Characterization of the morphological fine structure of commercial thermosetting resins through hygrothermal experiments

Abstract

This review collects some of the recent advancements and significative investigations on the sorption behaviour and moisture sensitivity of a class of widely utilized and investigated thermosetting resins: the epoxy systems. In the last few years complete studies on the diffusion of moisture in thermosets have revealed that complex sorption behaviours are often a consequence of dominant modes of sorption driven by structural and chemical differences. The diffusional transport of small amount of penetrant below the polymer glass transition may be described by the classical theory, even though the system is not purely viscous fluid mixture. Often, however, the relative movements of polymer and solvent can be affected by the rearrangement of the polymer morphology, leading to a history dependent diffusional transport, denoted as viscoelastic diffusion. Meaningful penetrant diffusion coefficients and equilibrium solubilities may be obtained from ordinary sorption tests if experiments are conduceted so that viscoelastic diffusion is avoided.

Due to the chemical structure, functionality and composition of their constituents, ordinary variations of the processing conditions as well as the quality of the raw materials have been observed to lead to changes of the fine structure which are often responsible of lower ageing resistence of the polymer. The data reported here correlate the morphology of some widely utilized epoxy matrices to the informations that can be obtained from the study of the sorption behaviours.