Fillers particle characteristics

To be able to control the PCM properties in the desired direction it is very important to know the relationships between the material composition and properties. Since melt viscosity is one of the most important characteristics of processability of PCM, there have naturally been a large number of equations proposed for describing the viscosity versus filler concentration relationship. For the purpose of this review it may be most interesting to discuss the numerous equations which have in common the use of the value < representing the maximum possible volume filling by filler particles packed in one way or another, as the principal constant. Here are a few examples of such equations. 

Chow demonstrated theoretically [143] that for anisodiametrical particles, the ultimate tensile stress is inversely proportional to square root of the effective or characteristic filler particle size (in this case by effective particle size the ratio of particle volume to surface area is implied). 

Generally speaking, to obtain, reliable rheological characteristics of disperse systems with fibre-like filler turned out to be a difficult methodological problem. Therefore, the question on the effect of the shape of a filler particles on the value of yield stress is left open at present. In the papers published we can encounter only individual examples and qualitative considerations concerning this question, which do not enable us to formulate general conclusions. 

It is well known that the particle size, structure, and surface characteristics are important parameters that determine the reinforcing ability of filler particle size is important because a reduction in size... 

The existence of a threshold yield stress which must be exceeded for flow to occur has been indicated in earlier discussion to be a common characteristic of highly filled polymer melts, associated with interaction between the filler particles. 

The reinforcement of filled rubbers is usually determined by the particle size and the surface characteristics of filler particles 1U U6). Recent studies have emphasized an important role of internal energy effects in reinforcement29). Hence, thermomechanical measurements provide a very important approach to the study of such reinforcement. 

This property depends on filler particle size and filler loading. Higher filler loading gives lower resilience. Rubber type plays a great role here in that no synthetic rubber can match the characteristic of high resilience of natural rubber. 

Furthermore, the effect of hydrated fillers on polymer fire retardancy will depend not only on the nature of the filler, including its particle characteristics (size, shape, and purity) and decomposition behavior, but also on the degradation mechanism of the polymer, together with any filler/ polymer interactions that might occur, influencing thermal stability of the polymer and possible char formation. 

The temperature dependence of the Payne effect has been studied by Payne and other authors [28, 32, 47]. With increasing temperature an Arrhe-nius-like drop of the moduli is found if the deformation amplitude is kept constant. Beside this effect, the impact of filler surface characteristics in the non-linear dynamic properties of filler reinforced rubbers has been discussed in a review of Wang [47], where basic theoretical interpretations and modeling is presented. The Payne effect has also been investigated in composites containing polymeric model fillers, like microgels of different particle size and surface chemistry, which could provide some more insight into the fundamental mechanisms of rubber reinforcement by colloidal fillers [48, 49]. 

The central point of the present survey is an attempt to show a complete analogy between the free volume of suspensions and that of molecular systems. It is characteristic that the limiting volume fraction of spherical filler particles leaves in the system another 25-40% of unoccupied volume. Precisely the same unoccupied volume exists in molecular systems if we liken them to a volume filled with spheres whose radii are calculated taking into account the Lennard-Jones potential. 

Bubble nucleation is affected by a number of conditions. Physically, the effects of temperature, pressure, and in some cases humidity are fairly obvious. Other important parameters are surface smoothness of the substrate, surface characteristics of filler particles, presence and concentration of certain surfactants or nucleators, size and amount of second-phase liquid droplets, and the rate of gas generation. 

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. 

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