Morphology Control and Stabilization in Immiscible Polypropylene and Polyamide 6 Blends with Organoclay

Abstract

In the current study, 70/30 (w/w) polypropylene (PP)/polyamide 6 (PA6)/organoclay ternary blends were prepared by melt mixing in three different blending sequences, i. e., organoclay premixed with PA6 and then mixed with PP (S1 blending sequence), organoclay premixed with PP and then mixed with PA6 (S2 blending sequence), and organoclay, PA6 and PP mixed simultaneously (S3 blending sequence). The effects of organoclay on the phase morphologies, rheological properties and mechanical properties of the blends are examined to reveal the role of organoclay in these immiscible blends. First of all, the dispersion and distribution of organoclay is investigated using XRD and TEM techniques. The organoclay is exfoliated and distributed in the dispersed PA6 phase as well as at the interface between PA6 and PP. Interestingly, more organoclay sheets are observed at the interface when the S2 or S3 blending sequences are utilized. From the SEM images, it is clear that the domain size of the PA6 phase decreases remarkably after introducing organoclay into the PP/PA6 blends. Two different rheological protocols are applied to probe the effect of organoclay on the morphology of the blend by in-situ monitoring the morphological evolution. The rheological results reveal that the phase morphology of the PP/PA6 blends remains relatively stable during shear for a wide range of shear rates when 1.0 wt% organoclay has been added. For the blends with a relatively high clay loading (5.0 wt%), a characteristic and pronounced “plateau” is observed in the low frequency range of the G′-ω curves, which indicates the presence of a percolating network of clay nanosheets. From the mechanical measurements, we find that the tensile strength of the blends increases slightly first and then declines dramatically with increasing organoclay content. Moreover, the elongation at break drops sharply as the organoclay content increases. In summary, it is clear that the organoclay can effectively reduce the domain size of the dispersed PA6 phase and stabilize the phase morphology in shear flow. However, the mechanical properties of the blends are not really improved by clay addition, even though a cocontinuous morphology with a percolated clay network was generated.