Analysis helps to understand fragmentation of catalyst particles in ethylene polymerisation
An X-ray study at DESY is pointing the way towards a better understanding of plastics production. A team led by Utrecht University investigated so-called Ziegler-type catalysts, the workhorses in the world’s polyethylene and polypropylene production, at DESY’s X-ray source PETRA III. As the scientists report in the journal JACS Au, the catalyst microparticles fragment into an astonishing variety of smaller particles during polymer production. The results allow for a better finetuning of desired polymer properties and may even help to further increase polymer yield.
Polyolefins, such as polyethylene (PE) and polypropylene (PP), play an important role in everyday life. Applications range from food packaging to increase the lifetime of the product to the sterile packing of medical equipment to the insulation of electrical cables. To prepare tailored polyolefins on demand, a versatile class of catalyst materials, such as the Ziegler-type catalysts, are used that consist of very small particles containing various metals such as titanium.
The catalyst particles have typical sizes of only a few tens of micrometres (thousandths of a millimetre), that is, less than the thickness of a human hair. Thanks to these catalysts, polyethylene can be produced at ambient pressure and temperature and with enhanced material characteristics. “Polyolefin research today focusses on specifically tailoring polymer properties to the demands of customers, and this is where insights about the polymerisation process such as the ones obtained in this study are crucial,” explains Koen Bossers from Utrecht University, first author of the study.
Read more on the DESY website
Image: 434 particles were imaged simultaneously with a resolution of 74 nm and identified and characterised individually with respect to their geometrical properties and fragmentation behaviour. The displayed rendering shows a virtual cut through the tomographic data set where each identified particle is color-coded for better visualisation. Most particles are about 5-6 microns in diameter. The data has further been segmented into regions of similar electron density to separate polymer from catalyst fragments within each particle; these regions are displayed in blue, green, orange, and red and visualised via the virtual cut though the 3-D representation of the catalyst particles. This segmentation allowed for a detailed analysis of the fragmentation behaviour of each particle
Credit: Utrecht University, Roozbeh Valadian