Particulate fillers, reinforcement elastomers

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. 

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

The paradox of reinforcement by particulate fillers is that there is a simultaneous increase of modulus and elongation at break. This fact is clearly illustrated by the comparison of stress-strain curves of pure and carbon-black-hlled elastomer (Fig. 8). 

Boonstra, B.B. (1979) Role of particulate fillers in elastomer reinforcement a review. Polymer, 20, 691. 

There is no filler reinforcement of the polyurethane akin to the reinforcement which takes place when reactive or particulate fine particle size fillers are added to non-strain-crystallizable millable elastomers. Fillers in polyurethane reduce strength approximately in proportion to their volume they too, however, increase stiffness and hardness and are cheaper to use for this purpose than additional diisocyanate which gives the same result through hard-segment increase. 

Boonstra B B (1979) Role of Particulate Fillers in Elastomer Reinforcement A Review, Polymer 20 691-704. 

The study of the mechanical properties of filled elastomer systems is a chaUenging and exciting topic for both fundamental science and industrial application. It is known that the addition of hard particulates to a soft elastomer matrix results in properties that do not follow a straightforward mle of mixtures. Research efforts in this area have shown that the properties of filled elastomers are influenced by the nature of both the filler and the matrix, as well as the interactions between them. Several articles have reviewed the influence of fiUers hke sihca and carbon black on the reinforcement of elastomers.In general, the strucmre-property relationships developed for filled elastomers have evolved into the foUowing major areas FiUer structure, hydrodynamic reinforcement, and interactions between fiUers and elastomers. 

Polymer-based multicomponent systems are abundant in many applications. The properties and performance of particulate-filled systems, such as elastomers and impact modified polymers, and also polymer blends, block copolymers, and fiber reinforced systems, depend to a large extent on the distribution of the components. Hence the local analysis of these distributions down to sub-100 nm length scales (dictated, e.g., by the size of primary filler particles) is of considerable significance. Materials contrast in several AFM approaches offers the possibility to address these issues directly at the surface of specimens or on bulk samples that have been prepared correspondingly. 

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. 

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