Fillers

Abstract

The popular perception is that fillers are used mainly to reduce costs, but many fillers have very beneficial effects on the properties of plastics. They can improve mechanical properties, especially the modulus; they can modify the electrical characteristics, change the density, improve the fire resistance, and reduce smoke evolution on burning. The use of fillers in thermosetting resins is often advantageous to reduce the excessive exothermic heating caused by the hardening reaction, which might otherwise crack the resin. On the other hand, the actual process of addition of particulate fillers to resins and plastics incurs an economic penalty, especially as fillers increase the viscosity of liquid resins during processing operations, making some fabrication processes more difficult, even when the adverse effects have been mitigated to some extent by surface treatment of the filler particles. The incorporation of fillers at high loadings can increase the likelihood of voids. The tensile and flexural strength and the ultimate elongation at break can be adversely affected, although this depends on the nature of the filler and the polymer, and on the filler particle size.