Provided that the ozone treatment is followed by an alkaline treatment.

Tab. 11.8 Comparison of ZP and PZ treatments on (E/O)

pretreated hardwood sulfite dissolving pulps [46].

Sequence Ozone charge

[kg odt–1]

Viscosity*)

[mL g–1]

Brightness Carbonyla

[lmol g–1]

Carboxyl

[lmol g–1]

Initital

[% ISO]

72 h, 105 °C

[% ISO]

P 640 87.2 81.8 16.8 34.4

PZ 2 575 93.2 87.9 22.9 33.7

4 460 94.3 88.8 29.9 36.6

6 390 94.4 88.4 38.4 42.7

ZP 2 529 94.3 91.0 22.3 31.3

4 463 95.4 92.8 21.0 35.0

6 390 95.4 92.5 24.2 40.9

A. CCOA method.

*) no borohydride treatment prior to viscosity measurement

Dissolving Grade Pulp

3 4 5 6 7

0.0

0.3

0.6

0.9

(E/O)-P

(E/O)-Z-P: 2 kg O

/odt

Kg O

/odt

Kg O

/odt

carbonyl content [a.u.]

Log Molecular Weight

Fig. 11.14 Profile of carbonyl groups generated

through ZP-treatment of an (E/O) pretreated

Beech sulfite dissolving pulp as a function of

Increasing ozone charges. For a more detailed

characterization, see Tab. 11.8 and [46]. Estimation

Of the carbonyl group profile by

Subtracting the contribution of the reducing

Endgroups from the total amount of carbonyls,

Assuming that the amount of reducing endgroups

Relates to the MWn determined from

GPC measurement [45]

The profile of carbonyl groups changes completely when the bleaching

Sequence is reversed and ozonation represents the final treatment. Parallel to a

Continuous increase of the overall carbonyl group content, the amount of carbonyl

Groups introduced into the high molecular-weight region increases relative to the

Amount generated into the low molecular-weight region, as depicted in Fig. 11.15.

The generation of carbonyls during ozonation gives rise to enhanced depolymerization

Of the oxidized cellulose in a subsequent alkaline hydrogen peroxide

Stage (P) due to b-elimination reaction, thus stabilizing the cellulose chain against

Further alkaline processing (e.g., steeping). The higher selectivity of a PZ over a

ZP treatment can be recognized by GPC measurement in LiCl/DMAc, while simple

Viscosity measurement additionally induces depolymerization due to strong

Alkaline conditions (Fig. 11.16; see Tab. 11.8).

Stabilization of the cellulose chain against alkaline degradation also improves

The brightness stability of pulps. The thermal-induced color reversion, measured

as standardized brightness change, DR/R(after 72 h treatment at 105 °C), relates

To the overall carbonyl group content, as depicted in Fig. 11.17

Pulp Properties and Applications

3 4 5 6 7

0.0

0.3

0.6

0.9

(E/O)-P:

(E/O)-P-Z: 2 kg O

/odt

Kg O

/odt

Kg O

/odt

carbonyl content [a.u.]

Log Molecular Weight

Fig. 11.15 Profile of carbonyl groups generated

through PZ-treatment of an (E/O) pretreated

Beech sulfite dissolving pulp as a function of

Increasing ozone charges. For more detailed

characterization, see Tab. 11.8 and [46]. Estimation

Of the carbonyl group profile by

Subtracting the contribution of the reducing

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