Wood Wood

Carbohydrates (CH) 70.6 50.9 47,2 73.3 46.6 48.6

Cellulose 42.2 42.0 39.1 42.0 40.4 36.2

Galactoglucomannan

(GGM)

19.0 5.3 3.2

Glucomannan (GM) 2.0 0.4 0.1

Arabinglucuronoxylan (AX) 9.4 3.6 4.9

Glucuronoxylan (X) 27.8 5.8 12.3

Other carbohydrates 1.5

Lignin (L) 27.2 1.7 1.6 24.5 1.2 1.3

Extractives, Ash 2.2 0.4 0.2 2.2 0.2 0.1

Sum of components

(Total Yield)

100.0 53.0 49.0 100.0 48.0 50.0

110 4 Chemical Pulping Processes

yield advantage of kraft over sulfite pulps in case of hardwoods (Tab. 4.1). On the

other hand, galactoglucomannan (GGM) is less degraded during sulfite pulping,

which in turn contributes to the higher yield of softwood sulfite pulps as compared

to kraft pulps. The yield advantage even increases when the pH is shifted to

neutral conditions in the first stage of a two-stage sulfite process due to an

increased retention of glucomannan [3]. It has been shown that neutral conditions

at elevated temperature are sufficient to account for almost complete deacetylation

of glucomannan. In this state, glucomannan may bind more closely via hydrogen

bonds to the cellulose microfibrils, thus being more resistant toward acid hydrolysis.

Kraft pulping has developed as the principal cooking process, accounting for

89% of the chemical pulps and for over 62% of all virgin fiber material. In comparison,

only 5.3% of the world chemical pulp production is obtained by the sulfite

process [2]. The soda process, using aqueous sodium hydroxide solution as

cooking liquor, is used primarily for the pulping of annual plants and, in combination

with small amounts of anthrachinone (ca. 0.05% on wood), also for the

pulping of hardwoods.

4.2