Viscose, coagulating solution rayon

Rayon. Viscose rayon is obtained by reacting the hydroxy groups of cellulose with carbon disulfide in the presence of alkali to give xanthates. When this solution is poured (spun) into an acid medium, the reaction is reversed and the cellulose is regenerated (coagulated). 

Rayon. Rayon, the first commercial manmade fiber, is composed of cellulose in a quite pure form. It is produced by the treatment of wood pulp with alkali and carbon disulfide to form a viscous solution of cellulose xanthate. This viscous solution, called viscose, is extruded through spinnerets into an aqueous acid bath that coagulates the cellulose xanthate, decomposes it, and regenerates the cellulose. 

Fiber, rayon viscose A regenerated cellulosic fiber made by treating wood pulp with caustic soda, and with carbon disulfide to form cellulose xanthate that is then dissolved in a weak caustic solution. It is from the latter that extrusion and coagulation forms the fiber. 

A horizontal spinning machine, as is used in viscose rayon production, was first adopted. However, there is an essential difference in the coagulation mechanism of PVA and viscose solutions. In the case of viscose rayon, hydrolysis of cellulose-xanthogenate to regenerated... 

The rayon filaments are formed when the viscose solution is extruded through very small holes of a spinnerette into a spin-bath consisting basically of sulfuric acid, sodium sulfate, zinc sulfate, surfactant, and water. Coagulation of the filaments occurs immediately upon... 

In spinning, the alkaline viscose solution is exposed to an acidic spin-bath under carefully controlled conditions to form filaments of rayon. The process as described by Vroom involves a complex series of chemical and physical reactions that take place almost simultaneously [170]. Initially, the action of the add or salt spin-bath causes the viscose to coagulate and forms a skin around the filament. Then, as the acid penetrates into the viscose filament, neutralization of the alkali occurs. At the same time, cellulose xanthate is decomposed regenerating cellulose and carbon disulfide from which it was made (Equation 10.12). 

Regenerated cellulose, cellulose acetate, acrylic and some other fibres are spun from solution, either by dry spinning, with evaporation of solvent, or by wet spinning into a coagulation bath. In viscose rayon, the solute is sodium cellulose xanthate, which is a chemical derivative of cellulose soluble in caustic soda, so that a chemical reaction is involved in fibre formation. 

Wet-spun fibers are formed by extruding a highly viscous polymer solution through a spinneret into an appropriate liquid bath, where it is solidified. The solidification is brought about by a diffusional interchange between the extruded polymer filaments and the bath. In this process, called coagulation, one or more components from the bath diffuse into the fiber while, in turn, solvent leaves the forming filaments. The net result is a solid fiber. In some fiber systems, such as viscose rayon, there is also a chemical reaction superimposed on the diffusional process [60-62]. In others, the situation is strictly diffusional. Only the diffusional process will be considered in this treatment. 

Natural polymers can be made into hbers through dissolution of the polymer in an appropriate solvent and then extmsion of the polymer solution into a coagulation bath. As an example, cellulose can be made into viscose rayon fibers, cuprammonium rayon, cellulose acetate and triacetate fibers, lyocell, and modal fibers depending on the processes used to make the fibers. Other natural polymers such as mbber, chitosan, alginic acid, and protein can also be made into fibers in an appropriate fiber-forming process. 

Wet spinning also involves pumping a solution to the spinneret. Now, however, the polymer is precipitated in an immiscible liquid. Polyacrylonitrile in dimethyl formamide, for example, can be precipitated by passing a jet of the solution through a bath of water, which is miscible with the solvent but causes the polymer to coagulate. Cellulose triacetate can be wet-spun from a methylene chloride-alcohol mixture into a toluene bath, where it precipitates. In other fibers, the precipitation can involve a chemical reaction. Viscose rayon is made by regenerating cellulose from a solution of cellulose xanthate. 

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