Xanthating chum

The first step in the manufacture of the foil involves the production of alkali cellulose. This is then shredded and allowed to age in order that oxidation will degrade the polymer to the desired extent. The alkali cellulose is then treated with carbon disulphide in xanthating chums at 20-28°C for about three hours. 

Cellulose xanthate, or more exactly, sodium cellulose xanthate or sodium cellulose dithiocar-bonate, is obtained by mixing the aged soda cellulose with carbon disulfide in a vapor-tight xanthating chum. Based upon weight of cellulose, the amount of carbon disulfide used will be in the range of 30 percent for regular rayon to 50-60 percent for modified varieties. 

Carbon disulfide [75-15-0] is a clear colorless liquid that boils at 46°C, and should ideally be free of hydrogen sulfide and carbonyl sulfide. The reaction with alkaU cellulose is carried out either in a few large cylindrical vessels known as wet chums, or in many smaller hexagonal vessels known as dry chums. In the fully continuous viscose process, a Continuous Belt Xanthator, first developed by Du Pont, is used (15). 

The matured crumbs are converted to xanthate by treatment with carbon disulphide. A weighed quantity of crumbs is placed in the chum (Fig. 6.8)... 

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