Molecular weight fractionation of high polydispersity native celluloses

Microcrystalline cellulose with high polydispersity was preferentially dissolved in 1-ethyl-3-methylimidazolium acetate (EMIMAC), an ionic liquid which has high ability for the dissolution and processing of cellulose. Either water, ethanol or acetonitrile as a non-solvent was carefully added to induce precipitation of cellulose fractions (Fig. 1). Ethanol or water addition led to quantitative precipitation of cellulose from EMIMAC solution. With the aprotic solvent acetonitrile, successive additions of this non-solvent promote fractional precipitation of cellulose into two coarse fractions. These two acetonitrile-induced precipitated cellulose fractions were revealed to have distinctly differing molecular weight profiles by size exclusion chromatography. The first precipitated fraction had proportionately higher molecular weight, more similar to the ethanol- and water-induced precipitates and the original cellulose, but with a relatively narrow polydispersity. The second fraction obtained by successive acetonitrile addition had relatively lower molecular weight and a similarly narrow polydispersity. Chemical characterisation confirmed this second fraction consisted of amorphous cellulose compared to other fractions containing crystalline celluloses. Thermogravimetric analysis also revealed the fractionated samples had relatively reduced thermal stability, consistent with the lower molecular weight of this fraction. Similarly, native cellulose can also be fractionated from chloride imidazolium-based ionic liquids with acetonitrile non-solvent to give low molecular weight fractions in 20-50% recovered yields. This relatively straightforward route to selective molecular weight fractionation of cellulose using acetonitrile non-solvent addition creates an opportunity for large-scale selective Mw fractionation of cellulose via ionic liquid processing.