Dilute solution properties of carboxymethyl celluloses of various molecular weights and degrees of substitution

The intrinsic viscosities of six carboxymethyl celluloses (CMC) of different degrees of substitution, molecular weights, and molecular weight distributions (MWDs) were measured as a function of pH, ionic strength, and temperature. The molecular weights and MWDs were determined by analytical ultracentrifugation. It was demonstrated that the raw viscosity data could be represented by the Fedors equation allowing for accurate determination of the intrinsic viscosity. Ionic strength, rather than pH or temperature had the strongest effect on the conformation of CMC. An estimate of the Mark-Houwink-Kuhn-Sakurada exponent (α=0.83) and calculations of chain flexibility and expansion factors indicated that CMC has semi-flexible, randomly coiling chains in solution with persistence lengths on the order of 8.8-24.5 nm in distilled water and 11.3-14.8 nm in 0.01 mol/L sodium chloride. It was also found that the lowest molecular weight CMC was most flexible among the tested samples.