An interesting result of the KRR Multiconfigurational Framework Constitutive Model is that it simplifies to the so-called K-BKZ theory as one limiting case. Normally, the K-BKZ theory is found inadequate to describe polymer melt rheology and other models, such as the Doi-Edwards reptation model, are invoked to explain behavior. Branched polymers are not expected to follow Doi-Edwards predictions because the branching suppresses reptation. Here we present results from experiments using single-step and reversing double-step strain histories that were performed on branched polyethylenes. Both torque and normal force responses were analyzed within the framework of the K-BKZ theory. The results expand on the findings of Chodankar, Schieber and Venerus that the K-BKZ model provides a good description of the response of branched polymers to the two-step strain histories including reversing histories. Of particular interest is that the Doi-Edwards model with the independent alignment assumption form is a special case of the K-BKZ model, hence of the KRR model. The present result may have important implications for molecular models of the rheology of branched polymers.
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