Loss of Adhesion at Al 8006/LDPE Interface in Containers for Food Packaging: A Case Study

摘要

A company recently reported, the unexpected and sudden failure of several containers, fabricated from aluminium 8006 and sealed using a polymeric film. The failure resulted when there was a loss of adhesion at the metal/polymeric lid interface, making the containers unusable. Some preliminary adhesion tests have highlighted that, containers, coming from various production batches and sealed using the same kind of lid, exhibited different adhesion strengths. To investigate the cause of the detachment of the lid from the edge of the container, the following parameters has been considered: (i) the iron content of the Al alloy, (ii) the effect of lubricant oil at the polymeric film/substrate interface, (iii) the topography of the contact surface between the lid and the container. The electrochemical behaviour of Al8006 was investigated by means of potentiodynamic polarization tests, both in an aerated aqueous solution of Na_2SO_4 (0.5 M) and in an aerated aqueous solution of NaCl (0.6 M). The results revealed a significant increase in corrosion rate for the samples with higher iron content, as well as the negative influence of oil on the surface. Roughness measurements have confirmed the importance of the surface profile: a surface showing Sku>3, provides better adhesion. Metallographic measurements demonstrated that high iron content in the alloy results in the development of numerous corrosion spots and prevents good adhesion between the sealant polymeric film and the aluminium foil.