Rheological properties of polypropylenes with different molecular weight distribution characteristics

Relationships 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 M-w and the molecular weight distribution M-w/M-n, and is higher as both characteristic values are larger. The die swell ratio at a constant shear rate depends on M-w, M-w/M-n, and M-z/M-w, 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 M-w and the molecular weight distribution M-w/M-n, and is proportional to M-z/M-w(2) in a log-log plot. The critical shear stress does not depend on the molecular weight, and is higher as is higher. The zero-shear viscosity is determined by a molecular weight of slightly hi e order than M-w, and the characteristic relaxation time is determined by M-z. The storage modulus at a constant loss modulus scarcely depends on the molecular weight, and is higher a's the molecular weight distribution M-w/M-n is higher. (C) 2002 Wiley Periodicals, Inc.