Viscosity of paste

The influence of plasticiser content on viscosity is shown in Figure 12.24. It is also to be noted that because of plasticiser absorption the viscosities of pastes do invariably increase on storage. The rate of increase is a function of the plasticiser used (Figure 12.25). 

In subsequent studies to determine the most appropriate water level for hydrating cowpea meal produced from the 1.0 mm screen, sufficient water was added to the meal to adjust the moisture content to 56, 58, or 60% (H). Preliminary studies had shown that a 54% water level produced a batter that was too thick for whipping, dispensing, and frying, and a 62% water level was too thin. Traditional paste made from soaked peas contains about 61% water and has a viscosity value after whipping of about 302 poise. By comparison, the viscosity of paste made from hydrated cowpea meal was 578 poise at the 56% water level, 441 poise at the 58% water level, and 333 poise at the 60% level. The 60% water level produced paste with flow properties and a cooked product with physical characteristics more like the traditional product than the other water levels. 

Special properties good gelation, increase in shelf life of pastes, low plasticizer absorption at room temperature, lowering viscosity of pastes, narrow particle size distribution, reduction of dila-tancy, small particle size, surface matt finish, transparency ... 

The reaction of clinker phases with water, together with the crystalUzation of hydrates, brings about the substantial changes of rheological properties of the paste. The formation of hydrated phases and, according to Locher [28], the morphology of hydrates crystallized in the liquid phase or on the surface of cement grains, leads to the reduction of distance between them and the viscosity of paste is enhanced. At... 

Designation system was developed for vinyl chloride thermoplastic resins which may be used as the basis of specification. In respect to plasticizers, the system allows to include in specification, plasticizer absorption at room temperature, viscosity of paste, and rheological behavior of paste. The second part of ISO standard gives a list of ISO standards used for testing of properties included in designation system and describes preparation of sample. 

Extenders or secondary plasticizers are relatively cheap materials that gel with PVC without themselves providing adequate plasticizing. Some fatty acid esters and hydrocarbon products can improve the flow properties of pastes. Chlorinated paraffins are flame retardant. Monomeric glycol methacrylate reduces viscosity of pastes, but polymerizes in the presence of an added catalyst on gelation to the end product, and increases its hardness. 

At and near T j -which is a low temperature for the liquid state of a polymer, whatever its absolute value may be-the viscosity of a polymer melt will be quite high, which is a direct consequence of the encumbered movement of the polymer chains past one another. 

Product Concentrate. An aerosol s product concentrate contains the active ingredient and any solvent or filler necessary. Various propellent and valve systems, which must consider the solvency and viscosity of the concentrate—propellent blend, may be used to deUver the product from the aerosol container. Systems can be formulated as solutions, emulsions, dispersions, or pastes. 

Thickeners. These are used to kicrease viscosity of shampoos to achieve certain consistency characteristics ki the product, from a thickened Hquid to gels and pastes. Among the most important materials used for this purpose are the alkanolamides. The chain length of the amide alkyl group and its solubiHty ki the shampoo system are important aspects to be considered ki thek use for effects on viscosity. In general, as the chain length increases the viscosity response improves. The viscosity increase also is related to the water solubiHty of the amide the more water-soluble forms provide a lower viscosity response than the less soluble amides. 

It is found that the viscosity of a paste made from a fixed polymer/plasticiser ratio depends to a great extent on the particle size and size distribution. In essence, in order to obtain a low-viscosity paste, the less the amount of plasticiser required to fill the voids between particles the better. Any additional plasticiser present is then available to act as a lubricant for the particles, facilitating their general mobility in suspension. Thus in general a paste polymer in which the pastes have a wide particle size distribution (but within the limit set by problems of plasticiser absorption and settling out, so that particles pack efficiently, will... 

The viscosity of PVC pastes may be reduced in many instances by the presence of certain polyethylene glycol derivatives and related materials. Because of their tendency to exude, the use of these viscosity depressants should be restricted to levels of less than 1% of the total mix. 

The first four types are most conveniently distinguished by reference to formulations A to D in Table 12.5. Formulation A is a conventional plastisol. The viscosity of the paste is largely controlled by the choice of type and amount of polymer and plasticiser. In order to achieve a sufficiently low viscosity for processing, large quantities of plasticiser must be added, thereby giving a product of lower hardness, modulus, tensile strength and other mechanical properties than would be the case if less plasticiser could be used. In many applications this is not a serious problem and plastisols are of some considerable importance commercially. 

Figure 12.25. Effect of storage on the viscosity of PVC pastes using different plasticisers. (The...

Figure 12.26. Effect on viscosity of partial replacement of a PVC paste polymer (Breon PI30/1) in a PVC paste with a non-porous suspension polymer of high packing density. (The Distillers...

It is well known, that under industrial conditions a method of introducing filler into the polymer mixture is used. In this case, the filler is introduced in the form of paste containing up to 60 per cent water in order to reduce viscosity, As heating is affected by viscous friction, the temperature conditions are not stable on mixing and, therefore, conductivity of the conducting polymer composite becomes unreproducible. Up to now this factor has not been taken into consideration. 

Kneaders, Z- and sigma-blade, and Banbury mixers as shown in Figure 7.20, are generally used for the mixing of high-viscosity liquids, pastes, rubbers, doughs, and so on. The tanks are usually mounted horizontally and two impellers are often used. The impellers... 

A typical liquid-crystal molecule, such as p-azoxyanisole, is long and rodlike (14). Their rodlike shape enables the molecules to stack together like dry, uncooked spaghetti they lie parallel to one another but are free to slide past one another along their long axes. Liquid crystals are anisotropic because of this ordering. Anisotropic materials have properties that depend on the direction of measurement. The viscosity of liquid crystals is least in the direction parallel to the long... 

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