Moisture absorption behavior of epoxies and their S2 glass composites

The influence of moisture exposure on the behavior of three toughened epoxy–amine systems (scrimp resins SC11, SC15, and SC79, Applied Poleramic, Inc., Benicia, CA) was investigated. Neat resin samples were conditioned by immersion in distilled water at 71°C and in an environmental chamber at 85% relative humidity and 87.8°C until saturation. The equilibrium weight gain ranged from 1.8 to 3.8% for the resins. The long‐chain, low‐crosslink‐density epoxy system (SC11) absorbed the highest amount of water and was saturated first, and it was followed by the medium‐crosslink‐density (SC15) and high‐crosslink‐density materials (SC79). The moisture diffusivity decreased with the increasing crosslink density of the resins. The percentage reduction of the glass‐transition temperature (Tg) at equilibrium moisture absorption was highest for the low‐crosslink molecule. The percentage reductions for the medium‐crosslink and higher crosslink systems were comparable. A net weight loss after drying was observed for the SC11 and SC79 resin systems. Fourier transform infrared analysis confirmed the segment breakage and leaching of molecules from the epoxy–amine network. The effects of moisture cycling on Tg were dependent on the epoxy–amine morphology. During the drying stage, Tg increased to a value higher than that of the unaged dry systems. The S2 glass composite samples were conditioned under identical conditions for the resin system. Composite systems absorbed less moisture than the neat resins as expected.