Erasure below glass‐transition temperature of effect of isothermal physical aging in fully cured epoxy/amine thermosetting system

Abstract

AbstractThe erasure below the glass‐transition temperature (Tg) of the effect of isothermal physical aging (at aging temperature Ta) in a fully cured epoxy/amine thermosetting system is investigated using the torsional braid analysis (TBA) dynamic mechanical analysis technique and the differential scanning calorimetry (DSC) technique. From the TBA temperature scans, the intensity of the localized perturbation of the moduli in the vicinity of the Ta (90°C), due to isothermal physical aging, is decreased by heating to below the Tg (Tg∞ = 177°C), indicating that the physical aging effect can be eliminated by heating to below the Tg. The isothermal aging effect in the vicinity of the Ta is almost completely eliminated by heating to 50°C above the Ta (i.e., 140°C); however, a competing aging effect occurs above Ta at higher temperatures during the heating. Erasure below Tg of the isothermal physical aging effect is inferred from DSC experiments from the diminished relaxation enthalpy in the vicinity of the Tg, which is measured from the difference in areas between the aged (Ta = 150°C) and deaged thermograms. A comparison of the TBA and DSC results is made. Implications on the heterogeneous nature of the amorphous glassy state of polymers are discussed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 396–404, 2001