Fillers non-reinforcing

Rubber fillers J A LINDSAY Role of fillers, non-reinforcing and reinforcing fillers, adhesion aspects... 

Non-reinforcing fillers (passive) Ground calcium carbonate (CaCO ) Reduce formulation cost adjust rheology, and mechanical properties. 

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. 

Reinforcement with carbon black or mineral ingredients is not possible. These reinforcing fillers affect the mechanical strength adversely and do not improve them. However the non-reinforcing fillers such as softer blacks and graphite and ebonite dust increase the resistance of ebonites to acids in an outstanding manner. 

Pretreatment for fillers. When used as a surface treatment for fillers or reinforcing materials, in which the silane is applied to the filler or fibre before incorporation into a resin matrix, the same factors as for pretreatment primers apply. In addition, the particle size and the absence/presence of water are important, and in a sense this application is only a variation on the former. It should be noted that silane treated fillers may have, or impart, different rheological properties to non-treated fillers, particularly particulates. A major disadvantage of this approach is that a general purpose silane may have to be used by a manufacturer rather than one specifically tailored to the use of a particular resin type and less than optimum properties are likely to be achieved in some cases. 

One reason for using extending (non-reinforcing) fillers is to reduce the cost of the compounded elastomer. They are exemplified by kaolin, diatomaceous earth, and minerals such as calcium carbonate. 

Non-reinforcing extending fillers are used in many silicone RTV sealant formulations. These include calcium carbonate, carbon blacks, talcs and other inorganic fillers. 

Mullins softening may be defined as the reduction of modulus caused by successive stretching (Bachmann et al, 1959 Boonstra, 1965 Bueche, F., 1965 Dannenberg, 1966 Harwood et al, 1967 Mullins, 1969 Mullins and Tobin, 1956 Sellers and Toonder, 1965). This phenomenon is characteristic of truly reinforcing fillers, but occurs to a lesser extent in gums and non-reinforced systems (Kraus, 1971). 

The inherent strength and resilience properties simplify the matching of the rubber to the application. Where optimum elastic properties are required, the rubber can be used in essentially unfilled (gum) vulcanizate form. If fillers are required non-reinforcing types can often be used, instead of the reinforcing fillers that are essential for low-strength rubbers. 

Non-reinforcing fillers, for a given increase in vulcanizate stiffness, generally give better permanent set, creep and dynamic properties than reinforcing types. The basic properties of natural rubber also show up to advantage in the fabrication of components. 

The subject of filler reinforcement on vulcanized rubber is very wide and complex. Fillers can be classified as reinforcing, semi-reinforcing and non-reinforcing. All fillers increase the hardness, modulus and stiffness of vulcanized rubber whether or not they are reinforcing or non-reinforcing. It has been established for a very long time that the term reinforcement has been widely used by the rubber technologist to denote the enhancement in the tensile... 

Polymer composites can be classified according to their particle size. Macro-filled composites contain filler particle size more than 10 pm. Midsize fillers are less than 10 pm and more than 1 pm while nanofillers have a particle size less than 1 pm and more than 0.1 pm. The micro-filled composite contains filler particle size less than 0.1 pm. The macrofiller generally is non-reinforcing filler and generally used for cost reduction particularly. 

Examples of semi-reinforcing and non-reinforcing fillers are given in Table 3. The ranking of such fillers is imprecise because it depends upon the use that may be made of them. Certain clays perform well in insulation compounds, and precipitated whitings are more than adequate to extend rubbers for components that are not subjected to high levels of stress. 

Table 3. Some non-reinforcing and semi-reinforcing fillers...

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