And density) as well as the fiber strength (dry and rewetted zero-span tensile

Strength) are unaffected by the hemicellulose content of spruce kraft pulps comprising

a cellulose:hemicellulose ratio between 3 and 9 (equal to a hemicellulose

content of 10–25%). On the other hand, the tensile index decreases by 30% when

the cellulose:hemicellulose ratio is increased from 3 to 9 when compared at the

Same density. In parallel with the decrease in tensile strength, the tear strength

increases by up to 100%. In contrast to fiber strength, the sheet strength is highly

Dependent upon the hemicellulose content. The stiffness of the fibers has been

Identified as the major influencing parameter of sheet strength properties. It has

Been shown that fibers become stiffer and more brittle with increasing proportions

Of hemicelluloses in the kraft pulp. One of several explanations for this is

that the shrinkage of the fibers during drying may increase with a decreasing cellulose:

Hemicellulose ratio. Fibers with higher shrinkage are subjected to higher

Stress during drying of sheets, which in turn increases the E-modulus of the fibers

[19]. Fibers with a high E-modulus show high tensile strength, but low tear

strength (see also Ref. [14]).

During kraft cooking, 4-O-methylglucuronic acid groups attached to xylan are

Partially converted to hexenuronic acid (HexA) groups (see Section 4.2.6.2, Modified

Kraft cooking, “Effect on carbohydrate composition”). These groups react

With electrophilic bleaching chemicals such as chlorine dioxide and ozone. Additionally,

Acid treatment at elevated temperature may also be used selectively to

Remove the HexA groups. Fully bleached kraft pulps with kappa numbers below 1

Contain only traces of residual HexA, as shown in Tab. 11.1.

In contrast to dissolving pulp specification, the standard characterization of

Paper-grade pulp does not include the determination of functional groups. However,

Many important pulp properties originate from carboxyl and carbonyl

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

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