Crystallization and enthalpic relaxation studies on a Copolymer of lactic acid

The effect of thermal behaviour and properties such as enthalpic relaxation, degree of crystallinity, development of crystallization, crystallization kinetics and melting behaviour of Co-poly (lactic acid) were studied using differential scanning calorimetry (DSC), FTIR spectroscopy and hot stage microscopy. Both glass formation and enthalpic relaxation have been measured on amorphous and partially crystalline samples produced by controlled cooling from the melt and the effect of the degree of crystallinity measured. Observation of the crystallization in thin films by hot-stage microscopy confirmed that the mechanism was that of the growth of heterogeneously nucleated disc spherulites. Both nucleation density and radial growth rates were measured but they exhibited different temperature dependence. FTIR spectroscopy has been used to study and characterize the change in structure of Co-PLA with temperature and time. Isothermal crystallization kinetics of Co-PLA was measured in the temperature range from 120 to 136 oc from these changes in the absorption of the IR bands and in particular the intensities of the crystalline and amorphous bands of the carbonyl ester group. In this way it was possible to analyse the kinetics of both primary and secondary crystallization directly from the relative crystallinity over extended periods with sufficient accuracy to test the validity of the Avrami equation