Study on the dissolution and degradation patterns of cellulose in phosphonate-based ionic liquids and the construction of ternary phase diagrams.

Abstract

The growing demand for sustainable materials necessitates green solvents for cellulose fiber production. This study addresses the unclear mechanisms of phosphonate-based ionic liquids (ILs) in cellulose dissolution and regeneration, which limit their industrial application. Five phosphonate-based ILs were synthesized and characterized: 1-butyl-3-methylimidazolium methylphosphonate ([Bmim]MP), 1-ethyl-3-methylimidazolium dimethylphosphate ([Emim]DMP), 1-ethyl-3-methylimidazolium ethylphosphonate ([Emim]EP), 1-ethyl-3-methylimidazolium methylphosphonate ([Emim]MP), and 1,3-dimethylimidazolium methylphosphonate ([Mmim]MP). Polarized light microscopy images demonstrate that cellulose can be dissolved in these ILs at 60 °C. Molecular weight analysis revealed that degradation patterns are influenced by both time and temperature, and the extent of degradation was objectively ranked according to measured molecular weight changes. The strongest hydrogen bonding of [Emim]MP to cellulose was calculated using density functional theory, with a bond strength of 124.24 kJ/mol. The ternary phase diagram obtained from turbidimetric titration visualizes the effect of regeneration conditions on the process, where ion size and chain length influence the outcomes. Furthermore, the regeneration capabilities of each ternary system were validated by determining excess enthalpy during regeneration using the COSMO-RS method. This study provides data and theoretical references for applying phosphonate-based ILs in the spinning process.