The solubility of fractionated sodium lignosulfonates (NaLS) in water-ethanol mixtures of different compositions and at room temperature was measured using a cloud point titration method. The solubilities of NaLS in the mixed solvents were correlated using the Flory-Huggins polymer solution theory. Three fractions of NaLS, having weight-average molecular weight of 82,500, 40,700, and 4,700 (size exclusion chromatography, sodium polystyrene sulfonate standards), were studied for solute volume fractions between 0.07 to 0. 13. The Flory-Huggins interaction parameters between water and NaLS was found to depend on the molecular weight of NaLS, while those between ethanol and NaLS change only slightly with NaLS molecular weight. Both of these interaction parameters were a weak function of NaLS volume fraction.
