PHASE-SEPARATION AND POLYMER INTERACTIONS IN AQUEOUS POLY(VINYL ALCOHOL) HYDROXYPROPYL METHYLCELLULOSE BLENDS

This paper discusses the compatibility of aqueous hydroxypropyl methylcellulose (HPMC)/poly(vinyl alcohol) (PVA) blended systems. Dynamic mechanical analysis and differential scanning calorimetry have provided clear evidence of two phases. Each phase precluded almost completely the other component. The HPMC-rich phase was amorphous with a constant T(g), while the PVA-rich phase showed a limited level of crystallinity and a constant T(g) for the amorphous part. Fourier-transform infra-red studies indicated hydrogen-bonding interactions involving the carbonyl and hydroxyl groups of like molecules but no detectable interactions between HPMC and PVA. A new hydrogen-bonding environment of the hydroxyls was observed in the blended system but was not capable of inducing any compatibility. The gross incompatibility was successfully predicted by the total solubility parameters of the two polymers and attributed to significant differences in the polar and hydrogen-bonding contributions. Surface energy analysis corroborated the inability of the two chains to participate in acid-base interactions between unlike molecules due to significant discrepancies in their Lewis acid-base characteristics. Finally, determination of the free energy of polymer-polymer interaction in water allowed approximate calculation of the Flory-Huggins parameters of aqueous PVA and HPMC systems.