Suspensions colloid mills

More recently, Brauns and Seiler (12), (13) extracted native lignin from spruce wood and then homogenized the wood in a colloidal mill. A suspension of approximately one gram of colloidal wood per liter of water was obtained. After the colloidal wood was changed to a solid form, it was found that its cell structure was completely destroyed. However, extraction of this wood with ethyl alcohol at room temperature did not yield further quantities of native lignin. These investigators have also reported the isolation of a lignosulfonic acid-carbohydrate compound. 

Colloidal suspensions, emulsions and solid dispersions are produced by means of colloid mills or dispersion mills. Droplets or particles of sizes less than 1 (im may be formed, and solids suspensions consisting of discrete solid particles are obtainable with feed material of approximately 100-mesh or 50 p,m in size. 

Continue to mix under vacuum until uniform. Pass suspension through the colloid mill at a gap setting of 100 to 150 micrometers. 

Add megestrol acetate and pass then suspension through a colloid mill or homogenizer to provide a uniform oral suspension. 

Prepare the two suspensions separately, mix, pass through a colloid mill and spray onto the tablet cores in a perforated coating pan (e.g. Accela Cota 24 inch) until a weight gain of 8 - 10% of the cores ist obtained. 

For the preparation of suspensions and emulsions, colloid mills and liuiiiogeiiizers, respectively, are used. Ultrasonic mills that utilize vibrating reeds in restricted chambers to reduce the particle size of the dispersed ingredients can also be employed. See also Colloid Systems. 

Figure 7.7 Examples of (a) a colloid mill and (b) a ball mill used for the preparation of suspensions by the dispersion method. Figure (a) courtesy Premier Mill, Reading, PA Figure (b) courtesy Paul O. Abbe Inc., Little Falls, NJ.

For this purpose a fast stirrer with zig-zag blade or a colloid mill such as a rotor-stator mill are useful. After the stirring or the passage through die mill is completed the formulation needs no further processing. Compared with the suspension/emulsion method, fewer vessels are required, low viscous fluids are handled and incorporation of the thickener is more easily achieved. 

Seber colloid mill 50 Relatively simple Energy dissipation — suspension heating... 

Colloid Mill Colloid mills are rotor-stator systems that can be used to reduce the particle size distribution of both liquid dispersions (emulsions) and solid dispersions (suspensions). The emulsion or suspension is pumped through a narrow gap that is formed by the rotating inner cone and the stationary outer cone. The width of the annulus can be adjusted by changing the relative position of the two cones. The principal size reduction in colloid mills is due to the high shear forces that are caused by the velocity difference between the rotor and the stator surfaces. To increase wall friction and reduce slip, surfaces are usually not smooth but are roughened or toothed, which, in turn, changes the flow conditions from laminar to turbulent, thereby increasing the shear forces in the annulus. 

Suspension of finely ground hard fat or emulsifier in a cool liquid oil with subsequent comminution using a homogenizer, colloid mill, or shear pump. 

Figure 86. Methods used for spherical agglomeration in suspensions , (a) Container with stirrer, (b) container with liquid circulation, (c) inclined disc, (d) horizontal drum, (e) colloid mill , (f) shaking container, (g) vertical mixer, (h) continuous mixer...

COLLOID MILLS. In a colloid mill, intense fluid shear in a high-velocity stream is used to disperse particles or liquid droplets to form a stable suspension or emulsion. The final size of the particles or droplets is usually less than 5 /rm. Often there is little actual size reduction in the mill the principal action is the disruption of lightly bonded clusters or agglomerates. Syrups, milk, purees, ointments, paints, and greases are typical products processed in this way. Chemical additives are often useful for stablizing the dispersion. 

Colloid mill is a general term for mills which are able to reduce the particle size of a suspension into the colloidal size range. 

FIGURE 1.91 Effective diameter and polydispersity (PD) as a function of the concentration of A-300 in the aqueous suspension ball-milled for 5 h. (Adapted from Adv. Colloid Interface Sci., 91, Gun ko, V.M., Zarko, V.I., Leboda, R., and Chibowski, E., Aqueous suspensions of fumed oxides particle size distribution and zeta potential, 1-112, 2001e. Copyright 2001, with permission from Elsevier.)... 

In colloid mills, the suspension flows axially through the conically shaped sUt between the two surfaces, which can be either smooth or toothed. The (adjustable) gap width typically lies in the range of a few hundred micrometres and the rotor operates with a speed of 1000-5000 min , which corresponds to tangential velocities up to 40 m/s. Colloid mills are usually operated under turbulent conditions, but laminar flow is also possible. 

Colloid Mill. A high-speed dispersion unit yielding a suspension of particles of the order of 1mm size. The original mill of this type was designed by H. Plauson... 

Sol-Gel Techniques. Sol-gel powders (2,13,15,17) are produced as a suspension or sol of coUoidal particles or polymer molecules mixed with a Hquid that polymerizes to form a gel (see Colloids SoL-GELtechnology). Typically, formation of a sol is foUowed by hydrolysis, polymerization, nucleation, and growth. Drying, low temperature calciaation, and light milling are subsequently required to produce a powder. Sol-gel synthesis yields fine, reactive, pseudo-crystalline powders that can be siatered at temperatures hundreds of degrees below conventionally prepared, crystalline powders. 

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