Vergnaud J M
Laboratory of Materials and Chemical Engineering, Faculty of Sciences, University of St-Etienne, France.
Adv Colloid Interface Sci. 1998 Nov 13;78(3):267-97. doi: 10.1016/s0001-8686(98)00065-7.
When a polymer is in contact with a liquid, generally some matter transfers take place: the liquid enters the polymer, while some additives leave the polymer. This fact is responsible for a reduction in the properties of the polymer and pollution of the liquid food is obtained. However, it is sure that, on account of their outstanding properties, food packages are becoming more and more based on polymers. The process of mass transfers is controlled by transient diffusion, and these theoretical problems are so complex that only numerical models are able to resolve them. New difficult problems appear with the desire of recycling old food packages made of polymers by reusing them as new food packages. Of course, because of the potential contamination brought with this recycled polymer, the package is made of bi-layer or tri-layer films where the reused polymer is located between two virgin polymer layers. As it takes some time for the contaminant to diffuse through the virgin layer, this latter plays the role of a functional barrier to pollution. The various difficulties in the whole problem are considered in succession: the coextrusion of the films where a contaminant transfer already occurs; and the effect of the liquid food which may enhance the diffusion of the contaminant. Various master curves are drawn by using dimensionless numbers, so as to make the results quite general and of use from a practical point of view.
当一种聚合物与液体接触时，通常会发生一些物质转移：液体进入聚合物，同时一些添加剂离开聚合物。这一事实导致聚合物性能下降，并造成液体食品污染。然而，可以肯定的是，由于其优异的性能，食品包装越来越多地采用聚合物材料。传质过程由瞬态扩散控制，这些理论问题非常复杂，只有数值模型才能解决。随着人们希望通过将旧的聚合物食品包装重新用作新的食品包装来实现回收利用，新的难题出现了。当然，由于这种回收聚合物可能带来潜在污染，包装采用双层或三层薄膜制成，其中回收的聚合物位于两层原始聚合物层之间。由于污染物扩散穿过原始层需要一些时间，原始层起到了防止污染的功能屏障作用。依次考虑了整个问题中的各种困难：已经发生污染物转移的薄膜的共挤出；以及可能增强污染物扩散的液体食品的影响。通过使用无量纲数绘制各种主曲线，以便使结果具有普遍性并从实际角度来看具有实用性。
