40207_10 - ORGANIC FIBERS L inda L . Clements 10 A...

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ORGANIC FIBERS 10 Linda L. Clements 10.1 INTRODUCTION Before the first aramid fibers were introduced in the 1960s and 1970s, organic fibers were rel- atively low performance materials, primarily used in textile applications. Now several dif- ferent types of high performance organic fibers exist, all competitive with inorganic fibers in some or even most of their properties. The market demand for these fibers exceeds one billion dollars (Adams and Farrow, 1993a). The main applications for high perfor- mance organic fibers today are in asbestos replacement, ballistics, rubber reinforcement, ropes and cables and composites. Most of the usage is of aramid fibers, with over 18000 metric tons used each year. Both usage and existing capacity for other organic fibers are only a fraction of this value (Adams and Farrow, 1993a). Tlus broad market for organic fibers is a direct outgrowth of applying the basic princi- ples of polymer science to produce a new and exceptional engineering material. In the 1950s it was recognized that if a means could be found to form certain intractable polymers into extended chain fibers, very high stiffnesses, strengths and use temperatures could be achieved. The difficulty of producing such fibers was solved in the 1960s by spinning from liquid crystalline solutions. The first fibers pro- duced by ths process were the aramids, which have since been followed by other such fibers. Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 A different type of hgh performance organic fiber, extended chain polyethylene fibers, was added in the 1970s. While inferior to inorganic fibers in some properties, organic fibers provide combinations of properties not available with inorganic fibers and so have made possible new designs and applications. In this chapter, only high performance organic fibers which are commercially avail- able will be discussed in detail, although fibers which are nearing commercialization will be discussed briefly. For a more complete review of both commercially available and experi- mental high performance organic fibers, see Yang (1989, 1992). 10.2 ARAMID FIBERS 10.2.1 OVERVIEW Aramid fiber is the generic term for a specific type of ’aromatic polyamide fiber.’ The US Federal Trade Commission defines an aramid fiber as ‘a manufactured fiber in which the fiber-forming substance is a long-chain syn- thetic polyamide in which at least 85% of the amide linkages are attached directly to two aromatic rings.’ Thus, in an aramid, most of the amide groups are directly connected to two aromatic rings, with nothing else intervening. It should not be surprising that aramids have quite dif- ferent properties from nylons and other conventional polyamides since the latter poly- mers contain few if any aromatic groups in the main chain of the polymer.
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Aramid fibers 203 Aramid fibers can be separated into two types: the para- aramids and the meta-aramids.
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40207_10 - ORGANIC FIBERS L inda L . Clements 10 A...

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