Migration modeling for non-polyolefins

Despite these limitations and problems encountered with non-polyolefin materials in Table 15-5 a set of provisional AP-values can be presented. These AP-values apply only in the simplified Eq. (15-1). 

With the set of AP-values given in Table 15-5 most of the calculated migration amounts from Table 15-4 are overestimations compared with the measured values. 

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. 

Other frequent phenomena are strong interactions between the plastic sample and the simulant. For example, the additive with Mr = 587 shows a 20-fold enhanced migration from PBT into 50 % ethanol/water at 40 °C compared to olive oil. The interaction effect is dramatic with PA, as can be seen from the migration of the same additive into 50 % ethanol (mp.t = 12.6 mg dm-2) compared to olive oil (mFt = 0.077 mg dm-2) after 10 days at 49 °C. 

As a conclusion, careful examination of all migration measurements is necessary for a correct evaluation of estimation results, because many processes are possible which are in direct conflict with the assumptions of the mathematics behind the simplified migration equations (Chapter 7). Overlooking these conflicts between assumptions and experimental behavior produces many pitfalls (Piergiovanni et al. 1999). 

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