Theoretically, each additive is added into a compound to enhance a single property of the polymer to allow a precise engineering application. Specific additives are sophisticated materials with high physical and/or sharp chemical activity. Apart the modified specific characteristic, they act also on the original characteristics. They modify:
* Aesthetics, mechanical, thermal, electrical, optical performances.
* The processing: moulding, extrusion etc, accuracy of shaping…
* The long-term behaviour: ageing (heat, sunlight, weathering, wet environment…), creep, relaxation, fatigue…
* The cost.
The compound properties can obey a law of mixture or other rules such as a percolation phenomenon.
When added to polymers, mineral fillers and fibres lead to an improvement of their thermal conductivity depending on the nature, form and addition level. For example, figure 1 shows the effect of quartz used for electric insulation on the thermal conductivity of an epoxy.The basic goal of plasticizers is to improve flexibility and impact resistance of polymers.