Particulate fillers, reinforcement rubbers

Higher costs and potential shortages of reinforcing carbon black have stimulated interest in the use of particulate fillers in rubber. Silica, clay, and other silicates are available at low cost in virtually unlimited supply, and in the presence of appropriate silane coupling agents, show rather creditable properties as reinforcing fillers. The nature and extent of adhesion between rubber and filler, however, has been somewhat of a mystery and clouded by contradictions ... 

Polymers, as well as elastomers, are reinforced by the addition of small filler particles. The performance of rubber compounds (e.g. strength, wear resistance, energy loss, and resilience) can be improved by loading the rubber with particulate fillers. Among the important characteristics of the fillers, several aspects can be successfully interrogated by AFM approaches. For instance, the particle and aggregate size, the morphology, and in some cases the surface characteristics of the filler can be assessed. 

The reinforcement of elastomers with particulate fillers is a process of great practical and technological importance. Most finished rubber articles are made from filled elastomers and, with a few exceptions, all amorphous rubbers which are incapable of crystallizing under strain require fillers to impart to them technologically useful mechanical properties. 

The word reinforcement will not be applied to particulate fillers, such as quartz or glass beads, because although these additives do increase the modulus, they cannot be relied on to improve the strength of the resin, nor will the word be applied to speciality rubber toughening agents that are used to improve the impact strength only. 

According to the theories on reinforcement of polymer melts and elastomers by particulate fillers, " the initial modulus of a filled rubber composite is given by diflerent contributions. Figure 2.8 reports the dependence of the shear complex modulus on the strain amplitude. 

The first hydrodynamic regime consists of randomly dispersed particulate filler in a rubber matrix, which gives an elastic reinforcement of the form given by Equation (3.1) ... 

Porosity is a characteristic property of carbon black and can be seen with other particulate type of fillers. Filler porosity can affect the properties of the vul-canizate. However, its effect on reinforcement is secondary. In most cases, the pores are too small for the polymers to enter although some smaller molecules in the compound may do so. Particulate fillers used in rubber industry in general can be classified as black and non-black , depending on their origin. 

G. Kraus, Reinforcement of elastomers by particulate fillers, Eirich FR edn., Science and Technology of Rubber. Academic Press, New York, 1978. 

Precipitated silica is obtained like silica gel by acidifying an aqueous solution of sodium silicate. Precipitated silica is used as filler in rubber for automobile tires and reinforcement particulate in elastomers, and as a flatting agent in paints and coatings for improving the... 

Surface Treatment. Carbon black remains the particulate filler of choice for rubber articles since the inherent reinforcing effect of the nonblack fillers in hydrocarbon elastomers is not comparable. This is primarily due to the nonbonded interactions established between the particulate filler and polymer functionality (28). Surface chemistry plays an important role in the interaction of the nonblack fillers and the polymer with contributions ranging from electrostatic interactions to covalent bonding to the polymer backbone. However, surface chemistry also strongly affects the interaction of the nonblack filler with other chemicals in the rubber compound, particularly active metal oxides, curatives, and antidegradants. 

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