Dissolution of cellulose in 1-allyl-3-methylimidazolium methyl phosphonate ionic liquid and its composite system with Na2PHO3.

An ionic liquid, 1-allyl-3-methylimidazolium methyl phosphonate (Amim(MeO)PHO2), was synthesized and used to dissolve and regenerate cellulose under mild conditions. The dissolution mechanism of cellulose in Amim(MeO)PHO2 was investigated by in situ NMR spectroscopy under different conditions. Inorganic salt Na2PHO3 with an anion structure similar to that of Amim(MeO)PHO2 was added to form a Na2PHO3/Amim(MeO)PHO2 composite system. The effects of the composite system on the cellulose structure were investigated by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and the measurement of the degree of polymerization. The results indicated that the regenerated cellulose was not derivatized; however, its thermal stability, crystallinity, and DP were lower than that of the original cellulose. Therefore, the dissolution mechanism of cellulose in Amim(MeO)PHO2, and its composite system with Na2PHO3 was investigated in this study, which might provide a simple guide for designing efficient and safe ionic liquids for the dissolution of cellulose.