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The nonlinear rheology of multilayer stacks of alternating isotactic polypropylene (PP) and polyethylene (PE) films with N layers was measured in shear and uniaxial extension. We show that the force to extend N-1 interfaces can lead to strain hardening. We studied three PE/PP pairs: A Ziegler-Natta catalyzed pair and two metallocene pairs, one with high density PE and one with linear low density PE. Interfacial tension was measured on matrix/droplet blends of each pair using small amplitude oscillatory shear measurements fitted with the Palierne model. Multilayer coextrusion was used to fabricate bilayers and sheets with hundreds of layers for each polyolefin pair. Under shear deformation, disentangling of chains in the N-1 interfaces led to a decrease in the overall shear viscosity, which is interpreted as an interfacial slip velocity and is in agreement with previous studies on multilayer films. Under extensional flows, the multilayers exhibited an increased transient extensional viscosity (tensile stress growth coefficient, η E, M +) and pronounced strain hardening, even when the constituent homopolymers exhibited no strain hardening behavior. A model based on a force summation was developed to predict this behavior with interfacial tension as a fitting parameter; the extracted interfacial tensions agreed reasonably well with those from the Palierne model. The "slip in shear" and "hardening in extension" behaviors highlight the role of interfacial polymer physics during rheological measurements and polymer processing.
|Original language||English (US)|
|Number of pages||11|
|Journal||Journal of Rheology|
|State||Published - Sep 1 2019|
Bibliographical noteFunding Information:
The authors would like to thank Dr. David Morse for helpful discussions on polymer physics, modeling, and chain entanglements, as well as editorial advice on this manuscript. This research was supported by a grant from Total S.A. with partial support by the Industrial Partnership for Research in Interfacial and Materials Engineering (IPRIME). Polymers were graciously provided by Total S.A. and ExxonMobil Corporation. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from National Science Foundation (NSF) through the MRSEC program.
© 2019 The Society of Rheology.
Copyright 2019 Elsevier B.V., All rights reserved.
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- 2 Finished
MRSEC IRG-3: Hierarchical Multifunctional Macromolecular Materials
Reineke, T. M., Bates, F. S., Dorfman, K., Dutcher, C. S., Hillmyer, M. A., Lodge, T., Morse, D. C., Siepmann, I., Barreda, L. & Ganewatta, M. S.
11/1/14 → 10/31/20
Project: Research project
MRSEC Program DMR-1420013
8/1/98 → 9/30/21
Project: Research project