Definition, classification and basic characteristics of high-performance fibers
I. The definition of high performance fiber High-performance fiber, as the name implies, is "high-performance", which refers to chemical fibers with special structure, properties and uses, or with some special functions. The early definition of high-performance fibers is based on mechanical properties, which often refer to fibers with a breaking strength exceeding 15cN/dtex, such as carbon fibers, para-aramid fibers, ultra-high molecular weight polyethylene fibers, etc., but this definition has certain limitations in actual production and application. Limitations; in a broad sense, fibers with high temperature resistance, radiation resistance, corrosion resistance, etc., are also called high-performance fibers, such as meta-aramid fibers, polytetrafluoroethylene fibers, polyphenylene sulfide fibers, etc. These products are mainly It is characterized by heat resistance and flame retardancy. II. Classification of high-performance fibers High-performance fibers can be classified according to the properties of the material and include metallic fibers, inorganic fibers, and organic fibers. Metal fibers are relatively small in the high-performance fiber family due to their high density and low specific strength. The main features of inorganic fibers are high temperature resistance, corrosion resistance and excellent mechanical properties. They are widely used in aerospace, weaponry and other fields, including carbon fibers, silicon carbide fibers, boron nitride fibers, silicon boron nitride fibers, alumina fibers, basalt fiber, glass fiber, etc. There are many varieties of organic high-performance fibers, which can be divided into flexible chain fibers and rigid chain fibers according to the characteristics of macromolecular chains. The typical representatives of flexible chain organic fibers are ultra-high molecular weight polyethylene fibers, high-strength polyvinyl alcohol fibers, etc., whose macromolecular main chain is composed of -CH2-, and the mechanical properties of the fibers are significantly improved due to the high orientation of the molecular chains. Rigid chain fibers include aromatic polyamide fibers (ie aramid fibers), polyarylate fibers, polyimide fibers, polyparaphenylene benzoxazole fibers (PBO), polybenzimidazole fibers, etc., of which the latter three This kind of fiber is also called aromatic heterocyclic fiber. In addition, organic high-performance fibers can also be classified according to the typical characteristics of the fibers, such as high-strength and high-modulus fibers (such as para-aramid fiber, high-strength polyimide fiber, PBO fiber, ultra-high molecular weight polyethylene fiber, etc.), high temperature resistance Fiber (meta-aramid fiber, polybenzimidazole fiber, polyetherimide fiber, etc.), etc. III. Physical and mechanical properties of high-performance fibers In addition to excellent mechanical properties, inorganic fibers have good heat resistance as their obvious advantages. Inorganic fibers also have the characteristics of low toughness, high density, and relatively complicated preparation. The properties of several typical inorganic fibers are shown in Table 1-1. Table 1-1 Mechanical properties of some inorganic fibers and metal fibers
Compared with inorganic fibers, organic high-performance fibers not only have excellent mechanical properties, but also have low density and high toughness, which make them widely used in the field of lightweight composite materials. The characteristics of some organic high-performance fibers are shown in Table 1- 2. Table 1-2 Properties of some organic high-performance fibers
There are many varieties of high-performance fibers, each showing different stress-strain behaviors. Figure 1-1 shows several typical fiber stress-strain curves. It can be seen that the elongation at break of the high-strength and high-modulus fibers is generally less than 4%, the stress-strain curve exhibits linear behavior, and the initial modulus is high. Heat-resistant fibers do not emphasize their mechanical properties, and their stress-strain curves are similar to ordinary fibers. Compared with traditional metal and inorganic ceramic materials, polymer matrix composites reinforced by organic high-performance fibers have the advantages of high specific strength, high specific modulus, and strong designability, and have been used in defense, military, aerospace, wind power generation. , building reinforcement, environmental protection, automotive industry and many other fields are widely used. As an important part of lightweight composite materials, the specific strength and specific modulus of reinforcing fibers are particularly important in some fields (such as aerospace, etc.). Figure 1-2 shows the comparison of specific strength and specific modulus of several typical high-performance fibers. It can be seen that organic fibers have obvious advantages due to their low density.