Permeability to Water of the Fibre Cell Wall Material of Two Hardwoods

Abstract

The permeability to water of the fibre cell wall of birch (Betula pubescens Ehrh.) and lime (Tilia x vulgaris Hayne) wood was measured in wood slices in which most of the void space was filled with paraffin wax or a polymerizing silicone elastomer. An osmotic technique was used with solutes of molecular weight great enough to prevent their molecules from penetrating the pores in the water-swollen cell wall. The solutes used were dextran and polyethylene glycol with molecular weights of 40 000 and 6000 respectively. Values for permeability k x 1021, as defined by the Darcy equation, ranged between 3-6 m2 for the tangential direction in birch, to 27 m2 for the longitudinal direction in birch. These results are in good agreement with previously measured values but are at least ten times less than theoretical values. It is calculated that total emptying or filling of a wood cell through the wall might be possible in as little as 5 min under a pressure difference of 0-1 MPa if other flow pathways were blocked.