Theoretically, each additive is added into a compound to enhance a single property of the polymer to allow a precise engineering application. For example, the improvement must concern any particular property such as:
* The original characteristics: 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.
* Eventually, some more specific characteristics…
Beside this theoretical point of view it is important to pose the same questions for medicines.
* What are the risks to alter other things?
* What are the possible interactions with other parameters?
* And be optimistic, what are the other beneficial possible effects?
Additives are useful to modify polymers for three basic features:
* They are chemically active and they react with the polymer to lead to a new chemical structure or they stop the degradation of the polymer…