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In this study six wood species (birch, chestnut, oak, beech, poplar and eucalyptus) were analysed separately. Lignin content, Polysaccharides content (cellulose and hemicelluloses), Yield, Hexenuronic acids were evaluated for three cooking temperatures (140ºC, 150ºC and 160ºC) and different cooking times. Common cooking conditions were applied and temperature program included cold impregnation, a plateau at 110°C (2.5 hours) to perform initial delignification separately followed by a second plateau at cooking temperature. The results of PCA show that the almost all parameters (excluding hexenuronic acids) are well correlated between them (total variance: 62%). For Eucalyptus and poplar species the hemicelluloses content aren’t well correlated with the previously parameter, caused by the difference observed for the higher temperatures. In some samples was observed that xylans are partially resistant and their elimination is only partial (30 to 40%) in the early stage of cooking. For the highest cooking time there were observed a significant difference between the three temperatures studied. Chestnut and oak wood species present a different behaviour compared with the other species, caused by their similar anatomical and chemical structure. For the 160º of cooking temperature in the second plateau was the poplar, beech and birch that present a different performance.

The main goal of this paper is to observe de differences of behaviour between six softwoods species during the kraft cooking sequence, knowing that morphological, physicochemical and hygroscopic characters are different. Six wood species (Scots pine, maritime pine, Aleppo pine, black pine, Douglas fir and Spruce) were analysed separately. Different parameters were evaluated (Lignin content, Polysaccharides content (cellulose and hemicelluloses), Yield, Hexenuronic acids) and for each wood species three temperatures (150ºC, 160ºC and 170ºC) and different cooking times, allowing to study the behaviour of the wood species. Common cooking conditions were applied and temperature program included cold impregnation, a plateau at 110°C during 2.5 hours to perform initial delignification separately followed by a second plateau at cooking temperature. Non-uniform cooking behaviour was observed; chestnut and oak trees consumed much more caustic soda and had a lower yield in the initial phase of the cook. It was possible conclude that in a genera way, the behaviour of the six softwoods is highly homogeneous, for the three temperatures studied. Data analysis was made with Principal component analysis (PCA) and ANOVA. The results of PCA show that all parameters: Yield (Y), Klason lignin (L), cellulose content (C), and effective residual alkali (EA) are well correlated. The cellulose content was negatively correlated with the other factors. The hexenuronic acids (HA) and hemicelluloses content was well correlated witch other. The coking time in the 2nd plateau influence all factors. Moreover, the three different temperatures are very similar they present statically differences with Tukey’s test (P<0.05). For the highest cooking time all parameter present lower values. The time on the 2nd plateau do not influence the yield and the delignification.