The role and potential of morpholinium-based ionic liquids in dissolution of cellulose

Abstract

The effective dissolution of cellulose prepares for its subsequently full utilization. Ionic liquids (ILs) are attractive options for “green” dissolution of cellulose. A series of morpholinium-based ILs were synthesized and applied in dissolution of cellulose. The ultrasonic assisted saturated calcium chloride solution was used to activate cellulose. The remarkable decrease (from 87% to 65%) in crystallinity of cellulose facilitated dissolution process. The type of head-corn cations significantly increased polarity (ET(30)) and hydrogen bond acidity (α) of ILs. N-Allyl-N-methylmorpholinium-based ILs showed the highest ET(30) and α (59.11kcalmol−1 and 0.51) compared to 1-Allyl-3-methylimidazolium-based ILs (57.41kcalmol−1 and 0.46) and 1-Allyl-3-methylpyridinium-based ILs (49.36kcalmol−1 and 0.33) owing to the electron-rich center of oxygen in the morpholine ring. The type of anions dominated the ability to accept hydrogen bond of ILs. Formate, acetate and bisulfate contributed more hydrogen bond basicity (β) (0.84, 0.88 and 0.91) for N-allyl-N-methylmorpholinium-based ILs in comparison with other anions. Additionally, morpholinium-based ILs exhibited appropriate viscosity. Above-mentioned performances jointly improved the dissolution of cellulose in morpholinium-based ILs. This study demonstrated the potential of using morpholinium-based ILs as a class of efficient solvents to dissolve cellulose.