Temperature dependence of two or more water species in delignified wood and lignocellulosic, tracked by LFNMR relaxometry

Abstract

Distributions of nuclear magnetic resonance (NMR) relaxation times provide detailed information about the water in wood. This study documents the water dynamics analysis of T₂ and T₁ distributions for saturated delignified sapwood (DSW), delignified heartwood (DHW) and lignocellulose (LC) samples at different temperatures. Results indicate that below the freezing point of bulk water, free water freezes, causing its signal to disappear from the distribution. Then, the low temperature distributions of the unfrozen bound water contain more information about its components, with DSW, DHW and LC containing two distinct states of bound water (OH bound water (B-water) and more freely bound water (C-water)). Furthermore, it was observed that within the temperature range of −3°C to −60°C, B-water in DSW, DHW and LC maintained a higher unfrozen water content (UWC) value than C-water, and the T₁/T₂ ratios for B-water were consistently higher than that for C-water, indicating that B-water has a greater antifreeze capacity. T₂ and T₁ distributions offer different kinds of information about water components, and all peaks within the distribution have been assigned.