Effect of filler size distribution

In order to study the effect of filler size distribution, it is necessary to work with uniform monodisperse particles. These would have to be available in different sizes so that controlled mixtures of two or three different sizes can be studied. There are various methods of getting uruform-sized particles and these have been discussed in a number of articles [102-106]. 

Figure 7 shows the effect of filler particle shape on the viscosity of filled polypropylene melts, containing glass beads and talc particles, of similar density, loading and particle size distribution. The greater viscosity of the talc-filled composition was attributed to increased contact and surface interaction between these irregularly shaped particles. 

Fig. 7. The effect of filler particle shape on the viscosity of polypropylene (PP) at 200 °C (A) neat PP ( ) PP containing 40% by weight glass beads (O) PP containing 40% by weight talc. (Filler size distributions similar, at 44 pm or less) [17]...

In semicrystalline polymers, fillers may act as reinforcement, as well as nucle-ation agents. For example in PP, nanoscale silica fillers may nucleate the crystallization resulting in spherulites that show enrichment in particles in the center of the spherulite (Fig. 3.64). For a quantitative analysis of, e.g., filler sizes and filler size distributions, high resolution imaging is necessary and tip convolution effects [137-140] must be corrected for. The particles shown below are likely aggregates of filler particles considering the mean filler size of 7 nm [136]. 

Tensile properties of composite propellants depend on the tensile properties of the matrix, concentration of the components, particle size, particle-size distribution, particle shape, quality of the interface between fillers and polymeric binder, and, obviously, experimental conditions (strain rate, temperature, and environmental pressure). Many authors (2, 3) have explained the effect of fillers on the mechanical properties of composites, the importance of the filler-matrix interface on physical properties, and the mechanism of reinforcement of the material. Other efforts have examined the effect of experimental conditions on the failure properties of filled elastomers. Landel and... 

Other models take into consideration the effects of shape, size, and interfacial resistance on thermal conductivity. However, these models are unable to predict the effective thermal conductivity accurately if contact among filler particles exists. The Cheng and Vachon (Tavman 2003) model assumes a parabolic distribution of disperse phase (spheres or fibers) in a solid matrix. When k, > kp, thermal conductivity of the polymer composite is given by equation (11.7) ... 

Polymers are often mixed with various particulate additives and fillers in order to produce a new class of materials termed polymeric composites [74]. This combination of materials brings about new desirable properties. For example, mineral fillers are added into the polymer matrix to improve mechanical properties, dimensional stability, and surface hardness. The effect of fillers on mechanical and other properties of the composites depends strongly on their shape, size and size distribution of the primary particles and their aggregates, surface characteristics, and degree of dispersion and distribution [75]. 

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... 

Table 8.1 Characteristics of filler particles investigated to study the effect of filler particle size distribution (PSD)...

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. 

Sirisinha et al. studied the effects of filler and mbber polarity on the distribution of filler in BR/NBR blends, using the DMTA technique. As 30-phr filler is added, the reduction in heights of tan 5 is attributed to the dilution effect. It has also been also found that small and large particle sized carbon black prefer to reside in BR phase compared NBR phase in the blends because of the lower viscosity and lower polarity of the BR phase. The addition of silica instead of carbon black leads to an increase in filler migration to the NBR in the 20/80 BR/NBR blend, which is attributed to the strong silica-NBR interaction. In addition, an increase in NBR polarity promotes carbon black migration to the BR phase. 

Chapter 4 investigates the rheological and the dynamic mechanical properties of rubber nanocomposites filled with spherical nanoparticles, like POSS, titanium dioxide, and nanosilica. Here also the crucial parameter of interfacial interaction in nanocomposite systems under dynamic-mechanical conditions is discussed. After discussing about filled mono-matrix medium in the first three chapters, the next chapter gives information about the nonlinear viscoelastic behavior of rubber-rubber blend composites and nanocomposites with fillers of different particle size. Here in Chap. 5 we can observe a wide discussion about the influence of filler geometry, distribution, size, and filler loading on the dynamic viscoelastic behavior. These specific surface area and the surface structural features of the fillers influence the Payne effect as well. The authors explain the addition of spherical or near-spherical filler particles always increase the level of both the linear and the nonlinear viscoelastic properties whereas the addition of high-aspect-ratio, fiberlike fillers increase the elasticity as well as the viscosity. 

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