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Ionic interactions in EMAA ionomer blends : a rheological and mechanical property investigation Najm, Marina


Polyethylene-co-methacrylic acid (EMAA) ionomers are functionalized polymers with up to 15% carboxylic acid groups neutralized by counterions such as sodium, zinc, or lithium. Due to the polarity difference between the polar cations and the nonpolar hydrocarbon chain, ionic groups aggregate into clusters which act as crosslinks leading to improved mechanical strength, viscosity, and self-healing properties. The analysis done in this study shows that binary mixtures of two different cations further enhance the rheological and mechanical properties such as complex viscosity, Young’s modulus, and yield strength. The enhancement is beyond what is calculated through the linear combination of the corresponding properties of the individual components forming the blends. The morphological change supporting the synergism is suggested to be an increased cluster strength and phase segregation for highly neutralized EMAA ionomers. However, this synergism is not observed for large stresses and deformations outside the linear region due to the deformation of clusters as a stress-release mechanism. Investigation of interaction in binary ionic binary blends of EMAA ionomers is measured using linear, nonlinear, and extensional rheology in the melt state, and using dynamic mechanical tensile testing in the solid state. A universal parameter, the “Molecular weight-normalized Neutralization” (NMW), is developed and found to be correlated to the presence of rheological and mechanical property enhancement for all binary blends. NMW is composed of the inverse of molecular weight and of neutralization. High NMW obtained through high degrees of combined cation neutralization and low combined molecular weight ionomers are correlated with higher degrees of enhancement. More significant synergism has been found for blends containing zinc counterions due to the high valency of their ionic charge compared to sodium or lithium counterions.

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