3. Isothermal viscoelastic model
Newtonian behavior is generally a first approximation to describe the rheological behavior of polymers, but this is incomplete. Polymers often exhibit pseudoplastic behavior: this means that viscosity depends on shear rate, as shown by cone-plane or capillary rheometry studies. This behavior can easily be introduced into a generalized Newtonian model.
3.1 Viscoelastic behavior and Maxwell's law
Taking into account the viscoelastic character of polymer melts in the spinning process is considerably more delicate. The most obvious manifestations of viscoelastic behavior in the process are, on the one hand, very significant swelling at the die exit (in the absence of stretching and for a Newtonian product this swelling is of the order of 13%, but it can be 100%...
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Isothermal viscoelastic model
Non-isothermal Newtonian model
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