HYALURONIC-ACID (HYDROXYPROPYL)CELLULOSE BLENDS - A SOLUTION AND SOLID-STATE STUDY

We report a study of the compatibility of a system involving a flexibl e polymer, hyaluronic acid (HA), and a semirigid polymer, (hydroxyprop yl)cellulose (HPC). The phase diagram of ternary mixtures composed of HA, HPC, and H2O showed a homogeneous solution at an overall polymer c oncentration lower than C-p approximate to 15%, but when the concentra tion was increased, two demixing areas were evidenced: the first (rang e C-p 15-21%) corresponds to an equilibrium between two isotropic phas es, while the second (over C-p = 21%) represents the coexistence of a HPC mesophase with an isotropic phase of both polymers. In contrast, o ptical and electron microscopy observations as well as X-ray, FT-Raman , DSC, and DMTA experiments carried out on blended films showed comple te HPC/HA compatibility in all the compositions. DMTA experiments reve aled a single glass transition temperature (T-g); its dependence as a function of composition was analyzed by Kwei's equation. Different val ues were found for dry and 65% relative humidity (RH) conditioned samp les, suggesting the important role of water as a plasticizer in HPC/HA blends.