Melt viscosity, elasticity, and morphology of reactively compatibilized polyamide 6/styrene-acrylonitrile blends in shear and elongation

The melt rheology of reactively compatibilized polyamide 6/styrene-acrylonitrile (PA 6/SAN) blends was studied in linear viscoelastic shear oscillations, simple elongation to a large stretch ratio, and subsequent recovery. In addition, we examined and quantified the blend morphology and the flow-induced changes of the morphology. Three PA 6/SAN blends with different composition ratios of PA 6 and SAN (70/30, 50/50, 30/70) were prepared. Our experiments reveal that the asymmetric properties of the compatibilized interface strongly influence the rheological and morphological properties of the blends. The linear viscoelastic properties were discussed by applying the fractional Zener model. In particular, the data of the PA 6/SAN 30/70 blend indicate that an elastic network between neighboring PA 6 domains was formed. In simple elongation, the transient elongational viscosity of this blend exceeded the linear viscoelastic prediction of the fractional Zener model, whereas for the PA 6/SAN 70/30 blend the theoretical prediction of the elongational viscosity agreed well with the experimental data. The recovered stretch of all blends was much larger than the recovered stretch of pure PA 6 and SAN. This increase of elasticity was caused by the interfacial tension driven recovery and by the effects of reactive compatibilization. The morphological analysis showed that during elongation the phase domains of all blends were strongly stretched and retracted to an isotropic shape during recovery.