Efficient utilization of lignocellulosic biomass as a sustainable alternative resource for biofuels and chemicals is of great importance in view of global warming and depleting fossil fuel reserves. Prof. Argyropoulos and colleagues demonstrated actual dissolution of wood in ionic liquids (IL), showing that regenerated cellulose from IL solutions can be hydrolyzed efficiently to glucose by a cellulase enzymatic treatment. Our studies present evidence for true molecular dissolution of cellulose in the IL 1-ethyl-3-methylimidazolium acetate and its mixture with polar aprotic solvent, using small-angle neutron (SANS)-, x-ray (SAXS)- and light scattering measurements. The results obtained provide values of the molecular weight, gyration radius and persistence length of the dissolved chains, indicating the absence of significant aggregation and an expanded coil conformation, characteristic of good-solvent conditions. The amphiphilic nature of the cellulose chains dissolved molecularly in IL is revealed when a cellulose/IL solution is mixed vigorously with oil and water, forming a stable oil-in-water emulsion. Imaging by cryo-transmission electron microscopy, indicates a unique structure of the cellulose coating. SANS measurements provide quantitative determination of the structure composed of a hydrophobic core with two concentric shells: an inner shell of cellulose hydrogel covered by an external coating of continuous amorphous cellulose. In view of the high cost of IL, cellulose-coated o/w emulsions were fabricated alternatively using aqueous NaOH (7 wt.%) at -16°C and regenerated to hydrogel particle suspension by dilution with water, and subsequently emulsified with hydrophobic solvent or oil using high-pressure homogenization. Moreover, addition of yeasts (S. cerevisiae) to the emulsification process formed an integrated structure of cellulose-coated micro-particles attached to the yeasts’ surface. Cellulytic enzymes can be attached to the cellulose surface coatings and the integrated structures exhibited effective simultaneous cellulose saccharification and fermentation to ethanol. Furthermore, we show that lipase (TLL), introduced to the aqueous emulsion medium, assemble at the inner oil-hydrogel interface so as to effectively catalyze transesterification reactions of heavy oil in the core. These results are promising steps towards “one-pot” processes for cellulose valorization by a cascade of biochemical reactions.

Cellulose solutions and emulsions: From polymer physics to micro-bioreactors

ACS Spring 2022

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