Morphological Study of HDPE Prepared with the Highly Active Silica Supported TiCl4/MgCl2 Catalyst

Abstract

Kinetic investigations were carried out on the effects of polymerization conditions and nature of aluminium alkyl cocatalyst on the morphology (size, shape, density, and texture) of nascent polyethylene synthesized with TiCl4/MgCl2/SiO2 catalyst. Depending on the nature of the cocatalyst, considerably different kinetic profiles are obtained. Fibrillar, globular, cobweb, ribbon-like, worm-like, and lamellar structures are identified according to the catalyst system and polymerization conditions. The formation of a worm-like texture is a common feature of the catalyst combined with Al(C2H5)3 at high catalyst efficiency, while globular texture is obtained at low catalyst efficiency. Polymerization at optimum temperature (80°C) and Al(C2H5)3 concentration (Al/Ti=60) without the addition of hydrogen produces a well-defined crystalline structure, folded lamella globule. A cobweb structure is observed when AlEt2Cl is used as the cocatalyst. The effect of polymerization conditions on the particle size distribution of nascent polyethylene is also investigated. Replication phenomenon was observed to depend on the catalyst yield and polymerization time. Generally, the average particle size of polymer particles becomes large as the rate of polymerization increases.