Polymer blend de-mixing and morphology development of immiscible polymer blends during tube flow

This work is an investigation of morphology and de-mixing of polymer blends during melt flow through a tube. Morphology is the relative size, shape and location of each distinguishable phase present in a polymer blend. De-mixing is the shear-induced migration of different types of polymers away from each other during the flow. The ability to tailor de-mixing during extrusion can potentially result in a new family of plastics waste recycling processes with mixed waste entering an extruder and separate streams of different polymer types leaving it. Also, control of morphology development can lead to the formation of layered structures without the need for two or more extruders and co-extrusion. This work is directed at elucidating morphology development and de-mixing of polymer blends in the most simple process design: melt flow through a tube. Shear-induced migration was quantitatively shown in various polyethylene-polypropylene, polypropylene-nylon 6 and polyethylene-nylon 6 blends. The migration observed was in accord with the hypothesis that the system tends to minimize its rate of energy dissipation for a fixed flow rate. The ratio of the viscosity of the dispersed phased to that of the continuous phase greatly influenced the morphology of polypropylene-nylon 6 and polyethylene-nylon 6 blends: a droplet-dispersed phase structure occurred at a high viscosity ratio, whereas a multi-layer structure resulted at viscosity ratios near unity. Shear-induced deformation and coalescence contributed to formation of the multi-layer structure.