Viscose, coagulating solution

The spinning is carried out by pumping the viscose through spinnerets into a solution of sulphuric acid. A variety of coagulating solutions are used. One example contains the following ... 

Low concentrations of sodium hydroxide cause a decrease in viscosity. A minimum was reached at about 0.5N sodium hydroxide. Higher alkali concentrations induce a strong increase in viscosity. The solution becomes more viscous than the original alkali-free solution. But no coagulation occurred with more concentrated... 

After the indicated lenth of time, the polymerization was stopped by pouring the contents of the bottle into 100 ml of a coagulant solution (100 gm of hydrated aluminum potassium sulfate and 100 ml of glacial acetic acid diluted to 2.5 liters with distilled water). The coagulated polymer was collected, washed with water, and dissolved in 150 ml of chloroform. Filtering this solution into 300 ml of methanol precipitated the polymer which was then separated by filtration, washed with methanol, and dried under reduced pressure. Inherent viscosities were determined in chloroform at 25°C. Tables III and IV contain the experimental data. 

The pulp is first steeped in an aqueous solution of sodium hydroxide (17 18%), which causes the fibers to swell and converts the cellulose to sodium cellulosate, commonly called alkali cellulose or white crumb. After steeping, the swollen mass is pressed to obtain a precise ratio of alkali to cellulose and then shredded to provide adequate surface area for uniform reaction in subsequent process steps. The alkali cellulose is aged under controlled conditions of time and temperature to depolymerize the cellulose by oxidation to the desired DP prior to reacting with carbon disulfide to form sodium cellulose xanthate. The xanthate, which is a yellow to orange crumb, is dissolved in dilute sodium hydroxide to yield a viscous orange-colored solution called viscose. The solution is filtered, deaerated, and ripened to the desired coagulation point (called salt index) appropriate for spinning. 

Viscose, Aqueous solution of cellulose xanthogenate. In the coagulating bath, viscose again becomes cellulose as a filament, film, or sponge. Viscose filament is one of the man-made fibres, viscose film is a packaging material, viscose sponge is a household article. 

The check of the above formula was done by comparing the drag coefficient data from the measurements [7] in Polyox coagulant solutions with an intrinsic viscosity of 17.8 dl/gr with present measurements of shedding frequency (with a similar type of polymer, possessing a measured intrinsic viscosity 15 dl/gr) and also with the shedding frequency measurements [8] with polyox WSR-301. All these experiments were carried out at a concentration of 100 ppm (Table 1). 

Figure 1 Evaluation of intrinsic viscosity for solutions in 0.1 M NaCl of the coagulant protein at 25°C. The Huggins (filled diamonds) and Kraemer (open triangles) plot give [t ] = 2.4 mL/g and [t ], = 2.6 mL/g, respectively.

Figure 2 Influence of anionic surfactants on the telative viscosity of solutions containing 0.05% of the coagulant protein in water at 25°C.

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). 

In the Shoe or one-shot method (4), formamide is used to coagulate sodium silicate. The silicate solution used in the Joosten method can be diluted with water to lower its viscosity. Concentrations of sodium silicate between 10—70% are used (viscosities of 2.5—50 mPa-s). Concentrations of formamide are between 2 and 30%. Other reactants such as CaCl2 and sodium aluminate are used in concentrations between 2.4—12 g/L of silicate solution. 

The resultant yellow sodium cellulose xanthate is dispersed in an aqueous caustic soda solution, where some hydrolysis occurs. This process is referred to as ripening and the solution as viscose . When the hydrolysis has proceeded sufficiently the solution it transferred to a hopper from which it emerges through a small slit on to a roller immersed in a tank of 10-15% sulphuric acid and 10-20% sodium sulphate at 35-40°C. The viscose is coagulated and by completion of the hydrolysis the cellulose is regenerated. The foil is subsequently washed, bleached, plasticised with ethylene glycol or glycerol and then dried. 

II Figure 1). Adsorption continually occurs around the bubbles to replace protein in areas of the interface where coagulation or stretching of the film is occurring. The actual bubble size in the foam depends upon the rate of protein adsorption as well as upon the ease of film rupture. The protein films on adjacent bubbles come in contact and trap the liquid, preventing it from flowing freely. This restriction is governed by the viscosity of the colloidal solution. The polypeptides of denatured proteins situate to positions where their hydrophobic side chains are directed outward toward each other. Because liquid... 

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