Filler synthetic production methods

Compared to the predominant applications of these carbon materials as adsorbents for drinking water, wastewater, and gas purification, as fillers in rubber production, or as refractory materials, however, their use in the catalyst market represents only a moderate share. The potential growth of the market for carbons in catalysis depends on (1) better understanding of the chemistry of carbon surfaces and fine tuning of the microstructure of these materials, which could then be exploited in the design of truly unique catalysts and (2) improvements in quality control and production methods, to supply constant-quality materials (synthetic carbons). There are additional opportunities to increase the market value of carbon materials in the near future, due to the rapidly advancing development of fuel cells, the use of novel carbon materials, the increasing need for catalytic... 

Of the various synthetic processes that are available, two are of most relevance in the present context - precipitation from aqueous solution and melt forming. These methods are used where it is not possible to produce adequate products directly from natural sources. This will be because there is no suitable mineral, due to the chemical nature of the product, of particle size and shape requirements, or to purity considerations. The other principal synthetic method in use for filler production is pyrolysis/combustion. This type of process in which the particles are formed in the gas phase is used where very small particles are required, such as with carbon blacks and some silicas. This type of filler is not widely used in thermoplastics and so these processes are not discussed in any detail here, although some information specific to the production of antimony oxide will be found later. 

A distinction between inactive and active fillers is at present hardly relevant, since the properties of the final product depend more or less strongly upon all the fillers utilized and their use has for a long time not been primarily determined in terms of cost reduction. The efforts of the fdler producers in the direction of improved processing methods and dedicated manufacturing processes take this development into account. The surface treatment of natural and synthetic fillers has also acquired great importance. For years there have been products which in the classic sense are not fillers at all, but are in fact active substances (e.g. silica aerosols). Apart from any cost reduction considerations, fillers have essentially the following functions ... 

The phenolic resins are condensation products of phenol and formaldehyde [144-146, 148]. These materials were among the earliest commercial synthetic plastics. Two different methods [144-146] are used to prepare them. In the first one, the condensations are base catalyzed, while in the second one, they are acid-catalyzed. The products formed with basic catalysts are called resols and with acidic ones novolacs. Phenolic resins are used widely in coatings and laminates. The pure resins are too friable for use as structural materials by themselves. They become useful plastics, however, when filled with various fillers. 

Up until World War II, almost all elastomers were based on natural rubber. During the war, synthetic rubbers began to replace the scarce natural rubber. Since that time production of synthetics has increased until it now far surpasses that of natural rubber. There are thousands of different elastomer compounds. Not only are there many different classes of elastomers, but also individual types can be modified with a variety of additives, fillers, and reinforcements. In addition, curing temperatures, pressures, and processing methods can be varied to produce elastomers tailored to the needs of specific applications. 

Improved methods of vulcanization, and the addition of fillers, most often carbon black powder, to dilute the ruhher, reduced the price and improved the reliability of the product. The issue grew in importance with the coming of World War II. Rubber became scarce while the need increased. In Germany the situation was critical. A synthetic rubber, known as Buna (from the starting monomer, Mtadiene and the metallic sodium, in German watrium, used to initiate polymerization), had been produced on a laboratory scale, but it was expensive and its properties were far from ideal. A more complex polymer, with two mixed types of monomer unit, polymerized by improved procedures, gave better results. Some material was produced in the infamous Buna factory in Auschwitz. The preferred material for tyres proved later to be a polymer made from styrene and butadiene ... 

Machalkova [643] has described analysis of polymer composites and rubber blends with emphasis on separation of low-MW additives by instrumental methods. Examples refer to analysis of inorganic filler- or synthetic fibre-reinforced plastics and laminated plastic Aims using PyGC and IR. The versatility of PyGC has further been exemplified by Jones [633] as a thermovolatilisation technique for direct determination of occluded volatiles and low-MW additives in lube oil, novolac resins and HDPE, of plasticisers and vinylchloride in PVC, and of solvent residues in paints and bitumens, etc. Dicumylperoxide (DCP) in LDPE was identified through detection of three main by-products of reaction, acetophenone, a-methylstyrene and 2-phenylpropan-2-ol [633]. 

Widely used methods in the synthesis of silica nanoparticles are the sol-gel process and flame synthesis [5]. The latter is an effective synthetic route to continuously produce extremely pure nanoparticles, but in many cases the final products are agglomerated or show low reactive surfaces that make them difficult to functionalize. Nevertheless, flame synthesis is a prominent method to commercially produce silica nanopartides in powder form [6]. It is being used since decades for the production of the so-called fumed siUca, which is a filler in many applications, for example, in the pharmaceutical or polymeric business [7]. The extension of this preparation route is the so-called flame spray pyrolysis that has expanded in the last two decades to many other material compositions and is a promising rapid technique for the production of nanopowders [8]. 

Synthetic silicon dioxide (siUea) can be produced either by precipitation or by a pyrogenic (thermal) proeess. According to the method of production, synthetic silicon dioxide ean be classified into two groups precipitated and pyrogenic (fumed) silica. " Precipitated silicas have been used extensively in many mbber applications, much more than fumed silica. " In the mbber industry, the use of fumed silicas is limited due to expense, mainly being used as reinforcing fillers for silicon mbbers. Non-black fillers such as silica are chosen over CB for one or more of the following reasons ... 

Diatomaceous Earth. Diatomaceous earth is a natural form of amorphous silica to which workers ean be exposed during mining, calcining, and bagging. Diatomaceous earth is almost exclusively mined by open-pit methods, and exposure levels of 0.1-2.0 mg/m dust of which 5% is quartz have been reported (20). When diatomaeeous earth is calcined, cristobalite is formed and can account for up to 40% of the hnal product. Diatomaceous earth is a major substrate for filtering or elarifying solvents, pharmaceuticals, beer, whiskey, wine, and municipal and industrial water. It is also used as a filler for paints, paper, synthetic rubber, and securing powders. 

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