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Wall slip of HDPEs: Molecular weight and molecular weight distribution effects
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10.1122/1.4801758
/content/sor/journal/jor2/57/3/10.1122/1.4801758
http://aip.metastore.ingenta.com/content/sor/journal/jor2/57/3/10.1122/1.4801758

Figures

Image of FIG. 1.
FIG. 1.

Master curves of the dynamic moduli and complex viscosity for ZN-HDPE-10, ZN-HDPE-13, and ZN-HDPE-16 polyethylene resins at  = 190 °C to show the effect of at constant PI.

Image of FIG. 2.
FIG. 2.

(a) The flow curves of ZN-HDPE-5 (exhibiting stick–slip discontinuity) in capillary extrusion at various temperatures. (b) The flow curves of m-HDPE-9 (exhibiting no stick–slip discontinuity) in capillary extrusion at various temperatures.

Image of FIG. 3.
FIG. 3.

(a) The master flow curve of ZN-HDPE-5 (exhibiting stick–slip discontinuity) at  = 190 °C, obtained by superposing the data plotted in Fig. 2(a) using shift factors determined from LVE. (b) The master flow curve of m-HDPE-9 (exhibiting no stick–slip discontinuity) at  = 190 °C, obtained by superposing the data plotted in Fig. 2(b) using shift factors determined from LVE.

Image of FIG. 4.
FIG. 4.

(a) The flow curves of several ZN-HDPEs having about the same and different PI at T = 190 °C. The stick–slip discontinuity in the flow curve is observed for all these polymers plotted due to their high and medium molecular weight distribution. (b) The flow curves of several m-HDPEs having a wide molecular weight distribution at T = 190 °C. No stick–slip discontinuity in the flow curve is observed for any of these polymers due to their wide molecular weight distribution (continuous flow curves).

Image of FIG. 5.
FIG. 5.

Criterion for the occurrence of stick–slip transition for HDPE resins at T = 190 °C. Open symbols represent resins with no stick–slip transition while filled symbols those that exhibit this transition. The continuous line is  = 12 × PI × M. In general, Eq. (1) represents the data adequately well.

Image of FIG. 6.
FIG. 6.

The weak dependence of the critical shear stress for the onset of stick–slip transition ( ) with the weight average molecular weight ( ) of HDPE resins at T = 190 °C.

Image of FIG. 7.
FIG. 7.

Scaling of the ratio of the higher, and lower, critical stresses for the stick–slip transition with the zero shear viscosity for HDPEs.

Image of FIG. 8.
FIG. 8.

(a) The Bagley corrected flow curves of m-HDPE-8 determined by using capillary dies having different diameters at T = 190 °C. The diameter dependence and disagreement between the capillary flow curves and the flow curve labeled as LVE are consistent with the assumption of wall slip. (b) The Bagley corrected flow curves of m-HDPE-11 determined by using capillary dies having different diameters at T = 230 °C. The diameter dependence and disagreement between the capillary flow curves and the flow curve labeled as LVE are consistent with the assumption of wall slip.

Image of FIG. 9.
FIG. 9.

(a) The slip velocity of m-HDPE-1 as a function of wall shear stress at different temperatures from 190 to 230 °C. (b) Shifted slip velocity according to the time–temperature superposition principle to produce the master slip velocity of m-HDPE-1 as a function of the wall shear stress at  = 190 °C. The shift factors have been obtained from LVE time–temperature superposition principle.

Image of FIG. 10.
FIG. 10.

The slip velocity of selected HDPEs having about the same and different PI which exhibit stick–slip as a function of wall shear stress at T = 190 °C. As seen the slip velocity in the low shear rate region increases with increase of polydispersity (PI) while the slip velocity at the upper branch is independent of molecular weight characteristics. At higher shear stresses, there is a transition from weak to strong slip and vice versa shown by the arrows for ZN-HDPE-10. The dashed lines represent the average velocity (plug flow) and as seen the velocity profile in the upper branch is nearly plug flow.

Image of FIG. 11.
FIG. 11.

The slip velocity of selected HDPEs having about the same polydispersity (PI) and different as a function of wall shear stress at T = 190 °C. As seen the slip velocity increases with decrease of . At higher shear stresses, there is a transition from weak to strong slip (nearly plug flow) not shown here and these data are independent of the .

Image of FIG. 12.
FIG. 12.

The master curve for the slip velocity of HDPEs (lower branch) studied in the present study and those studied by at 190 °C. The slip velocity increases with polydispersity (PI) and decreases with increase of molecular weight, .

Image of FIG. 13.
FIG. 13.

The slip velocities of m-HDPEs of wide molecular weight distribution (no stick–slip transition) versus wall shear stress for all the HDPE resins at T = 190 °C.

Image of FIG. 14.
FIG. 14.

The master curve for the slip velocities of m-HDPEs that do not exhibit stick–slip transition at T = 190 °C.

Image of FIG. 15.
FIG. 15.

Constructing the flow curve of ZN-HDPE-6 for a capillary die of D = 0.79 mm at T = 190 °C.

Tables

Generic image for table
TABLE I.

List of HDPEs used in this study and their different moments of molecular weight.

Generic image for table
TABLE II.

Characteristic dimensions of the capillary dies used in this study.

Generic image for table
TABLE III.

Plateau modulus and critical shear stress for the onset of stick–slip for HDPE resins.

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/content/sor/journal/jor2/57/3/10.1122/1.4801758
2013-04-17
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Wall slip of HDPEs: Molecular weight and molecular weight distribution effects
http://aip.metastore.ingenta.com/content/sor/journal/jor2/57/3/10.1122/1.4801758
10.1122/1.4801758
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