Mechanical and Thermal Properties of Polypropylene Blended with a Novel Hyperbranched Polyester Polymer

In this paper, the effect of four novel hyperbranched polyester polymers on the mechanical and thermal properties of polypropylene (virgin polypropylene VPP and recycled polypropylene rPP) has been investigated. All the polymeric blends were prepared using a twin-screw extruder with different weight percentages of HBP (5, 10, and 20 wt.%). The mechanical properties, such as tensile strength, elastic modulus, elongation at break, impact strength, and hardness, were studied. In addition, the thermal properties, such as melting temperature Tm, crystallization temperature Tc, and the degree of crystallinity Xc, were also investigated. Scanning Electron Microscope (SEM) and Melt flow rate (MFR) were investigated. Tensile results showed that the tensile strength, elastic modulus, and elongation at break for both virgin polypropylene (VPP) and recycled polypropylene (rPP) decreased with the addition of the four hyperbranched polyester polymers (HBPs). While impact strength has improved for the polymeric blends with the increase of hyperbranched polyester content, it has also been found that the best impact strength occurs at 10% HBPs for all blends. While there is a slight improvement in the Shore D hardness with the HBPs added for the blends, Differential scanning calorimetry (DSC) results showed that the melting temperature (Tm) improved slightly for both VPP and rPP blends. While the crystallization temperature (Tc) increased for VPP blends and decreased for rPP blends, In addition, the degree of crystallinity Xc was decreased for both blends. SEM results indicate that there is no interaction and dispersion between PP and HBP due to the absence of any compatibilizer, while MFR results indicate that there is an improvement in material flowability and thus improved processability.