Evolution of wood cell wall nanopore size distribution in the hygroscopic range

Abstract

Abstract Owing to technical difficulties, experimental assessment of wood cell wall pore size distribution (PSD) in the hygroscopic range still remains challenging. Here, a “trial-and-error” approach was proposed to calculate such distribution through bridging experimental and simulated sorption isotherms presented by the authors in the past. Two main assumptions were made in the calculations, namely, the generation of new and the swelling of existing cell wall pores during water sorption. The nanopore size distribution of dried cell wall derived from the experimental CO2 gas sorption isotherms was used as the initial boundary condition. Predicted pore size distributions were assessed to be fairly reasonable by comparing them at 95% relative humidity with the PSD of fully saturated cell walls derived from the solute exclusion method. The predicted distribution was relatively wide with several major peaks evolving in the hygroscopic range. The present work also showed that confounded by a wide PSD that includes mostly micropores, the shape of the experimental sorption isotherms was not reliable in assessing the sorption mechanism. The simulations suggested an alternative water sorption mechanism for wood, i.e. micropore filling of cell wall nanopores.