Contribution to the study of the amorphous phase of polyethylene terephtalate (PET) by the differential scanning calorimerty (DSC) experiments

In their semi-crystalline form, the polyesters can be studied by a two phases model in which, materials are described without transitional region between crystalline and amorphous domains. However, since 20 years there have been several attempts in order to describe easily such polymers, a three phase model with taking into account the rigid amorphous fraction has been proposed. The third phase of this model is a transitional region located between crystalline and mobile amorphous regions, it is called rigid amorphous fraction and it can be characterized easily by calorimetric measurements, because it does not participate in the glass transition of the amorphous phase (called amorphous phase mobile). PET is one of polymers for which, the three phase model has successfully described its thermal behavior. The aim of this contribution is to study the amorphous phase of this polymer by differential scanning calorimerty (DSC) experiments. The semi-crystalline form of PET can be obtained by quenching it in ice water at various temperatures lower than the melting point T_m or by annealing at temperature higher than its crystallization temperature T_C. The thermograms of DSC obtained after annealing the polymer at various temperatures varying between 110°C and 220°C during different times allowed us to estimate the crystalline rate, the mobile and rigid rates of the amorphous phase.