Recycling packaging materials 507 23.4.4 Considerations on migration evaluation Migration from a given food/plastic package system is essentially influenced by kinetical(diffusion in plastic and food) as well as thermodynamic (equilibrium partitioning between plastic and food) factors. It is useful to start in migration evaluations as a worst assumption with total mass transfer scenarios based on knowledge of the starting concentration of a given migrant in the plastic. If this calculation leads to exceeding a migration limit, then it is advisable and necessary to refine the evaluation strategy and take account of partitioning and diffusion as the crucial parameters for migration. Complete scientific background and guidance on how to proceed can be found in the literature. 2 The FDA suggests that dietary exposures to contaminants from recycled food ntact articles at a concentration of 0.5 ppb or less generally are of negligible risk.18,19,23 With help of so-called consumption factors(CF) these dietary exposures can be converted into migration limits. For recycled PET for food contact use, for instance, the FDA system applies a CF =0.05 as the currently valid consumption factor for post-consumer plastics and therefore the migration limit of PET recyclate-containing packages is 10 ppb for each individual substance. On the other hand. the migration limit can be converted into a maximum bottle wall concentration for any substance occurring in post consumer plastics(including substances from virgin polymers). For example, for Pet the maximum concentration in the pet material which correlates with 10 ppb dietary intake level is 0. 22 ppm for a typical PET container at thickness of 0.5 mm. This calculation is based on very conservative assumptions that all pet bottles are contaminated and that the contaminants are assumed to migrate completely from the bottle into the foodstuff. The contaminant limits calculated above also assume 100% recycled resin content in the finished article It is generally known that the diffusion-controlled migration is usually much lower than the complete transfer of substances into the foodstuffs, and this especially for low diffusivity polymers like PET. Migration from virgin and post consumer pet has been considered in numerous investigations where the low diffusion and migration rates have been reported and confirmed.2122, 24Therefore diffusion models25, 26, provide an interesting scientific tool for a more realistic correlation between the allowed upper migration limit in the packed foodstuff and the corresponding maximum allowable concentration in the polymer 8,19,28 generally recognised migration model based on diffusion coefficient estimation of organic chemical substances in polymers" has been finished recently within the European project SMT-CT98-7513 Evaluation of Migration Models in Support of Directive 90/128/EEC.29 Using this model the curves in Fig. 23. 1 were calculated hich presents a correlation between migration into food and the corresponding maximum allowable concentrations of the surrogates in the bottle wall in dependency of the molecular weight for a PEt bottle(assumption 1 I content with 600 cm packaging surface). The migration or the corresponding residual concentration in the bottle wall was calculated for 95% ethanol at contact conditions of 40C for 10 d. For most applications these scenarios are worst-case conditions overestimating the real migration situation by factors of at least 100. In23.4.4 Considerations on migration evaluation Migration from a given food/plastic package system is essentially influenced by kinetical (diffusion in plastic and food) as well as thermodynamic (equilibrium partitioning between plastic and food) factors. It is useful to start in migration evaluations as a worst assumption with total mass transfer scenarios based on knowledge of the starting concentration of a given migrant in the plastic. If this calculation leads to exceeding a migration limit, then it is advisable and necessary to refine the evaluation strategy and take account of partitioning and diffusion as the crucial parameters for migration. Complete scientific background and guidance on how to proceed can be found in the literature. 2 The FDA suggests that dietary exposures to contaminants from recycled food contact articles at a concentration of 0.5 ppb or less generally are of negligible risk.18,19,23 With help of so-called consumption factors (CF) these dietary exposures can be converted into migration limits. For recycled PET for food contact use, for instance, the FDA system applies a CF = 0.05 as the currently valid consumption factor for post-consumer plastics and therefore the migration limit of PET recyclate-containing packages is 10 ppb for each individual substance. On the other hand, the migration limit can be converted into a maximum bottle wall concentration for any substance occurring in post￾consumer plastics (including substances from virgin polymers). For example, for PET the maximum concentration in the PET material which correlates with 10 ppb dietary intake level is 0.22 ppm for a typical PET container at a thickness of 0.5 mm. This calculation is based on very conservative assumptions that all PET bottles are contaminated and that the contaminants are assumed to migrate completely from the bottle into the foodstuff. The contaminant limits calculated above also assume 100% recycled resin content in the finished article. It is generally known that the diffusion-controlled migration is usually much lower than the complete transfer of substances into the foodstuffs, and this especially for low diffusivity polymers like PET. Migration from virgin and post￾consumer PET has been considered in numerous investigations where the low diffusion and migration rates have been reported and confirmed.21,22,24 Therefore, diffusion models25,26,27 provide an interesting scientific tool for a more realistic correlation between the allowed upper migration limit in the packed foodstuff and the corresponding maximum allowable concentration in the polymer. 18,19,28 A generally recognised migration model based on diffusion coefficient estimation of organic chemical substances in polymers2 has been finished recently within the European project SMT-CT98-7513 ‘Evaluation of Migration Models in Support of Directive 90/128/EEC’.29 Using this model the curves in Fig. 23.1 were calculated, which presents a correlation between migration into food and the corresponding maximum allowable concentrations of the surrogates in the bottle wall in dependency of the molecular weight for a PET bottle (assumption 1 l content with 600 cm2 packaging surface). The migration or the corresponding residual concentration in the bottle wall was calculated for 95% ethanol at contact conditions of 40ºC for 10 d. For most applications these scenarios are worst-case conditions overestimating the real migration situation by factors of at least 100. In Recycling packaging materials 507