Polyethylene rheological properties

M. Ohgizawa, M. Takahashi and N. Kashiwa, Metallocene catalyzed polyethylene with unique rheological property , MetCon 95 Proceedings, USA, May 1995. 

Favorable rheological properties are an essential requirement for the commercialization of polyolefins like polyethylene. The ease of processability of the polymer melt, obtained through modifications in the microstructural features, is as important as the end use mechanical properties of these polymers. Presence of long-chain as well as short-chain branching, LCB and SCB, respectively, more or less dictates the rheological behavior of most commercial... 

Rheological properties, See also Rheology of dry foams, 12 16 of embedding materials, 10 10 of encapsulants, 10 12-13 of linear low density polyethylene,... 

If combs represent one extreme of the topological family of branched polymers, then another extreme is given by the case of dendritic polymers, which retain a branched structure at all timescales. The study of tree-like branched architectures is also motivated by the important commercial low density polyethylene (LDPE), which has remarkable rheological properties making it suitable for many processing operations [3]. 

Rokudai, M., Mihara, S., and Pujiki, T., Influence of Shearing History on the Rheological Properties and Processability of Branched Polymers. II. Optical Properties of Low-Density Polyethylene Blown Pilms, /. Appl. Polym. Set, 23, 3289 (1979) MaiUefer, C., Screw for Extrusion Apparatus, U. S. Patent 3,358,327 (1967)... 

Journal of Polymer Science Polymer Physics Edition 39, No.18, 15th Sept.2001, p.2159-67 RHEOLOGICAL PROPERTIES AND FOAM PROCESSABILITY FOR BLENDS OF LINEAR AND CROSSLINKED POLYETHYLENES Yamaguchi M Susuki K-I Tosoh Corp. 

Meissner, J. Modification of the Weissenberg rheogoniometer for measurement of transient rheological properties of molten polyethylene under shear. Comparison with tensile data. J. Appl. Polymer Sci. 16, 2877-2899 (1972). 

These experimental mixers enabled the study of the role of the rheological properties of the individual blend components on the mechanisms and rates of dispersive mixing. Three commercial polymers Dow Chemical Company polystyrene (PS686) and low density polyethylene (PE 132) and Chevron low density polyethylene (PE 1409) were used in the study. Figure 11.32 (a) shows the viscosities of the three polymers at 200°C (121). PS 685... 

For high density polyethylene the MWD represents one of the basic parameters which, together with average molecular weight, density, short and long chain branching content, determines the physical, mechanical and rheological properties of the polymer and therefore its end uses (Table 1). 

Rheology is defined as the science of the deformation and flow of matter. To enable polyethylene to be shaped into useful articles, the polymer must be melted and is typically heated to temperatures of -190 °C. Even at such temperatures, the molten polymer is very viscous. Hence, rheological properties of molten polyethylene are crucial to its end use and much study has been devoted to this subject. Strict mathematical treatment of polymer rheology can become quite complex and is outside the scope of this text. However, general discussions of polymer rheology (12) and specifically for polyolefins (13-15) are available. 

As previously discussed in Chapter 1, melt index (MI) is a standard method for measuring flow of molten polyethylene and is indicative of molecular weight of the polymer. However, melt index is a limited indicator of rheological properties. 

This standard covers measurement of the rheological properties of polymers with both stable and unstable melt viscosity parameters at various temperatures and shear rates. The test procedure lists typical test temperature conditions for polyethylene 190°C, for polypropylene 230°C, for poly(vinyl chloride) 170-205°C, however, this indicates that the most useful data are generally obtained at temperatures consistent with processing experience. The test method also prescribes using the Rabinowitsch shear rate correction (see above) and indicates that the basic rheology equations (17.10), (17.15) and (17.16) yield true shear rate and true viscosity for Newtonian fluids only for non-Newtonian fluids only the apparent shear rate and viscosity are obtained. 

Kiparissides C, Pladis P, Moen 0. From Polyethylene Rheology Curves to Molecular Weight Distributions. In Laso M, Perpete EA, editors. Multiscale Modelling of Polymer Properties, Computer-Aided Chemical Engineering. Volume... 

With this much interest in polyethylene, many attempts have been made to use low frequency NMR in either the time domain or frequency domain to monitor and control the production more rapidly. Auburn International (now part of Oxford Instruments) developed a widely adopted system based on the time domain spectrometers [21]. In this case, sample preparation is no longer an issue since the system accepts either powder or pellets and no solvent is used. The Auburn systems determine crystalline and amorphous ratios, viscosity, melt index and molecular weight For other types of polymers, the list of advertised measurements include tacticity, rubber content, copolymer analysis, and various rheological properties. These values are determined by correlating several routine but laborious methods with the decay of the NMR signal under various pulse sequences. The man-hours... 

When studying UHMWPE blended with low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE), it was found, using analysis of the log-additive rule, Cole-Cole plots, Han curves, and Van Gurp s plot, that the LDPE/UHMWPE blends were miscible in the melt [8]. However, the thermal properties and morphology of the blends were not consistent with the rheological properties. The latter showed liquid-solid phase separation as a result of the different rates of crystallization of LDPE and UHMWPE. However, the rheological properties and electron microscopy images of LLDPE/UHMWPE blends showed... 

H.-W. Shen, B.-H. Xie, W. Yang, M.-B. Yang, Thermal and rheological properties of polyethylene blends with bimodal molecular weight distribution. J. Appl. Polym. Sci. 129, 2145-2151 (2013)... 

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