Mechanical Properties and Deformation Mechanism of Bimodal-Rubber-Particle-Toughened Polyphenylene Ether/Polystyrene Blends

A core–shell polybutadiene-graft-polystyrene (PB-g-PS) copolymer with a core–shell ratio of 70/30 (wt/wt) was synthesized by redox-initiated emulsion graft polymerization. Compatible polymers of polyphenylene ether (PPE) and polystyrene (PS) blend were toughened by the addition of high-impact polystyrene (HIPS) and the PB-g-PS copolymer, and the content of PB rubber in the whole matrix was kept at 17.4 wt %. The influence of the matrix composition and synergistic toughening effect of different-sized rubber particles on the mechanical properties, morphology, and deformation mechanism of HIPS/PPE/PS/PB-g-PS blends was investigated. The results showed that sub-micrometer-sized PB-g-PS core–shell particles (318 nm) and large-sized HIPS rubber particles (1∼5 μm) had an excellent synergistic toughening effect, which could significantly improve the toughness of the PPE/PS blends, from 47 to 672 J/m. The impact strength, elongation at break, tensile strength, and degree of stress whitening of the blends increased with the increase of PPE content in the matrix, and when the content of PPE increased from 10 to 20 wt %, the brittle–ductile transition occurred. Transmission electron microscopy and scanning electron microscopy results showed that when the PPE content in the blends was low, the PB-g-PS copolymers would agglomerate and be unevenly distributed in the matrix, and the deformation mechanism of the blend was multiple crazing. With increased PPE content, the distribution of the PB-g-PS copolymers was significantly improved, and the deformation mechanism combined crazing and shear yield. With the further increase of PPE content, the rubber particles in the matrix became extensively elongated, and the deformation mechanism was wholly transformed to shear yield.