Reversible melting during crystallization of polymers studied by temperature modulated techniques (TMDSC, TMDMA)

Quasi-isothermal temperature modulated DSC and DMA measurements (TMDSC and TMDMA, respectively) were performed to determine heat capacity and shear mo dulus as a function of time during crystallization. Non-reversible and reve rsible phenomena in the crystallization region of polymers can be observed. The combination of TMDSC and TMDMA yields new information about local proc esses at the surface of polymer crystals, like reversible melting. Reversib le melting can be observed in complex heat capacity and in the amplitude of shear modulus in response to temperature perturbation. The fraction of mat erial involved in reversible melting, which is established during main crys tallization, keeps constant during secondary crystallization for PCL PET an d PEEK. This shows that also after long crystallization times the surfaces of the individual polymer crystallites are in equilibrium with the surround ing melt. Simply speaking, polymer crystals are 'living crystals'.