Melt Mass-flow Rate and Density

In addition, the volume of the polymer melt discharged through the nozzle per time interval can also be calculated from the piston movement. This test quantity, with a unit of cmVlO min, is called melt volume-flow rate. Usually, the abbreviation MFR is used for the test quantity of melt mass-flow rate and MVR for the melt volume-flow rate. However, the old abbreviation, MFI (melt flow index) is also often used. Another parameter is the ratio of MFR measured with a large test weight to that measured with a small test weight. This quantity designated as melt flow ratio is unfortu- 

Small differences in crystallinity affect the density. For an exact and reproducible density determination the specimen must be eonditioned and the history of the specimen preparation must be known. Density is often measured together with the melt mass-flow rate and both serve as characteristic material parameters. Therefore, preparation and conditioning method based on the ASTM D2839-87 Standard Practice for Use of a Melt Index Strand for Determining Density of Polyethylene has proved suitable The density is determined on extrudates fi om the melt mass-flow rate measurement after boiling in water for one hour. 

The measurement of melt mass-flow rate and density is usually the first step in the specification and identification of polyethylene materials. It should be noted that the density of the base polymer differs from the density of the finished geomembrane mixed with carbon black. The confusion, which can occur in the classification of the PE resin, has briefly been dealt with in Sect. 2.1. As a rule, only geomembianes coloured black by carbon black, and not their natural-coloured resin, reach a density which properly meets the classification of HOPE plastic material (see Sect. 2, Tables 2.2 and 2.3). However, one may not consider these classification limits as strict technical criteria even if the density of the black geomembianes is just below 0.940 g/cm, it may correspond to what is ealled HOPE geomembrane over the whole spectrum of its characteristics. 

The outdated standard DIN 16776-1 84 Polyethylene and Ethylene Copolymer Thermoplastics Classification and Designation and the replacing European standard EN ISO 1872-1 1999 Plastics Polyethylene (PE) Moulding and Extrusion Materials Part I Designation System and Basis 

Code letter Test condition Temperature/nominal load 

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