The principal means of producing highly purified dissolving pulp. When applying

These caustic treatments, the extent of purification can be controlled by adjusting

The appropriate conditions. The relationship between the process conditions, involving

Both sodium hydroxide concentration and temperature, and the course of

Pulp Purification

Reaction comprising the carbohydrate constituents of a selected hardwood sulfite

Dissolving pulp is described in the next section.

8.2

Reactions between Pulp Constituents and Aqueous Sodium Hydroxide Solution

Wood pulp obtained by the acid sulfite process still contains considerable amounts

Of low molecular-weight carbohydrates (hemicelluloses). These make the pulp less

Suitable for many purposes as known for the production of cellulose acetate, highpurity

Cellulose ethers or high-tenacity regenerated fibers. As mentioned previously,

the pulp is refined with alkali either at temperatures below 50 °C whereby

Strong solutions of sodium hydroxide are used (characterized as cold caustic

Extraction, CCE), or at higher temperatures using weaker alkaline solutions (characterized

As hot caustic extraction, HCE). In some cases, both processes are

applied subsequently (in any order: CCE before or after HCE) to obtain the highest

Purity dissolving pulp derived from the sulfite cooking process. It is well

Known that the extraction of wood pulp with strong sodium hydroxide solutions at

Low temperatures produces higher levels of alpha-cellulose than with dilute solutions

At high temperatures, while the yields obtained are considerably higher. The

Basis of both purification processes was developed during the 1940s and 1950s.

Hempel studied the solubility of viscose pulps at 20 °C in the range of NaOH concentration

between 1 and 20%, with the emphasis on maximum solubility [6].

Shogenji and associates treated chlorinated sulfite pulp at 25 °C with 3 to 12%

NaOH and investigated the alkaline solutions after treatment for total and combined

alkali [7]. Wilson and coworkers tested the alkali solubility of pulp in relation

To the alpha-cellulose determination, and stated that wood originally contains

appreciable amounts of gamma-cellulose of low degree of polymerization (10–30),

but no beta-cellulose [8]. The latter is formed during the pulping processes from

Alpha-cellulose. Many studies have been conducted to determine phase-transition

During the treatment of pulp or cotton linters with alkaline solutions of varying

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