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Rheology and capillary flow of sodium and zinc ionomers

University of British Columbia

Ionomers are an important class of polymers that contain a small number of ionic functionalities capable of forming reversible ionic associations. They are used in many applications such as self-healing materials, semi-permeable membranes, and in coating and food packaging. It is important to understand the interplay between the dynamics of these ionic functionalities and their role on the rheological and mechanical properties in order to explore their potential for new commercial applications. Using a parallel-plate rheometer equipped with a partitioned plate, and the Sentmanat extensional rheometer (SER) fixture, a full rheological characterization of several sodium and zinc poly(ethylene-co-methacrylic acid) and their corresponding parent copolymers has been carried out. Particular emphasis has been placed on the distribution of the relaxation times to identify the characteristic times, such as the reptation, Rouse, and lifetime of associations that are associated with entanglements, segmental dynamics and ionic and hydrogen bonding associations respectively. It was found that ionic interactions increase the linear viscoelastic moduli and the viscosity by up to one order of magnitude and cause significant strain hardening effects in the uniaxial extension of ionomers. The time-strain separability that can be used to formulate a K-BKZ constitutive equation (Wagner damping function), was found to hold for all ionomers and their corresponding copolymers. Their damping function was found to have different values indicating that their relaxation depends on the number of ionic associations. The relaxation of copolymers is faster mainly due to the absence of ionic interactions. Finally, the capillary flow properties of these ionomers were studied to assess their processability in terms of instabilities such as wall slip and melt fracture. It was found that the no-slip boundary condition is a valid assumption for these polymers due to the strong ionic associations and strong interactions with the capillary wall. All ionomers were found to exhibit gross melt fracture and no sharkskin, a characteristic of strain-hardening polymers. The critical shear stress for the onset of gross melt fracture was found to depend on the lifetime of associations, independent of temperature, molecular weight and type of ion.

Text

2020-04-09

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/73970

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/