The steady state and dynamic shear behavior of linear low density polyethylenes (LLDPE) blended with low density polyethylene (LDPE) and with-another LLDPE resin were measured in capillary and parallel plate geometries at T = 150, 190, and 230OC. The extrudate swell and the Bagley correction were determined. It was observed that the pressure correction plays a significant role in capillary flow of LLDPE/LDPE blends-an indication of immiscibility. Several other rheological functions also suggested a phase separation for the system. Nevertheless, the blend behaved a s a "compatible" mixture of emulsion type. By contrast, blends of two LLDPE resins show expected miscibility. However, even in this case additivity was not always observed. A new simple method of calculating the relaxation spectrum was developed. The method is analytical and its accuracy depends on adequacy of the semiempirical relation (proposed previously) to describe dynamic viscosity dependence on the test frequency. For all samples the spectrum allowed computation of storage modulus in good agreement with experimental findings.

The uniaxial extensional flow at 150°C of two series of blends: I. LLDPE/LLDPE and 11. LLDPE/LDPE was examined in full range of concentrations as well as that of accessible in the rheometer strains and strain rates. It was concluded that Series-I blends containing different LLDtype polymers are miscible. Their properties can be predicted on the basis of molecular weight and molecular weight distribution. By contrast, excepting low concentration limits, blends of Series-I1 are immiscible. Both series show strain hardening, due to higher values of the maximum strain at break. Series-I1 seems to be superior (under the test conditions). The stress growth function in shear, computed from the frequency relaxation spectrum, provided a good prediction of the linear viscoelastic component of the stress growth function in uniaxial extension.

The uniaxial extensional flow at 150°C of 11 linear low density polyethylenes (LLDPE) and one low density polyethylene was measured in a Rheometrics Extensional Rheometer. The presence of silicone oil did not affect the results. However, large effects of the molding time were observed. For specimens molded for 14 min, strain hardening was not observed for any gas‐phase polymerized LLDPE. As the molding time was increased to 40 min, the strain hardening was quite apparent, the elongational viscosity nearly doubled, the equilibrium plateau vanished, and the maximum strain at break Increased by about 20 percent. Explanation for the molding time effects can be found in the concept of low entanglement density in the virgin gas‐phase resins. The entanglement increases with time at temperatures above the melting point. The specimens molded for longer time show strain hardening.

The steady state and dynamic shear behavior of eleven commercial linear low density polyethylenes (LLDPE) and one low density polyethylene (LDPE) resin were measured in capillary and parallel plate geometries at T = 150 to 230°C. The extrudate swell and the Bagley correction were determined. A large pressure effect on capillary flow of narrow molecular weight distribution LLDPE was observed and a new corrective procedure was proposed. After the correction the steady state viscosity was found to be equal to the dynamic (not complex) viscosity: η(\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}) = η'(ω = \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}). A newly proposed four parameter relation between η and the deformation rate was found to provide a simple means for computation of the zero shear viscosity, ηo, and the primary relaxation time. Both these parameters showed a high degree of correlation. The expected relation: ηo ∝︁ Mw3.4 was observed for low molecular weight samples with low polydispersity. The LLDPE activation energy of flow, Eσ=29.9 ± 1.8 kJ/mole, was determined.

Ten commercial linear low‐density polyethylenes (LLDPE) were characterized by solution viscosity, size exclusion chromatography, SEC, and 13C nuclear magnetic resonance. The resins were copolymers of ethylene with butene, hexene, or octene. They were prepared in gas phase (with narrow or very broad molecular weight distribution), or in solution. The macromolecules were found to be linear. For all but the very broad molecular weight distribution resins the average comonomer sequence length was found to be 1; in the other case diad formation was observed. The weight average molecular weights calculated from SEC, and intrinsic viscosities agreed quite well. Mechanical degradation of LLDPE was observed during the solution viscosity measurements.