Development of sawdust cooking

The aim of this laboratory study was to compare conventional sawdust cooking with a modified cooking method. The modified cooking method included—in addition to common cooking and displacement stages—also an impregnation stage.

Two different air-dried wood raw material furnishes were used, one containing only sawdust, and the other one 80 % sawdust and 20 % softwood chips.Comparison of the conventional and the modified sawdust cooking method having an impregnation stage revealed the following benefits in modified cooking: lower kappa number at a certain H-factor, higher screened pulp yield, lower shives content and higher pulp viscosity at the same kappa number.

The sawdust pulps obtained were further bleached and refined to clarify the effects of the cooking concept on the paper properties. The bleaching of the pulps revealed no significant differences between the pulps regarding kappa number and brightness. The viscosity of the bleached pulp produced by modified cooking was still higher than that derived by conventional cooking which also consumed more chlorine dioxide.

PFI-beating of the bleached pulps also revealed some differences between the pulps. Modified cooking produced pulps with higher tear index, Scott Bond, Zero-span and opacity, whereas conventional cooking resulted in higher tensile index and air resistance (Gurley) at a given sheet density.