Effect of solvent exchange on the structure and rheological properties of cellulose in LiCl/DMAc

Effect of solvent exchange on the structure of cellulose was investigated by Fourier transform infrared spectroscopy, wide angle X-ray diffraction, and scanning electron microscopy analysis. The solvent exchange facilitated the dissolution of cellulose in LiCl/DMAc with no change of the crystalline structure of cellulose. In contrast, solvent exchange led to the fibrillation on the treated fiber surface and the trimmed rod-like particles, further confirming the occurrence of particle disintegration. The rheological properties of three cellulose samples with different degrees of polymerization (DP) and different concentrations were investigated. Results indicated that the cellulose LiCl/DMAc solutions were nonNewtonian fluids. At low deformation rates the cellulose solution behaved like a viscous liquid (loss modulus G" being larger than storage modulus G% but elastic properties developed at high angular frequency. The two domains of viscoelastic behavior were separated by the so-called crossover point for G' and G", which was slightly shifted to lower frequencies as the testing temperature increased from 50 to 80 degrees C. As the concentration and the average molecular weight (or DP) increased, the angular frequency at the crossover point increased also under the experimental conditions.