Abstract
The complex sorption behaviour of water in two widely utilized epoxy-amino thermosets is analyzed. The epoxy resins investigated are the diglycidyl ether of bisphenol-A (DGEBA) cured with a stoichiometric amount of triethylene tetramine (TETA) and tetraglycidyl diphenyl methane (TGDDM) cured with 20, 30 and 50 PHR of diamino diphenyl sulfone (DDS). Both vapour and liquid water sorption indicates the penetrant molecules are normally dissolved or immobilized by adsorption in “holes” of the glassy structure and hydrogen bonded to hydrophilic sites. The occurrence of the former mechanism of adsorption was tested by performing liquid water sorption under positive hydrostatic pressures ranging from 0 to 60 atm (relative). The application of a compressive stress indicated that hygrothermally induced microvoiding is unfavoured when a positive component of the applied stress is present, confirming the hypothesis of the crazing nature of the history-dependent damage observed. The sorption modes, the models properly utilized to describe them and the corresponding mechanisms of plasticization are discussed. The presence of three modes of sorption, namely solution, adsorption in holes and adsorption to hydrophylic sites, modified the vapor sorption isotherms of systems showing a different capability of interacting with water molecules. The possibility of performing accelerated ageing on such systems is also discussed.
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