Thermo-mechanical characteristics of thermally aged polyethylene/polypropylene blends

Polyethylene (PE), polypropylene (PP) and their blends have attracted a lot of attention due to their potential industrial applications. Therefore, the current work has been carried out with the main objective of investigating the impact of the thermal aging/treatment and blend ratio (composition range) on the mechanical (tensile and hardness) and thermal characteristics (using thermogravimetric analysis in a dynamic air atmosphere) of PE, PP and PE/PP binary blends. Samples of PE/PP blends containing 100/00, 75/25, 50/50, 25/75 and 0/100 wt.% were prepared via injection moulding technique and thermally treated/aged at 100 °C for 0, 2, 4, 7, 14 days. The tensile measurements indicated that the yield strength and the modulus decrease with increasing PE content. It was also observed that PE, PP and their blends deform in ductile modes. They undergo a uniform yielding over a wide range of deformation, which is followed by strain hardening and then failure. The strain to break for pure PE is found to be much higher than that for pure PP and for their blends, intermediate values have been observed. The hardness measurements have also revealed that increasing PE content in PE/PP blends reduced the hardness value of PP, however, thermal aging at 100 °C has not affected the polymers hardness which holds also true for the tensile properties, showing a good correlation between tested mechanical properties. The thermogravimetric analysis (TGA) in a dynamic air atmosphere and derivative thermogravimetric analysis (DTA) were conducted to study the thermal degradation and stability of thermally unaged and aged PE, PP and PE/PP blends in terms of the initial (Td and Td(1%)) and final (Td(99%)) decomposition temperatures and maximum decomposition rate temperature (Tmax). All polymers start to decompose at no less than 365 °C. As for mechanical properties, the blend ratio has affected the thermal properties however, aging time has not.