Introduction To Carbon Fiber

Carbon fiber is an organic precursor fiber such as polyacrylonitrile (or pitch, rayon), which is pyrolyzed and carbonized in a high temperature environment to form a carbon backbone structure, and an inorganic polymer fiber with a carbon content higher than 90%.

Carbon fiber has excellent mechanical properties and chemical stability, low density than aluminum, high strength than steel, among the high-performance fiber that has been in the mass production, carbon fiber has the highest specific strength and the highest specific modulus of the fiber, and has a series of excellent properties such as electric conductivity, heat conduction, corrosion resistance and a series of other materials can not be replaced.

Carbon fiber is widely used in aerospace, wind power blades, sports and leisure, pressure vessels, carbon/carbon composite materials, transportation construction and other fields.

Carbon fibers can be classified according to different dimensions such as the type of precursor, mechanical properties, tow specifications, and preparation process of the precursor. The classification standards for different types of carbon fibers are as follows:

Types of precursor: divided into Pan-based carbon fiber, pitch-based carbon fiber and rayon-based carbon fiber. Among them, PAN-based carbon fiber has quickly occupied the mainstream position since its introduction in the 1960s, accounting for more than 90% of the total carbon fiber due to its relatively simple production process, excellent mechanical properties and wide range of uses. The production scale of pitch-based and rayon-based is small. Therefore, at present, carbon fibers generally refer to PAN-based carbon fibers.

Mechanical properties: Mechanical properties are mainly used in the industry to classify. According to the classification of mechanical properties of the current national standard for polyacrylonitrile-based carbon fibers GB/T 26752-2020, PAN-based carbon fibers are divided into four categories: high-strength type, high-strength medium-modulus type, high-modulus type, and high-strength and high-modulus type.

Tow specifications: According to the number of carbon fibers, it can be divided into small tows and large tows. Generally, carbon fibers with a number of tows less than 24K are called small tows (1K represents 1000 filaments in a bundle of carbon fibers), and those above 24K are called Large tows. Small tow carbon fiber has excellent performance, low output and high price, and is generally used in high-tech fields such as aerospace, national defense and military industry. Large tow products have relatively low performance, low cost, and difficult production control, and are widely used in basic industries and civil fields.

Precursor preparation process: According to the selection of spinning solvent, the continuity of the polymerization process, the process method used for spinning, etc., the preparation of precursor can be divided into different process types. According to the spinning solvent, it includes DMSO (dimethyl sulfoxide), DMAC (N,N dimethylacetamide), NaSCN (sodium thiocyanate) and other different solvent categories. According to the continuity of the polymerization process, it can be divided into one-step method and two-step method. According to the spinning process, it can be divided into wet spinning and dry jet wet spinning.