Impact-resistant fibers

Not all synthetic polymers are used as fibers Mylar for example is chemically the same as Dacron but IS prepared in the form of a thin film instead of a fiber Lexan is a polyester which because of its impact resistance is used as a shatterproof substitute for glass It IS a polycarbonate having the structure shown... 

THPOH—Ammonia—Tris Finish. By far the most effective finish for polyester—cotton textiles was a system based on the THPOH—NH treatment of the cotton component either foUowed or preceded by the appUcation of Tris finish to the polyester component. This combined treatment appeared to be effective on almost any polyester—cotton blend. A large amount of fabric treated in this way was sold throughout the United States and much of the rest of the world. Shortly after the introduction of Tris finishing, Tris was found to be a carcinogen. Most of the Tris treated production was in children s sleepwear, and this created a situation in which almost aU chemical fire-retardant-treated textiles were unfairly condemned as dangerous. Manufacturers mshed to replace chemically treated textiles with products produced from inherently flame-resistant fibers. Nowhere was the impact more severe than in the children s sleepwear market. New, safer materials have been introduced to replace Tris. Thus far none has been as completely effective. 

Initially, DADC polymers were used in military aircraft for windows of fuel and deicer-fluid gauges and in glass-fiber laminates for wing reinforcements of B-17 bombers. Usage in impact-resistant, lightweight eyewear lenses has grown rapidly and is now the principal appHcation. Other uses include safety shields, filters for photographic and electronic equipment, transparent enclosures, equipment for office, laboratory, and hospital use, and for detection of nuclear radiation. 

Cured phenolics are universally brittle in nature. This is true of both resoles and novolacs and does not depend much on the source of methylene used to promote cure. Consequently, the fillers used in molded articles are highly important to the design of the manufactured product. With resoles, the fiber or filler are usually the primary component of the final composite, with the resole acting as a binder or impregnating agent. With novolacs the resin may be the major component in the molded part. Poly-silanes and other organic polymers are also added in some applications to promote impact resistance and toughness [192]. 

C. C. Chamis, M. P. Hanson, and T. T. Serafini, Impact Resistance of Unidirectional Fiber Composites, in Composite Materials Testing and Design (Second Conference), H. T. Corten (Chairman), Anaheim, California, 20-22 April 1971, ASTM STP 497, American Society for Testing and Materials, 1972, pp. 324-349. 

The performance properties of PEN present opportunities for replacement of rayon or polyamide in carcass construction. The use of PEN cord in these applications is currently being evaluated in both Asia and Europe. PEN has demonstrated acceptable flexural fatigue equivalent to polyethylene terephthalate (PET) and rayon. It has equivalent toughness to rayon, which is important for sidewall impact resistance. PEN s superior mechanical properties also afford opportunities to use less fiber in carcass construction enabling production of lighter-weight, more fuel-efficient tires. 

The principal use of acrylonitrile since the early 1950s has been in the manufacture of so-called acrylic textile fibers. Acrylonitrile is first polymerized to polyacrylonitrile, which is then spun into fiber. The main feature of acrylic fibers is their wool-like characteristic, making them desirable for socks, sweaters, and other types of apparel. However, as with all synthetic textile fibers, fashion dictates the market and acrylic fibers currently seem to be in disfavor, so this outlet for acrylonitrile may be stagnant or declining. The other big uses for acrylonitrile are in copolymers, mainly with styrene. Such copolymers are very useful for the molding of plastic articles with very high impact resistance. 

Polycarbonate can be readily injection molded. Polycarbonates typically require only a short injection molding cycle time, because the polymer flows into the mold easily and solidifies rapidly. We injection mold polycarbonate to produce a wide variety of commercial goods, including compact disks, jewel cases, aircraft windows, kitchen utensils, and clear refrigerators drawers. Polycarbonates are also found in a wide range of disposable medical devices, such as the flow locks on intravenous tubes and the hard, disposable components of dialysis machines. Impact resistant polycarbonate is used to manufacture sports and other safety helmets. Glass fiber reinforced polycarbonate is used in the housings for power tools. 

To improve the interfacial bonding between the PP fiber and a cementitious matrix, commercially available PP fibers with different geometries were fluori-nated and the effect evaluated with regard to crack control, impact resistance (AC1 Committee 544 Report), and water absorption (ASTM C-948).M,34a In all cases, as seen in Table 16.13, fluorination improved the induced properties. 

Phenolic resins are the cheapest of all molding materials, since they usually contain more than 50% filler—sawdust, glass fibers, oils, etc. Their main properties are heat resistance, excellent dielectrics, and ease of molding. However, they have poor impact resistance (they crack) and they don t hold most dyes very well, except black. Their use is thereby restricted— they re functional but not pretty. When the telephone companies started making phones in colors, they quit using phenolic resins and instead bought more expensive thermosets. 

Bowles, K.J, (1988). The eorrelation of low-vclocity impact resistance of graphite fiber reinforced composites with matrix properties. In Composite Materials Testing and Design (8th Conference), ASTM STP 972 (J.D, Whitcomb ed.), ASTM, Philadelphia, PA, pp. 124-142. 

These resins are characterized by unusual toughness and clarity. As shown in Table 15.7, the addition of glass fibers improves the heat resistance of PC but reduces the impact resistance it also reduces the clarity. PCs are hydrolyzed by water when large surfaces are available, but molded or extruded articles are resistant to water, aqueous salt solutions, and nonpolar solvents. However, because of hydrolyzable groups in the repeating units, PC is attacked by mineral acids and alkalis. 

There are several interesting applications reported in the literature, such as insulated wire and cable, UV cross-linking of drawn fibers, and tapes from ultra-high-molecular-weight polyethylene. Semi-interpenetrating networks (IPNs) from acrylates and polyurethanes are suitable as UV curable adhesives with high elasticity, good impact resistance, and excellent adhesion to a variety of substrates. ... 

Structural applications of composite materials require not only acceptable static mechanical properites but the ability to withstand the generation and propagation of cracks without premature failre. For example, impact resistance, fracture toughness and fatigue resistance are desireable composite properties. Fiber-matrix structure at the interphase can affect the values attainable for these properties. 

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