Test method melt index

Ionomer resins are produced in multiple grades to meet market needs, and prospective customers are provided with information on key processing parameters such as melt-flow index. Nominal values for many other properties are Hsted in product brochures. The ASTM test methods developed for general-purpose thermoplastic resins are appHcable to ionomers. No special methods have been introduced specifically for the ionomers. 

Melt Index or Melt Viscosity. Melt index describes the flow behavior of a polymer at a specific temperature under specific pressure. If the melt index is low, its melt viscosity or melt flow resistance is high the latter is a term that denotes the resistance of molten polymer to flow when making film, pipe, or containers. ASTM D1238 is the designated method for this test. 

A company usually sets product standards in such a way as to minimize the purification expenses. These standards are often empirical tests to ensure that the buyer will get the same product in each shipment. Examples would be the melt index of a polymer, the boiling-point range of the product, and the maximum amount of certain impurities. Another manufacturer using a different process would want to set different standards. His method of production will be different, and so the amount and kind of impurities will be different. Sometimes this means expensive purification steps must be installed to meet the specifications set by the initial manufacturer. If this competitor could have been the initial standard-setter then these steps would not be necessaiy. 

Some of the test methods being used to measure the processing stability of polypropylene include melt flow drift measurements at elevated temperatures using an extrusion plastometer (melt indexer), melt viscosity retention measurements using a torque rheometer, retention of melt flow after repeated extrusions, and injection molded spiral test measured by the flow in inches at various temperatures and the retention of melt flow of the injected spirals. The nine commercial resins were evaluated by these methods. 

Two methods (ASTM D-1218, ASTM D-1747) are available for measuring the refractive index of viscous liquids. Both methods are limited to lighter-colored samples for best accuracy. The latter test method (ASTM D-1747) covers the measurement of refractive indexes of light-colored residual fuel oil at temperatures from 80 to 100°C (176-212°F). Temperatures lower than 80°C (176°F) may be used provided that the melting point of the sample is at least 10°C (18°F) below the test temperature. This test method is not applicable, within reasonable standards of accuracy, to liquids having darker residual fuel oil (having a color darker than ASTM Color No. 4 ASTM D-1500). 

FIGURE 50 Pore volume distribution of Cr/silica-titania catalysts dried by various methods and then activated at 800 °C. The mesoporosity of the catalyst influences its activity and the polymer melt index (tested at 105 °C with 1.5 mol C2H4 L ). 

FIGURE 3.81 Melt index of plastics. The test measures the rate of flow of polymer melt. It provides an indication of the ease of processing. Standard test methods ASTM D 1238, BS 2782 method 105C, ISO R292. 

Standard test method for environmental stress-cracking of ethylene plastics Insulating and sheathing materials of electric and optical cables - Common test methods - Part 4-1 Methods specific to polyethylene and polypropylene compounds - Resistance to enviromnental stress cracking - Measurement of the melt flow index - Carbon black and/or mineral filler content measurement in polyethy-lene by direct combustion - Measurement of carbon black content by thermogravimetric analysis (TGA) - Assessment of carbon black dispersion in polyethylene using a microscope... 

Raw material characterization. A simple, rapid single-point melt index (MI) test is used (see Chapter 10). Although the MI does not completely characterize a resin, for purposes of SPC it does not need to. Also used is a simple time-dependent sampling method. The resin supplier should sequentially number each box/container in the preliminary runs. A sample from each box is measured, and results are plotted using a standard control chart format. 

Rheological data provides information about how a melted material will perform (flow) under processing conditions. Perhaps the most important rheological test used by plastics processors is the melt index test. Though rheologists scoff at this notion, it is nevertheless vitally important because virtually every manufacturer that employs an extruder, injection molder, or blow molder uses the test method or the data it yields. 

Melt Index A single point identification of resin melt viscosity, measured in grams per 10 minute period passing through a specific orifice size at a cenain temperature, as dictated by test method ASTM D1238. 

There are about 10 manufacturers of LDPE in North America. The top six include Equistar Chemicals, LP, The Dow Chemical Co., Exxon Mobil Corp., Chevron Phillips Chemical Co., DnPont, and Westlake Polymer Corp. Each company has their own trade names and specific grade slates for various applications. Data sheets and MSDSs are available from each snppUer and many have them available on their web sites. A typical product data sheet will cover resin characteristics snch as melt index and density, as well as typical final product properties, such as film tear and tensile and impact strength. The tests will identify the ASTM test methods and the data sheet will nsnally have the conditions imder which the test samples were made. There will also be an indication of the FDA and food contact statns of the resin and the applications for which the resin is suited. 

The melt flow index test method is used to monitor the quality of plastie materials. The quality of the material is indicated in this test by melt flow rate through a specified die under preseribed conditions of temperature, load, and piston position in the barrel as timed measurement is being made. The melt flow rate through a specified capillary die is inversely proportional to the melt viscosity of the material if the melt flow rate is measured under constant load and temperature. The melt viseosity of the material or MFR is related to the moleeular weight of the material if the molecular structures are the same. The extrusion plastometer as specified in... 

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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