Calorimetric and thermogravimetric studies of UV-irradiated polypropylene/starch-based materials aged in soil

We studied the biodegradability in soil of mixtures of polypropylene and a starch-based biodegradable additive. The changes in their properties were studied using calorimetry and thermogravimetric analysis. To observe the effect of UV radiation, the mixtures were photo-oxidized before biodegradation. The results were compared with those obtained from previous studies on non-photo-oxidized samples. Using calorimetry, we observed changes in the crystallinity of the samples and in their crystallization kinetics, which we analyzed using the Avrami equation. Photo-oxidation was found to reduce the crystallinity of the mixtures while degradation in soil increases it. Using thermogravimetry, we observed changes in the thermal stability and in the associated kinetic parameters, which we determined using an isoconversional integral method. Biodegradation tended to increase the thermal stability of the starch units and did not affect the polypropylene. Photo-oxidation tended to decrease the thermal stability of the mixture, although it may make the starch slightly more stable. The thermooxidative degradation of the mixtures was also studied.