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Author(s)

Paulo Henrique Pierin Macaubas

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2003-08-20

Examining board members

Nicole Raymonde Demarquette; Maria Regina Alcantara; Reinaldo Giudici; Mirabel Cerqueira Rezende

• Advisor: Nicole Raymonde Demarquette

Abstract

In this work, the linear and nonlinear viscoelasticity behavior of PP/PS blends, compatibilized or not with SEBS was studied. For the study of the linear viscoelasticity small amplitude oscillatory shear, and creep tests were carried out using a stress controlled rheometer. The possibility of extension of the linear viscoelasticity range obtained from direct measurements was studied using time-temperature superposition principle, and the relationship between relaxation and retardation spectra obtained from creep-recovery tests. The linear viscoelasticity behavior was also compared to theoretical models, which predict the dynamic behavior of polymer blends under moderate shear flows. The nonlinear viscoelasticity behavior was studied using stress relaxation tests carried out in a strain controlled rheometer. Steady shear tests using a strain controlled rheometer at low shear rates, and a sliding plate rheometer at high shear rates were also carried out for different shear histories. The behavior of shear stress was correlated to the morphology evolution both experimentally, by scanning electron microscopy, and theoretically, using nonlinear emulsion models. Also, a comparison between the predicted morphology for polymer blends under deformation and the one obtained from scanning electron microscopy was carried out. The results from the linear viscoelasticity showed that the application of time-temperature superposition was valid only for concentrations ofSEBS corresponding to the saturation of the PP/PS blend interface. A stress independent behavior of shear compliance was not observed for the blends under creep tests. A comparison between the experimental and theoretical linear viscoelasticity behavior allowed the calculation of interfacial tension for a PP/PS compatibilized with SEBS. ) The results from the nonlinear viscoelasticity behavior showed that separability between time and strain was not obeyed for the blends studied. The morphology evolution during steady shear tests was observed by overshoots and undershoots features, dispersed phase orientation, deformation, breakup and coalescence when the shear rate was varied. Modeling of the nonlinear viscoelasticity behavior of the blends allowed the study of dispersed phase breakup and coalescence, according to the flow conditions and addition of SEBS. The comparison of the morphology of sheared blends between theoretical prediction and scanning electron microscopy observation showed a significant discrepancy. (AU)