Relationship between thickness of polymer films and their oxidation on copper substrate

This research was undertaken to understand how the thickness of polyethylene films oxidized on a copper substrate influences the accumulation of carbonyl groups (measured by an IR‐spectroscopy technique) and of metal from the substrate (determined by polarography analysis). It was found that the whole polymer became inhibited by the time the copper stopped transferring into the specimen. Plots of copper concentration versus film thickness have two thickness sections: section I is found between 0 and 70 μm and section II between 80 and 170 μm. Between these two sections the metal concentration varies drastically. This situation can be explained by two schemes by which PE changes to inhibited condition. According to Scheme I (for section I, short oxidation time) this change has only one step: the inhibited layer gradually becomes thicker beginning from the interface and moving toward the outer surface. The second scheme (for section II) shows that the polymer becomes inhibited in two steps. It is typical of thicker films. In this case the oxidation process shifts and localizes in the outer surface because of longer treatment. As a result, transfer of metal and formation of an inhibited layer are interrupted for some time. The metal accumulation in the film only resumes when low‐molecular‐weight products of thermooxidative degradation—formed in the specimen outer surface—enter the region of adhesional contact. A so‐called second transfer stage for metal is realized during which the whole polymer becomes inhibited. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 671–675, 2003