Irreversible Network Disentanglement and Time-Dependent Flows of Polymer Melts
For small strains Lodge’s rubberlike-liquid theory is a valid description of rheological behaviour of polymer melts, but at higher strains the theory fails: The phenomenon of shear thinning is not explained which is characteristic for shear flow of nearly all polymer liquids, and in elongation deviation of experimental data from predictions of Lodge’s theory reflect also a flow thinning, and not a strain hardening in spite of the pronounced S-shape of the stress-strain diagrams. Comparing measured stress growth and stress relaxation data with predictions of the theory, it can be concluded that the temporary network structure of the polymer melt is destroyed increasingly with the magnitude of deformation. Hence, the number of entanglements decreases with increasing strain. Finally the irreversibility of the disentanglement process is considered.
KeywordsConstitutive Equation Stretch Ratio Polymer Liquid Strain Dependence Hencky Strain
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