Rheological properties of polypropylenes with different molecular weight distribution characteristics

Abstract

AbstractRelationships between the rheological properties and the molecular weight distribution of two polypropylene series with different molecular weight distribution characteristics were studied. The end correction coefficient in capillary flow is determined by the molecular weight Mw and the molecular weight distribution Mw/Mn, and is higher as both characteristic values are larger. The die swell ratio at a constant shear rate depends on Mw, Mw/Mn, and Mz/Mw, and is higher as the three characteristic values are larger. The critical shear rate at which a melt fracture begins to occurs depends on the molecular weight Mw and the molecular weight distribution Mz/Mw, and is proportional to Mz/Mw2 in a log–log plot. The critical shear stress does not depend on the molecular weight, and is higher as Mz/Mw is higher. The zero‐shear viscosity is determined by a molecular weight of slightly higher order than Mw, and the characteristic relaxation time is determined by Mz. The storage modulus at a constant loss modulus scarcely depends on the molecular weight, and is higher as the molecular weight distribution Mw/Mn is higher. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2128–2141, 2002