2010-02-10
10:15 at HCI J 574

Equibiaxial Elongational Flows of Polymer Melts using Continuous Lubricated Squeezing Flow

David C. Venerus

Department of Chemical & Biological Engineering, Illinois Institute of Technology

Equibiaxial elongation flow, where a fluid element is stretched equally in two directions while it contracts in the third direction, occurs in numerous situations that include the processing of synthetic polymers and foodstuffs. Despite its technological significance, the rheological behavior of complex fluids in equibiaxial elongational flow is largely unexplored. The simple reason for this is that methods for generating equibiaxial elongational deformations are either very complicated or generate non-homogeneous deformations. The most reliable method for generating rheologically controlled, equibiaxial elongational deformations is the rotating clamp method, or MultiAxiale Dehnung (MAD), developed by Meissner and co-workers at the ETH in Zürich. However, the extremely complicated nature of the MAD rheometer has resulted in a relatively limited set of experimental data. A promising method that has been used with some success is known as Lubricated Squeezing Flow (LSF), where a polymer melt is squeezed between lubricated solid surfaces. Unfortunately, uncontrolled lubricant thinning limits the LSF technique to Hencky strains of roughly one-half, or barely outside the linear viscoelastic limit. For the past 10 years, we have been developing a modified LSF technique that involves the continuous injection of lubricant through porous metal plates, which we refer to as Continuous LSF (CLSF). This development has involved a combination of experimental tests and modeling to significantly improve the CLSF setup and methods. This novel technique has been validated through comparisons with data collected using the MAD rheometer on a linear polystyrene melt and a branched polyethylene melt. New results obtained using the CLSF technique on a series of Metallocene-catalysed polyethylenes will be presented showing the effect of chain branching on rheological behavior in equibiaxial elongational flows.