Stabilization thermosetting of Spun Fiber

The pitch precursor fibers, as spun, are very weak and almost without exception, thermoplastic in nature, making it imperative that they are chemically treated to render them suitable for subsequent carbonization. This is best accomplished by some form of oxidation treatment in the gas phase using air, O2 or an O2/N2 mixture, ozone, NO [6], CI2 [7], SO2 or SO3, although it is possible to use alternative treatments in the hquid phase with HNO3, 

H2O2 [8] or KM11O4. The simplest, cheapest and most convenient process is air oxidation, which is an exothermic reaction. Air enriched with ozone does permit lower temperatures (60-70°C) to be used initially and could promote crosslinking similar to the ozonization of phenanthrene in solution [9]. 

There are basically two methods of air oxidation that can be employed, both of which 

Singer [16] showed that an oxidized mesophase fiber, after carbonizing at 1600°C, showed a fine domain texture retaining the as spun texture, whereas a fiber carbonized from an un-oxidized fiber showed larger domains, indicating some relaxation of the structure. 

Riggs [17] observed that a fiber with larger diameter filaments, spun from a mesophase pitch tended to elongate, whilst smaller diameter filaments shrank, presumably because they were more highly oriented. The elastic modulus of as spun fibers increased with the draw ratio, but decreased with increasing thermosetting temperature and is attributed to a relaxation effect. 

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