Pulp Properties and Applications. nantly determined from the wide-angle X-ray scattering (WAXS) pattern [50], and

nantly determined from the wide-angle X-ray scattering (WAXS) pattern [50], and

more recently also from solid state 13C-CP/MAS-NMR [51] and vibrational spectroscopy

(e.g., FTIR applying the ratio of the absorption intensities at 1370 cm–1

and 2900 cm–1) [52]. The degree of crystallinity of different cellulose I samples

(pulps) covers a rather narrow range, and depends on origin and processing conditions

Of the particular sample. The reduction of pulp molecular weight during

The final phase of acid sulfite cooking proceeds parallel to the degradation of the

Polysaccharide fraction (cellulose and hemicellulose), and occurs particularly in

The amorphous region. The preferred removal of amorphous hemicelluloses is

Finally expressed in a slight (but clear) increase in the degree of crystallinity when

reducing unbleached pulp viscosity from about 730 mL g–1 to 490 mL g–1. Crystallinity

Is further altered by subsequent bleaching and purification processes. This

Has also been reported by Fink et al., who identified an increase in the degree of

Crystallinity and a change of the crystallite dimensions due to recrystallization in

the course of full bleaching operations [53]. During bleaching with high dosages

Of ozone, crystallinity increases obviously due to removing amorphous pulp components,

While the amorphous regions are slightly extended by a subsequent hot

Caustic extraction. When cellulose undergoes a transition from the glassy to the

Softened state, the concentration of intermolecular bonds decreases and the segmental

Mobility increases. In the glassy state, virtually all hydroxyl groups are

Involved in intra- and intermolecular hydrogen bonds. The softened state favors

chemical reactions, and diffusion is accelerated [54].

The influence of pulping, bleaching and purification treatments on the degree

Of crystallinity of a beech acid sulfite pulp is detailed in Tab. 11.9.

As mentioned previously, the structural parameters also depend on the origin of

The pulp sample. The degrees of order differ only slightly among the dissolving wood

Pulps comprising different types of pulps (sulfite versus PHK) and purity levels,

Whereas the perfection of crystallite order is considerably higher in the case of cotton

linters. The same ranking clearly holds true for the anisometry of the crystallites –

That is, the ratio of length (D021) to width (D002), as depicted in Tab. 11.10.

Tab. 11.9 Degrees of crystallinity, xc, of a beech sulfite pulp

Subjected to prolonged cooking (unbleached viscosity), mild

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