Thermal degradation kinetics of plastics and model selection

The thermal decomposition behaviour of high and low-density polyethylene (LDPE and HDPE), polypropylene (PP), poly(lactic acid) (PLA) were investigated under inert condition by dynamic thermogravimetric analysis (TGA) in the temperature range of 303-973 K at seven different heating rates. Determination of distributed activation energy at various stages of degradation process and their implication in degradation process was investigated with the help of isoconversional methods. Reaction models (f(alpha)) were predicted using Criados masterplots. Corresponding values of pre-exponential factors were calculated using compensation effect. A comparative study of various isoconversional methods/models like Friedman, Kissinger-Akahira-Sunnose, Ozawa-Flynn and Wall (OFW), Starink and advance isoconversional method (AIC) was discussed and reliability of all these methods was examined. Reconstruction of the conversion profiles for different thermal history was performed and compared with experimental data to select the appropriate model.