Correlated X-ray Ptychography and Fluorescence Nano-Tomography on the Fragmentation Behavior of an Individual Catalyst Particle during the Early Stages of Olefin Polymerization

Abstract

A combination of X-ray ptychography and X-ray fluorescence tomography (XRF) has been used to study the fragmentation behavior of an individual Ziegler-Natta catalyst particle, ∼40 μm in diameter, in the early stages of propylene polymerization with submicron spatial resolution. The electron density signal obtained from X-ray ptychography gives the composite phases of the Ziegler-Natta catalyst particle fragments and isotactic polypropylene, while 3-D XRF visualizes multiple isolated clusters, rich in Ti, of several microns in size. The radial distribution of Ti species throughout the polymer-catalyst composite particle shows that the continuous bisection fragmentation model is the main contributor to the fragmentation pathway of the catalyst particle as a whole. Furthermore, within the largest Ti clusters the fragmentation pathway was found to occur through both the continuous bisection and layer-by-layer models. The fragmentation behavior of polyolefin catalysts was for the first time visualized in 3-D by directly imaging and correlating the distribution of the Ti species to the polymer-catalyst composite phase.