RELEASE OF DISSOLVED AND COLLOIDAL SUBSTANCES IN PRESSURIZED GRINDINGWITH 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 effect s of shower water pH, peroxide charge, intensity of treatment in the g rinder 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 i ncreased amounts of DCS measured as TOC. The amount of DCS released in creased with shower water pH and peroxide charge to the shower water, Removal of latency further increased the amount of TOC in the water ph ase containing DCS by 2-4 kg TOC/t. Addition of peroxide bleaching che micals to the shower water did not affect the total amount of carbohyd rates that dissolved during grinding. However, the composition of diss olved hemicelluloses was different. Mannose-rich glucomannans are adso rbed onto PGW fibres at higher pH values. The release of galacturonic acid-rich hemicelluloses (polygalacturonic acids) increased with incre asing shower water pH and peroxide bleaching chemical charge to the sh ower water The amount of dispersed pitch increased at higher shower wa ter pH, but the composition of the lipophilic extractives did not chan ge.