The objective of this work is to study the thermal degradation kinetic parameters of polypropylene (PP) and compare them to those of a polypropylene/starch blend (PP/S) (70/30 (wt %)), taking into account the effect of photodegradation caused by natural weathering. Samples were taken from tree shelters exposed to four years of natural weathering and compared to the unexposed material stored under laboratory conditions. Nonisothermal (dynamic) thermogravimetery was used with five different heating rates (β): 5, 10, 15, 20, and 25 °C min −1 . Several analytical model-free methods were used to determine the kinetic parameters, including the Friedman, Coats and Redfern, Kissinger, and Flynn−Wall− Ozawa (FWO) methods. The model-fitting method of Criado was also applied to determine the optimal mechanism of degradation that the polymers followed. In addition, an analytical solution was developed to mathematically model the experimental data and estimate the kinetic parameters. The analytical approach was developed based on each degradation stage of the PP/S blend, considering starch degradation at first, followed by PP. A change in the degradation mechanism could be deduced because of the effect of weathering and starch addition, which affected the kinetic parameters of the degradation reaction. The thermal stability of the materials was also affected, because of the natural weathering and addition of starch, which, on the other hand, affected the kinetic parameters of the degradation reaction.

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In this work, three plastic film products commonly used as commodity thermoplastic articles were analysed with the aim of characterizing their thermal behaviour and stability. The test specimens were subjected to a series of analytical tests to confirm their biodegradable nature. The specimens ranged between 30 and 70 μm in thickness and showed high concentrations of regulated metals, namely, lead (Pb), postchemical analysis which can lead to its migration to natural sinks. The specimens were also exposed to degressive media, namely, accelerated (UV induced) weathering and soil burial field testing. The weight loss measured exceeded 58% after soil burial indicating deterioration under natural environmental stressors. In addition, the thermal characterization campaign executed with the aim of determining the product’s thermal response followed internationally recognised experimental protocols for the determination of thermal stability. The methodology used followed the International Confederation for Thermal Analysis and Calorimetry (ICTAC) recommendation for thermal stability and the computation of kinetic parameters. The degradation reaction kinetics were also determined postexposure to degressive media. Thermogravimetric analysis coupled with differential scanning calorimetry heat flow analysis and Fourier infrared spectroscopy results was also used in studying the degradation behaviour of the specimens. Analytical kinetic estimation methods relying on model free solutions enabled the determination of the apparent activation energy (Ea) of the specimens postexposure to degradation media. A shift in the degradation mechanism was also detected after studying the kinetic parameters which showed a range of Ea between 86.64 and 226.90 kJ mol-1 depending on the type of specimens and exposure media. It can be concluded that the oxo-biodegradable films are well suited for thermal treatment in the future as discarded plastic solid waste (PSW) articles. This work also paves the way for developing national standards and future plans for societies burdened with PSW accumulation.