Acid stage Alkaline stage Unbleached pulps

Liquor

PH

Max.

Temp.

[°C]

Time at

Max.

Temp.

[h]

Liquor

PH

Max.

Temp.

[°C]

Time at

Max.

Temp.

[h]

Total

Time

[h]

Kappa

Calc.

Brightness

[% G.E.]

Scr.

Yield

[%]

Tearing

Resistancea)

[%]

Tensile

Strengtha)

[kN m–1]

1.8 140 3.0 8.0 26.2 44.4 52.9 58 4.8

3.7 160 4.3 7.3 20.5 45.2 54.8 62 5.8

3.7 160 2.5 8.5 169 1.5 7.0 27.2 60.5 53.2 100 5.8

a) after 20 min of beating time.

468 4 Chemical Pulping Processes

The two-stage cook showed the highest unbleached brightness and superior

tearing resistance compared to the one-stage cooked pulps. The yield, however,

was lower than that of the bisulfite pulp when comparing at the same kappa number

level.

As expected, the presence of thiosulfate exerts no undesirable effects up to very

high concentration levels (up to 6–8% on o.d. wood).

A very comprehensive comparison of multi-stage sulfite pulping of both softwoods

and hardwoods was presented by Sanyer et al. [18,19]. Selected results

using spruce wood Jack pine as a raw material and sodium as a base are shown in

Tabs. 4.65 and 4.66.

Tab. 4.65 Unbleached pulp yield and physical properties of

one-stage and multi-stage spruce pulps in comparison to a

spruce kraft pulp with a permanganate number of about 20

(according to [18]).

Processes Yield Tear factor Breaking

Length