Abstract
Recycling old polymer as new food packages is possible when bi-or tri-layer packages are made with a virgin polymer layer in contact with the food. The main problem consists of evaluating the time of food protection. During the processing of tri-layer containers, any contaminant initially in the recycled polymer layer is transferred through the package by diffusion with a temperature-dependent diffusivity. During the short period of cooling, the diffusivity is very high and the transfer is significant. A numerical model is developed, taking account of both the heat transfer by convection at the surfaces and by conduction, and the transfer of the contaminant. The profiles of contaminant concentration are thus obtained at the end of the processing. Another numerical model is built in order to evaluate the migration of the contaminant at room temperature through the package into the liquid food. The process in this new case is controlled by diffusion through the package with constant diffusivity and also by convection into the liquid. The kinetics of pollution of the food is thus obtained, as well as the time of food protection. Dimensionless numbers are used so as to obtain master curves.