2. Contamination kinetics controlled by molecular diffusion

Food contamination is controlled by the dispersion of additives or residues within the polymer matrix. In the case of fluid phases with the characteristic size of packaging (a few hundred micrometers), these mechanisms would have time constants of no more than a few seconds to a few minutes at room temperature. In condensed, cohesive phases such as polymers, the same phenomena can occur on a scale of several years. Additives are generally present in the polymer in trace amounts or at concentrations of no more than 1% by mass, generally in the 0.01-0.1% range, with the exception of plasticizers (1-30%). Interactions between contaminants are therefore unlikely, given additive-polymer interactions. Similarly, concentrations are generally too low for the loss of "small" molecules through the polymer to alter the properties of the polymer itself. The only exception is excessive loss of plasticizers....