Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer

ASTM D 1238-04, Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer  

For polyethylene, a standard test designation is 190/2.16, which means that the test is conducted at 190°C using 2.16-kg load (including piston). Besides, the following conditions have been found satisfactory for polyethylene 125/0.325, 125/2.16, 250/1.2, 190/0.325, 190/10, 190/21.60, and 310/12.5. However, 190/2.16 is the most often employed conditions. 

Most of plastics used in composite building materials have MFI that fall generally between 0.15 and 50 g/10 min, the range that is considered by ASTM D 1238 ( Procedure A ). Plastics that have MFI below 1 g/10 min (MFI 1.0) are commonly called fractional melt plastics. 

Nevertheless, the melt flow indexer is a very useful instrument besides measuring MFI. It can be used for studying plastic thermal degradation, by consecutive running of the same material or by running hot melt slow and recording MFI over time. By doing so, various antioxidants and their various amounts can be tested 

In order to overcome the shortcomings of the melt index method, high load MI (HLMI) has been introduced to indicate the grams of polymer pushed out of the barrel under the action of a heavier weight, usually 10 kg (or 21.6 kg). The ratio of the HLMI/MI indicate how shear thinning the resin is. The higher the ratio, the more shear thinning the polymer [8]. 

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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. 

ASTM Method 1238, Standard Test Method for Flow Rates of Thermoplastics by Extrusion Plastometer [6], completely defines the melt index, both the instrument and the experimental procedure. Temperatures and instrument configurations for common materials are given along with recommended calibration procedures and round-robin results. This method must be strictly followed if consistent melt index results are to be obtained. A melt index measurement is performed at low stress levels compared to capillary rheometers measurements (typical weights are in the range of 1.2-21.6 kg) and is sensitive to variations in operating procedure, instrument cleanliness (between tests), and operator bias (items such as packing and sample preparation). 

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