The Effect of Mixer Type and Processing Conditions on the Morphology of Polyamide/Polypropylene Blend

Abstract

The effect of mixer type and processing conditions on the morphology of immiscible binary polyamide/polypropylene blend was studied. Blends were prepared in seven different mixers operating at various screw speeds. Changing the screw speed altered the shear stress and mixing intensity applied to the melt, and also the viscosity ratio. Average panicle sizes of the dispersed phase (PP) and the particle size distributions were determined for extruded and for subsequently injection moulded blends. The number average particle size level achieved in the melt blending was fairly well transferred to the injection moulded blend although the size distribution was broadened after the injection moulding due to the formation of both small (≍1 μm) and large (>10 μm) particles. The morphology of the skin region was very different from that of the core region in both the extruded and the injection moulded blends. The dispersed phase droplet size was dependent on screw speed to some degree. This dependency was greatest for the single screw extruder. Particle size correlated strongly with shear stress, specific mechanical energy input, and mixing intensity of the mixer. Shear stress, we were led to conclude, is a more important factor in controlling the morphology than the shear-rate-dependent viscosity ratio. Mechanical properties of the blends were poor due to weak adhesion at the interface of the blend components. Additionally, we found that melt blending promoted a better and more homogeneous dispersion in the injection moulded blend.