A fiber shape factor and a twist angle of fiber cross section in paper were measured directly in the cross sections of handsheets with a technique involving resin embedding and confocal laser scanning microscopy. Wet pressing twists and collapses individual fibers as it brings fibers closer together. The degree of fiber collapse in the lightly pressed handsheets had an almost symmetrical distribution, but the distribution was narrowed and skewed to high values when the handsheets were pressed at the high pressures of 500 kPa and 4000 kPa. Measured out-of-plane deflections of the fibers showed no correlation between deflection and pressing pressure. The findings indicate that fiber twist, fiber collapse, and gap closure are the major mechanisms in paper structure densification. At low pressures, all three mechanisms act, but the gap closure is predominant. Increasing pressing pressure only increases the apparent density slightly, and the density increase is mainly contributed by the additional twist and collapse of the fibers at high pressing pressures. Application: Research offers a batter understanding of the mechanisms of densification in wet pressing by quantifying the way individual fibers change in a sheet.
|Number of pages||5|
|Specialist publication||TAPPI Journal|
|Publication status||Published - 1 Dec 2003|