Aspect ratio of filler

The aspect ratio of the filler has significant impact on flexural modulus (Figure 8.17). The values of coefficient, a, given on the graph are the values of coefficient from Einstein equation, Eq 8.2. This coefficient varies in proportion to aspect ratio of filler. The higher the aspect ratio the higher the steepness of graph. 

Increased barrier properties against gas transport through the nanocomposite. (Because of the high aspect ratio of filler.)... 

Lee et al. [33] predicted the coefficient of thermal expansion of composites with aligned isotropic fiber- and disk-like fillers and its dependence on the aspect ratio of fillers. They found that the longitudinal coefficients of thermal expansion decrease and approach that of fillers. However, the transverse coeflBcients may increase or decrease with the aspect ratios. They also developed a new model, based on... 

Wollastonite with an aspect ratio of 15 1 is useful as a replacement for asbestos and as a high-strength filler for plastics. The feed material with dgo of 45 [Lm was similarly ground. Beads of 0.3 mm gave faster grinding than 0.8 mm beads, and these corresponded to a bead-particle-size ratio of 19, confirming other results. 

Filler architecture Filler geometry to some extent is influenced by the way in which the fillers are extracted and processed. The aspect ratio (the ratio of filler length to diameter) is an important characteristic for any material to be used as filler. Thus fillers with high aspect ratio are long and thin, while those with low aspect ratio are shorter in length and broader in the transverse direction [1]. 

Carbon black is reinforced in polymer and mbber engineering as filler since many decades. Automotive and tmck tires are the best examples of exploitation of carbon black in mbber components. Wu and Wang [28] studied that the interaction between carbon black and mbber macromolecules is better than that of nanoclay and mbber macromolecules, the bound mbber content of SBR-clay nanocompound with 30 phr is still of high interest. This could be ascribed to the huge surface area of clay dispersed at nanometer level and the largest aspect ratio of silicate layers, which result in the increased silicate layer networking [29-32]. 

Where q0 is the length efficiency factor related to the aspect ratio of the filler and thus the stress build-up along its length it can take values from 0 to 1 and can be calculated using theoretical models, q, is an orientation factor that takes values of 1 for perfect alignment, 3/8 for alignment in the plane and 1/5 for random orientation. Equation (8.1) can be arranged as ... 

Glass beads act as a mineral filler with an aspect ratio of 1. Table 3.6 displays results for glass bead reinforced polyamide. The effect ratio is the performance of the reinforced polymer divided by the performance of the neat polymer. 

Interfacial structure is known to be different from bulk structure, and in polymers filled with nanofillers possessing extremely high specific surface areas, most of the polymers is present near the interface, in spite of the small weight fraction of filler. This is one of the reasons why the nature of the reinforcement is different in nanocomposites and is manifested even at very low filler loadings (<10 wt%). Crucial parameters in determining the effect of fillers on the properties of composites are filler size, shape, aspect ratio, and filler-matrix interactions [2-5]. In the case of nanocomposites, the properties of the material are more tied to the interface. Thus, the control and manipulation of microstructural evolution is essential for the growth of a strong polymer-filler interface in such nanocomposites. 

Recently, some models (e.g., Halpin-Tsai, Mori- Tanaka, lattice spring model, and FEM) have been applied to estimate the thermo-mechanical properties [247, 248], Young s modulus[249], and reinforcement efficiency [247] of PNCs and the dependence of the materials modulus on the individual filler parameters (e.g., aspect ratio, shape, orientation, clustering) and on the modulus ratio of filler to polymer matrix. 

Organic Extenders. Organic extenders are primarily of two types (1) fillers derived from organic materials and (2) low-cost, naturally occurring or synthetic resins. Of the first type, wood flour, shell flour, and other cellulosic fillers are the most common. They also provide a margin of mechanical property reinforcement because of their relatively high aspect ratio. Of the resinous types these are petroleum-based derivatives as well as soluble lignin and scrap synthetic resins. 

This paper represents an overview of investigations carried out in carbon nanotube / elastomeric composites with an emphasis on the factors that control their properties. Carbon nanotubes have clearly demonstrated their capability as electrical conductive fillers in nanocomposites and this property has already been commercially exploited in the fabrication of electronic devices. The filler network provides electrical conduction pathways above the percolation threshold. The percolation threshold is reduced when a good dispersion is achieved. Significant increases in stiffness are observed. The enhancement of mechanical properties is much more significant than that imparted by spherical carbon black or silica particles present in the same matrix at a same filler loading, thus highlighting the effect of the high aspect ratio of the nanotubes. 

The experimental values are compared with the Guth and Halpin-Tsai predictions using the respective aspect ratios of 70 and 90 to fit the data (Figure 12.11). These values are lower than expected from the average dimensions of the MWNTs but much higher than those previously published for MWNTs for hydrocarbon rubber / MWNTs composites (22,31) which is a result from a better filler dispersion. 

The crystal quality can be varied by careful adjustment of bismuth concentration, temperature, pH, pressure, reactor geometry, and by addition of surfactants. The usually tetragonal bipyramidal structure can be flattened to platelets with a high aspect ratio. Products with an aspect ratio of 10-15 show low luster and a very good skin feel and are used as fillers in cosmetics. Crystals with higher aspect ratios show an exceptional luster and are mainly used for nail polish [5.122, 5.123, 5.128, 5.130]. 

In many compounding operations it is necessary to split the feed streams. This may be required in order to 1) achieve disperse phase size of an impact modifier 2) retain aspect ratio of reinforcing fiber filler or 3) obtain high level of loading for either low bulk density filler or incompatible low viscosity additives. 

Mica fillers are obtained by separation of mica from other minerals which might compose 10-20% of mineral content. Mica is diy or wet milled and classified. The mechanical grinding produces flakes with a low aspect ratio in a range from 20 to 40. The process may include ultrasonic delamination which leads to a high aspect ratio of over 200. Flakes of mica fillers have a thickness in a range from 1 to 3 im and a width in a range from 10 to 450 pm. 

Aspect ratio is the length of a particle divided by its diameter. Table 5.7 provides information on aspect ratios of some fillers. 

A third important filler parameter is related to its shape. Figure 15.17 shows that the aspect ratio of carbon fiber affects conductivity. If the fiber is milled to almost spherical particles, its percolation threshold concentration is substantially increased. 

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