Sonication-assisted nonpolar-antisolvent approach to produce cellulose suspensions, disaggregated by a nonpolar-antisolvent with orthogonal Kamlet-Taft acidity/basicity: Roles of net-basicity and cosolvency

Abstract

This work reports a simple sonication-assisted approach to produce diluted (0.5 mg/mL) suspensions of cellulose in the non-functionalizing nonpolar-antisolvent tetrahydrofuran (THF), which has a purely basic character (null Kamlet-Taft acidity parameter, α = 0), by using it as medium to sonicate microcrystalline cellulose (MCC) at 40 kHz/70 Watts. The suspensions are obtained because of the high reactivity of the amorphous regions within MCC and its capability to behave as a (Turbak) acid, together with the low viscosity and surface tension of THF, and most importantly because of the positive 0.55 net-basicity of THF, comparable to that of ionic liquids (ILs) or deep eutectic solvents (DESs) used to dissolve cellulose in polar conditions. This was demonstrated by chloroform (CHCl₃), which cannot generate suspensions despite having similar values of viscosity, surface tension and molar volume than THF, however having a null basicity parameter, β = 0. (Complementary computational qualitative analyses using model molecules & conditions also show thermodynamic favorability of THF over CHCl₃). FTIR suggest a decrease of around 5 % in the crystallinity of cellulose after sonication in THF, while DLS show that adding CHCl₃ to the suspension in THF promotes disaggregation despite the THF-CHCl3 has a smaller net-basicity than THF, thus demonstrating cosolvency (instead of cononsolvency). (Complementary Langmuir trough experiments at the surface of water also demonstrate disaggregation because of CHCl₃ instead of moisture). Despite the THF-CHCl₃ pair has been used previously to analyze the supramolecular properties of different polymers, this work uses it to analyze disaggregation in two antisolvents. This approach could constitute a platform to perform studies of dissolution/regeneration under null polarity, using proper probes (e.g. ILs or DESs), substrates and matrices.