An experimental and theoretical mechanistic analysis of thermal degradation of polypropylene/polylactic acid/clay nanocomposites

Polypropylene/polylactic acid (PP/PLA) blends containing 5 wt% of nanoclay in presence and absence of an ethylene-butylacrylate-glycidyl methacrylate terpolymer as compatibilizer were prepared by melt-mixing process. A matrix-droplet-type morphology confirmed by transmission electron microscope (TEM) and scanning electron microscopy (SEM) studies is formed in presence and absence of the compatibilizer in which the clay platelets were mainly localized in the polylactic acid (PLA) dispersed phase. Degradation studies by means of thermogravimetry analysis (TGA) and analysis of degradation activation energy (E-a), T-max (maximum degradation temperature), and Delta T (difference between initial and final degradation temperatures) parameters for each polymer component of the system revealed that incorporation of less stable PLA phase to polypropylene (PP) decreases E-a and T-max parameters, and hence, reduces the thermal stability of PP phase, while incorporation of clay nanoplatelets to the neat blend further reduces its thermal stability attributed to their lack of localization in PP phase. Compatibilization of the filled system results in migration of clay nanoplatelets toward PP and improves E-a and T-max of PP phase. On the other hand, the E-a and T-max of PLA phase of the blend were increased with incorporation of clay and its localization within that phase, while compatibilization of the filled system slightly reduces thermal stability of PLA phase due to migration of clay toward PP. A correlation was found between E-a and intensity of the thermogravimetry analysis Fourier-transform infrared spectroscopy (TGA-FTIR) peaks of the evolved products. Using the Criado method, a detailed analysis on degradation mechanism of each component was performed, and the changes in the degradation mechanism of the developed systems were determined.