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

The erasure below the glass-transition temperature (T-g) of the effect of i sothermal physical aging (at aging temperature T-a) in a fully cured epoxy/ amine thermosetting system is investigated using the torsional braid analys is (TBA) dynamic mechanical analysis technique and the differential scannin g calorimetry (DSC) technique. From the TEA temperature scans, the intensit y of the localized perturbation of the moduli in the vicinity of the T-a (9 0 degreesC), due to isothermal physical aging, is decreased by heating to b elow the T-g(T-gx = 177 degreesC), indicating that the physical aging effec t can be eliminated by heating to below the T-g. The isothermal aging effec t in the vicinity of the T-a is almost completely eliminated by heating to 50 degreesC above the T-a (i.e., 140 degreesC); however, a competing aging effect occurs above T-a at higher temperatures during the heating. Erasure below T-g of the isothermal physical aging effect is inferred from DSC expe riments from the diminished relaxation enthalpy in the vicinity of the T-g, which is measured from the difference in areas between the aged (T-a = 150 degreesC) and deaged thermograms. A comparison of the TBA and DSC results is made. Implications on the heterogeneous nature of the amorphous glassy s tate of polymers are discussed. (C) 2001 John Wiley & Sons, Inc.