Viscometer operating conditions

Properties of EthanolIc Fructose Solutions. Published information on the properties of aqueous ethanolic fructose solution is very limited. As a result, solubility data from 25 to 60 °C was measured (Figure 1) and will be published separately. The equilibrium fructose/water mass ratio for zero alcohol, ranges from over 4 at 25 C to over 8 at 60 C (7,8). It can be seen that reasonable yields will only result with high alcohol additions (E/W at least 2). This is the range used in this study. Aqueous ethanolic solutions have a wide range of viscosities. These were measured at operating conditions using a Rheomat concentric cylinder viscometer. 

The following viscometer components and operating conditions are currently being used in the determination of relative viscosity versus sample depth in flowable samples ... 

Extrusion viscometer operated under high shear rates is used to determine viscosity of organosols and plastisols. A sample conditioned to proper temperature is placed in an extrusion chamber, and the extrasion pressure and the rate of flow through the orifice are measured and used for result calculations. The orifice has the inside diameter of 3.17 nun... 

Rotational viscometers often were not considered for highly accurate measurements because of problems with gap and end effects. However, corrections can be made, and very accurate measurements are possible. Operating under steady-state conditions, they can closely approximate industrial process conditions such as stirring, dispersing, pumping, and metering. They are widely used for routine evaluations and quahty control measurements. The commercial instmments are effective over a wide range of viscosities and shear rates (Table 7). 

In this experiment, a Tubing Shear History Simulator was coupled with a Reciprocating Capillary Viscometer to simulate the above conditions. Results from the experiment are given in Tables I and II and Figure 3, and were retrieved directly from the project data base. Total Instrument use time for this experiment was 17 hr, of which 16.5 hr were completely unattended operation.. Data analysis, including plotting of figures, required less than five minutes. 

The Saybolt viscometer works on a similar principle (ASTM D88)—the fluid is loaded to a tube calibrated to 60 ml. A cork is removed from the bottom of a narrow capillary and a timer is initiated. When 60 ml of the fluid is drained, the timer is halted. The time to drain the 60 ml volume is known as Saybolt seconds. The instrument operates at temperatures from ambient to as much as 99 °C. Because of the high sensitivity of viscosity to temperature, substantial efforts are devoted to maintaining isothermal conditions quoted uncertainties around the temperature are on the order of 0.03 °C. The accuracy of Saybolt viscometers is better than 0.2%. In order to ensure accuracy, they should be calibrated at regular intervals. For fully developed laminar flows, the drain time through the capillary at the base is directly proportional to viscosity. However, since the capillary section of the tube is short, a correction factor to the time is... 

The automatic relative viscometer is ideally suited for measuring dilute polymer viscosities. It provides faster analysis and greater precision than is obtainable with conventional glass tube viscometers (Ubbelohde or Cannon-Fenske), which it replaces. The principle of operation is based on measurement of pressure drops due to the continuous forced flow of solvent and sample through two stainless steel capillary tubes placed in series. The pressure drop across each capillary tube obeys Poiseuille s law. The pressme drop is measured by a differential pressure transducer. The sample solution is loaded into a sample loop via a syringe pump and then pushed into one of the two capillaries. A steady-state condition is reached when the sample solution completely fills capillary 2, solvent remaining in capillary 1 at all times. The relative viscosity of the sample solution is determined simply and directly by the ratio of the pressure drops. From the measured relative viscosity, all other solution viscosity measurements can be calculated. Solution viscosities are determined by the viscosity of the sample relative to the reference solvent. The relative viscometer measures the solvent and sample viscosity simultaneously, so errors due to temperatme fluctuation and solvent variations are avoided. The main advantages of this approach are ... 

The majority of published work on extrusion behaviour deals with compounded stock. Those papers reporting work on raw rubbers have usually been on the use of capillary rheometers to determine extrusion properties at higher shear rates than are possible with Mooney viscometers. Capillary rheometers are, in principle, quite simple to use, and the application of electronic, minicomputer and laser technology has reduced the operation and data analysis to a routine task. There are no standard ASTM or other test procedures, but under a specific set of conditions, once a material is characterized, the data can be used as standard for comparison of all subsequent batches. It is readily possible to characterize a raw rubber by an extrusion experiment to determine the viscosity/shear rate curve, extrudate swell, and stress relaxation.Both Sezna and Karg have shown how the Monsanto Processability Tester (MPT), a modified, computerized extrusion rheometer, can be used in predicting mixing behaviour. The MPT (shown schematically in Fig. 7) is a most versatile instrument. It has a larger than conventional barrel for minimal pressure drop in the barrel, a pressure transducer at the entrance to the orifice, a microprocessor system, and a laser device for... 

After the last evacuation of the viscometer (see operation 4) it may be filled with inert gas (nitrogen or argon). Otherwise it will contain only the vapour of the solvent (the best condition for measurements). 

At the same time that these application properties studies were going on work was initiated on melt flow behavior. At that time most melt flow studies were carried out at rather low shear rates. But polymers are processed at high shear rates under high pressures. We constructed a monstrosly riigged capillary viscometer in which press ires in excess of 20,000 psi could be achieved and flow studies inder conditions similar to actual processing operations were undertaken. 

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