Elastomers particulate fillers

Carbon blacks are the most widely used fillers for elastomers, especially vulcanised natural rubber. They cause an improvement in stiffness, they increase the tensile strength, and they can also enhance the wear resistance. Other particulate fillers of an inorganic nature, such as metal oxides, carbonates, and silicates, generally do not prove to be nearly so effective as carbon black. This filler, which comes in various grades, is prepared by heat treatment of some sort of organic material, and comes in very small particle sizes, i.e. from 15 to 100 nm. These particles retain some chemical reactivity, and function in part by chemical reaction with the rubber molecules. They thus contribute to the crosslinking of the final material. 

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. 

Below Tg of polystyrene the glassy domains also fulfill another useful role by acting like a reinforcing particulate filler. It is also an apparent consequence of this role that SBS polymers behave like carbon-black-reinforced elastomers with respect to tensile strength. 

The reinforcement of elastomers by particulate fillers has been extensively studied in the past, particularly in the 1960s and 1970s. The first reason is naturally the drastic changes in mechanical properties that induce fillers reinforcement Many of the usual applications of elastomers could not be envisaged without the use of particulate fillers. The other reason seems to us to be of a very different nature, and probably resides in the mystery of the reinforcement mechanism that has fascinated many scientists and remains, despite their efforts, mainly not understood today. 

As it will be discussed later, the size of the filler is probably one of the most important properties for reinforcement. So, particulate fillers obtained by grinding of minerals or by coarse precipitation are usually nonreinforcing fillers because of their size they are too big. Such fillers can even be used in elastomers but just confer them a very slight increase in modulus and a very significant drop in break properties occurs. 

Even if the term nanocomposite is usually not used in reinforcement by particulate fillers, it would be particularly adapted mixing of reinforcing solids and elastomers is not limited to the arithmetic sum of the properties of both taken independently but gives a synergetic alliance that achieves new properties. 

The quality of particulate filler dispersion in the elastomer matrix is of primary importance for compound mechanical and use properties (Gotten, 1983 Funt, 1986 Gerspacher and O Farrell, 1993 Bomo andMorawski, 1983 Richmond etal., 1993). 

Reinforced elastomers containing large quantities, about 30% by volume, of a finely divided reinforcing particulate filler such as carbon black. 

Reinforcements are used to enhance the mechanical properties of a plastic or elastomer. Finely divided silica, carbon black, talc, mica, and calcium carbonate, as well as short fibers of a variety of materials, can be incorporated as particulate fillers. Incorporating large amounts of particulate filler during the making of plastics such as polypropylene and polyethylene can increase their stiffness. The effect is less dramatic when temperature is below the polymer s Tg. 

---