Melt flow rates

Melt flow rate Melt-formed ceramics Melt fracture Melting temperature... 

Testing. Melt index or melt flow rate at 190°C, according to ASTM D1238, is the test most frequently appHed to the characterization of commercial acetal resins. The materials are typically grouped or differentiated according to their melt flow rate. Several other ASTM tests are commonly used for the characterization and specification of acetal resins. 

ASTM D4181 calls out standard specifications for acetal mol ding and extmsion materials. Homopolymer and copolymer are treated separately. Within each class of resin, materials are graded according to melt flow rate. The International Standards Organization (ISO) is expected to issue a specification for acetal resins before 1992. 

The resin must be of highest purity for optimum processing characteristics and properties. Degradation results in discoloration, bubbling, and change in melt flow rate. 

Sample designation Melt flow rate, dg/min Stiffness, MPa Tensile properties ... 

To reduce melt viscosity an aliphatic dicarhoxylic acid may be used to partially replace the carbonic acid derivative. Easy-flow grades with a melt flow rate of 80 are now available in order to meet the stringent flow requirements involved in compact disc production. Such an improvement in flow rate is, however, at the expense of heat distortion temperature. 

As the solid material is more dense than the melt, the melt flow rate must be greater in the ratio of the solid/melt densities. Therefore... 

Melt Flow Rate (also known as Melt Flow Index)... 

The Melt Flow Rate Test is a method used to characterise polymer melts. It is, in effect, a single point ram extruder test using standard testing conditions (BS... 

Metallocene isotactic polypropylenes (MET.PP) are accessible with different melting points under the commercial range of melt flow rate (Fig. 11). The variation of melting points in these polymers is linked with the presence of different lengths of isotactic sequences. Mechanical properties of polypropylene... 

Figure 17 Correlation of failure time and melt flow rate MFR 190/5 of sharp notched bars under stress for unimodal homopolymer and copolymers, and bimodal copolymers. Source Ref. 130.

Fig. 8-6 Melt flow rates as a function of molecular weight distribution.

A distinction should be made between machine conditions and processing variables. Machine conditions are basically temperature, pressure, and processing time (such as screw rotation/rpm, and so on) in the case of a screw plasticator, die and mold temperature and pressure, machine output rate (lb./hr), and the like. Processing variables are more specific such as the melt temperature in the die or mold, melt flow rate, and pressure used. 

Adequate PC and its associated instrumentation are essential for product quality control. The goal in some cases is precise adherence to a single control point. In other cases, maintaining the temperature within a comparatively small range is all that is necessary. For effortless controller tuning and the lowest initial cost, the processor should select the simplest controller (of temperature, time, pressure, melt-flow, rate, etc.) that will produce the desired results. 

The viscosity average molecular weight typically falls somewhere between Mn and 5.2.3.3 Melt Flow Rate... 

The rate at which a molten polymer flows through a capillary under standard conditions is known as its melt flow rate (MFR). The melt flow rate of a polymer is inversely related to its molecular weight. Theoretically, a melt flow rate can be converted to a molecular weight, but this is rarely done in practice. Polymer engineers commonly refer to melt flow rates when comparing material specifications and make comparisons directly based on these values. 

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. 

Figure 5.5 shows a schematic diagram of a melt indexer (which is also sometimes referred to as an extrusion plastometer). To determine the melt flow rate of a polymer resin, we place a suitable mass of it into the barrel, which is pre-heated to a standard temperature appropriate to the polymer. We then place a weighted piston on top of the sample. After allowing the polymer to reach the temperature of the barrel we allow it to extrude from the capillary orifice. The melt flow rate is the mass of polymer in grams that extrudes in ten minutes. 

What is meant by the term melt flow rate How is it related to molecular weight ... 

ASTM D1238-04c Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer, Book of Standards Vol. 08.011, ASTM International (formerly known as American Society for Testing and Materials), West Conshohocken, PA, USA. 

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