Natural Aging Effects in HMS-Polypropylene Synthesized by Gamma Radiation in Acetylene Atmosphere

High melt strength polypropylene (HMSPP) is produced by y-radiation process to improve the melt viscosity suitable for melt blow film process. The melt strength (MS) properties of a polymer increases with molecular weight and with long chain branching due to the increase chain entanglement levels in the polymer. The main scope of this study is to evaluate the stability of HMSPP prepared by gamma radiation with doses of 5, 12.5 and 20 kGy in comparison with virgin PP. The samples were subjected to the natural aging for a period of one year. These polymers were characterized by: Thermogravimetry analysis (TGA), Differential scanning calorimetry (DSC), Infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). These results show predominantly chain scissions degradation mechanism, owing to the reactivity of the tertiary carbon of macro chains. The chemi-crystallization caused by degradation processes (thermal and photodegradation) was detected in HMSPP.