Abstract
Metals used for food canning such as aluminum (Al), chromium-coated tin-free steel (TFS) and electrochemically tin-plated steel (ETP) were coated with a 2–3-µm-thick layer of polyaleuritate, the polyester resulting from the self-esterification of naturally-occurring 9,10,16-trihydroxyhexadecanoic (aleuritic) acid. The kinetic of the esterification was studied by FTIR spectroscopy; additionally, the catalytic activity of the surface layer of chromium oxide on TFS and, in particular, of tin oxide on ETP, was established. The texture, gloss and wettability of coatings were characterized by AFM, UV-Vis total reflectance and static water contact angle (WCA) measurements. The resistance of the coatings to solvents was also determined and related to the fraction of unreacted polyhydroxyacid. The occurrence of an oxidative diol cleavage reaction upon preparation in air induced a structural modification of the polyaleuritate layer and conferred upon it thermal stability and resistance to solvents. The promoting effect of the tin oxide layer in such an oxidative cleavage process fosters the potential of this methodology for the design of effective long-chain polyhydroxyester coatings on ETP.
Highlights
Canned food production is a global industry with a predicted turnover of 118 billion USD by 2023 and an estimated growth of 3.8% in the 2018–2023 period [1]
tin-free steel (TFS) is a Fe matrix with a thin chromium oxide layer (Cr 0.8% atom) and electrochemically tin-plated steel (ETP) is made of an iron matrix covered by a crust of Sn oxide (Sn 32% atom)
The corrugation is more pronounced on ETP, while on Al and, TFS, large holes contributing to the increment of the hmax parameter were detected (Table 1)
Summary
Canned food production is a global industry with a predicted turnover of 118 billion USD by 2023 and an estimated growth of 3.8% in the 2018–2023 period [1]. Because of their airtightness and high mechanical resistance, cans are a suitable format for long-shelf life and the long-distance logistics of ready-to-eat meals, vegetables, meat and seafood. One substance that has triggered concern about canned food safety is bisphenol A (BPA) This molecule was employed in the formulation of inner lacquers used to prevent direct contact between the metal body and the foodstuff; concerns about its negative effects on human health arose about a decade ago [2,3,4,5]. The migration of BPA from the can coating has been demonstrated, and instances in which it reached as much as a few hundreds of micrograms per kilogram of canned
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