Filament region

The cystine content of the low-sulfur intermediate filament regions is about 6% and is not uniformly dispersed between domains of an intermediate filament chain. The rod domain contains about only 3% half-cystine or as little as 1 half-cystine residue, whereas the N terminal domain contains about 11% half-cystine and the C terminal unit contains about 17% halfcystine. Fraser also suggested that these half-cystine residues are involved in disulfide linkages and that most disulfide residues exist in the matrix. 

All evidence suggests that the forming process creates in the filament region a new material whose properties have little relation to those of the original material. In fact, the new material usually does not behave like an homogeneous amorphous semiconductor. 

Studies have also been performed on surface filaments which form between more widely separated electrodes placed on the surface of the amorphous material. This permits easy access to the filament region for direct physical measurements. However, it is likely that entirely different phenomena dominate in such a scaled up model. For example, in the geometries used for the study of surface filaments, diffusion and thermal effects are enhanced by inefficient cooling and long thermal time constants. Nevertheless, these studies discussed below have contributed valuable insight into the dynamics of structure changes in these materials. 

Figure Bl.7.1. Schematic diagram of an electron ionization ion source source block (1) filament (2) trap electrode (3) repeller electrode (4) acceleration region (5) focusing lens (6).

Woddwide, the production capacity for polyester fiber is approximately 11 million tons about 55% of the capacity is staple. Annual production capacity iu the United States is approximately 1.2 million tons of staple and 0.4 million tons of filament. Capacity utilization values of about 85% for staple and about 93% for filament show a good balance of domestic production vs capacity (105). However, polyester has become a woddwide market with over half of the production capacity located iu the Asia/Pacific region (106). The top ranked PET fiber-produciug countries are as follows Taiwan, 16% United States, 15% People s RepubHc of China, 11% Korea, 9% and Japan, 7% (107—109). Woddwide, the top produciug companies of PET fibers are shown iu Table 3 (107-109). 

Mechanical Properties. Although wool has a compHcated hierarchical stmcture (see Fig. 1), the mechanical properties of the fiber are largely understood in terms of a two-phase composite model (27—29). In these models, water-impenetrable crystalline regions (generally associated with the intermediate filaments) oriented parallel to the fiber axis are embedded in a water-sensitive matrix to form a semicrystalline biopolymer. The parallel arrangement of these filaments produces a fiber that is highly anisotropic. Whereas the longitudinal modulus of the fiber decreases by a factor of 3 from dry to wet, the torsional modulus, a measure of the matrix stiffness, decreases by a factor of 10 (30). 

Electron impact (El) ion sources are the simplest type. O2, Ar, or another (most often noble) gas flows through an ionization region similar to that depicted in Eig. 3.30. Electrons from an incandescent filament are accelerated to several tens of eV by means of a grid anode. A 20-100 eV electron impact on a gas atom or molecule typically effects its ionization. An extraction cathode accelerates the ions towards electrostatic focusing lenses and scanning electrodes. 

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