Laboratories at Foggia University and those at CNR- IMCB of Naples, in co-operation with Novamont S.p.A, are studying materials with low environmental impact. Biodegradable films represent one of the most studied example in the filed of flexible films; they decompose naturally avoiding environmental problems once they are thrown in composting areas as waste. Up to now the use of these films in the field of food packaging has been rather rare and the scarce barrier properties to compounds with low molecular weight and above all to steam molecules are one of the main factor preventing their circulation. In fact we don't have to forget that besides influencing the microbial growth, the presence and the concentration of gas and vapour, as for example steam and oxygen, film can induce and aid physical processes and chemical and enzymatic reactions able to cause in a short time the qualitative decline of food products.
Polymeric films can extend the shelf-life of wrapped food controlling the permeation speed of compounds with low molecular weight towards the inside and towards the outside of packages. Technologies and process conditions, structure and polymer characteristics influence remarkably the properties of mass transport of such materials. This research studied biodegradable films obtained using different techniques. It has defined their barrier properties to steam and their mechanical properties in order to show how the chemical structure and the process conditions can influence such properties, and particularly which processes improve and make them suitable for long period applications.
Steam barrier properties
Some experiments show that polymers obtained by blending more components have water barriers higher than those of the corresponding omopolymers. This is probably due to the fact that the blending process brings about the beginning of an amorphous phase with a reduced macromolecular mobility. During the blending process we can reach such shapes to improve the barrier properties from 2 to 10 times compared to the starting polymer. As expected, metallization contributes to increase the omopolymers barrier properties. Also co-extrusion improves the barrier properties to water compared to the starting polymer.
As regards the mechanical properties and in relation to the experimental data we obtained, omopolymers always have an elasticity value lower than that of blended, co-extruded or metal films. The coefficient of elasticity of a half-crystalline polymer is bound to the characteristics of the amorphous part, to the crystalline level and to the distribution of shape and dimensions of the crystalline areas. Supposing that the dimensions of the crystalline areas are similar both for omopolymers and compounds, an increase in the value of the elasticity coefficient is related to the improvement of the properties of the amorphous phase.
Food Packges 8/2006
Publisher Artek snc