For some of the differences in dissolving properties of acid sulfite and PHK pulps.

The results show that all dissolving pulps investigated have a higher xylan content

In the surface layer than in the inner fiber wall. This is in agreement with

results obtained from paper-grade pulps [70,71]. The enrichment, however, is

Pulp Properties and Applications

1 10 100

Sulfite: Spruce Beech

PHK: Spruce Beech

Xylan content in peelings [wt%]

Peeled carbohydrates [wt%]

Fig. 11.25 Radial distribution of xylan in TCF-bleached spruce

And beech sulfite and PHK dissolving pulps, according to

Tab. 11.11. Xylan content determined in aliquots of the hydrolyzate

(mass % of carbohydrates), collected after 1, 3, 10 min

and 48 h of enzymatic peeling, and after total hydrolysis [70].

Highly dependent upon both the process and the wood species used. The high

Xylan content located in the outermost layers of the beech PHK fibers suggests

That xylan precipitation occurs in the final kraft cooking phase, as shown for cotton

Linters in Fig. 11.24. Beech sulfite dissolving pulp, however, shows a comparable

Even cross-sectional concentration profile, as was determined for paper-grade

pulps [71]. For spruce PHK and acid sulfite dissolving pulps, only a very thin outermost

Surface enrichment of xylan is found. But again, xylan is more enriched at

The surface of the PHK fibers as compared to the acid sulfite fibers. It is known

From practice that sulfite pulp behaves satisfactorily during the manufacture of

Cellulose acetate, whereas kraft pulp with a similar (average) chemical analysis

Does not. The enrichment of hemicellulose in PHK pulps may be one reason for

The impaired properties. Therefore, it is important to know if the pronounced

Xylan profile through the cell wall can be leveled out by reinforced purification

Conditions. Indeed, the enrichment of xylan was shown to decrease considerably

When prehydrolysis conditions were gradually intensified (increasing P-factor)

While the kraft cooking conditions were kept constant (Fig. 11.26).

A general characterization of the beech PHK pulps subjected to enzymatic peeling

Is provided in Tab. 11.12.

Dissolving Grade Pulp

50 500 1000 2000

Average Xylan Content [%]

at a peeling rate of 10 mass %

Xylan Enrichment on Surface [%]

P-factor

Xylan enrichment

Average xylan content

Fig. 11.26 Xylan enrichment on surface at a peeling rate of

10 mass % of beech PHK pulps prepared by increasing P factors

while Visbatch® cooking conditions were kept constant.

For enzymatic peeling conditions, see Fig. 11.25.

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