Abstract
The nanoscale wood-water interaction strength, accessible sorption sites, and cell wall pore sizes are important factors that drive water sorption and the hysteresis phenomenon in wood. In this work, these factors were quantitatively studied using molecular simulations based on a cell wall pore model, previously developed by the authors. Specifically, the wall-water interaction strength, the sorption sites network including their number, interaction range, strength, and spatial distributions were set at a series of theoretical values as simulation input parameters. The results revealed that most of the investigated parameters significantly affected both sorption isotherms and hysteresis. Water monolayers and clusters were observed on the simulated pore surface when the wood-water interaction and sorption site strength were set at unrealistically high values. Furthermore, multiple linear regression models suggested that wood-water interaction and sorption site parameters were coupled in determining sorption isotherms, but not in determining hysteresis.
Highlights
Owing to bound water’s pronounced influence on various physical and mechanical properties of wood and engineered wood products, great efforts have been devoted to study the wood-water fundamentals
The statistical models (1) and (2) indicated that the cell wall pore size, wood-water interaction strength (WWIS), and the sorption sites were coupled in affecting the critical properties of sorption isotherms, but the effect from the cell wall pore size was different in determining the critical points on adsorption and desorption isotherms (Hu and Hl, respectively)
Model (3) indicated the WWIS and the sorption sites were not coupled in determining hysteresis, but both factors were coupled with cell wall pore size
Summary
Owing to bound water’s pronounced influence on various physical and mechanical properties of wood and engineered wood products, great efforts have been devoted to study the wood-water fundamentals. Water layering and clustering are two proposed sorption mechanisms at low to medium relative humidity (H) regions [4,5,6,7], whereas capillary condensation is argued to take place at high or very high H (>98%) regions [8,9,10,11,12] Corresponding to these three mechanisms, nano-level wood-water interactions, accessible sorption sites (mainly hydroxyl groups) and cell wall pore size are three major factors that drive the sorption process in wood. The effects of sorption sites and wood-water interactions, their potential coupling, and possible interrelations with cell wall pore sizes were explored by molecular simulations based on a cell wall pore model. By exploring the extreme value scenarios of the investigated factors in the simulations, more insights may be gained into the formation of water monolayers and clusters, and the overall water sorption mechanism in wood
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