1Polymer Processing/Physics, Technical University Berlin 26.9, Federal Institute for Materials Research and Testing
This paper discusses the role of chemical bonds at the interface between evaporated aluminium and polyolefins. However, the fundamental differences in material properties require a smooth transition at the metal-polymer interface. For this purpose, covalently bonded flexible spacer molecules were introduced into the interface of evaporated Al and polymer to equalize the different properties of laminated materials.
These spacers were covalently bonded to functional groups at the polyolefin surface introduced by pretreatment. The spacers are equipped with terminal groups, which can react with formation of covalent Al-O-C or Al-O-Si bonds. Maximal adhesion strengths were achieved by inserting flexible aliphatic spacers coupled with silanes, which were bonded by silanol groups to evaporated aluminium. To hinder hydrolysis of these metal-spacer bonds, adjacent hydrophobic and therefore water-repelling siloxane units were also inserted into the spacer molecules. The siloxane units were formed by intermolecular linking of silane spacers. This condensed siloxane layer is a barrier to prevent ion diffusion across the interface and therefore to inhibit redox reactions leading to subsequent polymer degradation and formation of weak boundary layers. Such spacer-modified Al-polyolefin systems adhere so strongly that they could not be peeled even after 3 month exposure to 90% humidity at 40°C.
