The inherent shortcomings of polylactide (PLA) including brittleness, low glass transition temperature, and melt strength during processing were addressed through a facile melt blending of PLA with polybutadiene-g-poly­(styrene-co-acrylonitrile) (PB-g-SAN) core–shell impact modifier and poly­(methyl methacrylate) (PMMA). Highly tough PLA-based ternary blends with drastically enhanced glass transition temperature (≈ 21 °C) and melt strength were successfully prepared. The effect of PMMA content (ranging from 0 to 30 wt %) on the phase miscibility, morphology, mechanical properties, thermal behavior, rheological properties, and toughening mechanisms of PLA/PB-g-SAN/PMMA blends with 30% PB-g-SAN was systematically investigated. It was found that PMMA can effectively tune the interfacial interactions, phase morphology and performance of incompatible PLA/PB-g-SAN blend owing to its partial miscibility with PLA matrix and miscibility with SAN shell of PB-g-SAN, as evidenced by DMTA analysis. Increase in PMMA content promoted the phase adhesion and dispersion state of PB-g-SAN terpolymer in the blends and highly toughened blends were achieved which showed incomplete break of impact specimen. The significant effect of phase morphology on imparting tremendous improvement in impact toughness was clarified. The maximum impact strength (about 500 J/m), elongation-at-break and glass transition were obtained for ternary blend with 25% PMMA. The PLA crystallinity was gradually suppressed in ternary blends upon progressive increase in PMMA content. Rheological studies showed solid-like behavior with enhanced viscosities for ternary blends. Micromechanical deformations and toughening mechanisms were studied by post-mortem fractography. Massive matrix shear yielding was found as the main source of energy dissipation triggered by suitable interfacial adhesion and microvoid formation.

The fracture toughness and deformation mechanisms of un-vulcanized and dynamically vulcanized polypropylene/ethylene-propylene-diene terpolymer (PP/EPDM) blends and polypropylene/ethylenepropylene-diene terpolymer/multi walled carbon nanotube (PP/EPDM/MWCNT) blend-nanocomposites were investigated using the essential work of fracture (EWF) methodology followed by detail microscopy analysis. The effect of maleic anhydride grafted polypropylene (PP-g-MA) on the morphology and fracture toughness of the multicomponent system was also investigated. It was found that both the dynamic vulcanization and compatibilization using PP-g-MA increased the fracture toughness of blend and blend nanocomposite systems. The results illustrated that the dominant fracture mechanism related to the EPDM dispersed phase in un-vulcanized samples was the formation of dilatation bands due to cavitation and/or debonding of dispersed EPDM rubber particles. In vulcanized samples, developing of dilatation shear bands, resulting from repeated particle debonding, was suppressed and the formation of nanovoids and cavitation in rubber particles led to promoting shear yielding of adjacent matrix and dense plastic deformation. Incorporation of MWCNT into the PP/EPDM blend reduced the essential work of fracture ( e w ) and enhanced non-essential work of fracture ( p w β ). In the blend-nanocomposites, two mechanisms induced by MWCNT were observed. While large MWCNT aggregates acted as favor sites for crack initiation, the individual MWCNT impregnated fibrils arrested the crack propagation. The presence of PP-g-MA diminished negative effect of MWCNT and further enhanced its positive effect through decreasing the size of large aggregates (favor sites to initiate large cracks) and increasing in the number of dispersed individual MWCNT ropes (increase potential of impregnated fibrils formation), respectively.

A specific “percolated/interconnected” morphology of PA6/EPDM-g-MA core–shell modifier particles in PP matrix resulted in a tremendous enhancement of impact strength. Fracture behavior and toughening mechanisms were studied and proposed.

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Attempts were made to study the effect of reactive compatibilization via Friedel-Crafts alkylation reaction, using AlCl 3 as a catalyst, on rheology, morphology, and mechanical properties of polyethylene/polystyrene (PE/PS) blends. The results of linear viscoelastic measurements in conjunction with the results of the mixing torque variation indicated that PS showed much more degradation than that of PE in the presence of AlCl 3 . It was also found that while for PE-rich blends, the viscosity, and storage modulus increased by reactive compatibilization, they decreased for PS-rich blends. The variation of viscosity and storage modulus for 50/50 blend was found to be dependent on frequency ranges showing the competitive effects of PE-g-PS copolymer formation and PS degradation. The results of morphological studies showed that reactive compatibilization decreased the particle size and particle-size distribution broadness because of in situ graft copolymer formation. Reactive compatibilization enhanced the tensile strength and elongation at break for PE-rich blends. It was demonstrated that there is a close interrelationship between rheology, morphology, and mechanical properties of reactive compatiblized PE/PS blends. It was also demonstrated that rheological behaviors have a reliable sensitivity to follow the structural and morphological changes during compatibilization process, so that, those information can be used to predict the morphology as well as mechanical properties of the blends.