Preparation, characterisation and thermal-oxidative degradation of poly-L lactic acid (PLLA)

Thermal-oxidative degradation of PLLA was investigated under both isothermal and dynamic heating modes. The sample was prepared by a modified polycondensation process and was characterised by TG, DTG and DSC analyses. The global peak decomposition was observed 373.09°C. A paradoxically local maximum was also observed 286 °C due to impurities. A kinetic scheme of first order reaction was considered to describe uni-molecular thermal decomposition rate. Activation energy under dynamic heating was obtained by using Friedman plot through a new three stage mechanism, namely random, transition and specific stages. Frequency factor and activation energy for isothermal heating were achieved as well. It was found that the activation energy under isothermal heating is generally higher than that under dynamic heating. Oxygen atmosphere aggravates thermal degradation so that increases in the activation energy are obvious. In addition to effects of temperature and polymer loading, effects of pressure on the degradation rate were studied. Polymer loading was found to be inert for sample charges up to 10 gr. We found that the obtained activation energy is in good agreement with that reported by others

کلیدواژه ها:

Activation energy ، Dynamic heating ، Frequency factor ، Isothermal heating ، Thermal-oxidative degradation