The effect of mechanical treatment on softwood kraft pulp fibers.: Fiber wall

In an earlier study the authors found that reduced fiber strength resulting from the mechanical treatment of kraft pulp was caused by changes in the fiber wall, rather than by changes in fiber bonding or fiber deformations. This study focuses on the nature of the changes in the Fiber wall (pore structure) after mechanical treatment. The fiber wall structures of mechanically-treated and untreated fibers were studied in detail using different analytical techniques in order to gain information on the changes in the fiber wall pore structure and fiber wall swelling. The damage reduced the ability of the fiber wall to hold water, chances that Could be measured using water retention determinations and swelling experiments with alkaline iron chloride-sodium tartrate (EWNN, Eisen((111)) Weisensaure Natrium-Komplex freier Natronlauge) solution. Fiber wall accessibility was studied by solute exclusion (fiber saturation point, FSP), thermoposimetry and Simons' staining. The strength loss induced by mechanical treatment was concluded to be due to ultra-structural changes in the fiber wall, micropore closure and macropore opening, which also led to changes in water holding ability. A possible reason for the decreased strength of the mechanically-treated fibers could be that there were fewer bonding sites between the parts of the cell wall due to macro pore opening, in contrast to the cell walls of untreated fibers.