Analysis of the cell wall distribution in a growth ring on the water vapour transport in Spruce wood

In this paper we are going to present a method to link the macroscopically observed material properties to the micro structure of Spruce wood which varies even within each growth ring. In a first step, the Spruce wood is analysed by classical methods like the cup test to determine the water vapour resistance factor dependent on the directions of the growth rings. Parallel to the classical measurements we perform additional measurements and observations based on the real microstructure of wood as it can be observed by Scanning Electron Microscopy (SEM). This observed microstructure is further analysed by identifying the cell walls and the cell lumens. This bi-layered structure furthermore is analysed by numerical methods to extract the location dependent (within the growth ring) material properties. The main finding is that the water vapour diffusion resistance factors are dependent on the cell wall fraction to cell lumen fraction, which can be represented by the density distribution across the growth ring. We conclude that this analysis is a first step to analyse the cell geometry with water vapour permeability. In an additional step more complex behaviour like the dynamic moisture sorption behaviour should be analysed as we understand wood as a material with areas of high permeability and areas of high moisture sorption