Paper Number
PM6 

Session
Polymer Melts: From Molecular Rheology to Processing

Title
Rheology of molten polyolefin interfaces: Slip in shear, strain hardening in extension

Presentation Date and Time
October 16, 2018 (Tuesday) 1:30

Track / Room
Track 2 / Plaza I

Authors (Click on name to view author profile)

  1. Jordan, Alex M. (University of Wisconsin - Stout, Polymer Engineering)
  2. Kim, Kyungtae (University of Minnesota)
  3. Lee, Bongjoon (University of Minnesota)
  4. Ludtke, Ean (University of Minnesota)
  5. Bates, Frank S. (University of Minnesota, Department of Chemical Engineering and Materials Science)
  6. Macosko, Christopher W. (University of Minnesota, Chemical Engineering and Materials Science)
  7. Lhost, Olivier (Total)

Author and Affiliation Lines (in printed abstract book)
Alex M. Jordan1, Kyungtae Kim2, Bongjoon Lee2, Ean Ludtke2, Frank S. Bates2, Christopher W. Macosko2, and Olivier Lhost3
1Polymer Engineering, University of Wisconsin - Stout, Menomonie, WI 54751; 2Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN; 3Total, Feluy, Belgium

Speaker / Presenter 
Jordan, Alex M.

Text of Abstract
While isotactic polypropylene (iPP) and polyethylene (PE) are chemically similar, they are immiscible in the melt state and possess poor interfacial adhesion in the solid state. Here, we focus on the use of rheology to understand the iPP/PE interface in the melt. Using Ziegler-Natta catalyzed high density polyethylene (zHDPE) and isotactic polypropylene (ziPP) as well as single-site (metallocene) catalyzed high density polyethylene (mHDPE), linear low density polyethylene (mLLDPE), and isotactic polypropylene (miPP) we produced a range of multilayer films. Films with 2 layers, 160 layers, and 640 layers were fabricated via multilayer coextrusion using ziPP/zHDPE, mHDPE/miPP, and mLLDPE/miPP. In startup of steady shear the Ziegler catalyzed pair showed interfacial slip at ~10 kPa, well below the critical shear stress threshold for disentanglement.1 The interfacial slip at low shear stress was likely due to the build-up at the interface of low molecular weight oligomers that were below the entanglement molecular weight of iPP and PE. Interestingly the Ziegler catalyzed pair also displayed the lowest interfacial adhesion in the solid state, which was attributed to oligomer build-up at the interface.2 Conversely, using extensional rheology we observed strain hardening in the multilayers of the single-site catalyzed pairs, first with the miP/mLLDPE system at 160 layers. At 640 layers, effectively quadrupling the interfacial area in multilayer films, the strain hardening behavior became more pronounced in the mLLDPE/miPP system and strain hardening emerged in the mHDPE/miPP system, even though no strain hardening was observed in control mHDPE, mLLDPE, and miPP films. We correlate this strain hardening behavior with the narrow polydispersity of these single -site catalyzed polyolefins resulting in a high degree of chain entanglements in the melt interface. References: 1. P. C. Lee, et al., J. Rheol., 2009, 53, 893-915.; 2. A. M. Jordan, et al., Macromolecules, 2018, 51 (7), 2506-2516.