(628a) Transport and Reaction in Reconstructed Polyolefine Particles

The 3D spatial structure of porous polyethylene particles was reconstructed from their X-ray micro-tomography images. Several polyolefin particles with an artificial granular structure were also generated. Transport in reconstructed particles was calculated for the case of a monomer diffusing through both the pores and the polymer. The calculated degassing characteristics of reconstructed polyolefin particles can be compared to experiments. Monomer mass transport limitations are important not only in the early stage of particle growth, but also in fully-developed polyolefin particles. The problems and limitations of the developed method are discussed. The method developed allows prediction of the effect of particle structure on mass transport limitations for real particle structures.

We attempt to validate tomography-based spatially 3D model of polypropylene particle by comparison of model predictions with measured degassing characteristics of polypropylene powder samples. Statistically relevant number of porous PP particles from three particle size fractions is inspected by X-ray micro-tomography. The voxel size of reconstructed porous PP particles is between 1 and 5 microns. We show that closed porosity occurring in reconstructed particles has a negligible effect on the dynamics of particle degassing. It was found that the voxel size smaller than 3 microns is required for a good agreement between model predictions and experimental data. We demonstrate that tomography-based model is capable to address the problem of mass transport limitation during polymerization reaction in real particle structure. Two statistical descriptors suitable for the characterization of compact zones of polymers occurring in polypropylene particles are introduced.

Seda L., Zubov A., Bobak M., Kosek J., Kantzas A.: Tranport and reaction characteristics of reconstructed polyolefin particles. Macromol. React. Eng., 2, 495 (2008).