Aramid polymers

Aramid fibers, 13 372-373, 395 asbestos substitute, 3 314t chemical resistance of, 19 731t consumption of, 19 735t mechanical properties of, 13 376 properties of, 1.9 729-7301 as reinforcement materials, 26 756, 760 Aramid films/papers, properties of, 1.9 7331 Aramid polymer device, 16 1 Aramid products, economic aspects of,... 

Aramid polymers are much more expensive than the aliphatic polyamides. The use of aramid polymers is limited to those applications that justify the high cost. The present... 

Fig. 4. Threshold volume fractions Vp for incipience of a nematic phase plotted against the axial ratio x. The solid curve is theoretical according to Eq, (11). Experimental results on PBA in DMAc are shown by the open circles (Papkov and co-workers ), by the long dashed line (Kwolek et al. and by the triangle (Balbi et al. The short dashed line represents measurements (Bair, Morgan and Kilian on PPDT in concentrated HiSO, and the filled circles are for PPDT in 85 % aqueous H2SO4 (Nakajima, Hirai and Hayashi ). Concentrations reported in w/v units have been converted to volume fractions on the basis of a density of 1.46 g cm for the aramide polymers...

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 ... 

Isophthalic acid is produced from m-xylene by processes analogous to those used for terephthalic acid except that five to six times higher pressures are required. The product (m.p. 342°C) is chiefly used for the preparation of the high thermal stability aramid polymer, Nomex (Dupont), used for electrical insulation in thermally aggressive environments. 

Anti-Markovnikov addition, 220 D-Apiose, 988, 1011 Aprotic solvents, 322, 875 D-Arabinitol, 1009 D-Arabinose, 977, 1006, 1009 L-Arabinose, 976, 1001 Arachidic acid, 1018, 1025 Arachidonic acid, 1018, 1025 Aramid polymers, 809 Archaea, 58, 299 Arene oxides, 409, 948, 1064 Arenes, 54, 398-442 biological oxidation, 409, 417, 948, 1064 infrared spectra, 519 table nuclear magnetic resonance spectra carbon, 513 table proton, 495-496 Arenium ion, 444 L-Arginine, 1055, 1059... 

Aramid polymers are much more expensive than the aliphatic polyamides. The use of aramid polymers is limited to those applications that justify the high cost. The present U.S. market is about 20 million pounds per year. The applications are those where one needs very high flame resistance (clothing for firefighters and welders, welder s protective shield, upholstery and drapes), heat resistance (ironing board covers, insulation film for electrical motors and transformers, aerospace and military), dimensional stability (fire hose, V- and conveyor belts), or strength and modulus (circuit boards, bulletproof vests, fiber optic and power lines, ship mooring ropes, automobile tire cord, puncture-resistant bicycle tires). 

The structural formula of the aramid polymer Kevlar , used in bullet-proof vests, is shown in Scheme 6.14. Write the formulae of the... 

The first verification of the theoretical predictions of Onsager and of Flory that rod-like molecular chains might exhibit liquid-crystalline properties (see section 1.3.2 and chapter 12) was obtained in the 1960s and fibres from para-aramid polymers were commercialised under the name of Kevlar in 1970. These materials are very stiff and have excellent thermal stability many other materials of this class of rigid main-chain liquid-crystal polymers have been developed. They cannot, however, be processed by the more conventional processing techniques and this led to the development in the 1980s of another group of liquid-crystal polymers, the thermoplastic co-polyesters. 

A p-aramid polymer supporting a catalyst agent has been presented for several reactions. The composition exhibits an improved catalytic activity in comparison to m-aramid polymer catalyst support. The actual catalyst agent is adhered on or within the support. 

Aramid polymers have high melting points or melt with decomposition that makes fiber processing by melt spinning impractical [1] . Fibers are therefore spun from polymer solutions. These polymers not only do not melt but also are not easy to dissolve. Highly polar solvents, with or without the aid of inorganic salts such as lithium chloride or calcium chloride, or acids like concentrated sulfuric add have to be used [88]. 

DuPont s w-aramid polymer, MPDI, is polymerized using essentially a 1 1 molar ratio of w-phenylenediamine and isophthaloyl chloride [85]. Patent literature indicates that the fiber, Nomex, is spun directly from the polymerization solution in DMAc, which contains caldum chloride. MPDI polymer solutions containing >3% by weight calcium chloride are quite stable [2]. 

Solutions of w-aramid polymers are currently produced using dry-or-wet spinning processes. Processing steps after spinning can include drawing, drying, and heat treatment. 

Kwolek [106] demonstrated in her early work at DuPont that p-aramid fibers could be spun from amide and salt solutions using a conventional wet-spinning process. These solutions were typically of low concentration. The resulting fibers had low strength but high modulus after heat treatment. In later development,p-aramid fibers were spun from more concentrated solutions using dry-jet wet-spinning processes [107]. These solutions contained aramid polymer above a critical solids concentration and were anisotropic. 

Aramid polymers useful for spinning fiber can be obtained by the reaction of a diamine with a diacid chloride in solution. This reaction produces hydrochloric acid as a byproduct, which can be neu-trahzed by the addition of a basic compound to form a salt [30]. Fibers are then spun from this solution and the solvent must be removed from the fiber during its... 

An aramid polymer can be crosslinked in the presence of polymers from acrylic acid or methacrylic acid [48]. The crosslinked polymer is obtained by polymerizing a monomeric aromatic diamine with a monomeric aromatic diacid in the presence of poly(meth) acrylic acid, followed by a curing step. The curing step is simply a thermal curing. The crosslinked aramid polymer is then crosslinked via its amide bonds. Here it is not necessary to modify the aramid backbone with other monomers. 

Koch TA, Gabara V, Tokarsky EW, McEvoy JJ. Aramid polymer catalyst supports. US patent 6159 895, assigned to E.l. du Pont de Nemours and Company, Wilmington, DE 2000. 

Fibrous reinforcement in popular usage is almost synonymous with fibreglass, although other fibrous materials (carbon, boron, metals, aramid polymers) are also used. Glass fiber is supplied as mats of randomly oriented microfibrils, as woven cloth, and as continuous or discontinuous filaments. Hand lay-up is a versatile method employed in the construction of large structures such as tanks, pools, and boat hulls. 

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