Morphology of PP/COC composites: effects of shear rate and organoclay partitioning

TL;DR

This study investigates how shear rate and organoclay influence the morphology of PP/COC composites, revealing that organoclay partitioning significantly affects droplet deformation and fibril formation, with implications for material properties.

Contribution

It provides new insights into the effects of shear rate and organoclay partitioning on the microfibril morphology of PP/COC composites, highlighting the role of kinetic parameters.

Findings

Organoclay localization affects droplet size and fibril diameter.

High elasticity of COC promotes fibrillation despite viscosity ratio.

Organoclay inside COC droplets alters deformability and morphology.

Abstract

The blends and hybrid nanocomposites of polypropylene - cycloolefin copolymer were prepared by a twin-screw extruder followed by microfibril formation using a single screw extruder. The effects of shear rate and organoclay on the morphology of polypropylene - cycloolefin copolymer (PP/COC - 80/20 wt. %) blends were studied by using a combination of rheological measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that although the viscosity ratio of PP/COC blend was unfavorable for COC droplet deformation, the COC phase was converted to finely dispersed fibrils in PP matrix. This could be asserted to the high elasticity of the COC droplets that suppressed the droplet breakup in the favor of fibrillation process. The high glass transition temperature of COC (140 degree centigrade) could also assist restoring the generated microfibril morphology upon cooling. The experimental results also depicted that the droplet deformation and microfibril formation of PP/COC/organoclay nanocomposites mainly depend on the organoclay partitioning, which could be controlled predominantly by kinetic parameters. While the localization of organoclay in the PP matrix resulted in smaller COC droplets and fibrils with smaller diameter, the presence of organoclay inside COC droplets reduced the droplet deformability, leading to fibrils with larger diameter.