Monday 8 November 2021

Savvas G. Hatzikiriakos
Department of Chemical and Biological Engineering, The University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
Poly(ethylene-co-methacrylic acid) Ionomers and their Blends: Rheological Effects of Ionic Interactions
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Ionomers is a class of thermoplastic polymers that contain a small mole fraction of ionic functionalities (up to 15 mol%) covalently connected to the polymer backbone as well as a significant amount of groups capable of forming hydrogen bonding [1-3]. Recognized class of ionomers include those obtained from semi-crystalline ethylene-methacrylic acid copolymers which are neutralized with various metal ions, such as sodium and Zinc discussed in the present seminar. Using a parallel plate rheometer equipped with a partitioned plate, and an extensional fixture (SER), a full rheological characterization of several commercial ionomers has been carried to study the effect of ionic associations on rheological behavior by comparison with their corresponding ethylene methacrylic acid copolymers (no ionic interactions). The results are analysed in the context of relevant theories (Leibler, Rubinstein, Colby, Macromolecules,1991) to determine the characteristic relaxation times of these complex systems (Rouse, reputation and life time of ionic and hydrogen bonding associations). The experimental rheological data have been fitted to a viscoelastic integral model (K-BKZ model). The capillary flow of a commercial ionomer melt was also studied both experimentally and numerically to examine possible implications of associations in processing including melt fracture. The excess pressure drop due to entry in capillary flow, the effect of pressure on viscosity and the possible slip effects on the capillary data analysis were also studied. Viscoelastic K-BKZ simulations have revealed the effects of ionic associations on the entry pressure, vortex formation (size and strength) indicating its importance in processing. For example, it was found that the critical shear stress for the onset of melt fracture correlated with the lifetime of the ionic interactions, an observation that signifies the effect of ionic interactions in flows.

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