Structural changes in glassy polycarbonate induced by cyclic stresses

Glassy polycarbonate was subjected to cyclic stresses and the changes in its structure were studied by DSC, positronium annihilation lifetime spectroscopy (PALS), and SAXS. On increased exposure to cyclic loading, the enthalpy overshoot near T s increased in a manner similar to increasing physical aging. However, the 'hole' size as revealed by PALS increased, unlike physical aging. SAXS reveals an increase in the short range order and the amplitude of density fluctuation. These results are consistent with both the DSC and the PALS results. We conclude that mechanical loading does cause changes in the glassy structure.