Title: Paramylon: Processing routes for materials applications

Abstract

Unlike many polysaccharides produced by microalgae, for which cheaper alternatives exist from macroalgae or plants, paramylon from Euglena gracilis presents a unique macromolecular structure. This reserve glucan produced in the form of intracellular granules by the green microalgae contains only linear (1-3) linkages, resulting in the formation of triple helix by the polymer chains and a very high crystallinity. Processing and purification for applications as biomaterials requires the use of efficient and non-derivatizing solvents. While strong acids tend to induce depolymerization, strong bases have been showed to allow preserving the triple helix structure for the production of nanofibers. Recently, a commercial imidazolium ionic liquid was successfully used for solubilizing paramylon granules into biomaterial films for wound healing. As designed solvents, Ionic Liquids (ILs) may be used not only for such final polysaccharide shaping step, but also upstream during the extraction. For this purpose, we evaluated the solubility of paramylon in different biobased ILs. These ones have been synthesized combining choline hydroxide or choline esters with carboxylates derived from biobased acids or amino acids. The solubilization tests of the paramylon have been performed at different temperatures using sometimes ultrasounds. The influence of a co solvent (water or ethanol) was also studied and the best conditions are mild and in total accordance with green chemistry principles. The regenerated powder of the biopolymer was then analyzed via 13C NMR spectroscopy and X-Ray Diffraction; no chemical modification was observed overall, Furthermore, the IL can be recycled. From our results, we can state that the biobased ILs were at least as efficient as commercial immidazolium ionic liquids. Our biobased ILs are thus good candidates to extract and process paramylon as biomaterials.