Study on phase structure and properties of the toughened blends of polypropylene–polybutylene terephthalate (PP/PBT)

Abstract

The impact of styrene–butadiene–styrene (SBS) and maleated styrene–ethylene–butylene–styrene (SEBS-g-MA) weight ratios was studied on the microstructure and ultimate performance of PP/PBT/(SBS + SEBS-g-MA) (70/15/15) blends. Morphological observations revealed a gradual change in the dispersions state of modifier domains from isolated phases to stack formation and then to encapsulation morphology as the SEBS-g-MA proportion was steadily increased. This was accompanied by improved blend homogeneity and finer dispersion of PBT domains (a drop in particle size from ~ 3 μm to ~ 0.3 μm) with increase of SEBS-g-MA concentration in the rubbery fraction of the blend. The alteration of morphology was manifested in macroscopic mechanical properties of the blends. Young’s modulus declined (~ 20%) whereas yield stress (~ 17%), tensile strength (~ 16%), and tensile ductility (~ 210%) were steadily enhanced with increase of SEBS-g-MA concentration in the rubbery fraction of the blend. The notched Izod impact strength also monotonically rose (~ 150%) as SBS:SEBS-g-MA weight ratio was reduced. The improvement of mechanical properties of the blends was attributed to improved blend compatibility and interfacial adhesion followed by more homogeneous mixing state between blend components upon progressive replacement of SBS component with SEBS-g-MA phase. The crystalline- and phase structure of the blends were studied by DCS and DMTA analyses, respectively and correlated with the blend composition and morphology. The impact-fractured surface of the toughened blends was examined and the deformation mechanisms were clarified. Increased resistance against particle debonding along with the development of microvoids induced by rubber phase was responsible for the enhanced impact fracture energy of these blends. Graphic abstract: [Figure not available: see fulltext.] © 2021, Iran Polymer and Petrochemical Institute.