Aromatic polyamide Fiber properties

Aramid Fibers. Aromatic polyamide fibers exhibiting a range of mechanical properties are available from several manufacturers, perhaps the best known being Du Pont s proprietary fiber Kevlar. These fibers possess many unique properties, such as high specific tensile strength and modulus (see Fig. 4). Aramid fibers have good chemical resistance to water, hydrocarbons, and solvents. They also show excellent flame retardant characteristics (see High PERFORMANCE fibers Polyamdes). 

High performance polymer fibers (HPPF) have excellent mechanical properties compared to traditional textile fibers such as nylon. The typical HPPFs are aramid and polyethylene fibers (6). Aramid is a generic name for a class of aromatic polyamide fibers, most of which are varieties of poly(p-pheny-lene terephthalamide). Kevlar is the trade name of the varieties of aramid polymers introduced conunercially by Dupont. The molecules in the fibers of these materials are oriented in the axial direction. Poly(p-phenylene terephthalamide) is a rigid molecule with the following structure ... 

Most micromechanical theories treat composites where the thermoelastic properties of the matrix and of each filler particle are assumed to be homogeneous and isotropic within each phase domain. Under this simplifying assumption, the elastic properties of the matrix phase and of the filler particles are each described by two independent quantities, usually the Young s modulus E and Poisson s ratio v. The thermal expansion behavior of each constituent of the composite is described by its linear thermal expansion coefficient (3. It is far more complicated to treat composites where the properties of some of the individual components (such as high-modulus aromatic polyamide fibers) are themselves inhomogeneous and/or anisotropic within the individual phase domains, at a level of theory that accounts for the internal inhomogeneities and/or anisotropies of these phase domains. Consequently, there are very few analytical models that can treat such very complicated but not uncommon systems truly adequately. 

Definition Generic name for class of highly aromatic polyamide fibers which are characterized by flame retardant properties Uses Flame retardant protective clothing for military pilots, firefighters, etc. dust-filter bags tire cord bullet-resistant structures business machine components belts hoses ... 

PBT fibers show a very small strength loss of only 2% after an exposure of 65 h in air at 300 °C. This indicates a thermal stability of the mechanical properties which is even better than that of the aromatic polyamide fibers [31, 170].. 

Interest, academic and Industrial, In Liquid Crystal Polymers (LCP s) was sparked by the commercialization of Kevlar aromatic polyamide fiber In the early 1970 s. [1,2] This fiber can be made almost as stiff and as strong as steel, at one fifth of the density of steel. In addition. It has good resistance to chemical attack and outstanding resistance to heat. From a scientific point of view, LCP s are Interesting because they. In addition to displaying a variety of phenomena and properties seen with conventional Isotropic polymers, also exhibit many of the complex physical properties of small molecule liquid crystals.[3]... 

Because fibers from these aromatic polyamides have properties that differ significantly from the class of fibers known as polyamides (see Polyamides, fibers), the U.S. Federal Trade Commission adopted the term aramirf as designating fibers of the aromatic polyamide type in which at least 85% of the amide linkages are attached directly to two aromatic rings. 

The properties of aromatic polyamide fibers and films are sufficiently different from those of the products that preceded them that many new uses and... 

Fillers. Fillers used in molding compounds are glass fibers, aromatic polyamide fibers (like Kevlar and Arenka), mineral flour (mica, silica, wollastonite, talcum, and calcium carbonate), wood flour, cellulose, and caibon fibers. Fillers reduce shrinkage during cure, give higher compressive strength and stiffness, and improve thermal resistance, electrical properties, and flame retardancy. 

Thermal properties. See also Temperature of aromatic polyamides, 19 718 of asbestos, 3 300-304 of diesel fuel, 12 423 of ethylene—tetrafluoroethylene copolymers, 18 319-321 of fibers, 11 167 of filled polymers, 11 309—310 of gallium, 12 342 of glass, 12 588... 

Fiber Properties. One of the polymers, the poly(isophthalamide) of 4,4 -diaminoazobenzene (IV), was selected for investigation of fiber properties of aromatic azopolymers. Table III shows standard tensile data of the "as spun as well as the hot-drawn (1.5X, 350°C.) fiber. As shown, this polymer has tensile properties fairly typical of an aromatic polyamide. 

As pointed out in the preceding section, a second route for developing fibers having properties approaching the ultimate is the use of polymer chains that have high intrinsic stiffness and will remain extended in solution or melt. The development of aramid organic fibers based on aromatic polyamides met these requirements and added another chapter to the history of the development of synthetic fibers. Nomex aramid, a thermally resistant fiber based on a meta-oriented structure, was commercialized by the DuPont company in 1962. 

Liquid crystalline compounds are remarkable because of their ability to show spontaneous anisotropy and readily induced orientation in the liquid crystalline state. When polymers are processed in the liquid crystalline state, this anisotropy may be maintained in the solid state and can readily lead to the formation of materials of great strength in the direction of orientation. A particularly important example of the use of this property for polymers is in the formation of fibers from aromatic polyamides which are spun from shear oriented liquid crystalline solutions Solutions of poly(benzyl glutamate) also show characteristics of liquid crystalline mesophases, and both of these types of polymers are examples of the lyotropic solution behaviour of rigid rod polymers which was predicted by Flory... 

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