Effects of compatibilizers on mechanical properties of PET/PP blend

Polyethylene terephthalate (PET) and polypropylene (PP) are incompatible thermoplastics due to differences in chemical structure and polarity hence their blends posses inferior mechanical properties. Compatibilization with a suitable block/graft copolymer is one way to improve the mechanical properties especially impact strength of such a blend. In this work, the effects of two compatibilizers, maleic anhydride grafted polypropylene (PP-g-MAH) and maleic anhydride grafted styrene-ethylene/butylene-styrene (SEBS-g-MAH), were investigated for compatibilization of PET/PP blends and the results were compared. PET, PP, and compatibilizers were melt blended in a single step using a counter-rotating twin screw extruder with compatibilizer concentrations 0, 2, 4, 6, 8, and 10phr, respectively. Standard test samples were prepared by injection molding process. The resulting compatibilized blends were characterized by tensile, flexural, and impact tests. The results showed improvements in mechanical properties of the blends due to the in situ polymerization reaction between the ester groups of PET and the maleic anhydride (MAH) during melt extrusion. The incorporation of 4phr PP-g-MAH in the blends resulted in the highest tensile and flexural strength, while no significant improvements in Young's modulus were observed for both compatibilized blends. The maximum impact strength of the blends was obtained at 8phr of SEBS-g-MAH. Improvement of impact strength of the blends may be attributed to the elastomeric nature of the SEBS-g-MAH while greater improvement recorded for tensile and flexural strength is likely to be due to the affinity between PP-g-MAH with PP of the blend. Scanning electron microscopy shows the addition of PP-g-MAH and SEBS-g-MAH compatibilizers into the blends promote a better dispersion of PP into PET matrix.