Meaning
Mathematical transport models predict the migration rate of chemical substances from plastic packaging into food or environmental simulants. The Piringer diffusion equation calculates conservative estimates of the diffusion coefficient of polymer additives like antioxidants and plasticizers. This calculation uses the molecular weight of the migrating substance and the density of the specific polymer.
Migration Prediction
Food safety authorities accept these calculations as a way to prove regulatory compliance without conducting expensive laboratory migration tests. The formula assumes a worst-case scenario where the additive moves freely through the polymer matrix. It uses a polymer-specific parameter to account for the resistance that different plastics offer to migration.
Compliance Assessment
Sourcing teams use this mathematical approach during the packaging design phase. If the calculated migration exceeds the permitted limit, the material is rejected before tooling begins.
Model Limitation
The calculation assumes that the polymer is homogeneous and does not degrade during the processing step. This assumption means that for recycled resins or multi-layer films, the model might not represent actual behavior. In such cases, laboratory testing must be used to confirm compliance.
High-density structures and highly crystalline regions also alter the migration rate, sometimes rendering the standard equation overly conservative and necessitating empirical verification.
