Paste particle size distribution

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... 

In preparing akara from each milled product, too many large particles still remained in the 2 mm material to make a smooth paste. However, highly acceptable akara with uniform shape was produced from this material after the paste was ground to eliminate the large particles. With the 0.5 mm screen, the paste was very fluid and extremely difficult to dispense, behavior which closely resembled that exhibited by the commercial cowpea flour. Akara prepared from the 0.5 mm material was also extremely distorted. Of the three screen sizes compared, the 1.0 mm screen produced the most desirable particle size distribution although the paste produced from the 1.0 mm material was somewhat more fluid than desired, it appeared that adjustments could be made in hydration of the meal to achieve an appropriate batter viscosity. 

Figure 7. Particle size distribution of traditionally processed cowpea paste and mechanically milled cowpea flour. Reproduced with permission from Ref. 9. Copyright 1983, American Association of Cereal Chemists.

Paints behave similarly. Fig. 68 illustrates the color shifts which are observed in Pigment Yellow 1 pastes containing different particle size distributions (Sec. 1.7.1). The colors are identified according to their location on the DIN Color Chart, in which each color is defined by two values, x and y [4]. Increasing amounts of pig-... 

Laser diffraction is the most commonly used instrumental method for determining the droplet size distribution of emulsions. The possibility of using laser diffraction for this purpose was realized many years ago (van der Hulst, 1957 Kerker, 1969 Bohren and Huffman, 1983). Nevertheless, it is only the rapid advances in electronic components and computers that have occurred during the past decade or so that has led to the development of commercial analytical instruments that are specifically designed for particle size characterization. These instruments are simple to use, generate precise data, and rapidly provide full particle size distributions. It is for this reason that they have largely replaced the more time-consuming and laborious optical and electron microscopy techniques. 

A number of elegant studies over the past few years have also addressed the need to minimize particle size distributions through the use of segmented flow microfluidic systems. Such an approach removes the possibility of particle deposition on channels and eliminates the problems of residence time distributions that occur in single phase systems (where drag at the channel walls sets up a velocity distribution inside the channel). For example, Shestopalov et al. reported the two-step synthesis... 

The field of particle size distribution analysis has experienced a renaissance over the past five years and is now a rapidly growing and lively area of scientific and technological activity. This revitalization has been driven by advances in electronics and computer technology in conjunction with the market pull for particle size distribution analysis methods that cover a wide dynamic particle size range and have improved resolution. These technological advances are embodied in computer-aided, user-friendly, reliable, and cost-effective instrumentation. Three activities characterize this renaissance. 

Several new processes for formation of solid particles with defined particle size and particle size distribution using supercritical fluids were developed in the past years. Examples are crystallisation from supercritical fluids, rapid expansion of supercritical solutions (RESS), gas antisolvent recrystallisation (GASR), and PGSS (Particles from Gas Saturated Solutions)-process [1,2]. 

Kalamaki, M.S., Harpster, M.H., Palys, J.M., Labavitch, J.M., Reid, D.S., Brummell, DA. (2003). Transgenic overexpression of expansin influences particle size distribution and improves viscosity of tomato juice and paste. J. Agric. FoodChem. 51, 7456-7464. 

In Chapter 12 of this book, the mechanical properties of ceramic suspensions, pastes, and diy ceramic powders are discussed. Ceramic suspension rheology is dependent on the viscosity of the solvent with polymeric additives, particle volume fraction, particle size distribution, particle morphology, and interparticle interaction energy. The interparticle forces play a veiy important role in determining the colloidal stability of the suspension. If a suspension... 

Pastes are ceramic suspensions with particle volume fractions near the maximum packing value for the particular particle size distribution. 

Danfoss QueCheck Vision System performs a continuous analysis directly from the production line, typically at 0.5 s intervals. The final results of the measurement are available after 100-300 frames so that an equivalent sieve analysis is completed every 3 min. The particle size distribution is documented via an interface with database and printer. The material is fed in a fine stream, by means of a vibratory feeder, past a vision camera that calculates the size distribution as it falls. The system has been applied to measuring the size distribution of sugar crystals. Online image processing has also been applied to monitoring granule size distribution and shape in fluidized bed granulation [150]. 

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