AbstractA high shear, concentric cylinder viscometer was used to study polyethylene samples which differed in molecular weight. Viscosities were measured at several temperatures in laminar flow at shear rates up to 2.5 × 105sec.−1. Five high molecular weight normal alkanes were also studied in evaluating shear dependent flow. Viscosities of the normal alkanes and polyethylenes with molecular weights up to about 3300 were Newtonian over the shear range studied. Polyethylenes with higher molecular weights showed large and reversible decreases in viscosity with increasing shear. Viscosity results at high shear were compared with available theory. Previous concepts based on molecular orientation apparently cannot account for the abrupt onset of non‐Newtonian flow with increasing molecular weight. An alternate explanation of non‐Newtonian flow is offered in terms of molecular disentanglements. This concept permits a qualitative prediction of the magnitude of non‐Newtonian flow, as well as the molecular weights for which it will become i
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