Microstructural evolutions of LDPE/PA6 blends by rheological and rheo-optical analyses: Influence of flow and compatibilizer on break-up and coalescence processes

In this paper we investigate the relationships between flow and morphology in immiscible diluted non-Newtonian (LDPE and PA6) blends. Both rheological and rheo-optical techniques have been used. The effect of a steady shear flow on the blend microstructure has been studied at various shear rates. Moreover, the effects of a compatibilizing agent on rheology and morphology have been analysed. The compatibilizer causes decrease of average drop sizes and stabilization of the blend morphology during a steady shear flow. An attempt to relate the evolution of the volume-average radius with flow has been carried out by following the approach generally pursued for Newtonian polymer blends. The rescaling of both the capillary number and the viscosity ratio by using the shear-rate-dependent viscosity of blend constituents allows to roughly estimate the shear rate wherein severe drop break-up phenomena occur for the uncompatibilized system. Conversely, quantitative discrepancies between experimental data and theoretical expectations have been found for compatibilized blend. The coarsening behaviour in the early stages of an annealing process at rest has been studied, and simple model has been proposed to describe the volume average drop radius growth rate. The coalescence suppression detected for the compatibilized blend could be due to the shielding effect related to the presence of the copolymer layers at the interface between the phases.