Surface characterization of unbleached and oxygen delignified kraft pulp fibers

The chemical and morphological surface properties of different unbleached and oxygen delignified softwood kraft pulp fibers were evaluated by using different ESCA and SEM techniques. The results of the different techniques have revealed that the surface of unbleached and oxygen delignified kraft pulp fibers has a higher content of lignin and in some cases also extractives, in comparison with the bulk of the fibers. However, the amount of lignin obtained on the fiber surfaces differs substantially from one technique to another. The mercurization technique (mercurization followed by the determination of mercury by ESCA) gave about three to five times lower values on the surface coverage of lignin, in comparison with the normal ESCA procedure. Good correlation between the surface coverage of lignin and the total amount of lignin was obtained for all techniques, however, the best correlation was obtained for the mercurization technique. The results also show that the total and surface charges of the unbleached and oxygen delignified pulp fibers decreased with a decrease in kappa number and that the extent of fibrillation increased with a decrease in kappa number.