Analysis of Composition Distribution in High Impact Polypropylene Particles Using Synchrotron Infrared Microspectroscopy Imaging

Composition distributions in high impact polypropylene particles synthesized with Ziegler-Natta catalysts were investigated by using the SPring-8 infrared microscope apparatus. High impact polypropylene is prepared in two stages. At first the homopolymers are produced from propylene, and in the following stage copolymers are synthesized from propylene and ethylene. In most of the second stage, gas phase polymerization processes using heterogeneous Ziegler-Natta catalysts are applied. A particle of the heterogeneous catalyst is the aggregation of the first microparticles. In the polymerization reaction, gaseous monomers contact the microparticles to produce polymers around them, and the growing microparticles result in increasing the size of the second macroparticles. Several kinds of high impact polypropylene particles were cut into cross sections by means of single edge industrial blades. The composition distributions of the samples were measured by using infrared microspectroscopy imaging. It was found that the propylene-ethylene copolymer with high ethylene concentration spots was formed around the surface of the particles. In the case of the particle having voids inside, high ethylene concentration spots were formed not only around the surface but also near the interface of the voids. Mechanism of the formation of high ethylene concentration spots was considered.