Dimensional changes of cell wall and cell lumens upon water sorption revisited. Literature review and mathematical considerations based on the cylindrical model

Abstract

AbstractThe dimensional changes of the cell wall and cell lumens are revisited based on literature data and on the mathematical cylindrical model. The external swelling ratio in the cross-section of the wood cell is considered as a function of the moisture content (MC)mfrom the point of view of the swelling ratio of the cell wall, the swelling parameterk, which is defined as the ratio of the outer variation to the cell wall thickness variation, and the cell wall densityds. The swelling behavior of the cell lumen is evaluated based on the parameterkcalculated from experimental observations, which accounts for both the swelling direction and variation degree of the lumen: the lumen radius (i) decreases atk<1, (ii) remains fixed atk=1, and (iii) increases atk>1. The derived equation was applied to 176 wood species from the literature, and it was found that 0.4<k<1.4, while in most cases 0.8<k<1.0. In other words, the lumen radius in most wood species is decreasing with water sorption. As expected, the S2 layer swelling is differently restricted in the circumferencial direction by the S1 and S3 layers with their different cell wall architecture.