Particulate filler

Hancock, M., and Rothon, R. N. (1995). Principle Types of Particulate Fillers, Particulate-Filled Polymer Composites. Rothon, R. N., Ed., Longman Harlow, p. 77. 

The clarification of the mechanism of the reinforcing action of fillers is of great importance in the improvement of their physical and mechanical properties. The mechanism of the reinforcing action of fillers differs between plastics and rubbers, since, under service conditions, the latter are in elastic (rubber-like) state. We must also bear in mind that the mechanism of polymer reinforcement cannot be explained from any single point of view. To understand it, we have to take into account all factors influencing the properties of PCM the chemical nature of the polymer and the filler (particulate fillers, fibers, fabric etc.), the... 

Plastics. In the plastics industry, the term filler refers to particulate materials that are added to plastic resins in relatively large, ie, over 5%, volume loadings. Except in certain specialty or engineering plastics appHcations, plastics compounders tend to formulate with the objective of optimizing properties at minimum cost rather than maximizing properties at optimum cost. Table 2 fists typical plastic fillers and their uses. 

Directed Oxidation of a Molten Metal. Directed oxidation of a molten metal or the Lanxide process (45,68,91) involves the reaction of a molten metal with a gaseous oxidant, eg, A1 with O2 in air, to form a porous three-dimensional oxide that grows outward from the metal/ceramic surface. The process proceeds via capillary action as the molten metal wicks into open pore channels in the oxide scale growth. Reinforced ceramic matrix composites can be formed by positioning inert filler materials, eg, fibers, whiskers, and/or particulates, in the path of the oxide scale growth. The resultant composite is comprised of both interconnected metal and ceramic. Typically 5—30 vol % metal remains after processing. The composite product maintains many of the desirable properties of a ceramic however, the presence of the metal serves to increase the fracture toughness of the composite. 

Particulate fillers are divided into two types, inert fillers and reinforcing fillers. The term inert filler is something of a misnomer as many properties may be affected by incorporation of such a filler. For example, in a plasticised PVC compound the addition of an inert filler will reduce die swell on extrusion, increase modulus and hardness, may provide a white base for colouring, improve electrical insulation properties and reduce tackiness. Inert fillers will also usually substantially reduce the cost of the compound. Amongst the fillers used are calcium carbonates, china clay, talc, and barium sulphate. For normal uses such fillers should be quite insoluble in any liquids with which the polymer compound is liable to come into contact. 

There has also been some interest in polymers containing particulate mineral fillers. 

Commercial grades of polymer may contain, in addition to glass fibre, fire retardants, impact modifiers and particulate reinforcing fillers. Carbon fibre may be used as an alternative to glass fibre. 

Fillers may be broadly defined as solid particulates or fibrous materials, substantially inert chemically, incorporated in polymer compositions to modify the properties and/or to reduce cost. Cost reduction is not the primary reason to incorporate fillers in adhesives but they are used to impart specific properties such as flow, improved adhesion, mechanical, thermal, electrical and optical properties, chemical and weather resistance, and rheological behaviour. 

In other parts of the world, plywood adhesive fillers are obtained from local sources and may be quite different than those used in North America. In Southeast Asia, banana flour is quite important. In Europe, calcium carbonate (chalk) is often used. Nearly any fibrous material or fine particulate material capable of forming a functionally stable suspension can be made to work if the formulator is sufficiently skillful. However, the mix formulator will be very specific about the type and grade of filler to be used in a particular mix. Substitutions may lead to serious gluing problems. 

Fibrous fillers are now gaining more importance over particulate fillers due to the high performance in mechanical properties. The influence of fiber diameter on the tensile behavior of short glass fiber on polyimide was reported [95], At higher concentrations thick fibers seem to be more advantageous probably because of the... 

Particulate fillers provide better creep resistance than unfilled plastics but are less effective than fibrous reinforcements. 

In general adding reinforcing fibers significantly increases mechanical properties. Particulate fillers of various types usually increase the modulus, plasticizers generally decrease the modulus but enhance flexibility, and so on. These RPs can also be called composites. However the name composites Utterly identifies thousands of different combinations with very few that include the use of plastics (Table 6-18). In using the term com-... 

Modulus Rigid minerals Ductility Ductility produces a more rigid composite. Particulate fillers severely degrade impact strength. 

Then, for a particulate composite, consisting of a polymeric matrix and an elastic filler, it is possible by the previously described method to evaluate the mechanical and thermal properties, as well as the volume fraction of the mesophase. The mesophase is also expected to exhibit a viscoelastic behaviour. The composite consists, therefore, of three phases, out of which one is elastic and two viscoelastic. 

Thus, in the three-layer model, with the intermediate layer having variable physical properties (and perhaps also chemical), subscripts f, i, m and c denote quantities corresponding to the filler, mesophase, matrix and composite respectively. It is easy to establish for the representative volume element (RVE) of a particulate composite, consisting of a cluster of three concentric spheres, that the following relations hold ... 

Fig. 4. Heat capacity Cp of iron-epoxy particulates plotted against temperature with four different filler-volume fractions and for a particle diameter df = 0.40 x 10-3 m...

Table 1. The values of the characteristic parameters of a series of iron-epoxy particulates for various filler volume contents of... 

As soon as the Ar s were determined and the values of r s are found, the values of the adhesion coefficient A may be readily defined by using relation (27). The values of A s for the different inclusion-volume contents studied are given in Table I for iron-epoxy particulate composites with different amounts of fillers, up to 25 percent l4>. 

Fig. 10. The variation of the mesophase moduli Ej(r) for the various filler volume contents of iron-epoxy particulates, versus the polar distance from the filler-matrix boundary...

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