Compatibilization of styrene-butadiene-styrene block copolymer in polypropylene/polystyrene blends by analysis of phase morphology

Effect of compatibilization of styrene-butadiene-styrene (SBS) block copolymer in polypropylene/ polystyrene (PP/PS) blends was studied by means of small angle X-ray scattering (SAXS) and scanning electron microscope (SEM). According to SAXS, a certain amount of SBS was located at the interface in all the analyzed samples, forming the relatively thicker interface layer penetrating into homopolymers, and the thickness of the interface layer was quantified in terms of Porod light scattering theory. The incorporation of SBS into PP/PS blends resulted in a decrease in domain size following an emulsification curve as well as an uniform size distribution, and consequently, a fine dispersion of PP domains in the PS matrix. This effect was more pronounced when the concentration of SBS was higher. A critical concentration of SBS of 15% above which the interface layer approaches to saturation and domain size attains a steady-state was observed. Further, the morphology fluctuation of unetched fracture surface of umcompatibilized and compatibilized blends was analyzed using an integral constant Q based on Debye-Bueche light scattering theories. Variation of Q as a function of the concentration of SBS showed that, due to the penetrating interface layer, adhesion between phases was improved, making it possible for applied stress to transfer between phases and leading to more uniform stress distribution when blends were broken; accordingly, a more complicated morphology fluctuation of fracture surface appeared. (C) 2006 Wiley Periodicals, Inc. J Appl Polyrn Sci 103: 365-370, 2007