Reinforcing fillers structure

Reinforcing fillers in general and high-structure carbon blacks in particular improve the extrusion characteristics of elastomers by decreasing extrudate swell. The extrudate swell decreases with increasing carbon black content [33]. 

This is an extremely important area. Commercial polymers are very rarely prepared or used without additives and they often contain a combination of additives. These improve processability of the polymer, its durability, service life under adverse conditions (e.g., temperature, UV light and various chemical environments), strength (e.g., using reinforcing fillers), appearance (colorants), etc. A recent use of additives is to facilitate reprocessing or recycling or, alternatively, to promote decomposition (which is often difficult because the stability is inherent in the polymer s chemical structure). (The analysis of additives in polymers is the subject of Chapter 14.)... 

Most elastomers require reinforcing fillers to function effectively, and NMR has been used to characterize the structures of such composites as well. Examples are the adsorption of chains onto filler surfaces [275], the immobilization of these chains into "bound rubber" [276], and the imaging of the filler itself [277]. 

Mica is available in a variety of grades and finds application as a semi-reinforcing filler and more often as a processing dry lubricant owing to its flake-like structure. It is also used as a dusting agent. 

For applications where only mechanical properties are relevant, it is often sufficient to use resins for the filling and we end up with carbon-reinforced polymer structures. Such materials [23] can be soft, like the family of poly-butadiene materials leading to rubber or tires. The transport properties of the carbon fibers lead to some limited improvement of the transport properties of the polymer. If carbon nanotubes with their extensive propensity of percolation are used [24], then a compromise between mechanical reinforcement and improvement of electrical and thermal stability is possible provided one solves the severe challenge of homogeneous mixing of binder and filler phases. For the macroscopic carbon fibers this is less of a problem, in particular when advanced techniques of vacuum infiltration of the fluid resin precursor and suitable chemical functionalization of the carbon fiber are applied. 

By the addition of glass fibers, textile fibers, or chopped fabrics to crosslinkable polymers molding materials are produced with increased tensile strength, stiffness, and thermal stability compared to the filler-free polymers. The so-called reinforcing fillers, like carbon black, have good adhesion to the matrix due to their nonpolar structure and their characteristic geometry. 

Mica is a reinforcing filler which, due to its platelet structure, increases the stiffness more than spherical particles do. 

Discussion - The morphological properties of active fillers are important aspects of rubber reinforcement. The structure of the reinforcing filler is characterized by aggregates of primary particles, which form cavities for attachment and penetration of polymer molecules. The SEM pictures show that the three-dimensional morphology is basically maintained. 

The effect of strain amplitude is most pronounced in compounds containing reinforcing fillers and can result in a reduction in shear modulus of as much as a factor of 4 when going from a very small strain to about 10%. This is due to breakdown of filler structure which is associated with energy losses that cause a peak in the tan8 value. It was because of this that earlier British and international standards called for tests to be made at 2 and 10% shear strain, a sensible recommendation that has been overlooked in the present version. Turner6 produces an interesting model based on frictional elements to explain this behaviour. 

Fumed silica acts as a highly reinforcing filler in silicone elastomers. Its activity results fi-om its highly dispersed particle structure, high surface area and surface energy. To better understand the interplay of these properties first studies on gas adsorption of hexamethylsiloxane on hydrophilic and silylated silica have been conducted. The shape of the adsorption isotherm revels the existence of low- and high-energy adsorption sites, the latter qualitatively seem to be related to reinforcement of the silicone elastomer. Further quantitative studies in this field are needed. 

Film coatings are widely applied in forming concrete and reinforced concrete structures to accelerate concrete hardening and reduce crack appearance at setting. The film prevents evaporation of the water contained in the concrete, promotes hydration of the cement, and thus provides reliable contact of the cement stone and filler. It promotes an increase in concrete strength up of up to 30%, reduces damage and time of processing, and restricts moisture absorption. 

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