Alkaline degradation of cellulose

Golova and Nosova (22) have reviewed the alkaline degradation of cellulose and of oxidized celluloses ... 

The main processes occuring in the alkaline degradation of cellulose are the so called degradation of cellulose from the reducing end of the molecule and the alkaline hydrolysis of glycosidic bonds. The former process is observed almost exclusively at temperatures up to 150°C. 

Overall Process. Figure 7 illustrates the alkaline degradation of cellulose at elevated temperatures [102,106]. The existing reducing endgroups will... 

Figure 7 Alkaline degradation of cellulose at elevated temperature. (From Ref. 106.)...

Alkaline degradation of cellulose is important during alkaline pulping it produces non-volatile acids > which are, for the most part, D-gluco-isosaccharinates. " ... 

Smaller environments can exist even within one of these microenvironments. For example, within one piece of wood associated with metal, there can be regions of an electric field that would cause hydrolytic or alkaline degradation of cellulose or lignin. 

Although significant amounts of other organic acids are produced, lactic acid is the major product for the reaction conditions studied. As well as having numerous direct uses, lactic acid has the potential of being an important intermediate in the production of other valuable products (13. 14). Preliminary economic analysis indicates that production of lactic acid from alkaline degradation of cellulose has economic merit (9). It is also conceivable that all the hydroxy acids produced could be used together without separation to produce polyester materials. 

The physical structure data together with the alkaline reaction data permitted evaluation of the effects of physical structure on alkaline degradation of cellulose. 

Low molecular weight products from the alkaline degradation of cellulose have been identified by g.e.-m.s. of their trifluoroacetate derivatives. Both the residual aqueous phase and the floating oily product were examined and found to contain essentially the same products. These included unsaturated, aliphatic and alicyclic hydrocarbons, aldehydes, ketones, alcohols, and furans. The synthesis of molecules with more than six carbon atoms also occurred. 

Certainly, oxidative, acidic and alkaline degradation of cellulose must be included in any description of the modification of cellulose and indeed some commercially important products (e.g. microciystalline cellulose) are prepared by these reactions. 

The alkaline degradation of cellulose produce carbonyl groups (for example at the C-2 and C-3 positions) on the structural units which absorb light of the proper wavelength to produce the yellow color. 

During the alkaline degradation of cellulose and cellobiose, a yellow chromo-phore is formed whose spectral properties are dependent on pH e.g. Am 290 nm at pH 12 was shifted to 256 nm at pH 6 for both hydrocellulose and cellobiose. It is suggested that the chromophore is a jS-hydroxy-a-enone which, at acid pH values, tautomerizes to an aliphatic jS-diketone. It was concluded that the chromophore is a minor product since the molar absorption coefficients of such compounds are very large (> 1 x 10 ) and the apparent molar absorption coefficient for hydrocellulose was only about 900. 

According to Scheme 12, the alkaline peeling of cellulose should continue until the entire polymer is degraded. However, cellulose dissolves partially, but not completely, in hot alkali, and this remaining polysaccharide contains an increased carboxyl content.Thus, a second reaction is occurring that competes with the step-wise, peeling procedure. 

Glaus MA, van Loon LR, Chodura A, Fischer K. 1999. Degradation of cellulosic materials under the alkaline conditions of a cementitious repository for low and intermediate level radioactive waste. Part I. Identification of degradation products. Anal. Chim. Acta 398 111-122. 

Polysaccharides. See also. Carbohydrates, Cellulose, Dextran, Dextrins, Fructans, Glycogen, Glycosiduro-nic acids (poly-), Pectin materials, Starch, and Xylan, alkaline degradation of, 13,289-329 associated with wood cellulose, 10, 283-333... 

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