Other Synthetic Fillers

For some time titanium oxide and aluminum oxide manufactured by flame hydrolysis (see Section 5.8.4.1.1) have been marketed as fillers. 

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The mbber compound usually requires an inert inorganic filler and small particle sise carbon particle for reinforcement. The mbber polymers vary in inherent tensile strength from very high in the case of natural mbber to almost nonexistent for some synthetic polymers, eg, SBR. The fillers most commonly used for mbber compounds include carbon black, clay, calcium carbonate, siUca, talc (qv), and several other inorganic fillers. 

Mechanical properties depend considerably on the stmctural characteristics of the EPM/EPDM and the type and amount of fillers in the compound. A wide range of hardnesses can be obtained with EPM/EPDM vulcanisates. The elastic properties are by far superior to those of many other synthetic mbber vulcanizates, particularly of butyl mbber, but they do not reach the level obtained with NR or SBR vulcanizates. The resistance to compression set is surprisingly good, in particular for EPDM with a high ENB content. 

Organic Extenders. Organic extenders are primarily of two types (1) fillers derived from organic materials and (2) low-cost, naturally occurring or synthetic resins. Of the first type, wood flour, shell flour, and other cellulosic fillers are the most common. They also provide a margin of mechanical property reinforcement because of their relatively high aspect ratio. Of the resinous types these are petroleum-based derivatives as well as soluble lignin and scrap synthetic resins. 

Asbestos-reinforced organic binders (thermoplastics, duroplasts and elastomers) are widely utilized e.g. hardenable molding materials on the basis of asbestos-reinforced phenol or melamine resins for the manufacture of insulating components for combustion engines, components for electrical installations, cogwheels etc. Possible fiber substitutes are glass fibers, carbon fibers and other synthetic fibers (e.g. aramide fibers) and non-fiber fillers such as calcium carbonate, clay or talcum. 

Liquid drops dispersed in a second liqtiid medium are called emulsions and may be the most important of all colloids, including blood and milk. Sohd colloids suspended in liqtiid are called sols, or hydrosols, when waterborne. Sohd suspensions include ice cream, sedimentary rock formations, colored plastics and ceramics filled with pigment particles (as opposed to dyes), and other synthetic composites. Composites are made from two sofids to form a hybrid material with the desirable properties of each constituent for example, a plastic continuous phase for its light weight with a metal or ceramic filler for strength. 

Low cost biofibers such as jute, sisal, hemp, flax, ramie, banana, coir, etc., have received considerable attention in the recent years. These materials have successfully replaced the synthetic fibers glass in particular and other mineral fillers for fabrication of biobased composites used for engineering applications in various sectors such as aerospace, automobile, electronics, packaging, construction, etc. 

Low cost Emulsion polymers are low cost compared to most other synthetic elastomers. Also they can be compounded with a variety of low cost fillers for sealant and low bond strength applications. 

In synthetic fillers it is sometimes difficult to separate fundamental from aggregate shape but, where there is sufficient incentive, then ways will usually be found to overcome such difficulties. Such incentives arose in carbon blacks and more recently in precipitated silica, where shapes are very complex, but an understanding is critical to their high value usage in the tyre industry. Much work has been done, especially by Medalia and Heckman [16], and by Hess and co-workers [17], to develop automatic image analysis procedures. Using such procedures, all the aspects described previously have been investigated. This work has much to teach us about other filler particles. 

Fillers. The filler is usually selected from carbon materials that graphitize readily. As mentioned in Ch. 4, such materials are generally cokes, also known in industry as "soft fillers . They graphitize rapidly above 2700°C (the graphitization process is described in Sec. 2.4 below). Other major fillers are synthetic graphite from recycled electrodes, natural graphite, and carbon black (see Ch. 10). 

Synthetic composite materials have passed through intensive progress in the last fifty years. Originally, synthetic polymers were blended with inorganic fillei-s for the sake of price reduction on the other hand, fillers cause considerable change in many physical properties of polymei-s. Later, functional fillers bringing other effects to polymer composites, such as magnetic or electrical properties, bioactivity, reduced flammability, etc., were introduced in the 80 s and 90 s. Nanocomposites can offer both miique properties and multi-functionality, which are well applicable in various fields. Undoubtedly, if one wants to use polymer nanocomposites in specific applications, the structure-property relationships have to be fully understood in these miique materials first. 

PMMA was not the only type of polymer to be employed as a denture base material. Other synthetic polymers have also been introduced, including bakelite (phenol-formaldehyde) cellulose nitrate, nylon, epoxy resins, vinyl polymers (polyvinyl chloride and polyvinyl acetate) and polystyrene. Polycarbonates infiltrated with glass filler particles have also been used as denture based materials and, due to their filler content, have shown nine times higher impact properties than PMMA. Yet these materials have the disadvantage of more difficult molding than acrylics, since injection molding is required [97, 98]. 

Synthetics - Synthetic fillers, other than Ti02, are the silicas and aluminas. The silicas are either amorphous or crystalline, and are formed by precipitating various forms of silicon dioxide fi om acidified soluble silicates. The synthetics can be hydrated silica, simple alkaline earth metal silicates, or almninum silicates. 

Eatty bisamides are used primarily to kicrease sHp, reduce blocking, and reduce static ki polymeric systems. Other specialty appHcations kiclude cosolvents or coupling agents for polyamide reskis, fillers for electrical kisulation coatings, additives for asphalt to reduce cold flow, and synthetic waxes for textile treatments (68). Bisamides have been used ki all the traditional primary amide appHcations to kicrease lubricity and have become the amide of choice because of thek better efficiency. Bisamides have the highest commercial value ki the amide market. 

Some rubber base adhesives need vulcanization to produce adequate ultimate strength. The adhesion is mainly due to chemical interactions at the interface. Other rubber base adhesives (contact adhesives) do not necessarily need vulcanization but rather adequate formulation to produce adhesive joints, mainly with porous substrates. In this case, the mechanism of diffusion dominates their adhesion properties. Consequently, the properties of the elastomeric adhesives depend on both the variety of intrinsic properties in natural and synthetic elastomers, and the modifying additives which may be incorporated into the adhesive formulation (tackifiers, reinforcing resins, fillers, plasticizers, curing agents, etc.). 

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