Study on the Effects of Temperature, Time and the Policy of Prepolymerization on Particle Morphology in Propylene Slurry Polymerization with Heterogeneous Ziegler-Natta Catalysts

Abstract

The effects of temperature, time and the strategy of prepolymerization were studied on the morphology of polypropylene particles. propylene polymerization was carried out in slurry phase using 4th generation of Ziegler-Natta Catalyst, cyclohexylmethyl dimethoxysilane as external electron donor, and triethyl aluminum as co-catalyst. Prepolymerizations were carried out based on two strategies: isothermal and non-isothermal conditions. Particle imaging using SEM, bulk density, and particle size distribution was used to analyse the particle morphology. It was found that the variation of initial condition together with the change in the mechanism of particle fracture has a dominant effect on particle morphology. Each combination between the temperature and reaction time causes to have a special effect on the product particle morphology. It has become clear that in isothermal prepolymerization, spherical particles with identical properties were produced. In low temperature experiments particles with porous surface were observed. At increasing temperature, however, the pores disappeared. Non-isothermal prepolymerization produced different morphological types. In all experiments coreshell structures were observed that seemed to be related to the structure of catalysts.

Keywords

• prepolymerization
• morphology
• polypropylene
• ziegler-natta
• slurry polymerization