Soft fillers

The second addend in Equation 22.21 considers the energy stored in the substantially strained fragile but soft filler clusters ... 

The hardness of mineral fillers is of considerable importance in thermoplastics applications. In general soft fillers are preferred, as the harder ones tend to cause... 

Cyclic breakdown and re-aggregation of the residual fraction of fragile, soft filler clusters with weaker filler-filler bonds. 

In the following section, the low-temperature properties of composites are treated as a function of filler concentration, particle or fiber diameters, and fiber arrangement (1 and properties). The powder fillers and fibers to be considered exhibit a lower thermal expansion, specific heat, and Poisson s ratio, but higher thermal conductivity and elastic and fracture strengths. Soft fillers applied to increase the toughness of brittle resins are not considered. 

This theory was introduced by Vilgis el al The simplest model consists of randomly dispersed uniform soft spheres. There are two limiting cases if the modulus of the soft filler particles is zero, the matrix contains holes (resembling a Swiss cheese) and thus becomes softer. On the other hand, in the case of a very large modulus of the filler particles, the Einstein-Smallwood formula (Equation (3.1)) will be reproduced. For uniform soft filler particles with elastic modulus Gf > Gm the intrinsic modulus [/r], is given by... 

Figure 17.3 The improvements in stiffness and fracture toughness of epoxy based composite with soft, rigid, and rigid-soft fillers [36].

Hardness, which is usually expressed on the Mohs scale ranges from 1 for talc to 10 for diamond. Soft fillers (e.g., talc, caldte with Mohs hardness 3) are preferred against hard fillers (e.g., silica with Mohs hardness 7) that tend to cause excessive wear of processing equipment. 

No.17, 14th Aug. 2001, p.6039-51 EFFECT OF SOFT FILLER PARTICLES ON POLYMER DIFFUSION IN POLYBUTYL METHACRYLATE LATEX FILMS... 

Add soft fillers (large furnace and thermal carbon blacks, and mineral fillers and oils)... 

Fillers. The filler is usually selected from carbon materials that graphitize readily. As mentioned in Ch. 4, such materials are generally cokes, also known in industry as "soft fillers . They graphitize rapidly above 2700°C (the graphitization process is described in Sec. 2.4 below). Other major fillers are synthetic graphite from recycled electrodes, natural graphite, and carbon black (see Ch. 10). 

Laminated gaskets are fabricated with a metal jacket and a soft filler, usually of asbestos. Such gaskets can be used up to temperatures of about 750 F to 850 F and require less bolt load to seat and keep tight than solid-metal flat-ring gaskets. 

The mechanical properties of individual filler particles - as opposed to those of filled plastics - can be quite difficult to determine, and often the data are not readily available. Hardness is an exception, being one of the more frequently quoted mechanical properties of fillers, and the materials are sometimes divided loosely into hard and soft fillers. Hardness values, together vith density and refractive index, are listed for several fillers in Table 2. The density can be expressed either as true... 

Coohng water is then circulated and the batch cooled while mixing to 35—40 °C. In some cases, with high-shear input, soft fillers such as calcium carbonate can be added with the resin, particularly with modest levels of plasticizer, improving output. This is infrequently done in the laboratory, other than to simulate a factory procedure. It should be avoided with submicron fillers such as precipitated calcium carbonate, since these often will absorb plasticizer more rapidly than the resin does, leading to intractable lumps. When using ultrafine fillers, lubricants as well as plasticizer should be incorporated first. 

Kishimoto and Hanamura [15] reported on anisotropic conductive adhesive pastes using two different fillers Au-coated rubber particles (soft) and nickel particles (hard). The ACAs were used to bond a flip chip with Au-plated bumps to a board with copper metallization. With the application of pressure, the soft particles were brought into contact with surface pads and were deformed, which lowered contact resistance. The hard particles, however, deformed the bumps and pads, thus were also in intimate contact with the surfaces to help reduce contact resistance. The study showed that their choice of both hard and soft fillers in ACA materials had similar... 

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