Viscous fiber

Xanthation. The viscose process is based on the ready solubiUty of the xanthate derivative of ceUulose in dilute sodium hydroxide. The reaction between alkaU ceUulose and carbon disulfide must therefore be as uniform as possible to avoid problems with incompletely dissolved pulp fibers that wUl later have to be filtered out of the viscous solution. 

The Courtaulds semicommercial production system is iUustrated in Figure 8. Dissolving-grade woodpulp is mixed into a paste with NMMO and passes through a high temperature dissolving unit to yield a clear viscous solution. This is filtered and spun into dilute NMMO whereupon the ceUulose fibers precipitate. These are washed and dried, and finally baled as staple or tow products as required by the market. The spin bath and wash Uquors are passed to solvent recovery systems which concentrate the NMMO to the level required for reuse in dissolution. 

A viscous solution of poly(amic acid) can be processed into films, fibers, and coatings, and the final product undergoes thermal cyclo dehydration. 

Standard 0.25 or 0.50 lb (227 g) tin coated cans are used for packaging Hquid with neutral and mildly alkaline base formulas polypropylene is used for acid—base removers. Steel and polypropylene dmms are used for industrial removers. Viscous removers are packaged in removable top containers. Dry caustic removers are packaged in bag-lined boxes or fiber dmms. 

Fiber Slurry Pipelines. Pipelines to carry suspensions of wood, paper, sludge, etc, have found commercial acceptance. Most of them are less than 15 km long but have diameters of up to 500 mm. These slurries are often concentrated and display viscous plastic properties, although particle sizes may vary special pumps are used. One such hydrotransport system carries a cellulose slurry by pipeline from the plant to a paper plant near Heidenau, Germany. The 250-mm dia pipeline carries 60 t/d over the 3-km distance to thickeners. In Sweden, a 3.7-km, 500-mm dia pipeline moves cellulose by... 

The 3M Company manufactures a continuous polycrystalline alurnina—sihca—boria fiber (Nextel) by a sol process (17). Aluminum acetate is dissolved in water and mixed with an aqueous dispersion of colloidal sihca and dimethylform amide. This mixture is concentrated in a Rotavapor flask and centrifuged. The viscous mixture is then extmded through spinnerettes at 100 kPa (1 atm) the filaments are collected on a conveyor and heat-treated at 870°C to convert them to metallic oxides. Further heating at 1000°C produces the 10-p.m diameter aluminum borosihcate fibers, which are suitable for fabrication into textiles for use at temperatures up to 1427°C. 

Bacterial Cellulose. Development of a new strain of Acetobacter may lead to economical production of another novel ceUulose. CeUulon fiber has a very fine fiber diameter and therefore a much larger surface area, which makes it physicaUy distinct from wood ceUulose. Its physical properties mote closely resemble those of the microcrystalline ceUuloses thus it feels smooth ia the mouth, has a high water-binding capacity, and provides viscous aqueous dispersions at low concentration. It iateracts synergisticaUy with xanthan and CMC for enhanced viscosity and stabUity. 

Panel filters may use either viscous or dry filter media. Viscous filters are so called because the filter medium is coated with a tacky liquid of high viscosity (e.g., mineral oil and adhesives) to retain the dust. The filter pad consists of an assembly of coarse fibers (now usually metal, glass, or plastic). Because the fibers are coarse and the media are highlv porous, resistance to air flow is low and high filtration velocities can be used. 

Dry filters are usually deeper than viscous filters. The dry filter media use finer fibers and have much smaller pores than the viscous media and need not rely on an oil coating to retain collected dust. Because of their greater resistance to air flow, dry filters must use lower filtration velocities to avoid excessive pressure drops. Hence, dry media must have larger surface areas and are usually pleated or arranged in the form of pockets (Fig. 17-64), generally sheets of cellulose pulp, cotton, felt, or spun glass. 

Pressed Felts and Cotton Batting These materials are used to filter gelatinous particles from paints, spinning solutions, and other viscous liquids. Filtration occurs by deposition of the particles in and on the fibers throughout the mat. 

Automatic roll A motor-driven continuous roll of material, either viscous or fiber, which ensures a set pressure drop in the airflow. Its operation depends on sensors that record the pressure differential on either side of the filter. 

Gum Arabic (GA) or Acacia gum is an edible biopolymer obtained as exudates of mature trees of Acacia Senegal and Acacia seyal which grow principally in the African region of Sahe in Sudan. The exudate is a non-viscous liquid, rich in soluble fibers, and its emanation from the stems and branches usually occurs under stress conditions such as drought, poor soil fertility, and injury (Williams Phillips, 2000). 

Biefer, GJ Mason, SG, Electrokinetic Streaming, Viscous Flow and Electrical Conduction in Inter-Fiber Networks, The Pore Orientation Factor, Transactions of the Faraday Society 55, 1239, 1959. 

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