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Keywords:

  • PET;
  • diffusion;
  • functional barrier;
  • modeling;
  • food packaging

Abstract

Recycled plastics may be polluted by various chemicals available to consumers. When such materials are used to manufacture packaging materials intended to be in direct contact with food, these pollutants may migrate into food. The use of multilayer structures with a virgin polymer layer as a functional barrier may prevent such migration. This work deals with the possible diffusion of pollutants into and through the virgin layer during processing at high temperatures. A test is designed to measure diffusion coefficients in elastomeric and glassy polymers, in their molten state; 2.5-dimethoxyacetophenone was used as a surrogate pollutant, and its concentration profiles are monitored by UV microscopy. Based on diffusion coefficients and on activation energies, glassy polymers appear to be much better barriers than polyolefins, even in their molten state. We then focus on poly(ethylene terephthalate) (PET) bottle preforms, processed by injection molding. In a first approach, a worst case situation was simulated by numerical analysis, using both overestimated diffusion coefficient values and very low values of activation energy. It appears that migration into foodstuffs through functional barriers can only be observed with unrealistic high diffusion coefficients and low activation energies. These results were confirmed by experimental determination of the concentration gradients of model pollutants in multilayer structures. It appears that little diffusion occurs, despite at a very high temperature. The effects of temperature and thickness of the functional barrier are discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2859–2870, 2004