Abstract
The temperature dependence of water vapour sorption and diffusion in poly-(3-hydroxybutyrate) (PHB) was investigated. Equilibrium sorption and diffusion kinetics were determined by a quartz Mac Bain's vacuum microbalance technique in the temperature range of 303–333 K. The water molecule interaction with the polymer matrix was analyzed for wet PHB films by FTIR spectroscopy technique. Water sorption isotherms are interpreted as a superposition of free water sorption, estimated by the Flory-Huggins equation and water immobilized on carbonyl groups of PHB. The immobilization effect was described by a Langmuir type equation. The dependence of diffusivity on water concentration was described in the framework of Fujita's immobilization model in which the growing function Dw vs Cw . characterized the filling degree of carbonyl groups as sites of immobilization in the polymer. Enthalpy of free water sorption (12kJ/mol) and water immobilization (42kJ/mol) as well as the activation energy of water diffusion coefficients (71kJ/mol) in noncrystalline areas of PHB were determined.
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