Spinning Process Control

Fiber orientation uniformity is also affected by small-scale or timewise variations in polymer viscosity, related to breakage of polymer chains during the extrusion process. The degradation occurs as a result of residual moisture that immediately reacts to break chains, and by thermal degradation that occurs more gradually over time. Different residence times and temperature histories within the laminar flow streamlines lead to different viscosities, and hence different average orientation levels in the different fibers. 

Relative scales of the spinning processes for staple and filament products are depicted in Table 12.1. The industrial filament process is intermediate to the staple and textile filament processes, in terms of both spinning throughput and fiber orientation uniformity (here measured by spun birefringence level). Industrial yarns must be uniform enough to be drawn to much higher tenacity levels than staple yams, but are not dyed and therefore not subject to the more demanding uniformity requirements of textile yams. 

Parameter Staple fiber Industrial filament Textile filament 

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Because the polymer degrades before melting, polyacrylonitrile is commonly formed into fibers via a wet spinning process. The precursor is actually a copolymer of acrylonitrile and other monomer(s) which are added to control the oxidation rate and lower the glass transition temperature of the material. Common copolymers include vinyl acetate, methyl acrylate, methyl methacrylate, acrylic acid, itaconic acid, and methacrylic acid [1,2]. 

A variation on the wet-spinning technique involves extruding into a heated gas environment. In this dry-spinning process, the temperature and composition of the gas control the extraction process. 

Nitric acid synthesis, platinum-group metal catalysts in, 19 621 Nitric acid wet spinning process, 11 189 Nitric oxide (NO), 13 791-792. See also Nitrogen oxides (NOJ affinity for ruthenium, 19 638—639 air pollutant, 1 789, 796 cardioprotection role, 5 188 catalyst poison, 5 257t chemistry of, 13 443—444 control of, 26 691—692 effect on ozone depletion, 17 785 mechanism of action in muscle cells, 5 109, 112-113 oxidation of, 17 181 in photochemical smog, 1 789, 790 reduction with catalytic aerogels, l 763t, 764... 

Spinning rotor viscosity gauge a transfer standard for the laboratory or an accurate gauge for vacuum process control J. Vac. Sci. Technol., 20 (4), 1982,1148-1152... 

In man-made fibres, any stretching will irreversibly alter the crystallinity and there is no control of the lateral size of polymer crystals. Semicrystalline polymer networks typically consist of platelet type crystals whose width exceeds their thickness by several order of magnitudes because only the thickness is controlled by the chain folding [61]. In contrast to synthetic fibres, spider silk does not need any mechanical treatment by external forces the constituents self-assemble directly during the spinning-process. These examples clearly demonstrate the need for more detailed control of the mesoscopic structures for further development of man-made materials. 

Ru complexes much lower values of r were found, implying that a time-dependent process other than rotational reorientation is operating. Modulation of the ground state potential energy surface via a dynamic Jahn-Teller effect is suggested as the process controlling the electron spin relaxation in these compounds. 

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