PHYSICAL CHEMISTRY OF RESIN SOLUTIONS. PART III. VISCOSITY OF SHELLAC SOLUTIONS IN MIXED SOLVENTS.

The viscosity of shellac dissolved in a solvent mixture composed of two non-solvents, acetone and water has been studied over a wide range of concentration and temperature The viscosity-solvent composition curves show well-defined minimum at a definite ratio of water to acetone in the solvent mixture for shellac concentration of 25% and higher; the lower the temperature, the more sharp and well-defined are the minima. For lower concentrations of shellac below 20% the viscosity continually rises with increase in the proportion of water. This striking difference in properties in shellac solutions in aqueous acetone below and above 20% of shellac has also been noted in the case of some other properties. e.g., gelation capacity, temperature coefficient of relative viscosity, etc., for which either solvation or micelle formation has been suggested as explanation. The solvent power as determined by precipitation with an inert solvent like benzene, or by cooling, always shows a maximum at about 80% water content. Thus the idea that viscosity is a criterion of solvent power is shown to be of restricted validity