Viscometer laboratory instruments

The mechanical assembly and microprocessing unit permit analysis of a broad spectrum of molecular responses yielding data on viscous and elastic properties of the test material. A more generally available laboratory Instrument is the Haake Roto-visco viscometer which also features a cone-plate attachment. 

A variety of laboratory instruments have been used to measure the viscosity of polymer melts and solutions. The most common types are the coaxial cylinder, cone-and-plate, and capillary viscometers. Figure 11 -28 shows a typical flow curve for a thermoplastic melt of a moderate molecular weight polymer, along with representative shear rate ranges for cone-and-plate and capillary rheometers. The last viscometer type, which bears a superficial resemblance to the orifice in an extruder or injection molder, is the most widely used and will be the only type considered in this nonspecialized text. 

Critical measuring and test equipment identified as being critical parts of the quality system should be properly calibrated and maintained. Calibration should be traceable to recognized standards. This includes all in-process instruments identified as quality instruments, as well as test equipment used in the laboratory. Test equipment includes laboratory instruments such as spectrometers, viscometers and other apparatus, as well as reagents, buffer solutions and standard solutions. 

Figure 2.4 A commercial instrument, the Brookfield Digital Viscometer, based on the geometry of the concentric cylinder viscometer. (Photo courtesy of Brookfield Engineering Laboratories, Inc., Stoughton, Mass. 02072.)...

Historically, viscosity measurements have been the single most important method to characterize fluids in petroleum-producing applications. Whereas the ability to measure a fluid s resistance to flow has been available in the laboratory for a long time, a need to measure the fluid properties at the well site has prompted the development of more portable and less sophisticated viscosity-measuring devices [1395]. These instruments must be durable and simple enough to be used by persons with a wide range of technical skills. As a result, the Marsh funnel and the Fann concentric cylinder, both variable-speed viscometers, have found wide use. In some instances, the Brookfield viscometer has also been used. 

A computer-controlled rheology laboratory has been constructed to study and optimize fluids used in hydraulic fracturing applications. Instruments consist of both pressurized capillary viscometers and concentric cylinder rotational viscometers. Computer control, data acquisition and analysis are accomplished by two Hewlett Packard 1000 computers. Custom software provides menu-driven programs for Instrument control, data retrieval and data analysis. 

A wide variety of viscometers suitable for liquids are currently available, often with computer control. Many quality control laboratories use simple, cheap, robust instrumentation, which performs quite adequately in a day to day context. However these instruments can have a very narrow range and do not always give well-defined shear rates. This makes them less suitable for research and development work and we will not consider them further here. Figure 3.3 shows schematically the two main instrument types in common use controlled stress, where the stress is applied electrically via a motor leaving us to measure the strain and... 

The membrane viscometer must use a membrane with a sufficiently well-defined pore so that the flow of isolated polymer molecules in solution can be analyzed as Poiseuille flow in a long capillary, whose length/diameter is j 10. As such the viscosity, T, of a Newtonian fluid can be determined by measuring the pressure drop across a single pore of the membrane, knowing in advance the thickness, L, and cross section. A, of the membrane, the radius of the pore, Rj., the flow rate per pore, Q,, and the number of pores per unit area. N. The viscosity, the maximum shear stress, cr. and the velocity gradient, y, can be calculated from laboratory measurements of the above instrumental parameters where Qj =... 

The most popular viscosity test for products ranging in viscosity from 50 to 200,000 cP uses a rotating spindle instrument such as the Brookfield viscometer. The equipment used for this measurement is shown in Fig. 20.1. The instrument measures the resistance of the fluid to a spindle of certain size that is rotating at a predetermined rate. The method is relatively simple and quick. It can be adapted to either the laboratory or production floor. 

Characterization. Infrared spectra of bisdichloromaleimide monomers and polymers in KBr pellets were recorded, using a Perkin-Elmer 180 spectrophotometer. Elemental analyses were provided by Huffman Laboratories. Mass spectra were recorded at 70 eV on a Hewlett-Packard MS 5980 instrument by the direct inlet procedure. A DuPont 990 thermal analyzer was used to evaluate thermal behavior of bisdichloromaleimide monomers and polymers. Reduced viscosity of the polymers was determined in DMF at 30°C with a Cannon viscometer. Thermal polymerization was studied by heating a known weight of the material from room temperature to the desired temperature in a glass tube. The extent of curing was evaluated by extraction with DMF at room temperature. 

SEC experiments were carried out on a Watters 150CV instrument (Waters Associates, Milford, Massachusetts, U.S.A.) equipped with both differential refractive index single-capUlary viscometer detectors. The solvent/mobile phase was H20/0.02% NaNs, at the flow rate of 1.0 ml/ min. Pump, solvent, and detector compartments were maintained at 50°C. Separation occurred over a column bank consisting of three analytical columns preceded by a guard column Shodex KB-G, KS-802, KS-803, and KB-804 (Phenomenex, Torrance, California, U.S.A.). Universal calibration was performed using a series of oligosaccharides (Sigma, St. Louis, Missouri, U.S.A.), and PuUuIan Standards (American Polymer Standards, Mentor, Ohio, U.S.A., and Polymer Laboratories, Amherst, Massachusetts, U.S.A.). 

Laboratories determine oil viscosity experimentally using a viscometer (Fig. 5.203). The viscometer measures an oil s kinematic viscosity by the time (in seconds) it takes a specific volume of lubricant to pass through a capillary of a specified size, at a specified temperature. The kinematic viscosity is then derived by calculations based on constants for the viscometer and the time it took the sample to pass through the instrument. 

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