The influence of partial chemical component removal on water state at high relative humidity and cell wall saturation state

Abstract

Water sorption in wood is mostly determined by the cell wall pores and the availability of sorption sites. In this study, we partially removed hemicellulose and lignin to adjust hydroxyl accessibility and pore size distribution of the cell wall of beech (Fagus sylvatica). With the assistance of the two-dimensional time-domain nuclear magnetic resonance technique, the water state at high relative humidity (RH) regions and cell wall saturation state were investigated. Both hemicellulose removal and delignification brought newly created pore spaces, lowered the average pore size, and increased the specific surface area. At the same time, a decrease in hydroxyl accessibility was observed for the hemicellulose-removal samples, but an increase in delignified samples. Two cell wall waters (B-water and C-water) with different mobility and two cell lumen waters were categorized. At high RH regions, more water molecules accumulated in microfibril and its surrounding hemicellulose (the domain of B-water) with lower mobility after partial chemical components removal. In combination with the mobility change with the physiochemical environment of the water molecules, it may be established that the accumulation of B-water was affected more by the change in the physical environment. Furthermore, cell wall saturation may alter the matrix environment for both treated and untreated samples; following water saturation, the mobility of B-water increased in the delignified samples but decreased in the untreated and partially hemicellulose-removed samples.