RELEASE OF DISSOLVED AND COLLOIDAL SUBSTANCES IN PRESSURIZED GRINDING WITH PEROXIDE AND ALKALI

The release of organic dissolved and colloidal substances (DCS) during pressurized grinding with peroxide bleaching chemicals present in the shower water was studied using a laboratory-scale grinder, The effects of shower water pH, peroxide charge, intensity of treatment in the grinder and latency removal on the amount and composition of different DCS were examined with Norway spruce wood as raw material. Addition of alkaline peroxide chemicals to the grinder shower water resulted in increased amounts of DCS measured as TOC. The amount of DCS released increased with shower water pH and peroxide charge to the shower water, Removal of latency further increased the amount of TOC in the water phase containing DCS by 2-4 kg TOC/t. Addition of peroxide bleaching chemicals to the shower water did not affect the total amount of carbohydrates that dissolved during grinding. However, the composition of dissolved hemicelluloses was different. Mannose-rich glucomannans are adsorbed onto PGW fibres at higher pH values. The release of galacturonic acid-rich hemicelluloses (polygalacturonic acids) increased with increasing shower water pH and peroxide bleaching chemical charge to the shower water The amount of dispersed pitch increased at higher shower water pH, but the composition of the lipophilic extractives did not change.