Viscosity testing

A melamine laminating resin used to saturate the print and overlay papers of a typical decorative laminate might contain two moles of formaldehyde for each mole of melamine. In order to inhibit crystallization of methylo1 melamines, the reaction is continued until about one-fourth of the reaction product has been converted to low molecular weight polymer. A simple deterrnination of free formaldehyde may be used to foUow the first stage of the reaction, and the build-up of polymer in the reaction mixture may be followed by cloud-point dilution or viscosity tests. 

A number of instmments are based on the extmsion principle, including sHt flow and normal capidary flow (Table 6). These instmments are useful when large numbers of quahty control or other melt viscosity test measurements are needed for batches of a single material or similar materials. When melt viscosities of a wide range of materials must be measured, rotational viscometers are preferable. Extmsion rheometers have been appHed to other materials with some success with adhesives and coatings (10,161). 

Zahigkeits-einheit, /, unit of viscosity (or tenacity or ductility), -grad, m. (degree of) viscosity or ductility or tenacity, -mass, n. measure of ductihty (or tenacity or viscosity), -messer, m. viscosimeter, -probe, /. tough ness (or ductihty or viscosity) test or sample,... 

High shear/high temperature viscosity test, to assess the oil s capability for resisting shear, and so retaining its viscosity, at high temperatures. 

US Mil Spec JAN-C-99 (Ref 4) contains the requirements for each ingredient of rC, including a viscosity test for the finished PC as well as std tests for the ingredient under several Fed Specs. However, some of these Fed Specs are outdated and are currently being replaced. A recent PATR (Ref 8) made recommendations to update JAN-C-99... 

The effect of pH on the intrinsic viscosity testing gives a minimum at the isoelectric point at pH 5.1 for gelatin B to pH 9.1 for gelatin A. from electroviscous effect analysis shows that 0.001 M ionic strength the hydrodynamic radius is at its maximum. 

Although one-electron oxidations may occur with the intermediacy of the hydroxyl radical, viscosity tests that serve to inhibit the diffusion of HO have provided evidence against the formation of free hydroxyl radicals . This prompted the suggestion by Honk and coworkers that the hydroxyl radical is formed in a tight cage in aqueous solution, still capable of performing one-electron oxidations. 

Consistency of NC Test, Same as Viscosity Test of Nitrocellulose (See Vol 2 of this Encycl, p C122-R, test h)... 

How to determine any HC liquid viscosity. For the viscosity of most any HC, see Fig. A-3 in Crane Technical Paper No. 410 [3], If your particular liquid is not given in this viscosity chart and you have only one viscosity reading, then locate this point and draw a curve of cP vs. temperature, °F, parallel to the other curves. This is a very useful technique. I have found it to be the more reliable, even when compared to today s most expensive process simulation program. Furthermore, I find it to be a valuable check of suspected errors in laboratory viscosity tests. If you don t have the Crane tech paper (available in any technical book store), then get one. You need it. I have found that most every process engineer I have met in my journeys to the four corners of the earth has one on their bookshelf, and it always looks very used. 

The viscosity of a starch paste is often characterized differently by the starch manufacturer and by users in the paper industry. In the manufacturing plant, viscosity tests serve to control the starch modification process. As an example, the test is used to determine when to terminate a starch oxidation reaction for viscosity reduction. In the paper mill, viscosity testing is required to characterize the flow properties of starch-based coating formulations. 

Frequently used single-point viscosity tests in the starch plant are orifice pipettes,56 orifice funnels,57 the Hot Scott viscometer, and various methods to determine alkaline fluidity.58 For absolute measurements of the rheological properties, rotating viscometers with coaxial cylinders are used.59 The paper industry uses mainly the Brookfield viscometer and the Hercules viscometer for determining shear-dependent viscosity, pseudoplasticity, and thixotropy. Oscillatory and capillary viscometers are used for more detailed viscosity characterization, such as yield value, elastic properties, and viscoelasticity.60... 

There are also a number of specialty viscosity tests that employ their own relative units. These tests have been developed for specific industries such as paints and coatings. Generally, these viscosity units can be directly converted to poise. 

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. 

Data collection were correlated with viscosity, time, thermocouple temperature, and rheometer torque. The rotation speed of the rheometer was adjusted so that torque value fell between 80% to 100%. The gel formation time was defined as the time needed for a sample to increase its viscosity up to 10000 cP from its starting viscosity. Viscosity testing results are provided in Table 1. 

The compositions of the slags from these viscosity tests are listed in Table II. (The compositional data are normalized to 100% the median closure on raw analytical data was 94.2%.) Also included are several other parameters that traditionally have been employed to characterize coal-ash slags. It should be emphasized that, unless otherwise noted, all calculations discussed herein were based on slag composition data (as opposed to ash composition data). This was done primarily for two reasons ... 

Table II. Analysis of Low-Rank-Coal Slags Produced in Slag Viscosity Tests...

On this basis, the IRSID correlation gave a reasonably good fit to the experimental data (within 20%) for 3 of the 23 viscosity tests. Unlike the BCURA correlations, which tended to give constitu-ently low results, the error in the IRSID correlation tended to be random predicted viscosities were too high in 11 cases and too low in 9 cases. 

Since the Urbain method appeared to give a fair-to-good correlation for nearly two-thirds of the viscosity tests, efforts were directed toward modifying this procedure with the goal of optimizing the fit to the experimental data. The logarithmic form of the Urbain equation is... 

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