NEWSGRADE TMP FROM 3 DIFFERENT NORWAY SPRUCE (PICEA-ABIES) WOOD ASSORTMENTS IN MILL-SCALE

Three different spruce wood assortments-old-growth wood, sawmill chips , and first-thinnings-were refined separately at constant process cond itions at Enso Oy Varkaus TMP mill. The properties of obtained newsgra de thermomechanical pulps were determined and the observed differences were rationalized in terms of important wood and fibre properties. TM P from sawmill chips had the highest portion of long fibres, smallest proportion of fines, and had generally the coarsest and longest fibres , whereas TMP from first-thinnings was just the opposite. However, no differences were found in pulp specific energy consumption at a given freeness. A high proportion of dry heartwood in old-growth wood produc ed a slightly elevated shives content. TMP made from sawmill chips had the best tear strength, whereas that from old-growth wood gave the be st burst and tensile strength. Pulp from first-thinning, consisting la rgely of juvenile wood, produced generally inferior strength propertie s. Pulp optical properties were superior in TMP from first-thinnings. No noticeable differences, which could be attributed to fibre or parti cle morphology, were found in sheet density, bulk, porosity, or roughn ess between the three pulps. Differences found in the quality of TMP m ade from the above spruce assortments suggest that they could by pulpe d separately to obtain specific product characteristics and to minimiz e unnecessary variation in the raw material quality, and hence, pulp q uality and cost.