Viscosity 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. 

Evaluating the Polymer. The intrinsic viscosity (IV) of the polymer was determined at 25° C. with solutions in benzene or toluene containing 0.1 gram/liter polymer and calculated with the equation IV = (In rjTei)/C. In many cases some gel formation made I V determination for the whole polymer impracticable. Hoekstra viscosities of a number of polymers were measured at 100° C. with the Hoekstra (Wallace) plastometer (42). This instrument provides bulk viscosity data for rubbers on a scale 0 (low viscosity) to 100 (high viscosity). 

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. 

Rheometer re- a-m9-t9r [ISV] (ca. 1859) (plastometer) n. An instrument for measuring the flow behavior of high-viscosity materials such as molten thermoplastics, rubbers, pastes, and cements. The most widely used principle is that of the capillary rheometer of which a variety of makes and models are in daily use. Instruments for measuring the flow properties of less viscous fluids, e.g., dilute polymer solutions, are called viscometers but the terms rheometer and viscometer are often used interchangeably. Currently, computerized, on-hne capillary rheometers linked to a single control station can simultaneously monitor melt viscosity in ten or more extruders in a resin-finishing plant. 

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 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. 

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... 

Rheometer Also called plastometer. A rheological instrument for determining the flow properties of a plastic, usually of high viscosity or in the molten condition of thermoplastics, by forcing the melt through a die or orifice of specific size at specific temperature and pressure. 

Whiting, R and Jacobsen, P.H. (1979) The evaluation of non-Newtoiuan viscosity using a modified parallel-plate plastometer, /. Mat. Sci., 14, 307-11. 

Dreval, et al. present an extended review of the low-shear viscosity of various polymers, primarily in organic solvents, from an extensive series of papers largely not cited in western literature(37). Most measurements were made with capillary viscometers, but at larger viscosities recourse was had to a rotational viscometer and a shear-plate plastometer, at shear stresses sufficiently low that. .. changes... 

ASTM D1238 Flow Rate of Thermoplasties by Extmsion Plastometer (Melt Index) - Compound melted at a predetermined temperature is extruded by a piston loaded with a specified weight under conditions that are determined by the composition. The weight in grams of compound extmded in 10 minutes is the Melt Flow Index. A higher value means a lower melt viscosity. 

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