Time resolved mobility changes of ionic liquids in cellulose by in‑situ solid state NMR spectroscopy

The understanding of the interactions
between cellulose and ionic liquids are the founda-
tion for the development of new processes, to explore
new reactions and to establish a circular bioeconomy.
The main problem is that direct measurement, from
both quantitative and qualitative point of view is chal-
lenging. While there are methods to assess solution
strength and wettability of ionic liquids with cellulose
materials, the main challenge lies in the combina-
tion of a solid substrate and an applied liquid, limit-
ing the number of accessible methods. We demon-
strate in this paper that an in-situ solid-state NMR
spectroscopical approach is capable of monitoring in
real-time the mobility of ionic liquids in cellulose-
based substrates. Specifically, we employ 1H → 13C
cross polarization magic angle spinning (CP MAS)
NMR spectroscopy to examine mobility changes over
varying exposure times in paper samples treated with
ionic liquids. Through this approach, we capture the
temporal evolution of IL signals, which in turn pro-
vide insights into mobility changes of ILs and also
allow for identifying changes in cellulose crystallin-
ity. The approach allows for a simple, semiquantita-
tive assessment of cellulose solubility in ionic liquids
and is in principle applicable to other biomass materi-
als as well.