Fractal approach for modeling the morphology evolution of olefin polymerization with heterogeneous catalysts

Fractal theory and methodology were used to investigate the morphology of titanium-magnesium-supported polyethylene catalysts and their relevant polymer particles. Through an analysis of the submicrostructures using scanning electron microscopy images, the surface fractal dimensions of the related particles were estimated with the box-counting method. With consideration given to the fact that the growth process of a polymer is an evolving fractal process, which is controlled on the one hand by the initial conditions, including the initial fractal dimensions of the catalysts and the initial reaction conditions, and on the other hand by the previous morphology characteristics of the system, a novel polymerization fractal growth model was constructed. The simulation results showed good agreement with the experiment data. Moreover, the morphology evolution with the prepolymerization technique was predicted, and it was suggested that the duration of polymerization was 10-30 min. It was proven that the use of the surface fractal dimension as an important parameter describing the surface morphologies of the particles, either of catalysts or polymers, was real and effective.