Morphology Fractal Research Of Supported Polyethylene Catalysts

The key of polyethylene technology is ethylene polymerization and relative catalysts techniques. In the olefin heterogeneous polymerization, chemical composition and structure design is very important, however, the morphology of catalysts and polymer is also a vital aspect.The thesis studied morphology of the supported polyethylene (PE) catalyst with fractal and multi-fractal theory and analyzed intermediate products of the catalysts preparation.The pictures disposal and computer calculating methods were fractal and multi-fractal programmes based on scanning electron microscope(SEM), including of Cal, Dim/Pro,improved box-counting methods and multi-fractal computer programmes.Analysis on four supported PE catalysts was carried on using improved box-counting methods and multi-fractal programme. For these catalysts, the relationship between activity of the catalysts and their surface morphology, and parameters of fractal dimension and multi-fractal curves were studied. It was proved that the complexity of catalyst surface could be characterized by surface fractal dimension and catalyst activity rose with heightening of the complexity and its specific surface area. Besides, variety of fractal dimensions could be characterized by multi-fractal curves. Catalyst activity increased with expand of span and distribution of fractal dimension. Two of this kind of catalysts with different activity and relavent PE particles were studied using the improved box-counting method and the results showed that PE particles had the similar structures with their relavent catalysts, and the PE particles with low fractal dimensions were catalyzed by the catalyst with high fractal dimension, and vice versa.Intermediate products of the catalysts preparation, including of raw silica gel, physics activation, chemical activation, masterbatch blending products and finished catalysts, were studied with scanning electron microscope(surface and slice morphology), nitrogen BET adsorption test(specific surface area, pore volume and average aperture) and fractal dimension analysis(surface and slice morphology dimensions). The results showed that the carrier activation process was the key step to control catalyst morphology and some chemicals, such as the alkyl aluminium, could influence catalyst morphology.