Effect of alkali charge on the performance of Eucalyptus globulus kraft pulps for tissue applications

Abstract The present study aimed to evaluate the effect of active alkali charge, in kraft cooking of Eucalyptus globulus wood, on the properties of the laboratory-produced tissue paper. Eucalyptus wood chips were cooked under similar conditions at four different active alkali (AA) levels of 16, 19, 21, and 23 % and DEDED sequence was used for subsequent ECF bleaching. Pulps were analyzed for their intrinsic viscosity, chemical composition, and fiber morphology, while the corresponding papers (20 g/m2) were examined for their strength properties, absorptivity, and softness. It was demonstrated that changes in the AA upon cooking, not only affected the chemical composition of the obtained pulps and their intrinsic viscosity, but also the fiber’s shape (e.g., curl and kink). These changes caused variations in the properties of laboratory-produced tissue papers. Thus, the increase in AA led to paper with lower tensile strength, but with better softness. Even though the increase of AA in cooking led to bulkier papers, their absorptivity was not significantly enhanced. This was explained, at least in part, by the lower water retention of the pulps obtained from cooking with higher AA.