By the water retention value (WRV). The data in Tab. 11.1 indicate that the

WRV values of the selected pulps differ only slightly. The only significant difference

Is observed for beech kraft pulp, which seems to correlate with the enhanced

Carboxyl group content. The carbonyl group content of a pulp is made up of the

Reducing end-groups and oxidized groups such as keto and aldehyde groups,

Which are introduced by pulping and bleaching operations. The reliable and accurate

Determination of those oxidized structures in cellulose remains a major challenge.

A novel method based on fluorescence labeling with carbazole-9-carboxylic

acid [2-(2-aminooxyethoxy)ethoxy]amide (CCOA) allows the precise evaluation of

Paper-Grade Pulp

The carbonyl groups relative to the molecular weight, as it is combined with gelpermeation

chromatography (GPC) measurement [20,21]. Even though the average

Molecular weight is higher for sulfite pulps, their carbonyl group content is

Considerably higher as compared to kraft pulps (see Tab. 11.1). It may be assumed

That the high carbonyl content of sulfite pulps originates from low molecularweight

Hemicelluloses and oxidized groups along the cellulose chain. In a first

Approximation, the carbonyl group profile may be estimated by subtracting the

Contribution of the reducing end groups from the total amount of carbonyls,

Assuming that the amount of reducing end groups relates to the number average

molecular weight determined from GPC measurement [22]. The pattern of carbonyl

Groups along the polysaccharide chains has been determined for the hardwood

Paper pulps to obtain a first indication about the influence of pulping processes

On the generation of carbonyl groups. Figure 11.2 indicates that the major

Part of the carbonyl groups in the beech sulfite pulp is centered around a molecular

weight of about 13 kDa (DP ~80), whereas in both hardwood kraft pulps the

Maximum of carbonyl groups introduced along the polysaccharide chains is

shifted to a higher molecular weight (32 kDa or DP ~200).

3 4 5 6 7

0.0

0.3

0.6

0.9

Beech Sulfite Beech Kraft Eucalyptus Kraft

carbonyl content [a.u.]

Log Molecular Weight

Fig. 11.2 Profile of carbonyl groups relative to the molecular

weight of hardwood kraft and sulfite pulps [17]. For more

Detailed characterization, see Tab. 11.1.

The large amount of oxidized structures in sulfite pulps correlates well with

Their low R-values, and indicates the presence of an increased level of alkali-labile

Groups.

The majority of pulp constituents are composed of polymers of varying type and

Size. A polymer is typically characterized by its molar mass and molar mass distri-

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