Tenacity and elongation, corresponding to a so-called working strength, and the

amount of short-chain molecules characterized as DP <100 fraction.

Pulp Properties and Applications

Tab. 11.7 Characterization of a selection of representative dissolving pulps.

Preferred Application

Viscose Ether (HV) Viscose Acetate Acetate

Raw Material Hardwood Softwood Hardwood Hardwood Cotton

Cooking Process Sulfite Sulfite PHK PHK Linters

Brightness % ISO 92.2 90.2 90.7 92.2 87.9

R18 content % 93.4 95.2 97.9 98.2 99.0

R10 content % 87.6 93.8 93.3 97.7 97.4

Xylan % 3.6 3.1 1.5 0.9 0.2

Carbonyl lmol g–1 18.8 6.0 4.3 4.4 3.7

Carboxyl lmol g–1 35.6 59.8 32.0 15.0 12.4

DPw 1790 4750 1400 2100 1250

DPn 277 450 460 650 700

PDI 6.5 10.6 3.0 3.2 1.8

DP<100 wt% 9.0 0.5 2.5 2.0 0.3

DP>2000 wt% 26.8 61.0 19.9 35.0 15.5

0 3 6 9 12 15

* Tensile strength times

Elongation

Conditioned state

Laboratory Pulps HW-Sulfite SW-Sulfite HW-PHK SW-PHK

Commercial pulps Representative Selection

Working Strength [cN/tex*%]*

DP < 100 weight fraction in pulp [wt%]

Fig. 11.12 Maximum strength properties of

Dtex regular viscose fibers in the conditioned

state related to the DP <100 fraction of

Dissolving pulps covering the whole spectrum

of pulp purity (R18 93–99%). DP <100

Determined from GPC measurements carried

out according to [36]. Conditions for viscose

And viscose fiber production are described

elsewhere [7].

Dissolving Grade Pulp

The data in Fig. 11.12 also indicate that the viscose fibers derived from sulfite

pulps generally exhibit slightly lower mechanical properties at a given DP <100

Weight fraction as compared to those made from PHK pulps. This may be caused

By the higher carbonyl content of the sulfite pulps at a comparable purity level.

GPC measurements of the corresponding fibers indicate that the increase in the

Amount of low molecular-weight carbohydrates during alkaline degradation (ageing)

Is more pronounced for sulfite than for PHK pulps. Surprisingly, a clear correlation

Between the carbonyl content of the pulps and the working strength of

The regular viscose fibers made thereof could be established, as illustrated in

Fig. 11.13.

0 5 10 15 20 25 30 35

* Tensile strength times

Elongation

Conditioned state

Working Strength [cN/tex*%]*

Laboratory pulps HW-Sulfite

Commercial pulps Representative Selection

Carbonyl groups [μmol/g]

Fig. 11.13 Maximum strength properties of 1.3 dtex regular

Viscose fibers in the conditioned state related to the carbonyl

Content of dissolving pulps (selection of Fig. 11.12). The content

Of carbonyl groups was determined according to the

CCOA method [41].

The content of carbonyl groups reflects both the amount of reducing endgroups

(short-chain molecules) and the oxidized groups thus undergoing degradation

Reactions under strongly alkaline conditions.

Functional Groups (Carbonyl, Carboxyl)

Cellulose, particularly from wood pulp, contains small amounts of oxidized

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