Fillers for Thermosetting Resins

Fillers enhance most of the properties of phenoplasts and aminoplasts, but the resulting effects depend on the nature of the fillers and on their content in the composites. For example, the effect of wood flour content on the resistance to compression of molded objects goes through a maximum at about 25% by volume, as shown on Fig. 4.1. 

Fillers used for phenoplasts and aminoplasts include the following  

Substances of organic origin, such as wood flour, used for consumption products and in the production of electrical insulation cellulosic fibers (textiles, paper fibers and particles) used mainly to increase impact resistance fruit shell flour, which increases the fluidity of plastic materials under pressing and enhances the dielectric properties and appearance of final products protein flour—casein and soya flours for example—used with carbamides. 

Substances of inorganic origin, such as asbestos (chrysotile, anthophyUite), used to increase the resistance to heat and to acids and in fibrous forms to enhance mechanical properties mica, which gives good dielectric properties and good heat resistance lead and barium compounds, used as X-rays absorbents slate cement graphite silica sand talc and so on. 

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