And intensive ozone bleaching as well as reinforced hot caustic

Extraction (HCE).

Unbleached viscosity

[mL g–1]

Low ozone

Chargea

High ozone

Chargeb

Reinforced HCEc

490 55 56 54

599 53 55 51

729 52 54 52

a. 1–2 kg odt–1 (medium-consistency).

b. 4–5 kg/odt–1 (medium-consistency).

c. 75–115 kg NaOH odt–1, 85 °C.

Dissolving Grade Pulp

Tab. 11.10 Structural parameters of different dissolving pulps

Grades including cotton linters by wide-angle X-ray scattering

(WAXS) and wet chemistry methods (LODP, WRV).

Pulp xC

[%]

Cellulose II

[%]

Crystallite dimensions LODP WRV

[%]

D021

[nm]

D002

[nm]

HW-S 54 0 5.5 4.5 265 73

HW-PHK 56 0 6.7 5.0 190 71

HW-PHK-CCEa 58 64 175 80

Cotton linters 63 0 9.3 7.4 160 54

a. NaOH concentration of lye during CCE treatment about 10%.

The level-off DPs (LODP) show a clear dependency on the purity of the pulps

(expressed as R18 content), which is in agreement with results reported by Steege

and Philipp [55] and later by Sixta [56]. The mean length of fibrillar aggregations

(which is characterized by the LODP or limiting degree of polymerization)

Decreases in parallel with the removal of noncellulosic impurities in different levels

for sulfite and PHK pulps [56]. The lower LODP values of the PHK pulps and

Cotton linters might be explained by their lower polydispersity.

To summarize the structural characteristics of dissolving pulps shown in

Tab. 11.10, it can be concluded – in accordance with literature data [4] – that crystallite

dimensions decrease in the order cotton linters > PHK pulp > sulfite pulp.

Interestingly, the resistance to mercerization, which refers to the concentration of

NaOH required to rearrange native cellulose crystal structure, follows the same

Order (cotton linters highest, sulfite pulp lowest).

The alkali concentration necessary to promote lattice transition from cellulose I

To Na-cellulose I (and after neutralization to cellulose II) is an important criterion

For characterizing pulp reactivity towards alkali cellulose formation as an intermediate

For the production of viscose fibers and cellulose ethers. These intermediates

Exhibit a markedly enhanced reactivity compared with the initial cellulose

Substrate. The reagents can penetrate more easily into the swollen cellulose structure

And thus react with the hydroxyl groups. The lattice transformation is accompanied

With a disruption of microfibrils into smaller fibrillar units. This may well be the

Cause for the lowering of the LODP observed in acid hydrolysis of cellulose substrates

regenerated from alkali cellulose, as reported by Schleicher and Philipp [57].

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