The Bonding Mechanism of the Micro-Interface of Polymer Coated Steel

Abstract

As food and beverages require more and more green and safe packaging products, the emergence of polymer coated steel (PCS) has been promoted. PCS is a layered composite strip made of metal and polymer. To probe the bonding mechanism of PCS micro-interface, the substrate tin-free steel (TFS) was physically characterized by SEM and XPS, and cladding polyethylene terephthalate (PET) was simulated by first-principles methods of quantum mechanics (QM). We used COMPASS force field for molecular dynamics (MD) simulation. XPS pointed out that the element composition of TFS surface coating is Cr(OH)3, Cr2O3 and CrO3. The calculation results of MD and QM indicate that the chromium oxide and PET molecules compound in the form of acid-base interaction. The binding energies of Cr2O3 (110), (200), and (211) with PET molecules are −13.07 eV, −2.74 eV, and −2.37 eV, respectively. We established a Cr2O3 (200) model with different hydroxyl concentrations. It is proposed that the oxygen atom in C=O in the PET molecule combines with –OH on the surface of TFS to form a hydrogen bond. The binding energy of the PCS interface increases with the increase of the surface hydroxyl concentration of the TFS. It provides theoretical guidance and reference significance for the research on the bonding mechanism of PCS.

Chemical Reaction and Bonding Mechanism at the Polymer–Metal Interface

“…It is worth noting that the existence of Cr(OH) 3 is beneficial for the formation of hydrogen bonding between the polymer and coated chromium layer. 39,43 3.2. SEM and TEM Characterizations of the Cross Sections of the Laminated Steel-EAA Strip.…”

“…As for polymer co-rolled chromium-coated steel, there is no unified understanding about the interfacial bonding mechanism. Most scholars 39,41,42 agree with hydrogen bond theory, which was proposed by Tanaka et al 43 According to this theory, the carbonyl group (−CO) of the polyethylene terephthalate (PET) will combine with the H provided by the hydrated chromium oxide layer in the form of a hydrogen bond. Nevertheless, no clear experimental evidence for hydrogen bond formation was provided till now.…”

“…Duguet et al 37 Based on a large number of previous studies, there are five widely recognized theories explaining the bonding mechanisms of polymer−metal hybrid structures: mechanical interlocking, electronic interactions, diffusion, adsorption, and chemical bonding. 30,39,40 However, interfacial interaction and the bonding mechanism between metals and polymers are quite related to the material types and processing technologies, which means that specific analysis case by case is required for different hybrid structures or the same hybrid structure prepared by different processing technologies.…”

“…They analyzed the effect of hydroxyl concentration on the interfacial binding energy. 39 On the whole, there is quite limited experimental evidence for revealing the interfacial bonding mechanisms between chromium-coated steel and polymers, not to mention the laminated chromium-coated steel-EAA strip. Thus, utilizing advanced equipment and methodologies to characterize the buried interface is still urgent.…”

The Influence of the Roll-Laminating Process on the Bonding Quality of Polymer-Coated Steel Interface

“…The total thickness of the TFS is approximately 0.18 mm. The total thickness of the PET film is 25 um [26].…”