Viscosity Extrusion plastometer

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. 

Melt viscosity, or flow, is typically measured using extrusion plas-tometers (or melt indexers), capillary rheometers, and parallel plate rheometers. The extrusion plastometer measures the flow of a polymer melt under conditions specified by ASTM standard D 1238. This test yields a single, low-shear-rate value which is typically used to specify resins. Capillary rheometers determine viscosity over a range of shear rates in channel flow. While they are subject to error, these rheometers are still the only means of measuring viscosity at high shear rates (typically -y > 1000 s i). Parallel-plate rheometers also measure viscosity over a range of shear rates, but the maximum allowable shear rate is about 100 s i. 

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... 

The melt indexer (MI extrusion plastometer) is the most widely used rheological device for examining and studying plastics (principally TPs) in many different fabricating processes. It is not a true viscometer in the sense that a reliable value of viscosity cannot be calculated from the... 

The nanocomposite viscosity was characterized by the melt flow index (MFI). The measurements of MFI were performed on an extrusion-type plastometer with a capillary diameter of 2.095 0.005 mm, at a temperature of 240°C and a load of 2.16 kg. This sample was maintained at the indicated temperature for 4.5 0.5 minutes. 

The easiest indication of realtive molecular weight is melt viscosities at 315 C in a plastometer. Extrusion rates with a long (3.175 cm) orifice and a 325 g load are used to characterize low molecular weight polymers such as coating resins. Flow rates with a short (0.80 cm) orifice and a 5.0 kg load are used for injection molding grades. 

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