NMR Study on the Roles of Li ⁺ in the Cellulose Dissolution Process

LiOH/urea aqueous solvent is a very efficient system to dissolve cellulose. However, there is still no mature theory to explain the roles of the Li ⁺ ions in improving the dissolution ability of cellulose in the LiOH/urea solution. In this work, the existing forms of Li ⁺ and the interactions of the components in LiOH/urea/cellulose system were investigated by solid-state NMR techniques. It was observed that as many as four types of Li ⁺ existed in the LiOH/urea/cellulose system. Some direct evidence from the H-X( ¹³ C, ⁶ Li) 2D NMR experiments were provided to clarify the roles of Li ⁺ ions in the dissolution of cellulose in the LiOH/urea system, and a 3D interaction model was proposed. The interactions among the components in the system were discussed at the molecular level.