Using multiple‐mode models for fitting and predicting rheological properties of polymeric melts

Abstract

Several classes of multiple-mode rheological constitutive equations are tested for fitting and predicting viscoelastic flow properties of a typical low-density polyethylene melt. An optimization procedure is used to fit the phenomenological parameters of each model under consideration to experimental data taken in small-amplitude oscillatory shear flow and steady shear flow. These parameter values are then used to generate predictions for transient shear and uniaxial elongational flow experiments, and the predictions are then compared to experimental data. Model successes and failures are discussed, and the outlook for using rheological equations in real design processes is addressed.

Using multiple‐mode models for fitting and predicting the rheological properties of polymeric melts. II. Single and double step‐strain flows

“…Note that the predictions of this model have a distinct waviness with respect to time. As explained before, 1,16,17 this behavior is caused by the unrealistic Maxwellian type of relaxation assumed by this model. Figure 6 presents the theoretical predictions of the stress and modulus provided by the UGM model.…”

“…All the parameters thus obtained are tabulated in part I. 1 A schematic diagram of the strain versus the time is shown in Figure 1, which demonstrates that, theoretically, an instantaneous strain, g 0 , is applied at time t ¼ 0, but experimentally, the rheometer needs a certain amount of time (ca. 0.07 s) to reach the strain required.…”

“…1 It was a typical, industrially relevant LDPE sample. The LDPE sample was obtained from Exxon (Newark, NJ).…”

“…In part I of this study, 1 we presented a current assessment of the potential predictive capabilities of seven viscoelastic fluid models. Rather than focusing on the particular models popular today (which might not be popular a decade from now), we examined instead semiphenomenological models (i.e., models involving empirical parameters) that characterize a certain class of model types.…”

“…In part I, 1 we examined the performance of seven multimode constitutive equations in small-amplitude oscillatory shear flow (SAOSF), steady-state and transient shear flows, and uniaxial elongational flow. Further information is expected to be obtained through single and double step-strain flows.…”