Cellulose Dissolution in Ethylene Diamine/Salt Solvent Systems

Abstract

Ethylene diamine (EDA)/salt solvent systems can dissolve cellulose without any pretreatment. A comparison of the electrical conductivity of different salts in EDA was made at 25°C, and conductivity decreased in the order of KSCN>KI>NaSCN at the same molar concentration. Among the salts tested, potassium thiocyanate (KSCN) was capable of dissolving both high molecular weight (DP>1000) and low molecular weight (DP=210) cellulose, and this was confirmed by polarized light microscopy. 39K and 14N NMR experiments were conducted at 70°C with different cellobiose concentrations in EDA/KSCN. The results showed that K+ interacts with cellobiose more than SCN–. Wide angle X-ray diffraction studies revealed that cellulose, recovered by precipitating cellulose solutions with water, underwent a polymorphic transformation from cellulose I to cellulose II. Changes in the FTIR absorption bands at 1430 and 1317 cm-1 were associated with a change in the conformation of the C-6 CH2OH group. The changes in positions and/or intensities of absorption bands at 2900, 1163, and 897cm-1 were related to the breaking of hydrogen bonds in cellulose and were consistent with cellulose II.