Chemical structure and water diffusion in polyester resin-glass fibres composites

The effect of water on the chemical structure of unsaturated polyester resin-glass fibres composites has been examined for materials of different formulation in the interval of temperature 50-90°C. The major changes in the chemical structure of the material are due to the hydrolysis of terminal chain-segments of the polyester and of polyvinyl acetate (low-profile agent). The latter results in the formation of polyvinyl alcohol with modification of the hydrophilic/hydrophobic balance in the matrix. Other contributing factors in the water sorption behaviour of the material are the leaching of products of polymer hydrolysis, of styrene, of low-molecular weight fillers and additives, and the partial dissolution of ionic species from the glass fibres. Consequent alteration of the thermodynamic and kinetic parameters of water sorption/ desorption have been studied in details. The correlation between the evolving chemical structure of the material and its transport properties allows the development of a diffusion kinetic method to evaluate the properties of polymer composites.