On the methods of measurement of the flow properties of polyethylenes and their blends

Abstract

AbstractSamples of commercial LDPE, HDPE, LLDPE, and their blends were tested in the steady state (rotational and capillary), dynamic, and extensional modes. The steady state data at low rates of deformation followed the dynamic viscosity, η = η′, and at higher rates the complex viscosity η ≃ η*. In elongational tests strain hardening was observed for LDPE and some for HDPE. There was no strain hardening in flow of a standard LLDPE, and the equilibrium extensional viscosity η ≃ 3η′ in full range of deformation rates. In blends with ultrahigh molecular weight PE and with LLDPE strain hardening and an increase of the maximum strain at break, εb, were found. Some newer types of LLDPEs and their homologous blends show the strain hardening behavior. A brief review of the methods of measurement of the flow properties of polyethylene (PE) melt is provided. The text is divided into three parts: (1) types of melt flow; (2) comparative rheology of polyethylenes; and (3) linear low density polyethylene (LLDPE) blends. In the first part, the methods of measurement and correlation between the measured values are discussed. The steady state shearing, dynamic deformation, and uniaxial extensions are considered. In the second part rheological behavior of the three principal types of PEs, low density PE (LDPE), high density PE (HDPE), and LLDPE are presented. In part 3, the flow of four different types of LLDPE blends is reported on.