NMR Relaxometry Studies on the Drying Kinetics of Cellulose Nanofibers

Abstract

Nanocellulose is an emerging biopolymer with increasing interest from a variety of engineering fields. Given the complex textural properties and structural changes induced by drying, understanding the dehydration dynamics of nanocellulose is highly important. However, common bulk characterization techniques cannot be performed in real working conditions and usually require aggressive sample preparation. As an alternative, time-domain nuclear magnetic resonance (TD-NMR) can be applied with minimum interference. Here, well-established drying kinetic models and TD-NMR relaxometry were used to monitor water evaporation in a cellulose nanofiber slurry. The applied equations reasonably predicted the moisture contents from gravimetry but provided no information about the fluid/solid distribution during the drying event. As a complement, relaxometry results indicated the presence of water in different confinement environments based on obtained transverse relaxation time distributions. Free (bulk) water was observed during the initial 24 h of drying, and intrapore water presented a bimodal fashion with similar temporal trends but different rates. Lastly, the drying kinetic models were applied to the ratio of areas obtained from T2 curves with a notable fit. The results discussed here support the use of relaxometry experiments as a viable method for drying kinetic studies with potential expansion to a myriad of wetted systems.