2007-03-19
10:45 at HCI J 574

Melt flow properties of reactively compatibilized blends of polyamide 6 and styrene-acrylonitrile: Linear viscoelasticity, melt elongation, and morphology

Christian Sailer

Polymer Physics, Department of Materials, ETH Zürich

Reactive compatibilization of immiscible polymer blends has become a state of the art technology and is widely applied for various commercial blends. For example, the reactive coupling of polyamide 6 and styrenic polymers by reactive agents containing maleic anhydride is currently intensively investigated. In this work, the influence of reactive compatibilization on the melt rheology and morphology of polyamide 6/styrene-acrylonitrile (PA 6/SAN) blends was studied. We investigated the rheological behaviour in linear viscoelastic oscillatory shear flow, simple elongation and recovery after simple elongation. Furthermore, the blend morphology and the flow-induced changes of the morphology were examined by atomic force microscopy and quantified. Before blending the reactive agent, a styrene-acrylonitrile-maleic anhydride terpolymer (SANMA), was added to the SAN phase. Then three PA 6/SAN blends with different composition ratios (70/30, 50/50, 30/70) were prepared. Reactive compatibilization strongly influences the linear viscoelastic behaviour of all blends. In order to describe the linear viscoelastic data phenomenologically, the fractional Zener model was applied. The experimental data of the PA 6/SAN 30/70 blend gave strong evidence that an elastic network between neighbouring PA 6 domains was formed. In simple elongation, the transient elongational viscosity of this blend exceeded the linear viscoelastic prediction and showed strain hardening. On the contrary, for the PA 6/SAN 70/30 blend the theoretical prediction of the elongational viscosity agreed well with the experimental data. The morphological analysis revealed that during elongation the phase domains of all blends were considerably deformed. During recovery, the stretched phase domains retracted back to an isotropic shape. In addition, all blends showed a significantly larger recovered stretch compared to the blend components. The differences in the rheological behaviour between the PA 6/SAN 30/70 blend and the PA 6/SAN 70/30 blend were explained by the asymmetric properties of the compatibilized interface which stems from the asymmetric molecular architecture of the in-situ generated SANMA multi-grafted PA 6 chains.