Two-thirds of the neutral compounds are left in the unbleached pulp, while twothirds

consists of b-sitosterol [26]. During bleaching, the unsaponifiables are modified

To more polar compounds containing carboxyl groups; these compounds, together

With other polar extractives such as fatty acids, are favorable as surface

Active agents in the viscose process and account in part for good filtration of the

viscose prepared from this pulp [27,28].

Resins derived from pulps of high resin content – and particularly those containing

Higher amounts of nonpolar neutral substances such as hydrocarbons and

waxes – show a tendency to accumulate in the spinnerets. The deposits of resin

Inside the holes in the spinnerets increase the adhesion of precipitated zinc sulfide,

and this ultimately leads to clogging of the spinnerets [29]. In times of conventional

Bleaching, chlorination of extractives caused viscose turbidity, which

was closely associated with spinning jet clogging [30]. The introduction of hydrophilic

Groups by means of oxidation during bleaching operations (O, D, Z, P)

improves the dispersibility of pulp resin in sodium hydroxide [30].

Viscose quality was greatly affected by the ozone charge during the course of

TCF bleaching (O-A-Z-P) of an aspen PHK pulp [31]. A step-wise increase in

ozone charge from 1.0 to 3.3 kg odt–1 significantly decreased the content of acetone

Extractives while improving viscose quality, characterized as the relationship

Between the average particle volume and viscose filterability (Fig. 11.9).

Pulp Properties and Applications

0.20 0.15 0.10 0.05

Centricleaning

(3.3)

(1.9)

(1.0)

Particle Volume [ppm] PVC Filter value

PVC Filter Value Particle Content in Viscose

Acetone Extractives [% od]

Fig. 11.9 Relationship between the content of

Acetone extractives of a TCF-bleached aspen-

PHK pulp and viscose quality [31]. The reduction

Of acetone extractives was achieved by

Increasing charges of ozone and additional

Post cleaning with a centricleaner. Pulping

according to the VisCBC process: P-factor 750,

H-factor 600, EA concentration in cooking

liquor 0.875 g L–1; TCF-bleaching according to

O-A-Z-P to achieve brightness >91% ISO.

10 100

[5]

[4]

[3]

[2]

[1]

[5] 3.3 kg O

/odt and postcleaning

[4] 3.3 kg O

/odt

[3] 1.9 kg O

/odt and postcleaning

[2] 1.9 kg O

/odt

[1] 1.0 kg O

/odt

Frequency

Particle Diameter [μm]

Fig. 11.10 Particle size distribution of viscose samples made

From aspen PHK pulps of varying ozone charges and additional

post cleaning operations [31]. Pulping conditions

According to Fig. 11.9.

Dissolving Grade Pulp

Additional post cleaning by means of a centricleaner further reduced the

Amount of resins, thus improving viscose filterability. The particle spectrum in

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