Concentrations, using X-ray diffraction. Ranby studied the appearance of cellulose

hydrate when treating different cellulose substrates at 0 °C with increasing concentrations

of sodium hydroxide [9]. With cotton, the first indication of hydrate

cellulose occurs at 8% NaOH, whereas with wood pulp it occurs already at 6%

NaOH. The NaOH concentration necessary for transition is related to the water

Sorption of the original cellulose, which means that cellulose undergoing transition

At low NaOH concentration has a high water sorption. An electron-microscopic

Study of spruce holocellulose indicated that alpha-cellulose is built up of

Micelle strings about 8 nm wide, whereas gamma-cellulose contains no strings

[10]. The beta-cellulose fraction appears to be a mixture of short string fragments

And small particles. An X-ray investigation showed that both alpha- and beta-celluloses

Show the same type of lattice (cellulose II). The gamma-cellulose seems to

Consist of several phases different from cellulose II. The beta-cellulose is assumed

Reactions between Pulp Constituents and Aqueous Sodium Hydroxide Solution 935

To originate from alpha-cellulose by degradation during the pulping and bleaching

Processes.

The composition of the beta- and gamma-celluloses fractions removed from the

Wood pulp during cold and hot extraction processes with respect to the amount of

Unchanged carbohydrates has been the focus of few studies. Corbett and Kidd

Studied the degradation of a mixture of beta- and gamma-celluloses extracted by

hot alkali from spruce pulp [11]. These authors found that the insoluble residue

Essentially consists of glucan, and whereas the beta-cellulose fraction is made predominantly

Of xylan, the gamma-cellulose originates from a mixture of glucan

And mannan. In a recent study, the change in composition of the alpha- (residue),

Beta- and gamma-celluloses fractions created during treatment of a beech sulfite

Dissolving pulp with aqueous NaOH of various concentrations ranging from 20 to

340 g L–1 at 20 °C, 50 °C and 80 °C, was investigated [12]. The pulp consistency was

kept constant at 5%, which is a typical value for the industrial steeping process.

The profile of the xylan content of the residue (alpha-cellulose) and the weight

Fraction of the dissolved hemicelluloses (sum of beta- and gamma-cellulose)

Related to the initial amount of pulp is illustrated graphically in Fig. 8.1.

As expected, xylan removal is more efficient at 20 °C than at higher temperatures.

To obtain the lowest possible xylan content in the pulp residue (about 0.7%

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