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Effect of molecular structure on polyethylene melt rheology. III. Effects of long‐chain branching and of temperature on melt elasticity in shear
Author(s) -
Mendelson R. A.,
Finger F. L.
Publication year - 1973
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1973.070170312
Subject(s) - materials science , rheology , shear rate , branching (polymer chemistry) , shear modulus , composite material , polyethylene , elasticity (physics) , die swell , shear (geology) , strain rate , time–temperature superposition , shear stress , thermodynamics , polymer , extrusion , physics
The effects of long‐chain branching and of temperature on the melt elasticity in shear of polyethylene were investigated using die swell measurements and relating them to recoverable shear strain, normal stress, and shear modulus. Die swell measurements, as a function of shear rate, were obtained for high‐ and low‐density polyethylenes at temperatures ranging from 130° to 225°C. The samples were characterized by GPC and intrinsic viscosity for molecular weight distributions and degrees of long‐chain branching. The importance of annealing the extrudates at temperatures above the polymer melting temperature to achieve equilibrium, or strain‐free, values of die swell was demonstrated. The effect of long‐chain branch was to decrease elastic deformation. At constant shear stress, the melt elasticity of both high‐ and low‐density polyethylene was found to be essentially independent of temperature. Thus, at constant shear rate, elastic deformation decreased with increasing temperature, and it was demonstrated that this decrease could be quantitatively defined in terms of previously determined shear rate–temperature viscosity superposition shift factors.