THE INFLUENCE OF PROCESS VARIABLES ON THE STRENGTH PROPERTIES OF NSSC BIRCH PULP. TOWARDS THE LIMITS OF OPTIMIZATION: PART TWO-THE EFFECT OF TEMPERATURE AND COOKING TIME

The aim of this work was to establish the best mechanical and strength properties of NSSC pulps using operating conditions at which the lowest (optimal) spent liquors, cooking temperature and time of treatment could be obtained. Minimal and maximal limits of independent variables were proposed using real mill conditions as a starting point. The analyzed variables were: cooking time (13 to 15.5 min), cooking temperature (from 172 to 179 degrees C), liquor-to-wood ratio (from 1.2 to 2.2). In spite of the narrow ranges of controlled cooking variables, the large database and combined statistical methods (analysis of variance, parallel coordinates, principal component analysis) made it possible to distinguish the limits of the optimal ranges of the studied technological factors which determined the tested pulp's properties. The mechanical and strength testing of the pulp's sheets showed that the analyzed time, temperature and liquor-to-wood ratio influenced the CMT, SCT, Tear strength and, to some extent, Burst strength.