Comminution techniques

There are a number of routes for recovering and reeyeling of materials from thermoset composites. With the exception of the ERCOM project none of these are particularly well developed. The most promising for development are innovative comminution techniques for the preparation of relatively uncontaminated forms of scrap as a reinforcement for development of high value... 

Smear or comminution techniques are enormously rewarding because they provide a wealth of informational detail without a large time investment. The methods are more suited to industrial applications and have found little application in the literature. The techniques necessarily disrupt the long range structure of a product but are well suited to the identification and enumeration of particulates such as crystals (Figure 1), or the structure and microchemical composition of proteinaceous particulates, either of which can be the source of organoleptic issues such as graininess. 

The data listed in Table V illustrate the effect of top mesh size on pyritic sulfur removal. The coal samples were prepared by the same comminution techniques, and consequently the size distribution of the samples should be similar for each case (8, 9, 10, 11, 12). The %,-inch mesh was as received coal, while the 14 X 0 and 100 X 0 mesh samples were obtained by grinding a representative sample in a ball mill until it... 

A comminution technique that minimizes contamination is the fluid energy mill or jet mill . The particles are entrained in high velocity streams of fluid (generally gases such... 

Comminution techniques also effectively produce solid particle dispersions of absorber dyes. Aqueous... 

Nole that the shear stress is the product of shear rate and viscosity and hence it combines the emulsion properties with the properties of the comminution technique. 

In concluding these considerations, it is obvious that for subsequent polymerization reactions the preparation of emulsions by swelling (a condensation technique) has considerable advantages when compared to comminution techniques. 

The situation in the case of emulsions prepared by comminution techniques can be partly illustrated with the help of the characteristic quantities defined above. These data are summarized in Table 8.7 for two emulsions, namely one with an average drop size of 50 pm (e.g. prepared by a common rotor/stator device) and one with an average droplet size of 100 nm (e.g. prepared by ultrasonification). 

Finally, under well-defined conditions, it is possible to polymerize performed emulsion droplets. This is especially true for emulsions prepared by condensation methods where the conditions can be controlled in such a way that both secondary nucleation can be avoided and droplet or particle stability can be maintained during the entire polymerization. In the case of emulsions prepared by comminution techniques, suspension polymerization is a good example of a system where the (conditions) properties of emulsions can be converted into the corresponding properties of sols/suspensions. For smaller drop sizes, the solubility of the monomer in water is crucial, but unfortunately, very hydrophobic monomers are technically unimportant, at least nowadays. The addition of hydrophobic molecules needs tailored emulsification procedures regarding and DSD, and a certain maturation time to result in stable emulsions. Miniemulsion polymerization is a promising way, although the question as to what extent a 1 1 copy of an emulsion is possible is still waiting for an answer. 

To overcome these problems, another comminution technique—atomization—was developed. Atomization produces solid or aerosol particles with reduced sizes by spraying molten material or material solution or suspension under conditions such that it breaks down and then solidifies as fine powder [32]. In a typical atomization process, a molten material passing through a nozzle scatters into fine droplets by a highspeed medium (e.g., gas or water) and then the droplets solidify to powder. Obviously, the atomization technique is highly efficient for preparing micron and submicron powders at industrial scales and recent development has enabled atomization to produce nanoparticles of sizes down to 20nm [33]. 

The disintegrating behavior of substances with any such characteristics can be substantially improved by addition of carbon dioxide ice or by embrittlement with liquid nitrogen. The use of direct or indirect cooling, in combination with mechanical comminution techniques, facilitates adequate processing of many types and grades of plastic, rubber, organic tissue, pharmaceutical products, spice, herbs, and food samples. 

Thermoset composite materials can be recycled through mechanical comminution techniques, to reduce the size of the scrap to produce lecyclates, using thermal processes to break the scrap down into materials and energy (Pickering, 2006). 

The crude product is converted to a finished pigment by means of various comminution techniques. These include ball milling in the presence or absence of a solvent, attrition by kneading, acid swelling, or add pasting. The apphcation properties of the finished product and its ultimate shade (a function of partide size and shape as well as size distribution) are determined to a large extent by the technique seled-ed. 

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