Fillers, active reinforcing

Reinforcing fillers (active) Fumed Silica (Si02) precipitated calcium carbonate (CaCOi) carbon black Thixotropic reinforcing agents (non-slump), adjustment of mechanical properties (cohesion) provide toughness to the elastomer as opposed to brittle materials. 

One of the most important phenomena in material science is the reinforcement of mbber by rigid entities, such as carbon black, clays, silicates, calcium carbonate, zinc oxide, MH, and metal oxide [45 7]. Thus, these fillers or reinforcement aids are added to mbber formulations to optimize properties that meet a given service application or sets of performance parameters [48-53]. Although the original purpose is to lower the cost of the molding compounds, prime importance is now attached to the selective active fillers and their quantity that produce specific improvements in mbber physical properties. 

Silica is unique among nonblack fillers. Its reinforcing ability is comparable to that of carbon black, especially when mixed with a suitable coupling agent, and its transparency affords many products. Additionally, it is chemically synthesized, which means that a wide range of silica (in terms of diameter, surface area, or surface activity) may be produced depending on the reaction routes and reaction conditions. 

Silica fillers also react with the rubber causing an increase in viscosity and dry and unmanageable processing behaviour. Filler activators need to be added to silica-reinforced compounds to overcome these problems. The usual filler activators used are diethylene glycol, polyethylene glycol and amines such as triethanolamine. Some of these activators not only overcome the problems of processing and accelerator absorption, but depending on the cure system used, will also act as vulcanisation activators. 

As Table 2 shows, non-treated fillers and reinforcements have high energy surfaces. During the almost exclusively used melt mixing procedure, the forces discussed in the previous section lead to the adsorption of polymer chains onto the active sites of the filler surface. The adsorption of polymer molecules results in the development of a layer which has properties different from those of the matrix polymer [43-47]. Although the character, thickness and properties of this interlayer or interphase are much discussed topics, its existence is now an accepted fact. 

From a rubber it is essentially demanded to elongate under stress, to withstand stress without breaking and to reversibly find back to its original shape after the stress ceases. An unfilled, cured polymer will rarely fulfill these requirements this is a fact, which is true for most rubber-like systems. The industrial development of elastomers therefore is strongly related to the production of active reinforcing fillers. 

Bound rubber is the fraction of polymer which is not extracted by a good solvent from a rubber-filler mix. It is a measure of rubber reinforcement as well as of filler activity towards the rubber. This concept was introduced in 1925 by Twiss. Although, the traditional term bound rubber is commonly used for rubber compounds, the concept can also be applied to other macromolecular materials. The amount of bound rubber is given by the following equations ... 

Composite resins consist of blends of large monomer molecules, filled with unre-active reinforcing filler. As such, they are hydrophobic, which means that they are unable to bond to the hydrophilic prepared tooth surface [1]. Glass-ionomer cements, by contrast, consist of aqueous solutions of polymeric acid, typically poly(acrylic add) and powdered reactive glass. These two components react together in an acid-base reaction, and thus cause the cement to set. These materials are hydrophilic, and therefore capable of wetting the prepared tooth surface and forming tme adhesive bonds. 

The types of additives discussed here lead to important physical changes. Thus blowing agent use permits the production of cellular structures flame retardants improve thermal and combustion characteristics pigments and colorants change the aesthetic aspect while physical and mechanical properties are modified by active fillers and reinforcements. 

Relative variation of rubber compound properties as imparted by active (reinforcing) or inert filler. 

The metal fillers act as a reinforcing material that results in added strength and stiffness (126). They color the plastic gray for nickel, 2inc, stainless steel, and aluminum, and brown for copper. Metal additives are more expensive than carbon black or surface-active agents, but they get extensive use in EMI shielding appHcations. 

Conventionally fillers are divided into reinforcing, active, and inert ones. The reinforcing class includes mainly fibrous materials. Disperse fillers may also perform the reinforcing function, and then they are called active. For the criterion of activity of a filler it has been proposed to employ, for example, the extent of variation of the relative viscosity of the melt or solution caused by introduction of a filler [23] — the greater the variation the better the affinity between the polymer and the filler. 

The developed micromechanical model of reinforcement by active fillers allows for a better control of material properties and a more fundamental engineering praxis in mbber industry. In particular. 

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