Effect of filler agglomerates

Heat conductivity of composite materials are severely and adversely affected by structural defects in the material. These defects are due to voids, uneven distribution of filler, agglomerates of some materials, unwetted particles, etc. Figure 15.18 shows the effect of filler concentration on thermal conductivity of polyethylene. Graphite, which is a heat conductive material, increases conductivity at a substantially lower concentration than does quartz. These data agree with the theoretical predictions of model. Figure 15.19 shows the effect of volume content and aspect ratio of carbon fiber on thermal conductivity. This figure should be compared with Figure 15.17 to see that, unlike electric conductivity which does depend on the aspect ratio of the carbon fiber, the thermal conductivity is only dependent on fiber concentration and increases as it increases. 

Figure 18.9 shows the effect of filler particle size on extruder throughput for PP filled with talc. Several reasons account for reduction in throughput as the particle size decreases. Increasing the surface area of filler makes mixing more difficult because of agglomerate formation. Smaller particle sized talc has lower bulk density which decreases the conveying efficiency of screw. The relatively large amount of air supplied with the particles decreases the conveying efficiency and increases the time required to extract air. The amount of talc added affects the ratio of throughput, Q, to the screw speed. Ns (Figure 18.10). As the concentration...

More recently nanoscale fillers such as clay platelets, silica, nano-calcium carbonate, titanium dioxide, and carbon nanotube nanoparticles have been used extensively to achieve reinforcement, improve barrier properties, flame retardancy and thermal stability, as well as synthesize electrically conductive composites. In contrast to micron-size fillers, the desired effects can be usually achieved through addihon of very small amounts (a few weight percent) of nanofillers [4]. For example, it has been reported that the addition of 5 wt% of nanoclays to a thermoplastic matrix provides the same degree of reinforcement as 20 wt% of talc [5]. The dispersion and/or exfoliahon of nanofillers have been identified as a critical factor in order to reach optimum performance. Techniques such as filler modification and matrix functionalization have been employed to facilitate the breakup of filler agglomerates and to improve their interactions with the polymeric matrix. 

In the case of HAF N330 filler in its virgin first cycle that the resistivity increased up to 20% strain. They have attributed this initial increase in resistivity to the breakdown of the filler network structure in the rubber. They observed that when the applied tensile strain increases above this 20% strain, the resistivity with strain graph reaches a plateau. They suggested the occurrence of this phenomenon is a consequence of the orientation effects of filler imder strain and also the effect of the reformation of some of the conduction paths. When the load is removed, the resistivity does not return to its original value but increases further. This indicates that some of the breakdown of the filler agglomerate structure is permanent. 

Chapters 6 to 9 discuss the steady shear viscous properties, steady shear elastic properties, unsteady shear viscoelastic properties and extensional flow properties, respectively. The effect of filler type, size, size distribution, concentration, agglomerates, smface treatment as well as the effect of polymer type are elucidated. The tenth chapter has been... 

The effect of filler type, size, concentration, size distribution, agglomerates, surface treatment and polymer matrix on the rheology of the filled systems is discussed in detail in most cases. Only where information is lacking, such as in tire case of extensional flow properties in Chapter 9, are some of tiie effects missing, and the discussion is concise on the treated effects. 

Even dynamic measurements have been made on mixtures of carbon black with decane and liquid paraffin [22], carbon black suspensions in ethylene vinylacetate copolymers [23], or on clay/water systems [24,25]. The corresponding results show that the storage modulus decreases with dynamic amplitude in a manner similar to that of conventional rubber (e.g., NR/carbon blacks). This demonstrates the existence and properties of physical carbon black structures in the absence of rubber. Further, these results indicate that structure effects of the filler determine the Payne-effect primarily. The elastomer seems to act merely as a dispersing medium that influences the magnitude of agglomeration and distribution of filler, but does not have visible influence on the overall characteristics of three-dimensional filler networks or filler clusters, respectively. The elastomer matrix allows the filler structure to reform after breakdown with increasing strain amplitude. 

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