Within-Fiber Nonuniformities of Microfibril Angle

The pattern and extent of variation of microfibril angle of macerated spruce fibers were investigated by confocal laser scanning microscopy. All measurements supported the idea that the orientation of the microfibrils is not uniform along the radial wall of earlywood fibers. Microfibrils had an approximately circular form of arrangement around the bordered pits (inside the border). Between the bordered pits, lower microfibril angles were measured than in the other parts of the fiber. This phenomenon was interpreted by assuming the existence of crossed microfibrils in these zones. Variation of microfibril angle in earlywood fibers was observed only in the vicinity of the bordered pits, not in the nonpitted zones and tangential walls. Within the latewood fibers, microfibril angle was approximately uniform, even close to the pitted areas. The average orientation of simple pits in the crossfield region was consistent with the mean microfibril angle of the fibers; however, some of the measurements showed a highly variable arrangement in the areas between the simple pits