Fillers rubber affinity

Medalia [16] demonstrated a further usefulness of this approach by using graphitised carbon blacks, which are known to have a weaker surface-affinity towards rubber. Thus, the method provides a means of examining the filler-rubber interaction. However, by the conditions set for deriving Equation 8.10, its applicability is limited to a small deformation. Also, only bi-particle interactions are considered in the equation and multi-particle interactions are assumed to be negligible. For the filled-rubber with the normal loading of 40-50 phr, the carbon black particles are crowded and the multi-particle interaction is important. 

It has been shown that the spacial location of the rubber can have a profound effect on mechanical properties [80] and may be influenced by the relative chemical affinity of rubber and plastic matrix towards the filler, the imposed shear during blending and the procedure adopted to combine the component phases, i.e. sequential or simultaneous. 

Additionally for rubber compounds, the differences in polarity and unsaturation of the various polymers cause different affinities for fillers and curing additives. In blends of different rubber polymers, the reinforcing filler carbon black for instance locates itself preferentially in the phase with the higher unsaturation and/or polarity, leaving the lower unsaturation or nonpolar phase unreinforced. The affinity for carbon black decreases in the following order of polymers [2] ... 

An important role in the present model is played by the strongly non-linear elastic response of the rubber matrix that transmits the stress between the filler clusters. We refer here to an extended tube model of rubber elasticity, which is based on the following fundamental assumptions. The network chains in a highly entangled polymer network are heavily restricted in their fluctuations due to packing effects. This restriction is described by virtual tubes around the network chains that hinder the fluctuation. When the network elongates, these tubes deform non-affinely with a deformation exponent v=l/2. The tube radius in spatial direction p of the main axis system depends on the deformation ratio as follows ... 

Figure 6.5 shows various functional groups which may be detected on silica, talc, and clay surfaces. The surface character of carbon black differs in that it is mostly nonpolar whereas the surface of silica is polar. Thus carbon black is more compatible with hydrocarbon polymers which are also nonpolar. Silica and other similar fillers (talc, clay) have more affinity to each other than to nonpolar polymers. This is a major factor in the inferior performance in rubber applications where interfacial adhesion is reduced. 

Powders are commonly used as fillers for rubber mixes. The most popular are carbon black, silica, kaolin, or more modem like graphene, fullerenes and carbon nanotubes. The nature of their surface is the main attribute of fillers, as surface energy and specific area determine the compatibility of filler with mbber matrix and the affinity to other c ingredients. One of the major problems is the tendency of fillers to agglomeration - formation of bigger secondary stmctures, associated with lower level of filler dispersion, what is reflected by the decrease of mechanical properties of mbber vulcanizates [1]. Surface modification of powder can improve interaction between mbber matrix and filler. Application of low-temperature plasma treatment for this purpose has been drown increasing attention recently [2, 3]. 

There is considerable evidence that all the hysteresis effects observed in these materials and most of the viscoelastic behavior can be caused by the time dependent failure of the polymer on a molecular basis and are not due to internal viscosity [1,2]. At near equilibrium rates and small strains filled polymers exhibit the same type of hysteresis that many lowly filled, highly cross-linked rubbers demonstrate at large strains [1-8]. This phenomenon is called the "Mullins Effect" and has been attributed to micro-structural failure. Mullins postulated that a breakdown of particle-particle association and possibly also particle-polymer breakdown could account for the effect [3-5]. Later Bueche [7,8] proposed a molecular model for the Mullins Effect based on the assumption that the centers of the filler particles are displaced in an affine manner during deformation of the composite. Such deformations would cause a highly non-uniform strain and stress gradient in the polymer... 

However, a high vinyl rubber is also made. The styrene content may be varied widely. The chain-end may be modified to improve affinity to carbon black, resulting in a better dispersion of the filler. These variations in molecular architecture were developed for satisfying the requirements of automotive tyres for a low energy loss and a high skid resistance. The anionic polymerisation provides a flexibility in designing molecular architecture such a flexibility is unavailable for the current practice of other polymerisation systems. 

The second aspect is the affinity between filler and rubber which, affects incorporation. The stronger this affinity the easier that incorporation appears. Concerning the filler-... 

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