In the past, the latest forecasts reveal a slight change in this trend (see Chapter

A stabilization of the production amounts, followed by a pronounced

Growth until the year 2006 is predicted, mainly due to new installations of Viscose

(and presumably also Lyocell) plants manufacturing regenerated cellulose fibers

In Asia.

Alkaline and acid processing routes constitute the main applications of dissolving

Pulps. The former comprises the viscose and etherification processes, which

Involve steeping of the pulp in aqueous solutions of high NaOH concentration

(18–25 wt.%), followed by the addition of appropriate chemicals for subsequent

Derivatization (e.g., CS2 for xanthation or alkylhalides for cellulose ethers). The

Acidic esterification processes yield cellulose nitrate and cellulose acetate. The latter,

More important, conversion process involves a pretreatment with acetic acid

Prior to esterification to triacetate on the addition of acetic anhydride and a catalyst,

Usually sulfuric acid. In a second step, the triacetate is hydrolyzed to the socalled

Secondary acetate (DS between 1.8 and 2.5) on dilution with water and precipitation

Of the flakes. These are then dissolved in acetone to a spinning dope

(polymer concentration above 30%) from which fibers (e.g., filter tow, textile filaments),

Lacquers or plastic are processed.

Since the commercialization of the Lyocell process in 1992, the direct solution

Of pulp in an organic solvent without the formation of an intermediate cellulose

Derivative represents a new processing route for dissolving pulp comprising challenging

demands on pulp quality [10–12].

Dissolving Grade Pulp

For over 80 years, regenerated fibers of high quality and special uses have also

Been spun from a cuprammonium solution (cupram), a metal complex solvent for

cellulose. Less than 2% is estimated for cuprammonium rayon within the world

Rayon production. The high demand on processability and pulp quality requires

The use of high-purity cotton linters which, compared to the viscose process, is not

A decisive cost factor.

Table 11.5 provides a rough overview of the raw material sources, dissolving

Pulp technologies and main applications.

Tab. 11.5 Overview of different applications of dissolving pulps.

Product Simplified reaction scheme Raw material Pulping

Processes

Bleaching

Processes

Viscose

Staple CellOH _I_ NaOH__CellONa B, E, S, H, P*) AS, PHK ECF, TCF

Textile filaments CellONa _ CS2 _ Cell_OCSSNa_0_4_0_5 E, S, H, P*) AS, PHK ECF, TCF

Technical Filament H__Zn2__Na_ __CellOH _II_ P*),MHWPHK (CCE) ECF

Cuprammonium

Rayon

CellOH _I_ Cu__NH3 _4 _OH_2_ __CellOH _II_ CL,S SO, AS ECF

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