Thinning of Barrier Layers in Multiwall Thermoformed Packages

Abstract

The stretching of sides, edges and the bottom of some thermoformed containers were studied, focussing on thickness reduction of an aromatic polyamide barrier layer. The total and partial thickness were measured by a normal thickness gauge and were also recorded by microscopic observations at different positions, for a total of more than 3500 measurements. The total thickness along the sides, at the edges and on the bottom of the containers thinned according to different models, but it was always possible to estimate approximately the extent of stretching by simple equations which linked the thickness to the drawing depth of the containers. The thickness measurements of the barrier layer at the edges, before and after the thermoforming step led to a definition of ‘degree of barrier stretching’ and it was possible to correlate these figures with the depth of drawing. Moreover, it was also possible to correlate the residual barrier layer with absorption measurements made at 294.2 nm of the composite structure along the sides of the thermoformed containers, obtaining simple relationships which could be as very useful tools in packaging design as well as in shelf-life studies.