Experimental investigation of the influence of molecular weight distribution on the rheological properties of polypropylene melts

Abstract

An experimental study of steady shear and elongational flow Theological properties of a series of polypropylene melts of varying molecular weight and distribution is reported. Broadening the molecular weight distribution increases the non‐Newtonian character of the shear viscosity function and increases the principal normal stress differences at fixed shear stress. The behavior is compared to earlier rheological property‐molecular weight studies. Correlations are developed for these properties in terms of molecular structure. Elongational flow studies indicate that for commercial and broader molecular weight distribution samples, ready failure by neck development occurs and the elongational viscosity appears to decrease with increasing elongation rate. For narrower molecular weight distribution samples, the elongational viscosity is an increasing function of elongation rate, The implication of these experimental results to viscoelastic fluid constitutive equations and polymer melt processing is developed.

Experimental investigations of the influence of molecular weight distribution on melt spinning and extrudate swell characteristics of polypropylene

“…We have carried out such measurements in an earlier study. 28 In Figure 6 we compare the results of elongational viscosities determined from local point by point spinline measurements and from simple elongational flow. For the PP-H-N and the PP-M-N, the x values from the simple elongational flow experiments are equal to 3710 at low elongation rates and increase at higher rates of deformation.…”

Nitroxide‐mediated controlled degradation of polypropylene

“…Fox and Flory theory has been confirmed by numerous investigations (Fox and Loshaek (1955), Fox et al (1956), Baumann andSteingiser (1963), Gruver et al (1964), Kraus and Gruver (1965), Minoshima et al (1980)). Generally, it was found that for polydisperse systems that molecular weight which should be used is the weight average MW (M w ).…”

Cellulose Acetate for Thermoplastic Foam Extrusion

“…The observed polydispersity index ranges from 3 to 5. This is comparable to branched PP [12,51] or blends of different types of PS [15,52]. Table 4.…”