Study on Morphology and Viscoelastic Properties of PP/PET/SEBS Ternary Blend and their Fibers N. Mostofi, H. Nazockdast, H. Mohammadigoushki Polymer Engineering Department, Amirkabir University of Technology, Tehran, Iran Received 10 August 2008; accepted 22 March 2009 DOI 10.1002/app.30612 Published online 17 August 2009 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The morphology development of polypropyl- ene (PP)/polyethylene terephthalate (PET)/styrene-ethylene- butylene-styrene (SEBS) ternary blends and their fibers were studied by means of scanning electron microscopy (SEM) in conjunction with the melt linear viscoelastic measurements. The morphology of the blends was also predicted by using Harkin’s spreading coefficient approach. The samples vary- ing in composition with PP as the major phase and PET and SEBS as the minor phases were considered. Although SEM of the binary blends showed matrix-dispersed type morphol- ogy, the ternary blend samples exhibited a morphological feature in which the dispersed phase formed aggregates con- sisting of both PET and SEBS particles distributed in the PP matrix. The SEM of the blend samples containing 30 and 40 wt % of total dispersed phase showed an agglomerated structure formed between the aggregates. The SEM of the PP/PET binary fiber blends showed long well-oriented microfibrils of PET whereas in the ternary blends, the micro- fibrils were found to have lower aspect ratio with a fraction of the SEBS stuck on the microfibril fracture surfaces. These results were attributed to a core-shell type morphology in which the PET and SEBS formed the core-shells distributed in the matrix. The melt viscoelastic behavior of the ternary blends containing less than 30 wt % of the total dispersed phase was found to be similar to the matrix and binary blend samples whereas the samples containing 30 and 40 wt % of dispersed phases exhibited a pronounced viscosity upturn and nonterminal storage modulus in low frequency range. These results were found to be in good agreement with the morphological results. V V C 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 3737–3743, 2009 Key words: ternary blends; core-shell morphology; microfibrillar morphology; viscoelastic properties INTRODUCTION The blending of two or more different polymer has widely been used as a flexible and economical tech- nique for production of polymeric materials with desirable properties. During the last two decades, a considerable number of researches have been conducted toward multicomponent polymer blends consisting of at least three or more immiscible poly- mers. A large range of phase morphologies can be generated, which could directly influence the whole set of properties. 1–5 The effect of different parame- ters on the morphology and properties of ternary polymer blends have been studied by many researchers. Hobbs et al. 1 used Harkin’s spreading coefficient concept 6 to predict the phase morphology of different ternary blends. For a ternary system with A as the continues phase and B and C as the dispersed phases, the spreading coefficients k BC and k CB are defined as: k BC ¼ c AC  c AB  c BC (1) k CB ¼ c AB  c AC  c BC (2) where c ij is the interfacial tension between i and j phases. A positive value of k BC and negative value of k CB will lead to encapsulation of C phase by the B phase. If k BC and k CB are both negative, two minor components form separate dispersed phases. In the case, both k CB and k BC are negative and k AC is posi- tive one phase will partially encapsulate the other phase. 7 Guo et al. 8 also developed a model to predict phase morphologies of multiphase polymer blends based on minimizing the relative interfacial free energy (RIE). According to these, Model 3 morpholo- gies namely as: (1) two minor Phases B and C dis- perse separately (B þ C). (2) Phase B encapsulates Phase C (B/C). (3) Phase C encapsulates Phase B (C/ B) are available. The interfacial free energy of each of these morphologies are expressed as follows: G ¼ X i n i l i þ X i6¼j A i c ij (3) G BþC ¼ðn 1 l 1 þ n 2 l 2 þ n 3 l 3 ÞþðA B BþC c AB þ A C BþC c AC Þ (4) G B=C ¼ðn 1 l 1 þ n 2 l 2 þ n 3 l 3 ÞþðA B B=C c AB þ A C B=C c BC Þ (5) Journal of Applied Polymer Science, Vol. 114, 3737–3743 (2009) V V C 2009 Wiley Periodicals, Inc. Correspondence to: H. Nazockdast (nazdast@aut.ac.ir).