RELATIVE IMPORTANCE OF WOOD DENSITY AND CARBOHYDRATE CONTENT ON PULPING YIELD AND PRODUCT QUALITY

SUMMARYThe purpose of this study was to evaluate basic density, chemical composition and fiber dimensions of ten Eucalyptus sp wood samples and verify the impact of this set of parameters and their combination on the Kraft pulping process yield and on bleached pulp quality. Ten eucalypt woods of different species, with basic densities varying from 365 to 544 kg/m3 and total wood carbohydrate contents varying from 70.0 to 74.5%, were transformed into kraft pulp of kappa number 17-18 and bleached to 90% ISO brightness by the sequence OD(PO)D. Wood basic density showed stronger correlations with fiber dimensions, pulping yield and pulp quality than did chemical composition. Lighter woods resulted in higher yields. However, wood specific consumption was lower for denser woods, even though these demanded more drastic pulping conditions to achieve a given kappa number. The pulp quality results suggest that lower density woods should be directed towards fabrication of refined paper (printing and writing grades) while the denser woods be directed to the sanitary papers segment (tissue grades).