DISSOLUTION AND DISPERSION OF SPRUCE WOOD COMPONENTS INTO HOT-WATER

The dissolution and dispersion of components from Norway spruce (Picea abies) wood were examined in laboratory experiments to determine the factors influencing variations in dissolved and colloidal substances i n mechanical pulp suspensions. Finely ground, fresh spruce wood was su spended in water at 90 degrees C and was agitated intensively for up t o 12 h, after which the concentrations of dissolved and dispersed lipo philic extractives, lignans, carbohydrates and lignins were determined . Sapwood and heartwood were studied separately. Effects of pH and add ed electrolytes on the dissolution and dispersion of wood components w ere also investigated. Higher amounts of lipophilic extractives, and e specially of triglycerides, were dispersed from sapwood than from hear twood. The release of Lipophilic extractives continued for up to 3 h, after which the concentrations in the suspensions leveled off. At this stage the composition of the dissolved and dispersed lipophilic extra ctives equaled that of the wood. The amount of lipophilic extractives in the suspensions increased with increased pH, in the range of 4.5-6. 7, but was lower in the presence of electrolytes. The dissolution of c arbohydrates continued even beyond 3 h of agitation. The high water te mperature induced hydrolytic reactions, thereby releasing especially a rabinose. The release of arabinose through the hydrolytic cleavage fro m polysaccharides was more extensive at pH 4.5 than at pH 5.5 and 6.7. More polysaccharides containing galacturonic acid units (pectins) wer e dissolved at a higher pH. Much more polysaccharides containing gluco se, most probably starch, were present in the sapwood suspensions. The dissolution of lignins also continued throughout the 12 h experiment. The measured UV-absorption, after extraction of lignans, was roughly the same for sapwood and heartwood suspensions. Slightly less lignins were released in the presence of electrolytes. Lignans were released o nly from heartwood.