Formation of Non-Polymer Fibers

Many different methods can be used to produce non-polymer fibers. For example, carbon fibers are made by high temperature treatment of eaibon precursors in an inert atmosphere. Glass fibers and some ceramic fibers eanbe directly spun from their melts. Ceramic fibers also can be obtained by the ealeination of ceramic pre-cnrsor fibers or by the chemical vapor deposition of precursor gas on a carbon fiber substrate. This chapter discusses the formation of two important non-polymer fibers carbon and glass fibers. 

Carbon fibers typically are produced by the high temperature treatment of stmc-turally stable precursor fibers that have been thermally, mechanically, and/or chemically pre-treated. Based on the precitrsor type, carbon fibers can be divided into four major classes, namely (i) polyacrylorritrile (PAN)-based, ( ) mesophase pitch-based, (Hi) cellulose-based, and (iv) vapor grown carbon fibers. 

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The author emphasizes the importance of the formation of non-equilibrium states and the kinetics of transition to equilibrium states for cases of processing rigid-chain polymers into fibers and films. 

In the following sections some examples are given of the ways in which these principles have been utilized. The first example is the use of these techniques for the low temperature preparation of oxide ceramics such as silica. This process can also be used to produce alumina, titanium oxide, or other metal oxides. The second example describes the conversion of organic polymers to carbon fiber, a process that was probably the inspiration for the later development of routes to a range of non-oxide ceramics. Following this are brief reviews of processes that lead to the formation of silicon carbide, silicon nitride, boron nitride, and aluminum nitride, plus an introduction to the synthesis of other ceramics such as phosphorus nitride, nitrogen-phosphorus-boron materials, and an example of a transition metal-containing ceramic material. 

Under most conditions oxide glasses behave as Newtonian fluids, i.e., the strain rate, dbildt, is a linear function of the applied shear stress, t. An important consequence of this behavior is that when we draw glasses, such as during the formation of optical fibers, the cross section reduces at a constant rate. In other words, we do not get necking of narrow sections of the fiber. At high stress levels non-Newtonian behavior, which is common in polymers, may be observed in oxide glasses. 

Polyimide fiber n. A manufactured fiber formed from the condensation polymer of an aromatic dianhydride and an aromatic diisocyanate. The fiber is produced by dry spinning. It is a high-shrinkage fiber used in the formation of mechanically stable non-woven fabrics. These fabrics are made without binders or resins bonding apparently results from the local temperature and pressure that develop during shrinkage. 

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