Cellobiose as a model compound for cellulose to study the interactions in cellulose/lithium chloride/N-methyl-2-pyrrolidone systems

To investigate the solvent/solute interactions that take place during the dissolution of cellulose, cellobiose was employed as a model of the longer-chain cellulose molecule in a dissolution study of the cellobiose/LiCl/N-methyl-2-pyrrolidone (NMP) system, conducted using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), 13C, 35Cl, and 7Li NMR spectroscopy, and conductivity measurements. For the LiCl/NMP system, FTIR and 13C NMR analyses of the NMP carbonyl moiety showed a strong dependence on the LiCl concentration, which suggested an association between the Li+ cations and the carbonyl groups of NMP. As the cellobiose molecules are dissolved in the LiCl/NMP solvent, the Li+–Cl− ion-pairs in LiCl/NMP are dissociated. Strong hydrogen bonds are then formed between the hydroxyl groups of cellobiose and the Cl− anions, resulting in breakage of the intermolecular hydrogen bonds of cellobiose. Meanwhile, the Li+ cations are further associated with the extra free NMP molecules. However, the NMP molecules do not directly interact with the dissolved cellobiose. Based on these results, we propose that our study is conducive to a more in-depth comprehension of the dissolution mechanism of cellulose in LiCl/NMP.