Seven fractions of isotactic polypropylene ranging in molecular weight from 1.1×10
5 to 7.7×10
5 and five blends with molecular weight of approximately 1.7×10
5 were used to investigate the melt flow behavior at 250°C through capillary. A non-newtonian parameter,
N(=
d ln η/
d ln
D) increases with increasing molecular weight and molecular weight distribution (MWD), and another parameter proposed in this paper
a(=
d{1/ln η}/
dln τ) strongly depends upon MWD. The three methods of determining the zero-shear stress viscosity η
0 were discussed.η
0 from method 1 (plots of ln 1/4η
a vs.τ) and method 2 (plots of In η vs.τ) were less precise than that from method 3 (linear plots of 1/ln η vs.τ) because of the curvature of the former plots. The following equations were obtained between η
0, and viscosity average molecular weight
Mv, respectively
_??_
and
_??_
Melt viscosity of blends is usually smaller than that of the fractions having the same
Mv. Irregular shapes of the extruded filaments appear at constant shear stress τ
c≈1×10
6 dyne/cm
2 for the fractions irrespective of
Mv.τ
c for the blends is greater than that of the fractions however. Dependence of Barus effect on molecular weight was well explained with the theory proposed in the preceding paper.
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