Powder mixing Shear

Powder Mixing High shear mixer granulator, fluidized granulator (bubbling bed, spouted bed)... 

Applications in the pharmaceutical industry included determining the end points of high-shear and fluid bed granulation [128-130], fluid bed drying, powder mixing [131], crystallisation [132] and obtaining information from other processes involving particulates [133]. 

For cohesive powders, mixing depends on shear rate, and rotation rates are very important. 

Bone cements used to fill the void and improve adhesion between implants and the host bone tissue have been reinforced with various fibers to prevent loosening and enhance shear strength. The typical bone cement is PMMA powder mixed with a methacrylate-type monomer that is polymerized during fixation. Low volume fractions of graphite, carbon, and Kevlar fibers have been added to PMMA matrices to increase fatigue life and r uce creep deformation. ... 

A mixture of catalyst powder, PTFE and a pore former (e.g., sodium carbamate) is first prepared by blending them with isopropanol. Afterwards, the blend mix is filtered and dried to remove the solvents and water. The mix is then fed to a pair of heated vertical rollers. The shear force applied between the rollers eonverts the powder mix into a sheet of uniform thickness. This sheet is further pressed onto the GDL in a hydraulic press and finally, the resulting electrode is soaked in warm water to remove the pore former. 

Lacey (1954) identified three mechanisms of powder mixing (1) shear mixing ... 

In shear mixing, shear stresses give rise to slip zones and mixing takes place by interchange of particles between layers within the zone. Diffusive mixing occurs when particles roll down a sloping surface. Convective mixing is by deliberate bulk movement of packets of powder around the powder mass. 

If either criterion is not met, powder mixing and shear characteristics will dominate this is the mechanical dispersion regime. Viscous or poorly wetting binders are slow to flow through the powder pores and form nuclei. Drop coalescence on the powder surface (also known as pooling ) may occur and create a very broad nuclei size distribution. In the mechanical dispersion regime, the liquid binder can only be dispersed by powder shear and agitation. 

Cartensen et al. (1976) Lactose, sucrose, and starch powder mixed with water High shear Binder dispersion... 

In the sheet-forming process, stainless steel, bronze, nickel-base alloys, or titanium powders are mixed with a thermosetting plastic and presintered to polymerize the plastic. Sintering takes place in wide, shallow trays. The specified porosity is achieved by selecting the proper particle size of the powder. Sheet is available in a variety of thicknesses between 16 x 30 mm and as much as 60 x 150 cm. A sheet can be sheared, roUed, and welded into different configurations. 

Alternatives to compounding in the melt are solution mixing or powder blending of solid particles. Mixing with the aid of solvents can be performed at lower temperatures with minimal shear. However, difficulties in removal of the solvent results in plasticization of tJie polymer matrix and altered erosion/drug release performance in addition to residual solvent toxicity concerns. Powder blending at room temperature minimizes thermal/shear stresses, but achieving intimate mixtures is difficult. 

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