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Detailed Understanding of the DBU/CO2 Switchable Solvent System for Cellulose Solubilization and Derivatization
journal contribution
posted on 2017-11-27, 00:00 authored by Kelechukwu
N. Onwukamike, Thierry Tassaing, Stéphane Grelier, Etienne Grau, Henri Cramail, Michael A. R. MeierIn
this article, we present an optimization study of the switchable
solvent system DBU/CO2 for cellulose solubilization and
derivatization via online Fourier transform infrared spectroscopy
(FT-IR). By varying temperature, CO2 pressure, and solubilization
time, we succeeded in achieving cellulose solubilization within 10–15
min at 30 °C. Compared to traditionally used ionic liquids, the
system presented here is cheaper, is easier to recycle, and enables
a very fast cellulose solubilization under mild conditions. The efficiency
of our optimized mild conditions were further confirmed by X-ray diffraction
(XRD) experiments showing the typical transformation from cellulose
I to II upon regeneration. In addition, we prove the existence of
the in situ formed carbonate anions by trapping them with benzyl bromide
or methyl iodide as electrophiles, leading to the successful synthesis
of cellulose benzyl carbonate and cellulose methyl carbonate, respectively,
under utilization of CO2 as a renewable building block
for cellulose derivatization. The synthesized cellulose carbonates
were characterized by FT-IR, 1H NMR, and 13C
NMR spectroscopy. A degree of substitution (DS) value of 1.06 was
achieved for the cellulose benzyl carbonate as determined by 31P. This study thus provides deep insight into the possibilities
of the studied switchable solvent system for cellulose solubilization
and offers unprecedented possibilities for novel derivatization protocols
of cellulose.