Polymer rheology melt flow index

High density (HDPE), 52 Irregularities, 52 Linear low density (LLDPE), 52 Low density (LDPE), 52 Molecular weight, 52 Melt flow index, 53 Melting temperature, 51 Moisture absorption, 51 Polymeric forms, 52 Resistance to chemicals, 52 Resistance to oxidation, 52 Shrinkage, 54 Unsaturations, 54 a-transition, 51 P-transition, 51 y-transition, 51 Polyisocyanate, 79 Polylactic acid, 79, 91 Polymer alloys, 48 Polymer processing additives, 646 Polymer rheology, 619 Polymeric forms, 52 Polyphase PlOO, 451 polypropylene (PP), 2, 11 Polypropylene homopolymer, 70... 

More details about the viscosity are described in Chapter 4, which deals with rheology of polymers. The industry prefers to measure melt fluidity (inverse viscosity), by using a standard rheometer, named Melt Flow Indexer. The measured property (mass of polymer that flows through a standard capillary under determined load and temperature, for 10 minutes) is also known as MH (Melt Flow Index). Because MFI is inversely related to melt viscosity, it is important to remember that low values of MFI are obtained by high MW polymers. 

Some type of melt viscosity is included in the specification for almost every polymeric or plastic product. This is because viscosity is related to the molecular weight and to the performance of a polymer. Equipment used for rheological measurements range from the simple and ubiquitous melt flow indexer to the precise and quantitative capillary and cone-and-plate rheometers. 

Shenoy, A.V. and Saini, D.R. (1986) Melt flow index more than just a quality control rheological parameter. Advances Polymer Technol, 6, (Part I) 1-58, (Part II) 125-45. 

Shenoy, A. V, Saini, D. R., and Nadkami, V. M., Melt rheology of polymer blends from melt flow index, Int. J. Polym. Mater., 10, 213-235 (1984). 

In most monographs and texts on polymer rheology, the Melt Flow Indexer has been treated briefly because it has generally been considered an instrument meant only for quality control. However, it has been shown in the recent past [66] that the Melt Flow Indexer provides more than just a quality control rheological parameter. As the main accent of the present book is to show the multiple uses of the data from the Melt Flow Indexer, this particular instrument will be treated in the utmost detail. However, the discussion will not be done in this subsection but will be carried forward to the next chapter where thorough justice will be done. 

The General Rheological Model [87] was basically developed for master curves of viscosity versus shear rate for polymer melts using the melt-flow index (MFI) as a normalizing parameter. It can be written in a general form applicable to any viscosity versus shear rate curve of a polymer melt simply by putting MFI as unity to give... 

Shenoy, A. V. and Saini, D. R., Upgrading the melt flow index to rheogram approach in the low shear rate region, J. Appl. Polym. Sci., 29, 1581-1593 (1984). Minoshima, W., White, J. L., and Spruiell, J. E., Experimental investigation of the influence of molecular weight distribution on the rheological properties of polypropylene melts, Polym. Eng. Sci., 20, 1166-1176 (1980). 

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. 

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