EFFECT OF DIFFERENT FOOD PRESERVATION TECHNOLOGIES OVER THE MORPHOLOGY AND PROPERTIES OF POLYMERIC PACKAGING MATERIALS ABSTRACT For most food products, packages are a fundamental part of their preservation system, often being exposed, together with the food item, and sometimes alone, to different treatments for increasing the product’s shelf-life by means of the reduction of the initial microbial load, as well as through the inactivation of certain enzymes. Some of these preservation treatments, like the thermal sterilization in autoclave (retorting), can provoke negative effects in the packages’ properties, as it happens in the case of ethylene vinyl alcohol (EVOH) copolymers, materials commonly used as high barrier layer in most retortable food packages. These materials, even protected by layers of hydrophobic polymers, suffer, during retorting, a considerable increase in oxygen permeability. Thus, the objectives of this work were: - Understand, from a structural and barrier properties point of view, the effects of industrial retorting over the copolymers. - Model the deterioration of barrier properties and propose solutions to diminish the morphological damages induced by retorting in the copolymers. - Find alternative materials for the substitution of EVOH in retortable packages and propose and study the effects of new preservation technologies like high hydrostatic pressure and irradiation over EVOH copolymers. It was observed that retorting in autoclave induced in EVOH copolymers, apart from the well-known plasticization, morphological damages and, therefore, several strategies, based in the reinforcement of the structure through thermal treatments, were investigated, which diminished the harmful effects of retorting. Furthermore, blends of EVOH with amorphous polyamide and polyamide-containing ionomer were also investigated and, although they showed improved performance from a morphological view point, they did not show the expected barrier properties after retorting. Regarding the potential substitution of EVOH in these applications, the effects of retorting over other high-barrier polymeric materials (an amorphous polyamide and one experimental grade of aliphatic polyketones) were also studied. Both materials showed better behaviour when submitted to the retorting treatment than EVOH copolymers. Finally, and with the aim of adapting the thesis to technological advances in food preservation technologies, it was decided to study the behaviour of EVOH copolymers, when exposed to other food preservation technologies like high hydrostatic pressures and irradiation. While high hydrostatic pressure treatments do not affect significantly the properties of EVOH materials, irradiation causes an increase in the oxygen permeability at the equilibrium which, although lower than the increase caused by retorting in autoclave, it was found to be irreversible.