Fillers, which were once added to compounds to increase bulk and reduce cost, have to work a lot harder nowadays. They are increasingly called upon to provide other value-added functions, such as mechanical properties, UV or heat stability, thermal or electrical conductivity, dimensional stability or flame retardancy. John Murphy explains.
The potential for additional contributions is determined by the chemistry of the filler and especially by its physical aspects, the size and geometry of the particles, surface area and surface energy. But (going back to 'Square One') the weight of the filler is also important: minerals are, basically, heavy, and there is interest in cellulose fillers and also hollow particles, such as ceramic or glass microspheres.
Value-added properties
To offer better value, fillers are coated and surface-modified, and special manufacturing processes are used to control the size and geometry of the particles. Researchers are going down to microscopic - and now even nano scales - to modify the surface of the material and improve the interface bond.