Morphological analysis of high-impact polypropylene using X-ray microCT and AFM

• The 3D distribution of pores and EPR zones was visualized by microCT.
• AFM phase imaging shows fine EPR network spread over entire hiPP particles.
• Simultaneous AFM phase and height imaging determines EPR covering particle surface.
• EPR does not cover whole particle surface at medium-degree of coverage.
• The EPR squeezed out of the microtomed surface causes artifacts on AFM images.

Detailed visualization and understanding of high-impact polypropylene (hiPP) particle morphology and its evolution on the scale of entire particles is important for obtaining the required mechanical and optical properties of this material and for the quantitative description of mass transport in hiPP particles. Shape and size of hiPP particles as well as the spatial distribution of pores, PP homopolymer and ethylene-propylene rubber (EPR) phases in individual particles is visualized by micro-computed tomography (microCT) and atomic force microscopy (AFM) techniques. The morphology of each hiPP particle depends on many factors including catalyst system, the initial pore structure of porous catalyst and homopolymer particles, reactor conditions and particle history. These factors affect the required content, the constitution and the spatial distribution of EPR phase. To understand particle morphology and its evolution in a quantitative way we need a high-quality morphology data. The presented results include the AFM visualization of rubber layer on the surface of hiPP particles, the microCT visualization of not only porous homopolymer PP particles but also of large rubber domains in hiPP particles and the AFM mapping of the fine networked structure of EPR rubber and pores in hiPP particles.

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