Recycling packaging materials 511 FDA threshold of regulation concept the intended application was con- sidered to be safe Multi-layer PET bottles for soft drink applications In 1996 a study was published> in which the effectiveness of a virgin PET layer in limiting chemical migration from recycled PET was investigated. For this purpose three-layer bottles were prepared with an inner core(buried layer)of PET which was deliberately contaminated. The model contaminants used were toluene, trichloroethane, chlorobenzene, phenyl decane, benzophenone, phenyl cyclohexane and copper(ln) acetylacetonate. As a result no migration was detected through a barrier of virgin PET of 186 t 39um thickness into 3% acetic acid using general migration test conditions of 10 days at 40C and also after 6 months storage at room temperature. Also migration testing with 50% and 95% ethanol as severe contact media which are relatively aggressive to PET did not lead to measurable migration rates. Consideration of diffusion models using limonene as substance for which diffusion coefficients were available, gave estimates that for a 100um thick PET layer a breakthrough of a substance with comparable molecular weight would take place after 7.5 years or 0. 8 years at room temperature or 40oC, respectively. It was concluded that an intact PET bottle layer in contact with the food represents an efficient functional barrier against migration from any possible contaminant encapsulated in a recycled PET material under normal conditions of use for soft drinks. Today, multi-layer PET soft drink bottles have received clearance for use in Austria, Belgium, Finland France, Norway, Sweden and the United Kingdom Studies on multi-layer PET and PET films for food packaging In another project, several coextruded three-layered PET films spiked in the core layer with surrogates(toluene and chlorobenzene)and having a PET barrier layer thickness between 20 to 60um, were systematically investigated with respect to their migration behaviour under different test and contact medium conditions. It was observed that the migration measured through the different barrier layers was predictable, and a diffusion model for predicting the functional barrier properties of layered films based on Fickian diffusion was presented. Also the effects of diffusion from the core layer to a virgin barrier layer during the coextrusion process was found necessary to be considered for reliable prediction of migration. On the basis of the presented mathematical model, maximum allowable concentrations can be established for a core layer for a given barrier thickness while still fulfilling threshold or specific migration limit requirements In similar studies with symmetrical three-layer films spiked again in the core layer with toluene and chlorobenzene the functional barrier behaviour of high impact polystyrene(HIPS)was investigated. The applied thicknesses of the HIPS barrier layer ranged higher than the above PEt example and were 50um 100um and 200pm. The contact medium was 50% ethanol which is a recognised medium for fatty food products for this plastic, and testing was carried out atFDA threshold of regulation concept18 the intended application was con￾sidered to be safe. Multi-layer PET bottles for soft drink applications In 1996 a study was published35 in which the effectiveness of a virgin PET layer in limiting chemical migration from recycled PET was investigated. For this purpose three-layer bottles were prepared with an inner core (buried layer) of PET which was deliberately contaminated. The model contaminants used were toluene, trichloroethane, chlorobenzene, phenyl decane, benzophenone, phenyl cyclohexane and copper(II) acetylacetonate. As a result no migration was detected through a barrier of virgin PET of 186  39 m thickness into 3% acetic acid using general migration test conditions of 10 days at 40ºC and also after 6 months storage at room temperature. Also migration testing with 50% and 95% ethanol as severe contact media which are relatively aggressive to PET did not lead to measurable migration rates. Consideration of diffusion models using limonene as substance for which diffusion coefficients were available, gave estimates that for a 100m thick PET layer a breakthrough of a substance with comparable molecular weight would take place after 7.5 years or 0.8 years at room temperature or 40ºC, respectively. It was concluded that an intact PET bottle layer in contact with the food represents an efficient functional barrier against migration from any possible contaminant encapsulated in a recycled PET material under normal conditions of use for soft drinks. Today, multi-layer PET soft drink bottles have received clearance for use in Austria, Belgium, Finland, France, Norway, Sweden and the United Kingdom. Studies on multi-layer PET and PET films for food packaging In another project,36 several coextruded three-layered PET films spiked in the core layer with surrogates (toluene and chlorobenzene) and having a PET barrier layer thickness between 20 to 60m, were systematically investigated with respect to their migration behaviour under different test and contact medium conditions. It was observed that the migration measured through the different barrier layers was predictable, and a diffusion model for predicting the functional barrier properties of layered films based on Fickian diffusion was presented. Also the effects of diffusion from the core layer to a virgin barrier layer during the coextrusion process was found necessary to be considered for reliable prediction of migration. On the basis of the presented mathematical model, maximum allowable concentrations can be established for a core layer for a given barrier thickness while still fulfilling threshold or specific migration limit requirements. In similar studies with symmetrical three-layer films spiked again in the core layer with toluene and chlorobenzene the functional barrier behaviour of high impact polystyrene (HIPS) was investigated.27 The applied thicknesses of the HIPS barrier layer ranged higher than the above PET example and were 50m, 100m and 200m. The contact medium was 50% ethanol which is a recognised medium for fatty food products for this plastic, and testing was carried out at Recycling packaging materials 511