Mechanical damping spectra have been measured between the fl and ~ transitions on specimens of polycarbonate deformed by traction or cold pressing in the pre-yield region and left thereafter to recover at room temperature for given periods of time. The deformation is always applied to samples previously aged for 2 years at room temperature after quenching from above the glass transition temperature. The deageing effect induced by small applied deformation is apparent on the damping spectra by the enhancement of two peaks: the :t' peak precursor of the ~ transition and the :t" peak partially merging with the :t' peak and at a lower temperature with the fl loss process. Several experimental parameters such as the mode, amount of deformation and the recovery time after release of the stress are chosen to investigate the enhancement conditions and the relaxation behaviours of the :t' and :t" loss processes. The location of the :~' peak is well understood in terms of a classical formalism together with the hypothesis that a change in the structural temperature of the sample occurs as a result of the small deformation. At present, no interpretation of the ~" loss process has been proposed, but it is obvious from the present data that the existence of a strain-induced ~t" loss process contributes significantly to the deageing and further physical ageing effects probed in the vicinity of room temperature by mechanical damping measurements.
Посилання на статтю:
Influence of mechanical deageing and subsequent physical ageing on the loss curve of polycarbonate / J. Othmezouri-Decerf // Polymer. – 1994. – Vol 35. – P. 4734-4742.