Effects of processing conditions on the phase morphology and mechanical properties of highly toughened polypropylene/polybutylene terephthalate (PP/PBT) blends

Abstract

The effects of processing conditions were studied on the phase morphology and mechanical properties of the polypropylene/polybutylene terephthalate (PP/PBT) blends toughened by styrene-butadiene triblock copolymer thermoplastic elastomers. Highly toughened PP-based blends that exhibited increased impact strength (seven- to ninefold) and little loss of stiffness (< 15%) in comparison with neat PP resin were successfully developed through manipulation of the dispersion state and interfacial interactions in the blend systems. A combination of core–shell and separately dispersed morphologies was predicted theoretically and identified by scanning electron microscopy (SEM) observations. It was found that the mixing order and intensity (screw speed) significantly affected the dispersion state of the modifier domains in the blends, which in turn, profoundly influenced the mechanical performance of the resulting blends. The phase interactions and crystalline structure of the blends were examined by DMTA and DSC analyses. The results indicated that the two-step melt blending approach with properly selected mixing parameters was more effective in producing toughened PP/PBT blends with superior impact resistance than the one-step melt mixing procedure. The toughened blends revealed enhanced crystallization behavior in the form of higher cold-crystallization temperature of the PP matrix and larger crystallinity degree over the neat PP resin. Fractography analysis showed numerous voids in the matrix and around the dispersed PBT domains which affected the energy absorbing mechanism during impact loading. Graphic abstract: [Figure not available: see fulltext.] © 2021, Iran Polymer and Petrochemical Institute.