When the additives are added to a polymer to manufacture parts or goods, the theoretical amount of each additive isn't the real amount in the compound or the part because of
* Loss during compounding
* Losses during processing, storage, and service life.
Moreover into the compound or parts, the amount isn't the same in all spots because of:
* Insufficient dispersion
* Heterogeneous distribution
* Hoards of fibres or other fillers during injection moulding
* Partition of the additive between eventual different phases of the compound
* Consumption of antioxidants at the surface…
This is not a purely theoretical point of view but a tangible fact with practical consequences for the considered part and its environment.
All properties can be degraded such as, for example:
* Aesthetics affected by blooming, migration…
* Mechanical characteristics affected by plasticizer desorption…
* Ease of processing affected by release of processing aids, plasticizers…