of various materials, carbon fiber glasses are a special kind of glasses. To better understand this kind of glasses, it is necessary to have a detailed understanding of the material from which it is made, which is the carbon fiber that this article will talk about.

Below is a pair of carbon fiber sunglasses with a double bridge, fitted with a single black sun lens.

Carbon fiber refers to high-strength and high-modulus fibers with a carbon content of more than 90%. High temperature resistance ranks first among all chemical fibers. It is made of acrylic fiber and viscose fiber, which is oxidized and carbonized at high temperature. It is an excellent material for manufacturing aerospace and other high-tech equipment.

Carbon fiber is mainly composed of carbon elements. It has the characteristics of high temperature resistance, friction resistance, heat conduction and corrosion resistance. Orientation has high strength and modulus. Carbon fiber has a low density, so its specific strength and specific modulus are high. The main purpose of carbon fiber is to compound with resin, metal, ceramics and carbon as a reinforcing material to manufacture advanced composite materials. Carbon fiber reinforced epoxy resin composites have the highest specific strength and specific modulus among existing engineering materials. The diameter of carbon fiber is only 5 microns, equivalent to one tenth to one-twelfth of a hair, but its strength is more than four times that of aluminum alloy.

The history of carbon fiber materials.

In 1879, Edison used cellulose fibers such as bamboo, flax or cotton yarn as raw materials to first produce carbon fibers and obtained a patent. However, the mechanical properties of the obtained fibers were very low at that time, and the process could not be industrialized, so it 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, high specific modulus and high temperature resistance were urgently needed. Filament, this process laid the foundation for the industrialization of carbon fiber. For more than 40 years, carbon fiber has undergone major technological advancements.

In the early 1950s, the Wright-Patterson Air Force Base in the United States used viscose fiber as raw material to successfully trial-produce carbon fiber. The product was used as ablation material for rocket nozzles and nose cones, and the effect was very good. In 1956, Union Carbide Corporation of the United States successfully trial-produced high-modulus viscose-based carbon fibers, and the trade name "Thornel-25" was put on the market. At the same time, it developed the technology of stress graphitization to improve the strength and modulus of carbon fibers.

In the early 1960s, Akio Shindo of Japan invented a method of producing carbon fibers from polyacrylonitrile (PAN) fibers and obtained a patent. In 1963, Nippon Carbon Corporation and Tokai Electrode Corporation developed polyacrylonitrile-based carbon fibers using Shinto's patents. In 1965, Nippon Carbon Corporation succeeded in the industrial production of ordinary polyacrylonitrile-based carbon fibers. In 1964, the British Royal Aeronautical Research Center (RAE) trial-produced high-performance polyacrylonitrile-based carbon fibers by adding tension during pre-oxidation. It is industrially produced by Courtaulds, Hercules and Rolls-Royce using RAE's technology.

In 1969, Nippon Carbon Corporation successfully developed high-performance polyacrylonitrile-based carbon fibers. In 1970, Japan's Toray Textile Inc. 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 Corporation put high-performance polyacrylonitrile-based carbon fiber products (Torayca) on the market. Subsequently, the performance, variety and output of the products continued to develop, and it is still in the leading position in the world. Since then, Japan's Toho, Asahi Kasei, Mitsubishi Rayon and Sumitomo have successively invested in the production of polyacrylonitrile-based carbon fibers. (see polyacrylonitrile-based carbon fiber)

In 1970, Japan Kureha Chemical Industry Co., Ltd. adopted the patent of Otani Sugiro, and first built a production plant with an annual output of 120 tons of ordinary (GPCF) pitch-based carbon fibers. In 1978, the output increased to 240 tons. After the product was used as a cement reinforcement material, the effect was found to be very good. In 1984, the output increased to 400 tons, and in 1986 it increased again to 900 tons. In 1976, United Carbide successfully produced high-performance mesophase pitch-based carbon fiber (HPCF), with an annual output of 113t, which increased to 230t in 1982 and 311t in 1985.

Since 1982, Japan's Toray, Toho, Nippon Carbon, American Hercules, Celanese, and British Courtaulds have successively produced high-strength, ultra-high-strength, high-modulus, ultra-high-modulus, high-strength medium-mode and high-strength high-modulus And other types of high-performance products, the tensile strength of carbon fiber is increased from 3.5GPa to 5.5GPa, and small-scale products reach 7.0GPa. The modulus has been increased from 230GPa to 600GPa, which is a major breakthrough in carbon fiber technology and brings application development into a new high-level stage.

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

Viscose-based carbon fiber has not been developed since the mid-1960s, and only a small amount of products are produced for military and special departments.

Carbon fiber manufacturing process.

The route of modern carbon fiber industrialization is the precursor fiber carbonization process. The composition and carbon content of the three raw material fibers used are shown in the table.

The name of the fibrils used to make carbon fibers Chemical composition Carbon content/% Carbon fiber yield/% Viscose fiber (C6H10O5) n4521~35 Polyacrylonitrile fiber (C3H3N) n6840~55 Pitch fiber C, H9580~90

The process of using these three kinds of fibrils to make carbon fibers 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 argon atmosphere). In order to improve the bonding performance of carbon fiber and composite matrix, surface treatment, sizing, drying and other processes are required.

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

Classification and naming

At present, 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 raw fibers, processes and final carbon fiber properties. The term "carbon fiber" is actually a general term for a variety of carbon fibers, so classification and naming are very important.

In the late 1970s, the International Union of Theoretical and Applied Chemistry (IUPAC) made regulations on 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 (indicates heat treatment temperature, below 1400 ° C), hht (heat treatment The temperature is above 2000°C), and then add symbols indicating performance (such as HT for high strength, HM high modulus, SHT super high strength, HTHS high strength and high strain, IM medium mode and UHM super high mode, etc.). At the same time, it is pointed out that polyacrylonitrile-based, viscose-based and ordinary pitch-based carbon fibers are all non-graphitizable polymer carbons, while mesophase pitch-based carbon fibers and gas-phase grown carbon fibers are easily graphitizable carbons.

At the Third International Carbon Fiber Conference (London, 1985), it was suggested that carbon fibers be divided into the following 5 grades according to their mechanical properties.

Ultra-high modulus grade (UHM): the modulus is above 395GPa;

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

Medium modulus grade (IM): the modulus is between 255 and 310GPa;

Ultra-high-strength grade (UHT): the strength is above 3.5GPa,

Modulus below 255GPa;

High-strength grade (HT): the strength reaches 3.5GPa.

Both grading methods have shortcomings. Now the classification of high-performance carbon fiber products is marked by the manufacturer: the type of fibrils, the number of single-filament holes, the diameter, the arrangement (such as parallel, entangled, twisted, etc.), whether there is surface treatment (and its type), whether there is sizing (and type of slurry), etc. Some important high-performance trade names and properties can be seen in polyacrylonitrile-based carbon fiber and pitch-based carbon fiber.

Below is a pair of carbon fiber frames with elastic b-titanium temples. 

As a light and high-strength material, carbon fiber is mainly used in the fields of national defense, aerospace, automobile industry, energy equipment, construction engineering and other fields with the continuous development of carbon fiber technology. With the development of glasses technology, it was gradually applied to the glasses industry in the 1990s. Carbon fiber glasses are the lightest of all other glasses materials. Its weight is only half that of titanium glasses, and it has better impact resistance, so once it comes out, it is welcomed by many people, especially in the field of sports glasses.

 

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