TABLE OF CONTENTS As was said many times, after the first book by Crank [1], laying the way of diffusion, or rather the mathematical treatment at least, various studies have been conducted by using mass transfer whose driving force is diffusion. These works have been oriented in many directions for example:
in pharmacy with dosage forms whose drug release is controlled by diffusion as well as with the drug transfer through various human tissues [2, 3];
in various materials, such as wood which exhibits a typical anisotropy in threedirections and with three values of diffusivity [4];
in elastomers and rubbers where sometimes the swelling largely exceeds 100% in volume;
in thermosetting resins - those materials which are replacing iron or steel more and more and thus becoming metal substitutes [5];
and last but not least, in food packages made of polymers.
In the last application of diffusion, with the food packages where the protection of the consumer's safety is concerned, various orientations have been followed in research.
The first is devoted to the usual food package, when the virgin polymer is used for the first time, and the problem which occurs is the diffusion of the additives disseminated into the polymer in order to provide the essential qualities of the polymer. For this reason, a list of non-authorised additives has been drawn under the guidance of the European Community and the Food and Drug Administration (FDA, Washington, DC, USA).
As the pollution of the surrounding atmosphere, this time, by the polymer packages...
