Constitutive equations represent a powerful tool for a prediction of the basic rheological properties of polymer melts and they are cricially important during modelling of the polymer processing. Their application allows direct investigation of usually unknown relationships between molecular structures of the polymers and their rheological responses during the modern processes which can be both steady and transient. At present there exist a series of the differential constitutive equations for the polymer melts (as e.g. Leonov, modified Leonov, modified White-Metzner, Phan-Tien-Tanner, Giesekus, Pom-Pom, eXtended Pom-Pom, PTT-XPP models, etc.) but only some of them are based on the molecular arguments. The aim of this project is to investigate and compare the predictive/fitting capabilities of the selected models for the individual classes of polymer materials under different flows situations. Based on these findings there will be proposed a new model and/or modified the chosen ones. Attention will be also paid to the empirical models describing non-monotonous behaviour of viscosity.
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