Porosity Centrifuge: Analysis of the Porous Structure of Paper in Contact with Water Under Hypergravity Condition

Abstract

The characterization of pore sizes in paper is an important parameter, as numerous modifications of paper fibers influence or even aim to change them. yet, most methods for determining pore size only work in the absence of water (e.g. mercury porosimetry or computed tomography). However, the influence of swelling on pore size caused by water is of great interest, especially, but not only, for the porous material paper. Here we present a new method for determining the characteristic pore radius of paper sheets, being in direct contact with water. We call our device “porosity centrifuge”, in which the capillary forces that develop during the wetting and swelling process within a paper sheet are counter-balanced by a matching centrifugal force. While the capillary pressure is determined by the pore radius of the porous structure, some paper intrinsic parameters lead to a reduction from the predicted imbibition distance calculated from the force balance between centrifugal and capillary forces. Since we are able to modulate the degree of this reduction by changing the fiber type or by applying various fiber pretreatments, such as beating, reduction of fines content or calendering, we refer to it as “substrate coefficient”. Our method enables a simple and fast determination of characteristic pore radii in paper sheets using water as liquid.