Fiber length distribution and sheet properties: Some new considerations

Although fiber length is one of the most often measured property of paper raw materials, the pure effect of it on paper properties is not usually clear. The reason for that is the difficulty to vary only the fiber length while other properties such as fiber width are kept unchanged. To get a more accurate understanding of the significance of fiber length, fractions with different narrow-distributed fiber lengths were produced in the laboratory from the same original pulp by using a defined cutting procedure, which enables to change only the length dimension of fibers but keeping other properties such as fiber width rather unchanged. Commercial pulps - bleached kraft pine pulp, and spruce CTMP - were used as fiber material. The fiber dimensions and related properties of the resulting fiber material were determined with kajaani FiberLabT. Handsheets were produced following a certain procedure and subsequently treated in a laboratory calender to investigate the effect of fiber length especially on surface and strength properties. As results, the development of surface roughness, gloss, apparent density and strength properties (tensile and tear) with a narrow fiber length distributions are presented. A surprising conclusions for the significance of fiber length and its distribution for paper property development is that the fiber length distribution has obviously no significant effect on the strength development if the cross-sectional dimensions of the fibers remain rather unchanged, and that the use of average values is sufficient to describe property developments of paper.