Groups, depending on the amount and their distribution along the polysaccharide

Chains (see Tab. 11.7, Dissolving pulp characterization). The carboxyl groups,

Mainly derived from uronic acid side chains of hemicelluloses, and aldonic acid

Groups created by the oxidation of reducing end groups, determine the surface

Charge (distribution) and hydrophilicity, which in turn exhibits an influence on

Wettability of the pulp (the ability of the sample to absorb liquids). The carboxyl

Groups relate also to the swelling behavior of a pulp sample, which may be estimated

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).

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Дата добавления: 2015-10-21