Inhibiting degradation of cellulose dissolved in ionic liquids via amino acids

Abstract

Although ionic liquids (ILs) are efficient solvents for dissolving cellulose, long time dissolution (for example ≥24 h) could lead to cellulose degradation, especially at high temperatures (for example ≥130 °C), limiting the use of ILs in the cellulose industry. On the premise of sufficient dissolution, inhibiting cellulose degradation in 1-butyl-3-methylimidazolium chloride [C₄mim]Cl, 1-ethyl-3-methylimidazolium chloride [C₂mim]Cl and 1-allyl-3-methylimidazolium chloride [Amim]Cl at 130 °C was achieved by the addition of amino acids. The results show that the cellulose regeneration rate increased from 0.00% to 90.02% at 130 °C for 24 h when 1.25 wt% of L-arginine was added to [C₄mim]Cl. It is concluded that L-arginine can form an intermolecular hydrogen bond with one of the three ipsilateral hydroxyls of cellulose, which prevents the cation [C₄mim]⁺ or anion Cl⁻ from simultaneously forming three hydrogen bonds with the three ipsilateral hydroxyls of cellulose, successfully inhibiting cellulose degradation. This work expands the application of ILs in the cellulose industry.