Fiber reinforced plastic is a mixture of reinforcing fillers and plastic resins called matrixes. This technique increases the tensile strength and flexural modulus of the composite. These fillers also increase the heat deflection temperature of a material as well as cause it to resist shrinkage and warping. The extent to which these attributes are enhanced depends on the mechanical properties of the fiber and the matrix, their volume relative to each other and the length and orientation of the fiber within the matrix. Many organic and inorganic fillers are used to create fiber reinforced plastics. You may have heard of carbon fiber as it is being used increasingly in the automotive industry right now and is often in the news. But there are plenty of other useful fiber reinforced polymers! In this post we focus on the fibrous mineral filler Basalt and man-made aramid fibers such as Kevlar.TM
Basalt fibers are found in volcanic rock. They are extremely fine fibers made from basalt mined from a quarry that have been crushed, washed and melted with no other materials added. Basalt is composed of the minerals plagioclase, pyroxene, and olivine. To create the fibers, Basalt is melted at a temperature of about 1,400°C (2550°F) and then extruded through small nozzles to produce continuous filaments. Basalt fiber is known to have excellent corrosion resistance, high abrasion resistance and inherent fire resistance. It is also known for retaining its performance at cold temperatures and for not degrading under UV or electromagnetic radiation. Before 1995 basalt fiber technology used in military and aerospace applications was classified by the U.S. government.
The strength of basalt is higher that both fiberglass and carbon fiber and is just slightly less than that of steel. Also, basalt composite plastics are more water resistant and chemically stable. Basalt is used as a replacement for asbestos as it is fireproof and the filament diameter of its fibers are far above the human respiratory limit. It is used in car bodies, sports equipment, ship hulls, windmill blades, concrete reinforcement, camera tripods, and more.
Aramid fibers are synthetic and made from a family known as aromatic polyamides. The Federal Trade Commission defines aramid fibers as a manufactured fiber in which the fiber-forming substance is a long-chain synthetic polyamide in which a least 85% of the amide linkages (-CO-NH-) are attached directly to two aromatic rings. One of the best known is Kevlar™ because of its use in the protective vests worn by the police and military. Aramid fibers were first developed by DuPont in 1965 and became commercially available in 1973. Other aramid fibers are known under the following tradenames: Nomax, Conex, Arawin, New Star, X-Fiper and Kermel.
Kevlar™ is made using a special weaving method called the aramid weave. It resists corrosion and heat. It is very lightweight and is strong as well as flexible. It has no melting point but begins to degrade at 500°C. Kevlar™ has a chemical structure in which the bonds are aligned along the fiber axis. This construction gives aramids superior strength, in addition to flexibility and resistance to abrasion. Chlorine causes Kevlar to degrade, making it one of the few substances that can damage this strong material.
Kevlar is used to make bulletproof vests and body armor. It is also used to make bicycle frames and boat hulls and is used to replace brake pads and linings in place of asbestos. Another variation of this material, called Nomex™, is used to make fireproof suits, helmets, and gloves. Aramids are also used to make strings for tennis racquets, hockey sticks, running shoes, and skis.
Other inorganic reinforcing fibers include glass, carbon, and boron. Stay tuned for a post on these fiber reinforced polymers coming in the next few weeks.
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