High-density polyethylene melt flow rate

Shear stress versus shear rate for a high density polyethylene melt showing flow instabilities and evidence of slip. Adapted from Uhland (1979). 

Fig. 2.7. Drop off of doubled extinction angle 2"/ during stress-relaxation after cessation of steady shear flow according to Wales (59). Measurements on the melt of a high-density polyethylene (Marlex 6002) at a measurement temperature of 147° C. Shear rate of the steady shear flow q = 0.06 sec-1...

TABLE XII Qualitative expression of effects on high density polyethylene of changes in melt flow rate, density, and distribution of molecular weight... 

Figure 3.66 shows the steady-shear viscosity for a polymer system at three molar masses. Note the plateau in viscosity at low shear rates (or the zero-shear viscosity). Also note how the zero-shear viscosity scales with to the power 3.4. (This is predicted by Rouse theory (Rouse, 1953).) Figure 3.67 shows the viscosity and first normal-stress difference for a high-density polyethylene at 200 C. Note the decrease in steady-shear viscosity with increasing shear rate. This is termed shear-thinning behaviour and is typical of polymer-melt flow, in which it is believed to be due to the polymer chain orientation and non-affine motion of polymer chains. Note also that the normal-stress difference increases with shear rate. This is also common for polymer melts, and is related to an increase in elasticity as the polymer chain motion becomes more restricted normal to flow at higher shearing rates. 

In order to improve properties and compatibility of PP/EPDM blends, ternary blends and composites are sometimes prepared from the PP/EPDM blends. For instance, Sanchez et al. (10) prepared ternary blends of PP, high density polyethylene and EPDM with several blending ratios and investigated the melt rheological behaviors. They discussed the effect of the shear rate on the viscosity and flow curve in terms of the exponent of low power for a non-Newtonian liquid. They showed that addition of an elastomer to the polyolefin blends changes the shape of the viscosity-composition curve, and they discussed it in terms of the possible morphology of the blend. Similar works have been also reported by Ha et al. (11,12). 

HDPE High-density polyethylene LDPE Low-density polyethylene MER Melt flow rate PBSU Polybutylene succinate Reproduced with permission from T. Fujimaki, Polymer Degradation and Stability, 1998, 59, 209. 1998, Elsevier Science [53] ... 

A eomposite fiber with an island-in-a-sea cross section comprises at least two different polymers, one of whieh is a water-insoluble PO and the other is a water-soluble polymer. The islands have an average fineness not greater than 0.5 denier per filament and are uniformly distributed across the cross section of the fiber. A molten blend of highly crystalline PP and linear low density polyethylene (LLDPE) is melt-spun to produce biconstituent fibers having a denier of less than 30 [102]. The improvement is that the LLDPE used has a melt flow rate in the range of 12-120 g/10 min [103]. 

Of polymer melts, the viscosity at very low shear rates (< 0.01 s ) in low-density polyethylene, for example) where viscosity is independent of shear rate and the melt is essentially Newtonian. In some models of pseudoplastic flow, a second limiting viscosity (poo) approached as shear rate rises to extreme values and observed in some polymer solutions at high (but not infinite) shear rates. (Munson BR, Young DF and Okiishi TH (2005) Fundamentals of Fluid Mechanics, John Wiley and Sons, New York Patton TC (1964) Paint Flow and Pigment Dispersion, Interscience Publishers, Inc., New York)... 

Low density polyethylene (LDPE), high-impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS), and linear low density polyethylene (LLDPE) resins were used for this study. All resins were manufactured by The Dow Chemical Company. The flow rates for these resins are shown by Table 1. Coefficients of dynamic friction, shear stresses at the interface, and melting fluxes were reported previously for similar resins, but the data were not as comprehensive as those reported here, and most did not extend to high temperatures [1,3,5,9,10-12]. 

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