The numerical evaluation of the MWD, as well as additional pulp quality parameters,

Are included in Tab. 11.7. As expected, the sulfite dissolving pulps (viscose,

High-viscosity ether) reveal a rather broad MWD, as indicated by the high PDI.

This is also reflected in the higher amount of short-chain molecules (DP <100),

Lower values for the alkali resistances, and the large difference between R18 and

R10 when comparing at a similar viscosity level. In the case of a high-viscosity

Ether pulp, the comparison is not valid because the entire molecular weight is

Shifted to higher values (Tab. 11.7).

There are many reports which confirm that the chain-length distribution in the

dissolving pulp is a crucial property in the production of rayon fibers [37]. The

short-chain molecules represent the weakest part in the fiber: the shorter the molecules,

The lower will be the number of molecules linking the crystalline regions.

Avela et al. were able to show that all strength characteristics are significantly

reduced with an increase in the low molecular-weight fraction [38]. Treiber

Dissolving Grade Pulp

3 4 5 6 7

Cotton Linters

HW-PHK

Acetate

HW-PHK

Viscose

SW-Sulfite

HV-Ether

HW-Sulfite

Viscose

dW/d(log M)

Log Molecular Weight

Fig. 11.11 Molecular weight distribution

(MWD) of different grades of sulfite and PHK

Wood dissolving pulps and cotton linters. GPC

measurement of cellulose solutions in LiCl/

DMAc with MALLS/RI detection according

to Schelosky et al. [36]. Detailed characterization

Of these pulps including numerical evaluation

Of GPC measurements is included in

Tab. 11.7.

Reported an increase in wet strength of regular and high wet modulus viscose

fibers with decreasing amount of the DP <200 fraction in the dissolving pulp

[39,40]. Clearly, the physico-mechanical properties of fibrous substrates are influenced

Not only by the macromolecular properties but also by the crystallite dimensions,

The degree of lateral order, and the orientation with respect to the fiber axis.

In order to bring out the effect of MWD on the strength properties of viscose

Fibers more clearly, the conditions of viscose preparation and viscose fiber production

Must be kept constant. Recently, detailed bench-scale trials were conducted

Imitating the regular production of rayon fibers. To obtain a representative view

On the suitability of dissolving pulps for viscose fiber production, laboratory pulps

Covering all four categories of dissolving pulps, namely HW-sulfite, SW-sulfite,

HW-PHK and SW-PHK, as well as a selection of commercial dissolving pulps

Were converted to regular viscose rayon staple fibers with a titer of 1.3 dtex. The

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