Viscosity system applications

Like the high-build epoxy paints, these are solvent-free low-viscosity systems which are readily applied onto a prepared level substrate to provide a jointless thin (thickness approximately 1.5 mm) chemically resistant flooring in a single application. ... 

Viscosity determinations at the highest convenient concentration are of practical value, because in most of the applications of nitrocellulose, solutions of these concentrations are used, and there is usually little difference between the concentration in use and that used for the determination. All nitrocellulose solutions that are not very dilute show more or less abnormal viscosity, i.e. the rate of flow is not proportional to the applied stress or pressure. The ease of flow of a solution at one degree of stress cannot then be inferred from a viscosity determined at another. Nevertheless the measured viscosity of a comparatively concentrated solution is in general useful information. This advantage is sacrificed in what is the most rational of all viscosity systems, the German I.G. Method. Measurements are made in dilute solutions and the results are expressed in terms of the Eigenviscositat (k) of Fikentscher and Mark [99] a function which to a large extent is independent of concentration ... 

There are notable exceptions, however, such as the CEP Lodge Stressmeter . This rheometer is unique in that it measures both viscosity and first normal stress difference, Nl. Both laboratory and in-line configurations are available. The instrument is shown in Figure 4.13. The Lodge Stressmeter is applicable to low-viscosity systems and available commercially from Chemical ElectroPhysics Corp. (Delaware, NJ). 

Radiation Curing. The cross-linking of acrylate-modified polyester resins with U V radiation or an electron beam is an energy-saving alternative to the heat-curing systems. Reactive diluents (e.g., polyfunctional acrylates) are required to adjust the viscosity for application although they increase reactivity, they reduce the flexibility and substrate adhesion of the paint film. 

For bonding to enamel to succeed, this liquid resin layer needs to penetrate well into the roughened etched tooth surface. This favours low viscosity systems, which implies in turn a composition without any filler. Unfilled resins can thus be used to provide the first layer of a bonded composite resin system. Unfortunately, such a layer experiences proportionately greater polymerization shrinkage than a filled composite system. To an extent, this problem is overcome by composite systems that have been formulated with at least some filler loading, but a low enough application viscosity to allow the liquid to flow into the roughened surface [3]. 

Power curves for many different impeller geometries, baffle arrangements, and so on are available in the literature [Skelland, 1983 Hamby et al., 1992 Tatterson, 1992, 1994 Ibrahim and Nienow, 1995], but it must always be remembered that though the power cmve approach is applicable to any single phase Newtonian liquid, at any impeller speed, the curve will be valid for only one system geometry. Adequate information on low viscosity systems is now available for the estimation of power requirements for a given duty under most conditions of practical interest. 

Gas dispersion in agitated tanks may be described in terms of bubble size, gas hold-up, interfacial area and mass transfer coefficient. While gas dispersion in low viscosity systems [Smith, 1985 Tatterson, 1991 Hamby et al., 1992] has been extensively studied, little is known about the analogous process in highly viscous Newtonian and non-Newtonian media, such as those encoim-tered in polymer processing, pulp and paper manufacturing and fermentation applications. 

The above systems of nanoemuisions are attractive for cosmetic applications (i) Low viscosity for applications in sprayables. (ii) Efficient delivery of active ingredients through the skin, (iii) Ability to penetrate through the rough skin surface. 

Low viscosity mixing applications can usually be handled efficiently with impeller systems consisting of one or more turbines. To obtain adequate mixing under the laminar flow conditions encountered in high viscosity applications, on the other hand, close-clearance impellers such as anchors and helical ribbons are required. These impellers sweep the whole wall surface of the vessel and agitate most of the fluid batch through physical contact. Helical ribbon impellers are typically used for industrial applications where the viscosity is in the range 20 000 to 25 000 Pa s. Wall scrapers can be mounted on the impeller blades to improve heat transfer. 

Adhesive dispensing systems for applying single-component adhesives can be fed by either a pressure-feed container for light viscosity adhesives or ram-mounted dmm pumps for medium to heavy viscosity adhesives. Application can be manual or automatic. 

Viscosity markedly changes the picture and, usually, increasing viscosity lowers the mass-transfer coefficient. For the common application of waste treating and for some of the pubhshed data on biological slurries, data for kiO (shown in Fig. 18-28) is obtained in the literature. For a completely new gas or liquid of a liquid shiny system. Fig. 18-26 must be obtained by an actual experiment. 

A wide range of polyurethane-type products has become available in recent years for coating applications. These include simple solutions of linear polyurethanes, two-pot alkyd-isocyanate and polyether-isocyanate systems and a variety of prepolymer and adduct systems. The coatings can vary considerably in hardness and flexibility and find use mainly because of their toughness, abrasion resistance and flexibility. Uses include metal finishes in chemical plant, wood finishes for boats and sports equipment, finishes for rubber goods and rain-erosion-resistant coatings for aircraft. One type of coating is potentially competitive with PVC leathercloth. Both alkyd-di-isocyanate and adduct-diisocyanate compositions may be coated on to fabrics from solutions of controlled viscosity and solids content. Such coated fabrics are soft, flexible and, unlike PVC leathercloth, free from plasticisers. 

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