Measurement of wet fiber flexibility of mechanical pulp fibers by confocal laser scanning microscopy

Abstract

We measured the fiber flexibility of mechanical pulp with confocal laser scanning microscopy (CLSM) based on Steadman’s method. Pulp fibers were wet pressed and bent over a glass wire and CLSM was used to image the three-dimensional deformation of the fiber. A fiber neutral bending plane was defined for freespan length measurement, which was subtracted from a transverse optical section of a fiber. We measured the moment of inertia of the fiber from the cross-sectional geometry and calculated the elastic modulus of the fiber wall from the fiber flexibility and the moment of inertia. Results show that the flexibility of chemithermomechanical pulp (CTMP) fibers correlated well to interfiber bonding strength and sheet structural properties. A bleaching or refining process significantly increased the fiber flexibility, mainly through altering the elastic modulus of the fiber wall.