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An empirical model relating the molecular weight distribution of high‐density polyethylene to the shear dependence of the steady shear melt viscosity
Author(s) -
Bersted B. H.
Publication year - 1975
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.1975.070190810
Subject(s) - molar mass distribution , shear rate , shear (geology) , thermodynamics , polyethylene , viscosity , volume fraction , chemistry , newtonian fluid , materials science , mechanics , composite material , polymer , physics
An empirical model has been developed to relate molecular weight distribution to the shear dependence of the steady shear viscosity in high‐density polyethylene melts. It uses a molecular weight, M c , which partitions molecular weights into two classes; those below M c contribute to the viscosity as they do at zero shear, and those above M c contribute to the viscosity as though they were of molecular weight M c at zero shear. Each individual molecular weight species contributes on the basis of its weight fraction. M c is proposed to be a unique function of the shear rate. Using this method of treating the molecular weight distribution, and the zero shear relation for relating η0 to molecular weight, the calculated steady shear viscosities at various shear rates for polyethylene samples of widely varying polydispersities agree well with experimental results. The model makes no judgment on the existence or importance of entanglements in non‐Newtonian behavior since it has no specific parameters involving an entanglement concept. Use of the model suggests that for the samples studied, only the upper portion of the molecular weight distribution contributes toward the experimentally observed decrease of steady shear viscosity with shear rate for shear rates of up to 10,000 sec −1 . The lower molecular weight species are assumed to behave in a Newtonian manner.