Effect of Mechanical Treatment on Softwood Kraft Fiber Properties: Fiber Strength Properties

In the pulp mill the pulp is mixed, pumped and shear forces are applied to the fiber at different temperatures and under different chemical conditions. Mechanical treatment at the end of cooking and homogenisation at room temperature of kraft pulp fibers increased the number of fiber deformations. The increase in fiber deformations did not reduce single fiber strength but did affect the strength properties of the fiber network. The fiber damage induced by mechanical treatment also decreased the z-directional strength of the fiber network, which was concluded to be due to separation of the structural elements on the fiber surface layer. The separation of structural elements could enhance the irregularities on the fiber surface layer and so reduce the bonding area. The zero-span tensile strength of fibers was not dependent on the degree of fiber deformation, but according to the hypothesis presented above, on the 3-dimensional arrangement of the structural elements in the fiber wall. This 3-dimensional arrangement of the structural elements in the fiber wall defines the axial load bearing ability of the softwood kraft fiber.