Viscose deaeration

Viscose Aging, Filtration, and Deaeration. After the dissolution step, the viscose cannot be spun into fibers because it contains many small air bubbles and particles. Furthermore, the degree of xanthation is too high, with too many of the xanthate groups in positions dictated by their accessibihty and not in the ideal positions for uniform dissolution. 

Continuous deaeration occurs when the viscose is warmed and pumped into thin films over cones in a large vacuum tank. The combination of the thinness of the Hquid film and the dismption caused by the boiling of volatile components allows the air to get out quickly. Loss of water and CS2 lower the gamma value and raise the cellulose concentration of the viscose slightly. Older systems use batch deaeration where the air bubbles have to rise through several feet of viscose before they are Hberated. 

The dark blue solution containing 5—10% of cellulose with a DP of 1000—2000 is filtered through a series of plate-and-frame filter presses using fine mesh metal screens to remove any particles that might block the spinneret holes. It is then deaerated under vacuum and stored ready for spinning. Unlike viscose dope, the cuprammonium cellulose [9050-09-3] solution is relatively stable. 

When selecting a suitable feed symp, the main criteria are optimization of enzyme productivity and minimization of the formation of by-products. Typical feed symp specifications are shown in Table 5. Higher symp concentration and higher viscosity results in a reduced isomerization rate due to diffusion resistance in the pores of the immobilized enzyme. A deaeration step is desirable to remove dissolved oxygen that would otherwise iacrease the formation of by-products. The pH is adjusted to the optimum level for the productivity of the enzyme. 

In the deaeration of high-viscosity fluids such as polymers, the material is flowed in thin sheets along solid surfaces. Vacuum is apphed to increase bubble size and hasten separation. The Versator (Cornell Machine Co.) degasses viscous liquids by spreading them... 

The flash photolysis of s-trinitrobenzene (TNB) aerated solns in alcohols generated a transient species with absorption maxima at 430 and 51 Onm (Ref 27). The yield of the transient was a function of oxygen concn, and its rate of formation was viscosity dependent. In deaerated solns, instead of the transient, a brown permanent product, identified as a charge transfer... 

Quantum yields of photodegradation were measured using an automatic viscosity timer modified so that the samples could be irradiated and deaerated in situ. 

Today rayon is made by either the viscose or the cuprammonium process. The latter process is based on Schweitzer s discovery in 1857 that it is possible to dissolve cellulose in cuprammonium hydroxide, the soln being due to the formation of a Cu cellulose complex. The mfg procedure involves processing the cuprammonium soln by filtration and deaeration prior to pumping it thru holes in a spinneret into si alkaline w which coagulates the Cu-cellulose soln into rayon filaments. The filaments are then stretched to the desired fineness (Ref 11). The viscose process is the most widely used because of its great versatility and low cost operation. 

Fig. 12.5. Flow diagram for manufacture of viscose yarn (1) cellulose sheets and caustic soda (2) steeping press (3) shredder (4) xanthating churn (5) dissolver (6) caustic supply (7) ripener (8) filtration (9) deaeration (10) filtration (11) continuous process (12) tire cord (13) pot spinning (14) staple spinning.

Auxiliaries to decrease viscosity of PVC-plastisols improve the coating properties and deaeration of PVC-plastisols. Do not change the thermo-stability and light-fastness. 

Dense-phase flow properties can be predicted by measuring the viscosity and deaeration rate of a fluidized bed in a laboratory test (117). This method appears to be especially useful for evaluating the flow characteristics in standpipes. The viscosity is measured by means of a Brookfield viscometer, which consists of a cylindrical wire-screen spindle rotated about its axis by an electric motor through a torsion spring. The torque required to rotate the spindle is measured by displacement of the... 

In PVC coating formulation fillers play a role. Filler choice mostly depends on the way the filler affect viscosity. The filler should not absorb the plasticizers nor interfere with the pseudoplastic behavior of the paste which is determined by the resin properties and by the choice of plasticizers. Fillers must be completely dispersed, since the gaps between the coated substrate and the knife are very small. There must be no lumps. Fillers should not interfere with deaeration which is... 

As an illustration, consider the problem of removing solids and water droplets from deaerated bituminous froth produced from the oil sands hot water flotation process (see Chapter 13 and reference 35). This is a nonaqueous suspension from which the particles and water droplets must be removed before upgrading and refining. At process temperature (80 °C) the suspension viscosity is similar to that of bitumen alone, but the density, because of the dispersed solids, is higher. Taking rj = 500 mPa s (35), px = 1.04 g/mL and p2 = 2.50 g/mL, the rate of settling of 10 pm diameter solid particles under gravitational force will be very slow ... 

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