The temperature dependency of water vapor sorption and diffusion in poly(3-
hydroxybutyrate) (PHB) was studied for the first time. Equilibrium sorption
and diffusion kinetics were determined by a quartz McBain's vacuum microba
lance technique in the temperature range of 303-333 K. A probability of wat
er molecule interaction with the polymer matrix was analyzed for wet PHB fi
lms by FTIR spectroscopy technique. Sorption isotherms are interpreted as t
he solution of free water molecules estimated by the Flory-Huggins equation
and the sorption of water molecules immobilized on the carbonyl groups of
PHB. The immobilization effect was described by a Langmuir-type equation. T
he dependency of diffusivity on water concentration was described in the fr
ames of Fujita's immobilization model in which the growing function D-w ver
sus C-w characterized the filling degree of carbonyl groups as sites of imm
obilization in the polymer. Enthalpy of free water sorption (12 kJ/mol) and
water immobilization (42 kJ/mol), as well as the activation energy of wate
r diffusion coefficients (71 kJ/mol), in noncrystalline areas of PHB were d
etermined. (C) 1999 John Wiley & Sons, Inc.