Determination of the Surface Layer of Kraft Pulp Fibers by Field Emission Scanning Electron Microscopy (FE-SEM)

The surfaces of commercial softwood kraft pulp fibers were observed by FE-SEM to determine the surface layers of the fibers. Unbleached pulp fibers were covered by fibrils running in random fashion, and the fibrils sometimes extended to a pit area, which were characteristics of the primary wall. The existence of primary wall on the surfaces of unbleached kraft pulp fibers would cause the higher lignin content of the surfaces of the fibers than that of the whole fibers. Large parts of the primary wall were removed during bleaching process, and the fibrils running densely perpendicular to the fiber axis were observed on full bleached pulp fibers, which was a characteristic of the outer layer of secondary walL The degree of the primary wall removal was different between the pulp samples. In one pulp sample, large amount of the primary wall was removed during oxygen delignification stage, although, in another pulp sample, some removal took place during oxygen delignification stage.