Phase separation in aqueous mixtures of hydrophobically modified cellulosederivatives with their nonmodified analogues

Mixtures of hydrophobically graft-modified cellulose derivatives and their nonmodified analogues have been studied in aqueous solution. A qualitativel y similar behavior was found in the phase behavior of nonionic as well as o f cationic polymer systems. Over a large range of total polymer concentrati ons and mixture ratios the solutions phase separated into two phases of sim ilar polymer concentration, with one of the phases enriched in the hydropho bically modified polymer. From the manufacturing process the cellulose deri vatives investigated are likely to contain polymer chains with a rather con tinuous distribution in degrees of substitution and, possibly, substitution patterns. This causes a complex phase behavior that cannot be adequately d escribed by a ternary representation. The multicomponent nature became appa rent from composition analyses of the phases in equilibrium. It may thus be more appropriate to view the phase separation as a fractionation. A phase of small relative volume with a highly enhanced hydrophobe content (compare d to the original hydrophobically modified polymer sample) was created. Thi s was particularly obvious in more dilute solutions. Sometimes the phase se paration was difficult to observe because the phases in equilibrium had sim ilar polymer concentrations and, therefore, similar refractive indices. The observations presented here call for the attention of producers and users of these types of polymers.