Filler choice

Furan Mortars Furans have the broadest range of resistance to both acid and alkali (pH 0-14) and temperatures of all the resin mortars. Furan mortars can accept temperatures up to 350°-360°F. Modified furans are available that can withstand continuous temperatures of up to 425°F and intermittent temperatures to 475°F. Unlike the other mortar materials, furans have excellent resistance to strong alkalies as well as non-oxidizing acids and many organic chemicals. However, furan mortars are attacked by some organic solvents such as aniline. Furans are available with silica, carbon or barytes fillers, the filler choice depending upon the environmental conditions. 

Melting temperatures of fillers are given in the tables for individual fillers in Chapter 2. These temperatures are usually so high that they do not have much relevance to filler choice. The only area when the melting or decomposition temperature of the filler may become relevant is in the processes of filler recoveiy Irom waste plastics. Such studies were not found in the literature. 

The application of polymer affects choice of filler. For example, to prepare conductive materials, special fillers must be used to obtain the required properties. Also, the method of processing imposes certain constraints on the choice and treatment of the filler before its use. For example, polymers processed at high temperature require fillers which do not contain moisture. This affects both the choice of the filler and/or its pretreatment. The choice of additives used to improve the incorporation of the filler depends on the application and the properties required from a product but it is also determined by the processing method. For example, the viscosity of a melt is reduced by special lubricating agents whereas the viscosity of filler dispersions is controlled by the surface treatment of filler. In some cases, the order of addition is important or a special filler pretreatment is used to achieve the desired results. These methods are discussed in special section in the table. Some fillers simply caimot be used with some polymers. In other cases, special care must be taken to ensure polymer stability or filler may interact with some vital components of the formulation. This subject is discussed in special considerations of filler choice. 

In PVC coating formulation fillers play a role. Filler choice mostly depends on the way the filler affect viscosity. The filler should not absorb the plasticizers nor interfere with the pseudoplastic behavior of the paste which is determined by the resin properties and by the choice of plasticizers. Fillers must be completely dispersed, since the gaps between the coated substrate and the knife are very small. There must be no lumps. Fillers should not interfere with deaeration which is... 

The mechanism of cure has an important influence on the filler choice. In reactive systems such as polyurethanes, water present in formulation adversely affects sealant stability (shelf-life) which imposes the additional selection criterion of water content. If water is present in the filler it must be removed by additional operations either by an expensive drying process or through the use of chemical moisture scavengers which is also an expensive approach. 

E. M. Dannenberg, Filler choices in the rubber industry. Rubber Chem. Technol. 55,860 (1982). L. D. Albin, Current trends in fluoroelastomer development. Rubber Chem. Technol. 55, 902 (1982). 

Cross-link density and filler choice (based on type, quantity, and choice of plasticizers) are key factors for property optimization. 

Nerve guidance conduit can be hollow or filled with matrix to support axonal elongation. A popular filler choice is natural polymeric gel. Ideally, the... 

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. 

The initial uses of colorants in plastics were as extenders and additives. Carbon black and titanium dioxide were and are stiU used as fillers (qv) because of their low cost. Almost from plastics inception the limitation of black and white did not offer sufficient color choices for end users looking to differentiate their products. The increase in aesthetic requirements along with different performance requirements and resin compatibiUties led to a great expansion in the number of different chemical classes of colorants and forms in which these colorants are available in today s market. 

The electrical-insulating and dielectric properties of the pure EPM/EPDM are excellent, but in compounds they are also strongly dependent on the proper choice of fillers. The electrical properties of vulcanizates are also good at high temperatures and after heat-aging. Because EPM/EPDM vulcanizates absorb Htde moisture, their good electrical properties suffer minimally when they are submerged in water. 

In summary, then, design with polymers requires special attention to time-dependent effects, large elastic deformation and the effects of temperature, even close to room temperature. Room temperature data for the generic polymers are presented in Table 21.5. As emphasised already, they are approximate, suitable only for the first step of the design project. For the next step you should consult books (see Further reading), and when the choice has narrowed to one or a few candidates, data for them should be sought from manufacturers data sheets, or from your own tests. Many polymers contain additives - plasticisers, fillers, colourants - which change the mechanical properties. Manufacturers will identify the polymers they sell, but will rarely disclose their... 

The choice of filler depends on the end use. Metal fillers will improve machineability, hardness and thermal conductivity but may in some cases inhibit cure. 

Colour. The colour of resins ranges from water-white to dark brown. Colour may be an important factor in resin choice depending on end use. Pale colours are necessary in some types of adhesives, whereas darker colours may be tolerated in rubber formulations, especially where carbon black filler is incorporated. Medium-coloured resins can be used in most adhesive formulations. 

An interesting example of judicious choice of braze filler is to be found in the selection of silver alloys for the brazing of stainless steels to be subsequently used in a tap-water environment . Although the brazed joint may appear to be quite satisfactory, after a relatively short exposure period failure of the joint occurs by a mechanism which appears to be due to the break-down of the bond between the filler and the base metal. Dezincifica-tion is a prominent feature of the phenomenon and zinc-free braze alloys based on the Ag-Cu system with the addition of nickel and tin have been found to inhibit this form of attack. A similar result is obtained by electroplating 0-007 mm of nickel over the joint area prior to brazing with a more conventional Ag-Cu-Zn-Cd alloy. 

So far there is no cover-all recipe for remedying these undesirable phenomena yet recommendations have been made for some special cases which included proper choice of process conditions and methods, rational design of molds and articles allowing one to minimize the negative effect of filler and matrix orientation in the manufacturing process [370],... 

As far as conducting fillers are concerned, we have rather a wide range of choice. In addition to the traditional and long used fillers, such as carbon black and metal powders [13] fiber and flaky fillers on organic or metal bases, conducting textures, etc recently appeared and came into use. The shape of the filler particles varies widely, but only the particle aspect ratio, the main parameter which determines the probability... 

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