The role of the MMT on the morphology and mechanical properties of the PP/PET blends

Polypropylene/poly(ethylene terephthalate) blends containing montmorillonite (MMT) were prepared using a twin screw extruder followed by injection molding. The MMT dispersion was evaluated by X-ray diffraction and transmission electron microscopy. The results showed a better dispersion of the MMT when maleic anhydride grafted polypropylene (PP-MA) was used. The clay was preferentially situated in the PP/PET interphase and in the PET phase. The effect of the addition of the PP-MA and MMT on the morphology and mechanical properties was also evaluated. Scanning electron microscopy revealed the presence of elongated PET domains and fibers, besides the spherical shapes. The mechanical properties were studied through tensile and impact tests. The yield stress, Young modulus, and elongation at break increased when MMT and PP-MA were used without impair the impact strength. The dynamic mechanical properties were also evaluated. Higher E′ values were observed for PP/PET/PP-MA/MMT, and a shoulder in the E′′ curve, in intermediate Tg’s of the pristine polymers, suggests the formation of an interphase between the two polymer domains.