Morphology and properties of compatibilized PP/PET melt spun fibers

This work provides a study on the influence of a rubbery compatibilizer on the morphology and on the physical properties of polypropylene (PP)/polyethylenetherephthalate(PET) melt spun fibers at different hot draw ratios. In particular, a sample of SEBS copolymer grafted with maleic anhydride was used as compatibilizer. Both the uncompatibilized PP/PET blend and the compatibilized one were prepared by melt compounding in a counter-rotating twin-screw extruder. The materials have been characterized from a rheological, morphological and mechanical point of view. The addition of the compatibilizer increased the viscosity in shear flow of the uncompatibilized blend, and significantly improved the rheological behavior in non-isothermal elongational flow of the blend. The improved and more refined morphology of the compatibilized blend strongly influenced the mechanical behavior of the isotropic sheets of binary blend. In particular, the elongation at break dramatically increased, while modulus and tensile strength decreased because of the presence of the rubbery phase. The anisotropic fibers obtained by melt spinning showed a different behavior. Indeed, the presence of the compatibilizer did not lead to any significant difference in the mechanical properties if compared with those of the binary blend. Although the average diameter of the microfibrils of the dispersed phase in the compatibilized blend generated during the hot drawing was much smaller that of the microfibrils of the same particles of the uncompatibilized blend, the mechanical properties remained almost unchanged. This behavior was mainly attributed to smaller diameter of the droplets of the dispersed phase of the ternary blend that gives rise to shorter fibers. Finally, a brittle-ductile transition at low values of the draw ratio was observed for the blends.