Viscous materials, mixing

David B Todd/ Ph D / President, Todd Engineering Member, American Association for the Advancement of Science (AAAS), American Chemical Society (ACS), American Institute of Chemical Engineering (AIChE), American Oil Chemists Society (ADCS), Society of Plastics Engineers (SPE), and Society of the Plastics Industry (SPl) Registered Professional Engineer, Michigan. (Paste and Viscous Material Mixing)... 

Ko//M //s. When dispersion is requited ia exceedingly viscous materials, the large surface area and small mixing volume of roU mills allow maximum shear to be maintained as the thin layer of material passiag through the nip is continuously cooled. The roUs rotate at different speeds and temperatures to generate the shear force with preferential adhesion to the warmer roU. 

When it is deleterious, laminar flow can be avoided by mixing over the cross section. For this purpose static mixers in line can be provided. For very viscous materi s and pastes, screws of the type used for pumping and extrusion are used as reactors. 

Figure 7.29 shows a Sulzer type SMX static mixer where the mixing element consists of a lattice of intermeshing and interconnecting bars contained in a pipe 80 mm diameter. It is recommended for viscous materials in laminar flow. The mixer shown is used in food processing, for example mixing fresh cheese with whipped cream. 

Several successful cyclizations of quite complex structures were achieved using polyphosphoric acid trimethylsilyl ester, a viscous material that contains reactive anhydrides of phosphoric acid.58 Presumably the reactive acylating agent is a mixed phosphoric anhydride of the carboxylic acid. 

Dosing solutions were mixed on a Fisher Rotorak for 45 min. Difficulty was encountered in weighing and preparing the technical grade dicofol. Whereas chlorobenzilate was a viscous material, dicofol was almost a wax. It was necessary to warm a small amount of the latter material in an aluminum weighing dish until it flowed. The liquid was taken up with a disposable pipet and quickly transferred to a tared volumetric flask on a balance. The effect of the heat (if any) on the material was not known. 

The disadvantages are that (1) they are not suitable for services that are dirty, abrasive, viscous, or mixed-flow (gas with liquid droplets, liquid with vapor bubbles), or that have low Reynolds numbers (below 20,000) (2) the available choices in materials of construction are limited (3) the pulse resolution (number of pulses per gallon or liter) drops off in larger sizes (4) the pressure drop is high (two velocity heads) and (5) substantial straight runs are required, both upstream and downstream. 

A mixture of the 50 50 polycaprolactone (PCL) matrix and the appropriate weight nicotine drug load were placed in an oil bath at 150°C. A Teflon stirrer slowly mixed the viscous material in a polypropylene cup for thirty minutes. After visually inspecting for homogeneity, the PCL/drug mixture was allowed to cool in the freezer until it hardened and could be removed from the cup with ease. It was then stored at room temperature until ready for pressing. To create... 

PETN mixed with uncured Sylgard 182 silicone rubber and curing agent at 80% PETN and 20% rubber, forms a thick viscous material that can be extruded... 

Figure — The higher values of the molecular weight of viscous materials correspond to the laminar mixing region...

One common connection between viscous fluids, pastes, and doughs is the twes of equipment used to mix or process them. While often designed for a specific process objective or a certain fluid characteristic, most types of viscous mixing equipment have some common characteristics. The nature of all viscous materials is their resistance to flow. This resistance is usually overcome by a mixer that will eventually contact or directly influence all the material in a container, particularly material near the walls or in corners. Small clearances between rotating and stationary parts of a mixer create regions... 

The dispersion blade in Fig. 18-49 was developed to provide higher compressive shear than the standard sigma blade. The blade shape forces material against the trough surface. The compressive action is especially good for dispersing fine particles in a viscous material. Rubbery materials have a tendency to ride the blades, and a dispersion blade is frequently used to keep the material in the mixing zone. 

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