Migrants, Migration plasticizers

This difftision rate is related to the resistance, within the plastic wall, to the movement of gases and vapors. Important aspects of the diffusion process are permeability and migration of additives. Possible migrants from plastics can include the many different additives and fillers used (Chapter 1). 

The considerable influence of the food simulant can be observed in many cases for non-polyolefins. For example, the migration of an additive with Mr = 549 from IPS into 50 % ethanol in water in Table 15-4 shows a decrease of the migration amount measured at 49 °C after an initial contact temperature of 66 °C This phenomenon cannot be explained by changes in diffusion. The decrease in migration must be a consequence of a strong increase of the partition coefficient, KPR with decreasing temperature that shifts the equilibrium concentration of the migrant to the plastic phase. 

One of the most important migration problems occurs if a liquid food or food simulant F with the volume Vp and density pp comes in contact with a plastic layer P of thickness dp and density pp. The mass transfer takes place across an interface with area A between two different media with different characteristics, e.g., with different diffusion coefficients Dp and Z>p of the migrant. If the value of a quantity is desired, for example, the concentration of the substance transported across the interface in one of the two media, then a mass balance must be considered that takes into account the ratio of the contact surface area and the volume of the corresponding medium. The model describing this process is based on the following assumptions ... 

When applying the conventional food contact ratio the worst-case migration potential did not exceed the SML for any of the substances derived from plastics nor did the calculated worst-case exposure exceed the ADI/TDI or other exposure restriction value in any products. However, when the actual food contact ratio was applied the ADI/TDI or other exposure restriction value of several substances could theoretically be exceeded. The worst-case calculations assume that intimate contact is made with the entire surface of the packaging. This is not the case for the majority of snack foods that are solids or semi-solids and so the actual area of contact made will be less than the total area available for contact (e.g. crisps). The levels of those migrants (diisobutyl phthalate, dicyclohexyl phthalate, dibutyl sebacate, diphenyl 2-ethylhexyl phosphate and 2-ethyl-1-hexanol) that had the potential to exceed the assigned restrictions, assuming 100% migration, were determined in foods. Of the five substances tested for, only one, dicyclohexyl phthalate, was detected in one of the foodstuffs (tortilla corn chips), at a concentration of 0.60 ppm. 

The kinetics of migration of additives from the package into the (food) contents depends on the characteristics of the plastics such as density or free volume, crystallinity, glass transition temperature (Tg), as well as the polarity, molecular mass, and boiling point of the migrant species. Migration rates also depend on the temperature, relative humidity, pH value, and the composition of the food contents (Sajilata et al., 2007). Given the number of variables that can affect the results, reported data must be compared cautiously. 

Migration is the result of diffusion and equilibrium processes involving the transfer of low molecular mass compounds from a plastic package into a food or food simulant. The migrants diffuse through the amorphous portion of the polymer matrix toward the interface where they are partitioned between the two media until their chemical potential values in both the polymer and the food reach equilibrium. Migration can be mathematically described by Pick s second law (Equation 13.1) ... 

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