Common particle reinforcements

Figure 1.1 Common particle reinforcements and their respective surface area/volume ratios [4],...

Carbon black is probably the most common particle reinforcement through its extensive use in the rubber fabrication industry. 

Of these, the reinforcement system in a cmnposite material strongly determines the properties achievable in a composite. It is thus convenioit and common to classify composites according to the characteristics of the reinforcement. These can include the shape, size, orientation, composition, distribution, and manner of incorporation of the reinforcement. For the purposes of a discussion of biomedical composites, this results in two broad groups, namely, fiber-reinforced and particle-reinforced composites. Figure 12.2 shows further divisions within these groups. 

The most important compounds are polyetherols, polyesterols, and graft polyols (Figure 1). Polyetherols are the most common polyols and most commercial products are made chiefly from ethylene oxide and propylene oxide. Polyesterols are widely used in elastomeric polyurethanes. Typical compounds are aliphatic polyesters, such as poly(ethyl-ene adipate), made so that there are only hydroxyl end groups, with no residual acid groups. Graft polyols (also called polymer polyols) consist of a matrix of a conventional polyol, which also contains rubbery (such as styrene/acrylonitrile copolymer) particles chemically bound to polyol molecules. These grafted particles reinforce the final polyurethane, giving improved physical properties. 

Particle reinforced composite systems can be either large particle or dispersion strengthened. If a composite is reinforced by large particles (larger than 0.1 [xm and equiaxed, which are harder and stiffer than the matrix), mechanical properties are dependent on volume fractions of both components and are enhanced by increase of particulate content. Concrete is a common large particle strengthened composite where both matrix and particulate phases are ceramic materials. 

Large particle reinforced composite systems are utilised with all three types of materials (metals, ceramics and polymers). Concrete is a common large particle strengthened composite where both matrix and particulate phases are ceramic materials. 

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. 

The furnace process involves injecting low end fraction of cmde oil, eg. Bunker Euel C, into a heated chamber. The temperature, shape of the injectors of the oil, rate of injection, and other factors are controlled to produce black fillers of different particle si2e and stmcture. The particle si2e and stmcture control the reinforcing character of the carbon black. There are 30 common grades of carbon black used in the mbber industry. There are numerous specialty grades produced, and several hundred are used in plastic, conductive appHcations, and other uses. 

When employed in elastomeric systems it is commonly observed that the finer the particle size the higher the values of such properties as tensile strength, modulus and hardness. Coarser particles will tend to give compounds less strong than compounds with the filler absent, but if the particle size is sufficiently fine there is an enhancement in the above-mentioned properties (at least up to an optimum loading of filler) and the phenomenon is known as reinforcement. The particle shape also has an influence for example, the somewhat plate-like china... 

Fumed silicas (Si02). Fumed silicas are common fillers in polychloroprene [40], natural rubber and styrene-butadiene rubber base adhesives. Fumed silicas are widely used as filler in several polymeric systems to which it confers thixotropy, sag resistance, particle suspension, reinforcement, gloss reduction and flow enhancement. Fumed silica is obtained by gas reaction between metallic silicon and dry HCl to rend silica tetrachloride (SiCU). SiC is mixed with hydrogen and air in a burner (1800°C) where fumed silica is formed ... 

The mechanical properties of pure polymeric materials are often inadequate for particular applications, and to overcome this problem these materials may be reinforced in some way. The most common method is to include a substantial amount of a rigid filler or fillers, generally as finely divided powder, or as rods or fibres. For certain materials, elastomeric particles may be used, and these have the effect of reducing brittleness. 

Among the conventional hUers that have been used widely in polymers are carbon black of different sizes and shapes, sUica, and clay. Among ah these, carbon black and sihca are known as reinforcing hUers. Carbon black particles, which are commonly used in the mbber industry, have a particle size... 

The results obtained by Kuila et al. and Acharya et al. [63,64] from the EVA elastomer blended with lamellar-like Mg-Al layered double hydroxide (LDH) nanoparticles demonstrate that MH nanocrystals possess higher flame-retardant efficiency and mechanical reinforcing effect by comparison with common micrometer grade MH particles. Kar and Bhowmick [65] have developed MgO nanoparticles and have investigated their effect as cure activator for halogenated mbber. The results as shown in Table 4.2 are promising. 

There are several methods of layering in common use ( ) thick layers shrunk together (2) thin layers, each wrapped over the other and the longitudinal seam welded by using the prior layer as backup and (3) thin layers spirally wrapped. The code rules are written for either thick or thin layers. Rules and details are provided for all the usual welded joints and nozzle reinforcement. Supports for layered vessels require special consideration, in that only the outer layer could con-triDute to the support. For lethal service only the inner shell and inner heads need comply with the requirements in Subsec. B. Inasmuch as radiography would not be practical for inspection of many of the welds, extensive use is made of magnetic-particle and ultrasonic inspection. When radiography is required, the code warns the inspector... 

It is a common phenomenon that the intercalated-exfoliated clay coexists in the bulk and in the interface of a blend. Previous studies of polymer blend-clay systems usually show that the clay resides either at the interface [81] or in the bulk [82]. The simultaneous existence of clay layers in the interface and bulk allows two functions to be attributed to the nanoclay particles one as a compatibilizer because the clays are being accumulated at the interface, and the other as a nanofiller that can reinforce the rubber polymer and subsequently improve the mechanical properties of the compound. The firm existence of the exfoliated clay layers and an interconnected chain-like structure at the interface of CR and EPDM (as evident from Fig. 42a, b) surely affects the interfacial energy between CR and EPDM, and these arrangements seem to enhance the compatibility between the two rubbers. 

In order to make brittle ceramic materials tougher, several techniques can be applied. All of these have in common that they reinforce the ceramic matrix by means of particles, fibres, irregular masses or by introducing a layered structure. All these possibilities can be seen in figure 14.2. 

Whiskers provide a better reinforcement than particles from the point of view of the effect of dispersoid shape on toughness based on theoretical predictions (Shalek et al., 1986). The most commonly used whisker... 

Fluorosilicones can be compounded by the addition of mineral fillers and pigments. Fillers for such compounds are most commonly silicas (silicon dioxide), because they are compatible with the elastomeric silicon-oxygen backbone and thermally very stable. They range in surface areas from 0.54 to 400 m2/g and average particle size from 100 to 6 nm. Because of these properties, they offer a great deal of flexibility in reinforcement. Thus, cured compounds can have Durometer A hardness from 40 to 80. Other fillers commonly used in fluorosilicones are calcium carbonate, titanium dioxide, and zinc oxide. 

Fillers are available in many forms including particles, fibers, and mats or fabrics. Table 9.4 lists common forms of fillers and reinforcements that are used with epoxy adhesives. Note that epoxy adhesive film carriers such as fabrics or mats can be considered as a type of filler. 

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