Alkali cellulose, aging

FIGURE 10.65 Alkali cellulose aging drum. (Courtesy of Chemiefaser Lenzing, A.G. Lenzing, Austria.)... 

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. 

Cotton linters or wood pulp, usually in the form of sheets, is steeped in strong alkali (18-50%). The swollen sheets are then pressed to force out most of the excess alkali solution. This alkali cellulose is then shredded, and aged if low viscosity is desired. The aging process is the one followed in the viscose industry and is fully explained in any discussion of that process. More alkali may be introduced during the shredding, either as a concentrated solution or as solid alkali.18 The alkali... 

Cellulose (VIII) is spun into fiber or cast into film by using a chemical reaction to convert it into a soluble xanthate derivative (Turbak, 1988). This is achieved by treating cellulose with 18-20% aqueous sodium hydroxide solution at 25-30°C for about 0.5-1 h. Much of the sodium hydroxide is physically absorbed into the swollen polymer some of it may be in the form of cellulose alkoxides. The excess alkali is pressed out of the cellulose pulp and the mass aged to allow oxidative degradation of the polymer chains to the desired molecular weight. The alkali cellulose is then treated with carbon disulfide at about 30° C and the resulting mass dissolved in dilute sodium hydroxide to form the sodium... 

Fig. 12 Alkalization of cellulose and aging of alkali cellulose (beech sulfite pulp). DSco (right) and differential MWD (left) after steeping and different aging times. Reprinted with permission from Biomacromolecules (2002) 4 743. Copyright (2002) American Chemical Society...

Hydroxyl Radical Trapping in Alkali Cellulose During Aging. 188... 

Using the same technique of CP/MASS I3C-NMR, Kamide et al.133) disclosed that in aged solid alkali cellulose the molecular motion is relatively rapid, as compared with solid cellulose intramolecular hydrogen bonding is present, and the sodium ion selectively coordinates to the hydroxyl oxygen at the C2 position of cellulose. 

The sheets of alkali cellulose, in the state in which they emerge from the press, are broken up into crumbs in a shredding machine consisting of a drum inside which blades with serrated edges rotate. The crumbs are removed and aged by storing in galvanized containers for 2 or 3 days, the... 

Viscose is a solution of cellulose xanthate in caustic soda. This solution can be processed into rayon or cellophane. The production of viscose consists of two steps. First, certain forms of cellulose, mainly from sulfite pulp and cotton linters, are reacted with pure caustic soda. This reaction converts the -OH groups on the cellulose unit to -ONa. The caustic soda must be pure and is obtained from mercury cells. Caustic soda from diaphragm cells contains sodium chloride which makes it unusable without purification. This solution must be aged for 2-3 days. Aging reduces the length of the cellulose chain which makes it easier to dissolve into caustic soda. The second step involves the reaction of the alkali cellulose and carbon disulfide in excess caustic soda. The net reaction of viscose is ... 

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