Atomic Layer Deposited TiO₂ and Al₂O₃ Thin Films as Coatings for Aluminum Food Packaging Application.

Vanessa Dias,Mariana Fraga,Homero Maciel,Anderson Lobo,Fernanda Marciano,Rodrigo Pessoa

doi:10.3390/ma12040682

Abstract

Titanium dioxide (TiO2) and aluminum oxide (Al2O3) coatings have been investigated in a wide range of bio-applications due to their biodegradation and biocompatibility properties, that are key parameters for their use in the food packaging and biomedical devices fields. The present study evaluates and compares the electrochemical behavior of the non-coated, commercial resin-coated, TiO2-coated and Al2O3-coated aluminum in commercial beer electrolyte. For this, TiO2 and Al2O3 thin films were deposited on aluminum (Al) substrates using atomic layer deposition (ALD). The evaluation of the corrosion barrier layer properties was performed by linear sweep voltammetry (LSV) during 10 min and electrochemical impedance spectroscopy (EIS). In addition, profilometry, grazing incidence X-ray diffractometry (GIXRD), scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FT-IR) analyses were performed to investigate the physical and chemical properties of the pristine and / or corroded samples. TiO2 and Al2O3 films presented an amorphous structure, a morphology that follows Al substrate surface, and a thickness of around 100 nm. Analysis of LSV data showed that ALD coatings promoted a considerable increase in corrosion barrier efficiency being 86.3% for TiO2-coated Al and 80% for Al2O3-coated Al in comparison with 7.1% of commercial resin-coated Al. This is mainly due to the lower electrochemical porosity, 11.4% for TiO2-coated Al and 20.4% for Al2O3-coated Al in comparison with 96% of the resin-coated Al, i.e. an increase of up to twofold in the protection of Al when coated with TiO2 compared to Al2O3. The EIS results allow us to complement the discussions about the reduced corrosion barrier efficiency of the Al2O3 film for beer electrolyte once SEM and FT-IR analyzes did not show drastic changes in both investigated ALD films after the corrosion assays. The above results indicate that ALD TiO2 and Al2O3 films may be a viable alternative to replace the synthetic resin coatings frequently used in aluminum cans of use in the food industry.

Highlights

The food industry is always looking for new technologies for improving packaging techniques in order to maintain the food quality and assuring food safety
The thickness of the TiO2 film is in agreement with previous work of Chiappim et al that deposited by thermal atomic layer deposition (ALD) TiO2 thin films on Si(100) surface at 100 ◦ C using TiCl4 + H2 O
TiO2 and Al2 O3 thin films have been coated onto Al substrates using ALD method in order to improve the corrosion resistance for food packaging application

Summary

Introduction

The food industry is always looking for new technologies for improving packaging techniques in order to maintain the food quality and assuring food safety. The CO2 -containing beverages such as beer and carbonated drinks have acidity and chlorides in the composition and, when packed in Al cans, can promote the corrosion process by coming into contact with the Al material. To mitigate this problem, commercial Al cans are internally spray coated by synthetic resins, generally natural or synthetic epoxy, that aims to protect the Al surface from direct contact with the beverage [4,5,6]. There is a concern that BPA may leach into the liquid contained inside beverage cans [8] These problems may cause loss of product quality and integrity. If the contaminated product reaches the final consumer it can be harmful to human health [8,9]

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Conclusion