High LODP, the high modulus in the stress-strain curve, the excellent swelling

properties [15,16], the low tear strength, and the high beating rate of sulfite pulps

Were attributed to the greater amounts of crystalline and paracrystalline regions

Compared to kraft pulps.

Sulfite pulps contain large amounts of crystalline and paracrystalline cellulose,

While kraft pulps consist predominantly of amorphous cellulose domains. Page

Recognized an increase in tear strength of a pulp with increasing proportion of

amorphous cellulose. This is also reflected in the low modulus of the stress–strain

Curve of a single fiber, as illustrated in Fig. 11.1.

0 2 4 6 8

0,0

0,5

1,0

1,5

Bleached Kraft+16% NaOH Bleached Kraft + 7% NaOH Kraft, 60% yield

Acid Sulfite, 63% yield Holocellulose

Stress [GPa]

Strain [%]

Fig. 11.1 Stress–strain curves of single fibers prepared by

Various pulping treatments using black spruce with low fibril

angles (0°–10°) [13].

Fibers, particularly of low fibril angle between 0° and 10°, have shown that the

shape of the stress–strain curve depends on the pulping process. Figure 11.1 illustrates

The decreasing modulus with increasing proportion of amorphous cellulose.

The modulus decreases in the order holocellulose > acid sulfite > 60% kraft >

bleached kraft + 7% NaOH > bleached kraft + 16% NaOH, which corresponds

Well with the order of decreasing beating rate and increasing tear strength. The

Rate at which a pulp beats is virtually a measure of the rate at which the wet cell

Wall splits and breaks up while applying mechanical stress. Fibers of amorphous

Structure thus containing viscoelastic properties are more likely to withstand

Stress without fracture, since the stresses will be relaxed and the energy dissipated

In the viscoelastic regions. Fibers of high modulus and elasticity tend to peel their

Bonds at low strains, while those of low modulus will peel at larger strains because

Pulp Properties and Applications

Paper-Grade Pulp

They relax stresses in viscoelastic elements. From that it has been concluded that

Higher tearing strength is likely to be associated with a higher proportion of amorphous

Regions.

The differences between sulfite and kraft pulps are also reflected in their chemical

And macromolecular properties. Representative fully bleached commercial

Soft- and hardwood kraft and sulfite paper pulps have been selected for comprehensive

Chemical and macromolecular characterization. Additionally, elemental

Chlorine-free (ECF) and totally chlorine-free (TCF) -bleached pulps have been chosen

From each softwood kraft and sulfite pulps. A comparison of the four categories

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