EFFECT OF DRY AND FROZEN WOOD ON GROUNDWOOD PULP QUALITY

It is widely known that dry or frozen logs tend to produce lower-quality mechanical pulps than fresh wood. The effects of the dry content of wood in atmospheric grinding (GW) have been reported in the literature. However, no corresponding information has been published for pressurized grinding (PGW). Pilot-scale trials were conducted at the Tampella Research Center in Inkeroinen, Finland, to study the effects of dry and frozen wood on pressurized grinding and on PGW pulp properties. Both atmospheric and pressurized groundwood pulps were produced from fresh wood, frozen wood and wood with different moisture levels. Remoistened logs were also used as raw material. The trials showed that the use of dry and frozen logs significantly reduces pulp strength and the amount of long fibers. Changing from fresh to frozen wood as raw material gave same relative changes in the GW and PGW pulp properties. However, with dry wood, the change in pulp quality was less pronounced in pressurized grinding than in conventional atmospheric grinding. The PGW process thus allows more variation in the dry content of wood without a significant change in pulp quality. Remoistened logs also yielded a high-quality PGW pulp.