Polyethylene melt

Circulatory flow o low-density polyethylene melt in a rectangular domain 932 1,000 0.000... 

L. L. Blyler and T. K. Kwei processed their own experimental data in an incorrect way polyethylene melts with dissolved nitrogen have the same viscosity as pure melts. Dissolved nitrogen cannot change the value of the free volume of the PE melt hence, L. L. Blyler s and T. K. Kwei s formula is incorrect. 

Nikolaeva NE (1984) Flow of gas-containing polyethylene melts on extrusion molding. Thesis (in Russian). MITHT, Moscow... 

Many authors studying the formation of ECC from melts and solutions suggested that preliminary unfolding and extension of macromolecules occurs. Keller and Maehin25 have shown that in all known cases (including such extreme variants as the crystallization of natural rubber under extension and a polyethylene melt under flow) the same initial process of linear nucleation occurs and fibrillar structures is formed by the macromolecu-lar chains oriented parallel to the fibrillar axes27. ... 

Fig. 9. a Density vs. birefringence (proportional to preorientation f ) for a polyethylene melt, b Degree of crystallinity vs. f vor polychloroprene... 

In the poly(alkylene arylate) series, Tm decreases with increasing length of flexible — (CH2) — moieties and, as in the aliphatic series, approaches the limiting value of polyethylene melting point for large n values (Table 2.6). Aromatic -aliphatic polyesters with even numbers of methylene groups melt at higher... 

Fig. 21. Recoverable strain as a function of shear stress for polystyrene/toluene solutions with different molar masses at 5 wt%. (+) polyacrylamide/water solutions, ( ) 2 wt%, (x) 2 wt% (with surfactant), (O) 4 wt% and polyethylene melts...

The MRI technique has also been used with systems of more practical importance, such as a polymer melt [19]. Here a low density polyethylene melt was... 

Fig. 4.2.12 Image showing the velocity in the horizontal direction versus position in the vertical direction for a low density polyethylene melt.

Fig. 4.2.13 Velocity profile for low density polyethylene melt. The line refers to a fit of the data based on a parabolic velocity profile.

The melt flow rate of a polymer is the weight of polymer in grams that extrudes from a standard capillary die under a standard load, at a standard temperature, over a ten minute period. The term melt index is used exclusively for polyethylene melt flow rate is the preferred term for all other polymers, We measure melt flow rates using a piece of equipment called a melt indexer . The capillary dimensions, testing temperature, and load are specified for a given polymer by the National Institute for Standards and Testing. 

Figures 8 and 9 show the dependence of the self-diffusion constant and the viscosity of polyethylene melts on molecular weight [47,48]. For small molecular weights the diffusion constant is inversely proportional to the chain length - the number of frictional monomers grows linearly with the molecular weight. This behavior changes into a 1/M2 law with increasing M. The diffusion...

Fig. 9. Kinematic viscosity v = r /p (r viscosity, p density) divided by S2/M (S2 = mean square radius of gyration, M molecular mass) as a function of M for polyethylene melts at the same monomeric friction coefficient. (Reprinted with permission from [48]. Copyright 1987 American Chemical Society, Washington)...

Fig. 12a, b. Dynamic structure factor for two polyethylene melts of different molecular mass a Mw = 2 x 103 g/mol b Mw = 4.8 x 103 g/mol. The momentum transfers Q are 0.037, 0.055, 0.077, 0.115 and 0.155 A-1 from top to bottom. The solid lines show the result of mode analysis (see text). (Reprinted with permission from [36]. Copyright 1994 American Chemical Society, Washington)... 

We are now going to compare the results of mode analysis with measurements of viscosity on polyethylene melts. With the aid of Eq. (30), which links the viscosity to the relaxation times, we can predict the viscosity using the results of spin-echo measurements and compare it with the viscosity measurement... 

Fig. 15. Comparison of the viscosities either directly measured or calculated from the spin-echo results for polyethylene melts at 509 K as a function of molecular mass ( experimental result o viscosities calculated on the basis of mode analysis). (Reprinted with permission from [52]. Copyright 1993 The American Physical Society, Maryland)...

Fig. 28. NSE spectra in polyethylene melts at 509 K for three different polymer volume fractions in Rouse scaling. Upper diagram 0 = 1, central diagram O = 0.5, lower diagram O = 0.3. The solid lines correspond to a fit with the Ronca model. (Reprinted with permission from [60]. Copyright 1993 American Chemical Society, Washington)...

In the temperature range between 400 and 550 K, NSE spectra on the same undiluted polyethylene melt were recorded. These data were analyzed with respect to the entanglement distance. The result for the temperature-dependent entanglement distance d(T) is shown in Fig. 30. An increase in the tube diameter from about 38 to 44 A with rising temperature is found. 

Simulation of the Birefringence of Uniaxially Stretched Polyethylene Melts. 

Phys., 117, 5465 (2002). Atomistic Monte Carlo Simulation of Strictly Monodisperse Long Polyethylene Melts through a Generalized Chain Bridging Algorithm. 

Fig. 3.29 Neutron-spin echo spectra from polyethylene melts of various molecular weights. The Q values correspond to squares Q=0.03 A circles Q=0.05 A triangles (up) Q=0.077 A diamonds Q=0.096 A triangles (down) Q=0.115 A crosses Q=0.15 k Filled symbols refer to a wavelength of the incoming neutrons A=8 A and open symbols refer to A=15 A. For lines, see explanation in text (Reprinted with permission from [71]. Copyright 2002 The American Physical Society)...

Control of polyethylene melt strength and melt viscosity has been used to produce foamed articles. 

SOLUBILITY OF GASES IN A POLYETHYLENE MELT AND ITS IMPORTANCE FOR THE PREPARATION OF PLASTICS FOAMS BY A PHYSICAL METHOD... 

The experimental evidence concerning the effects of LCB on the non-Newtonian behaviour of polyethylene melts is not as extensive as might be wished. Guillet and co-workers (167) studied fractions of both linear and branched polyethylenes and found that, for a given low shear-rate viscosity. 

Mendelson (169) studied the effect of LCB on the flow properties of polyethylene melts, using two LDPE samples of closely similar M and Mw plus two blends of these. Both zero-shear viscosity and melt elasticity (elastic storage modulus and recoverable shear strain) decreased with increasing LCB, in this series. Non-Newtonian behaviour was studied and the shear rate at which the viscosity falls to 95% of the zero shear-rate value is given this increases with LCB from 0.3 sec"1 for the least branched to 20 sec"1 for the most branched (the text says that shear sensitivity increases with branching, but the numerical data show that it is this shear rate that increases). This comparison, unlike that made by Guillet, is at constant Mw, not at constant low shear-rate viscosity. 

Fleischer A1) reported on a PGSE study of linear polystyrene and linear and branched polyethylene melts (M g 53000) at 200 °C. A rapidly-attenuated echo component at low x (see eq. 2) was also 32) attributed to low-molecular-weight traces some enhancement of D at the shortest t was thought to arise from gel-like fluctuations. The results follow eq. (7) with n = —2 since this slope holds below as well as above Mc, the reptation interpretation 26,27) is in doubt. 

Shroff, R.N., Shida,M. Correlation between steady state flow curve, and molecular weight distribution for polyethylene melts. Polymer Eng. Sci. 11, 200-204 (1971). 

Lodge,A.S., Meissner,J. Comparison of network theory predictions with stress/time data in shear and elongation for a low density polyethylene melt. Rheol. Acta 12, 41-47 (1973). 

Fig. 1.5. An and An sin2 vs. shear stress pa for a high density polyethylene melt at 190° C (Wales, unpublished)...

Hill and Barham [133] showed by transmission electron microscopy that blends of high and low molar mass polyethylene melts were homogeneous with no detectable phase separation. The blends were prepared by solution mixing to obtain an initially homogeneous blend before the thermal treatment in the melt. It should be realised that the mechanical mixing of high and low molar mass linear polyethylenes to obtain a homogeneous melt may require considerable work and time. 

Figure 2.31 Reduced first normal stress difference coefficient for a low density polyethylene melt at a reference temperature of 150°C.

The material functions, k i and k2, are called the primary and secondary normal stress coefficients, and are also functions of the magnitude of the strain rate tensor and temperature. The first and second normal stress differences do not change in sign when the direction of the strain rate changes. This is reflected in eqns. (2.51) and (2.52). Figure 2.31 [41] presents the first normal stress difference coefficient for the low density polyethylene melt of Fig. 2.30 at a reference temperature of 150°C. 

Table 2.11 Material Parameter Values in eqn. (2.96) for Fitting Data of High Density Polyethylene Melts at 170°C...

Fig. E3.5 Steady-state shear viscosity rj and first normal stress coefficient i, obtained from dynamic measurements versus shear rate for a low-density polyethylene melt, melt I. [H. M. Laun, Rheol. Ada, 17, 1 (1978).]...

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