Flow resistance of wet and dry sheets used for preparation of liquid packaging board

摘要

The present work has shown that an evaluation of the flow resistance of wet and dry sheets can be used to identify how to improve the resistance against edgewise liquid penetration in liquid packaging board. By application of liquid extrusion measurements it was possible to determine the wet and dry structure of liquid packaging board made from CTMP and chemical pulps typically used in the production of packaging board. The expansion of the papers upon wetting induces a large difference between the dry and wet sheet structure, and the wet pore volume is three to four times the dry pore volume. Sheets made from kraft pulps only expand moderately, whereas sheets made from CTMP expand to a higher extent. Both porosities and flow resistances, calculated from pore volumes, display a large impact of both the wet and dry sheet density. From these results it is clear that CTMP sheets resist flow much less than sheets based on kraft pulps, and even considerably reducing the porosity of CTMP sheets only gives a small effect in the magnitude of the flow resistance. Finally at high levels of sizing it will be difficult to compensate changes in sheet structure with an additional size addition in order to prevent liquid penetration