Contraction flow of ionomers and their corresponding copolymers: Ionic and hydrogen bonding effects

The contraction flow of several commercial ionomer melts and their corresponding copolymers was studied numerically using a viscoelastic integral constitutive model developed by Kaye and Bernstein, Kearsley, and Zapas, known as the K-BKZ model. First a detailed rheological characterization was performed to calculate the parameters of the K-BKZ model used in the flow simulations. The effects of ionic and hydrogen bonding associations have been studied on the entry pressure drop, on the corner vortex in the capillary contraction, as well as on the vortex strength. In all cases, the ionomers exhibit much more significant effects compared to their copolymers, the more so as the number of ionic associations present in their backbone increases. This is due to strong ionic associations present in the ionomers that give rise to strong strain hardening effects important in entry flows. Compared to ionic associations, the effects of hydrogen bonds are insignificant particularly at levels less than 5 mol. %.