Grinding drawbacks

In comparison to the approach of Ginski et al. [48], the Miyazaki s method appears to be more elaborate and complex and is thus coming closer to the in vivo situation. The device can simulate various effects of pH on dissolution and is, as an open system, closer to in vivo conditions compared to a closed one. However, it exhibits the drawback of not freely adjustable pH values acting on the drug. Low flow rate in the dissolution vessel may limit applications of complete dosage forms and allows predominantly only the use of granules, pellets, or grinded tablets. Furthermore, the application of compendial dissolution devices appears to be a more robust approach. 

The particle-size and size-distribution of solid materials produced in industrial processes are not usually those desired for subsequent use of these materials and, as a result comminution and recrystallization operations are carried out. Well known processes for particle size redistribution are crushing and grinding (which for some compounds are carried out at cryogenic temperatures), air micronization, sublimation, and recrystallization from solution. There are several practical problems associated with the above-mentioned processes. Some substances are unstable under conventional milling conditions, and in recrystallization processes the product is contaminated with solvent, and waste solvent streams are produced. Applying supercritical fluids may overcome the drawbacks of conventional processes. 

Natural sources of ATH (Gibbsite extracted from Bauxite) and magnesium hydroxide (Brucite) are available but generally have large particle size as a result of grinding operations and contain significant amounts of impurities. In wire and cable applications, finer particles sizes are utilized for higher FOI values, improved mechanical properties, lower brittleness temperatures, and smoother surface characteristics despite the drawback of increased mixture viscosity.75... 

A drawback to this device is that it is not possible to regrind a minor fraction of larger-than-desired particles since it takes a reasonable amount of sample to provide a minimum charge. Hence the grinding must be adequate the first time through. 

The main benefit of this technique lies in the fact that it is, in chemical terms, essentially identical to bulk polymerisation. Any recipe which has been optimised by grinding and sieving of bulk materials could be transferred directly to the pores of preformed beads. The main drawback is that quite careful experimental technique is required when filling the pores and carrying out the polymerisation to avoid undue aggregation of beads. The final volume of imprinted polymer is also obviously limited by the space occupied by the original bead structure. This could range from about 5% to 40% or more. Suitable beads with low polydispersity can also be quite expensive, which makes the technique unattractive for some applications. 

Reaction was also applied on coupling of aliphatic carboxyUc acids and amines (Table 3.14), and the chiral bis-amides were likewise obtained from diamines without the loss of chirality, suggesting that mechanochemical conditions are apphcable for the synthesis of chiral amides. In addition, several dipeptides 114 were prepared (Scheme 3.31). Racemization was not noticed which is the usual drawback of conventional solution-based procedures (Table 3.15). In dipeptide synthesis 2 equiv. of DMAP were used as the base to deprotonate the unprotected amino acid, and as the activator of EDC HCl and sodium chloride were added as the grinding auxiUary. 

Hence, another drawback of fly ash cements becomes evident— the veiy low strength increase at low temperatures. The improvement of strength development can be achieved by very fine fly ash grinding. 

Particles in the submicrometer scale (typically 0.3-10 pm) can be obtained through this method. The synthesis is similar to the monolithic technique, but an excess of porogenic solvent is used. As particles grow, they become more insoluble in the organic solvent, and precipitation of nano- and microparticles is finally produced to form a polymer monolith. The main drawback is the larger amounts of template needed because of the dilution factor, but the particles work better than those obtained by grinding and sieving procedures. This method has been... 

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