Flow Behavior of Sparsely Branched Metallocene-Catalyzed

Flow Behavior of Sparsely Branched Metallocene-Catalyzed Polyethylenes

Phillip J. Doerpinghaus, Jr.

Dissertation submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY IN CHEMICAL ENGINEERING

Advisory Committee:

Dr. Donald G. Baird, Chairman Dr. Richey M. Davis Dr. Timothy E. Long Dr. Peter Wapperom Dr. Garth L. Wilkes

August 8, 2002 Blacksburg, VA

Keywords: metallocene, polyethylene, rheology, melt fracture, contraction flow behavior

Copyright 2002, Phillip J. Doerpinghaus

Flow Behavior of Sparsely Branched Metallocene-Catalyzed Polyethylenes Phillip J. Doerpinghaus (ABSTRACT) This work is concerned with a better understanding of the influences that sparse longchain branching has on the rheological and processing behavior of commercial metallocene polyethylene (mPE) resins. In order to clarify these influences, a series of six commercial polyethylenes was investigated. Four of these resins are mPE resins having varying degrees of long-chain branching and narrow molecular weight distribution. The remaining two resins are deemed controls and include a highly branched low-density polyethylene and a linear lowdensity polyethylene. Together, the effects of long-chain branching are considered with respect to the shear and extensional rheological properties, the melt fracture behavior, and the ability to accurately predict the flow through an abrupt 4:1 contraction geometry. The effects that sparse long-chain branching (Mbranch > Mc) has on the shear and extensional rheological properties are analyzed in two separate treatments. The first focuses on the shear rheological properties of linear, sparsely branched, and highly branched PE systems. By employing a time-molecular weight superposition principle, the effects of molecular weight on the shear rheological properties are factored out. The results show that as little as 0.6 LCB/104 carbons (