Analysis of water content in wood material through 1D and 2D 1H NMR relaxometry: Application to the determination of the dry mass of wood

Abstract

There is an increasing interest on wood as it is an environmentally sustainable product (e.g., biodegradable and renewable). Thus, an accurate characterisation of wood properties is of extreme importance as they define the kind of application for which each type of wood can be used. For instance, dry mass of wood is a key parameter itself and is needed to calculate Moisture Content (MC) of wood, which is correlated to its physical properties. Due to the limitations of commonly used drying methods, preliminary work has shown the potential of 1 H NMR to measure dry mass of wood, but it has never been validated. Here, we performed a critical analysis of 1D and 2D 1 H NMR relaxometry methods for obtaining the dry mass of wood, and we compared their performance to three commonly used drying methods. This showed that commonly used drying methods do not remove all water from wood. Moreover, we are able to classify them accordingly to their performance. In addition, we showed that MC values obtained by 1 H NMR relaxometry methods are higher (up to 20%) than values from commonly used drying methods. This empathises the importance of accurate values of dry mass of wood and the utility of 1 H NMR relaxometry on wood sciences. When comparing both NMR relaxometry methods, 2D should provide the more accurate results, but 1D measurements would also be a recommended choice as they are faster than 2D and their results clearly overcome commonly used drying methods in a noninvasive and nondestructive manner.