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Phase morphology and mechenical properties of iPP/aPS blends compatibilized by SEP block copolymer

Supermolecular structure and phase morphology of the ternary isotactic polypropylene/atactic polystyrene/ poly(styrene-b-ethylene-co-propylene) (iPP/aPS/SEP) compression molded blends with 100/0, 90/10, 70/30, and 50/50 iPP/aPS weight ratios and with different amounts of added SEP compatibilizer was studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and wide-angle X-ray diffraction (WAXD). OM revealed that all samples exhibited uniform morphological texture without skin-core effect except iPP/aPS/SEP blends with 50/50 weight ratio of iPP/aPS which reveal cocontinuous morphology as confirmed also by SEM. SEP significantly reduces dispersed aPS particles size enabling spherulitization in iPP matrix to be well-developed. Also, iPP spherulites in ternary blends with 90/10 iPP/aPS weight ratio became larger in comparison to the pure iPP. TEM revealed that SEP formed continuous interface layer around the dispersed aPS particles even when only 2.5 wt.-% of SEP was added. Particles size distribution is didstinctly bimodal. When SEP content is increased to 10 wt.-% dispersed aPS particles start to form aggregates joining together smaller and bigger particles. Additionally, both amorphous components (aPS and SEP) influenced crystallization process of iPP matrix and changed, consequently, its final supermolecular structure. SEP compatibilizer does not strongly affect crystallite orientation (its effect has even opposite reorientation character). The increase of the crystallite sizes, which is obviously more affected by the addition of aPS than by the addition of SEP, seems to be influenced by the solidification effect rather than by the phase morphology of the blends. Even 2.5 wt.-% of SEP added to iPP/aPS blends can improve the notched impact strength, elongation at yield, and elongation at break compared to non-compatibilized iPP/aPS blends. 10 wt.-% of SEP compatibilizer converted the brittle iPP/aPS blend to quite resistant polymeric material, especially in the case of iPP/aPS weight ratio 90/10. In the case of iPP/aPS weight ratio 50/50 no significant improvements in terms of better mechanical properties was obtained probably due to the cocontinuous phase morphology of wsuch blends where the compatibilizer efficiency is reduced because the interphase surface became too large.

mechanical properties; phase morphology; polymer blends

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