SIMPLIFICATION OF NETWORK THEORY FOR POLYMER MELTS IN NONLINEAR OSCILLATORY SHEAR

Giacomin and Oakley (1991) have shown that an upper convected Maxwell model with a structure-dependent relaxation spectrum incorporating the three-parameter kinetic rate equation proposed by Mewis and Denn (198 3) works remarkably well for a molten LDPE in large-amplitude oscillat ory shear (LAOS). In a search for a simpler framework for interpreting LAOS based on network theory, four nonlinear, differential constituti ve equations, each with less than three parameters, were evaluated. Th ese models are compared with the Mewis-Denn model and a two-parameter model has been found to work just as well for molten IUPAC LDPE X. The LA OS behavior of molten LLDPE is also adequately described by this m odel.