NMR Relaxometry Studies on the Drying Kinetics of Cellulose Nanofibers

Nanocellulose is an emerging biopolymer with increasing interest from a variety of engineeringfields. Given thecomplex textural properties and structural changes induced bydrying, understanding the dehydration dynamics of nanocellulose ishighly important. However, common bulk characterizationtechniques cannot be performed in real working conditions andusually require aggressive sample preparation. As an alternative,time-domain nuclear magnetic resonance (TD-NMR) can beapplied with minimum interference. Here, well-established dryingkinetic models and TD-NMR relaxometry were used to monitorwater evaporation in a cellulose nanofiber slurry. The appliedequations reasonably predicted the moisture contents fromgravimetry but provided no information about thefluid/solid distribution during the drying event. As a complement, relaxometryresults indicated the presence of water in different confinement environments based on obtained transverse relaxation timedistributions. Free (bulk) water was observed during the initial 24 h of drying, and intrapore water presented a bimodal fashion withsimilar temporal trends but different rates. Lastly, the drying kinetic models were applied to the ratio of areas obtained fromT2curves with a notablefit. The results discussed here support the use of relaxometry experiments as a viable method for drying kineticstudies with potential expansion to a myriad of wetted systems.