SHEAR MODULUS OF FLOWING POLYETHYLENE MELTS

Tests on three low‐density polyethylene melts over a range of temperatures and shear rates, using a Weissenberg rheogoniometer, have enabled the reduced shear modulus to be obtained as a function of shear rate at the initiation of shearing and at various subsequent stages. For the two polymers which gave plateau values of modulus during the course of shearing these were in good agreement with figures quoted in the literature, but the initial modulus (measured on one polymer) was an order of magnitude higher. This supports the view that a network structure exists in the polymer at rest and is disrupted in the early stages of shearing. It was not possible to obtain unequivocal evidence that the equilibrium modulus decreases with amount of shearing, as required by the hypothesis that rheological breakdown is caused by a reduction in molecular entanglements. Copyright © 1969 John Wiley & Sons, Inc.