Light‐scattering studies on solutions of cellulose in the ammonia / ammonium thiocyanate solvent system. II. Quasielastic light‐scattering and liquid crystal study

Abstract

SYNOPSISThis is the second part of a two-part study of the NH,NH,SCN cellulose solvent system. Quasielastic light scattering was used to determine the diffusion coefficients of cellulose in solution and the effective hydrodynamic radius of the dissolved molecules. Additionally, the system was studied using light microscopy to determine the minimum critical volume fraction or liquid crystal formation. Very little change was found in the diffusion coefficients with change in cellulose concentration indicating little interaction between the chains in solution. Values of 7.69 and 2.66 X 10' cmz/s were measured for samples having a degree of polymerization of 153 and 969. The value of the coefficient relating the hydrodynamic volume to the radius of gyration was found to be in the range of 0.33 to 0.53, indicating an extended coil conformation according to the Kirkwood-Riseman theory. The minimum critical volume fractions necessary for liquid crystal formation, u ; , were 0.039, 0.038, and 0.048 for the three solvent compositions studied. The values calculated for u; based on the measured persistence lengths were much larger than the predicted values, indicating strong deviation from theory or possible aggregation in the system.

Comparison of various solvents for determination of intrinsic viscosity and viscometric constants for cellulose

“…The curve can be used to estimate the constant K in a solvent, if exponent a in a solvent is known. For example, De Groot et al29 reported values of 0.74, 0.98, and 0.92 for exponent a in the solvent system of NH 3 /NH 4 SCN with three compositions of (27/73, w/w), (25.5/74.5, w/w), and (24.5/75.5, w/w), respectively. The corresponding values of K can be estimated to be 61.7 × 10 −3 , 3.00 × 10 −3 , and 6.38 × 10 −3 , respectively.…”

New solvents for cellulose: Hydrazine/thiocyanate salt system

“…Evidence of the anisotropic phase was observed above 6% (w/w) cell I (DP210) in the NH 2 NH 2 /KSCN and NH 2 NH 2 /LiSCN systems and above 8% (w/w) in the NH 2 NH 2 /NaSCN solvent. These concentrations suggest that the orienting behavior of cell I (DP210) in the NH 2 NH 2 /salt system is quite similar to that in the NH 3 /NH 4 SCN system in which liquid‐crystal formation take places at a 7.5% (w/w) minimum cell I (DP210) concentration 34. Chanzy and Dubé6 first reported a nonmodified cellulose solution with a strong birefringence in the NMMO/H 2 O system depending on the water content and temperature.…”

“…Recently, morphological studies32–36 have disclosed that the cellulose/NH 3 /NH 4 SCN system experiences gelation and liquid‐crystal formation dependent on cellulose concentration, cellulose DP, and temperature. Also, liquid‐crystalline properties of chemically unmodified cellulose have been discussed in a few solvent systems 7, 37, 38.…”