Mass balance estimation of worst case styrene migration

1 Mass balance estimation of worst case styrene migration 

The simplest estimation of migration is to use the mass balance calculation shown in Eq. (14-1) below. This equation assumes that all of the styrene found in the polymer will migrate into the food instantly. This is of course not realistic but the estimation gives an upper limit to the possible migration that could occur at the end of the product s shelf life. 

The ratio can be the actual package surface area to food mass ratio or a conventional ratio like 0.6 cm2 g-1 (6 dm2 kg-1) (used in the European Union) or 0.645 cm2g 1 (1 in2/10 g) (used by the U.S. FDA). The density of polystyrene is approximately 1.08 g cm-3. 

The initial concentration of styrene in the polymer (P), cp,o (mg kg-1), is known either from the manufacturer of the material or has been determined by analysis of the material. In the absence of initial styrene monomer concentration data one could assume as a worst case a level of 1000 mg/kg which is the highest level usually seen in commercial PS materials. Usually the level found in the material is 500 mg/kg or less which is the industry standard for food grade polystyrene. 

For simplification one can assume the density of the polymer and food are approximately equal to one, pF pp 9 1.0, without large error. 

---