Abstract
AbstractA high‐pressure, nitrogen‐driven capillary viscometer has been used to study the extrusion flow properties of polyethylene samples which differed in molecular weight, molecular weight distribution and density.Results obtained indicate that the effects of narrowing the molecular weight distribution of polyethylene whilst retaining the same intrinsic viscosity are to decrease its flow rate under conditions of high shear stress, and to decrease its flow parameter ‘n’. Such changes do not, however, have any effect on the flow rate which occurs under conditions of low shear stress, on the maximum shear stress which can be applied consistent with steady smooth flow, or on the activation energy of viscous flow at constant shear stress. High‐pressure polyethylenes, by comparison with linear polyethylenes of similar melt index, show flow irregularities at relatively low shear stresses and they have appreciably higher activation energies of viscous flow.
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