Aging of Alkali Cellulose

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...

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. 

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... 

The viscosity of the viscose, an important processing parameter, and the final rayon properties are dependent on the average chain length or DP of the cellulose. Control of this variable is achieved by aging the alkali cellulose crumb under conditions yielding the appropriate extent of depolymerization for the type of rayon produced. 

Ageing ageing aims to decrease the polymerization degree of alkali cellulose to the desired level. This process allows the alkali cellulose under controlled humidity and temperature conditions to obtain the required viscosity for spinning. 

H. is produced by - alkoxylation of alkali-cellulose suspended in solvents, such as acetone, isopropanol or tcrt.butanol 0.8-1.5 moles of alkali per AGU are necessary. To decrease viscosity, the alkali-cellulose is degraded by aging (- cellulose) before reaction or by adding hydrogen peroxide to the alkaline reaction mixture. For better efficiency, the addition of ethylene oxide is carried out in two stages. After the first reaction step, only catalytic amounts of alkali are necessary. Reaction takes place in 1-4 h at 30-80 °C and is stopped by neutralization with hydrochloric or acetic acid. Salts are removed by washing with alcohol/water mixtures. If retarded dissolution in water is desired, the wet product is treated with glyoxal. 

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... 

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