Effects of annealing above Tg on the physical aging of quenched PLLA studied by modulated temperature FTIR
The effect of the annealing few degrees above the glass transition temperature (Tda = 62 C) on the physical aging (Tpa = 51 C) of amorphous quenched poly(L-lactide) is investigated by an implementation of variable temperature Fourier transform infrared (FTIR). By using a temperature program composed of a linear heating ramp superimposed to a temperature modulation (modulated temperature FTIR), the reversing and nonreversing intensity variation of selected bands, related to highenergy gg and low-energy gt conformers, is investigated. It is observed that the annealing above Tg changes irreversibly the conformation distribution of the liquid polymer. The glasses obtained from annealed and nonannealed liquids behave differently, evolving in the physical aging toward their own liquid state and retaining the memory of their original condition before the vitrification. The recovery through Tg of the relaxation occurred in the physical aging depends not only from aging conditions but also by the thermal history of the sample above the Tg.