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Author(s)

Cássia Alves de Freitas

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2005-04-18

Examining board members

Nicole Raymonde Demarquette; Reinaldo Giudici; Adriana Martinelli Catelli de Souza

• Advisor: Nicole Raymonde Demarquette

Abstract

The properties of the ternary polymer blends, as well as of any polymer blends depend on their morphologies. In the case of ternary polymer blends, the morphology of the materials can be predicted through using the values of interfacial tension between the components of the blend. In this work, ternary polymer blends PP/PS/PMMA (polypropylene, polystyrene, polimethylmethacrylate) compatibilized with graft copolymer PP-g-PS and PP-g-PMMA, and triblock copolymer SEBS (styrene-ethylenebuthylene-styrene) were studied. To predict the morphology of the blends studied, the interfacial tension between PP/PS and the influence of the addition of compatibilizer on the interfacial tension between those two polymers was evaluated. The interfacial tension between PP/PMMA and PS/PMMA, as well as the influence of the addition of compatibilizer on the value of interfacial tension among these polymers, necessary to predict the morphology of the ternary polymer blends, were taken from the literature. The interfacial tensions for compatibilized and non compatibilized PP/PS blends were evaluated using the rheological method that consists of analyzing the rheological behavior of the blend when submitted to small amplitude oscillatory shear. The interfacial tension can be inferred from the rheological measurements fitting the rheological data to emulsion models or analyzing the relaxation spectrum of the blends that presents relaxation times that are directlyproportional to the value of interfacial tension between the polymers forming the blends. To infer the interfacial tension between PP and PS a 80/20 blend was used. The concentration of copolymer added to the blend varied from 2 to 20% with respect to the dispersed phase. The composition of the ternary polymer blend was PP/PS/PMMA (80/15/5) and the copolymer concentration was of 10% with respect to the dispersed phase, depending of the copolymer. ) The morphologies of the ternary polymer blends were predicted using the phenomenological models that predict the morphology of the blend as a function of the interfacial tension between the components of blend (spreading coefficient, free energy minimization and normal tensions). The morphologies were studied experimentally by scanning electron microscopy (SEM). The evolution of the morphology as a function of time of processing was also studied. The rheological emulsion model did not fit the rheological behavior of the binary blends studied most likely due to coalescence of the drops of the dispersed phase during small amplitude oscillatory shear. The relaxation spectra of the non compatibilized blends and of the blends compatibilized using graft copolymers presented three relaxation times whereas the relaxation spectrum of the blends compatilized with SEBS presented four relaxation times. Two of these relaxation times corresponded to the pure phases of the blend, on to the relaxation of the shape of the dispersed phase when sheared (third relaxation time) and to the process of relaxation of the compatibilizer (fourth time). The values of those relaxation times were used to evaluate the interfacial tension between PP/PS and the influence of the addition of the compatibilizers on the interfacial tension between those polymers. It was observed that the interfacial tension decreases with the increase of the copolymer concentration. The values of interfacial measured in this work as well as the ones from the literature were used to predict the morphology of the ternary polymer blends. A core-shell morphology with PS as shell and PMMA as core was observed experimentally. All the phenomenological models corroborated the experimental results, except for the case of compatibilization with PP-g-PMMA. ) Most likely due to the fact that they do not take into consideration the composition of the ternary blend and due to the imprecision in the values of interfacial tension. The results of evolution of morphology showed that in the initial instants of the processing, PMMA is at the surface of PS. With time PMMA starts to be encapsulated by PS, although it still continues in the surface of the PS at the end of the mixture. (AU)