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. 2024 Dec 3;29(23):5702.
doi: 10.3390/molecules29235702.

Enhancing Permanence of Corrosion Inhibitors Within Acrylic Protective Coatings for Outdoor Bronze Using Green Nanocontainers

Giulia Pellis  1 , Fabrizio Caldera  1 , Francesco Trotta  1 , Thais Biazioli de Oliveira  1 , Paola Rizzi  1 , Tommaso Poli  1 , Dominique Scalarone  1
Affiliations

Enhancing Permanence of Corrosion Inhibitors Within Acrylic Protective Coatings for Outdoor Bronze Using Green Nanocontainers

Giulia Pellis et al. Molecules. .

Abstract

Outdoor bronze statues are constantly exposed to weather conditions and reactive compounds in the atmosphere that can interact with their surfaces. To avoid these interactions, a commonly used method is the application of coatings with corrosion inhibitors. However, a significant limitation of these inhibitors is their gradual loss over time. In this study, we aimed to improve the durability of 5-ethyl-1,3,4-thiadiazol-2-amine (AEDTA), the inhibitor chosen to formulate new acrylic coatings for outdoor bronzes. Methyl-β-cyclodextrin (Me-β-CD) was selected to host the inhibitor due to the capability of cyclodextrins to form complexes incorporating small organic molecules. The complexes of Me-β-CD and AEDTA were prepared and the inclusion of AEDTA was proved by Fourier-transform infrared spectroscopy, X-ray diffraction and nuclear magnetic resonance spectroscopy. Then, acrylic coatings were prepared at different concentrations of the Me-β-CD/AEDTA system. They were thermally aged and monitored every 24 h. To evaluate the volatilization of the corrosion inhibitor, solid phase microextraction-gas chromatography/mass spectrometry (SPME-GC/MS) and thermal desorption-GC/MS (TD-GC/MS) analyses were performed during the first 72 h. The results were compared to those of pure AEDTA films and Incralac®. The outcomes showed that Me-β-CD/AEDTA complexes are promising candidates for developing coatings with improved stability and longer retention of AEDTA.

Keywords: bronze statues; corrosion inhibitors; cyclodextrins; inclusion complexes; protective coatings.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
5-ethyl-1,3,4-thiadiazol-2-amine (AEDTA) and methyl-β-cyclodextrin.
Figure 2
Figure 2
ATR-FTIR spectra of AEDTA, Me-β-CD, their complex, and physical mixture. The box shows the spectral region with the characteristic absorption band of AEDTA and its shift due to complexation.
Figure 3
Figure 3
XRD diffractograms of AEDTA, methyl-β-cyclodextrin, their complex, and their physical mixture.
Figure 4
Figure 4
1H-NMR spectra (600 MHz, D2O) of AEDTA, methyl-β-cyclodextrin, and their complex.
Figure 5
Figure 5
Zoom in on NMR spectra of methyl-β-cyclodextrin and the complex.
Figure 6
Figure 6
NMR spectra of AEDTA, methyl-β-cyclodextrin, and their complex.
Figure 7
Figure 7
Job’s plot of H3 and H5 of Me-β-CD.
Figure 8
Figure 8
FTIR monitoring during aging at 80 °C: acrylic coating with 2% w/w of complexed AEDTA (left); acrylic coating with 5% w/w of uncomplexed AEDTA (centre), and Incralac® (right).
Figure 9
Figure 9
Detail of SPME-GC/MS curves obtained from acrylic coatings treated with uncomplexed AEDTA: (A) unaged coating, (B) coating aged 72 h at 80 °C. The arrow highlights the AEDTA peak.
Figure 10
Figure 10
Detail of the TD-GC/MS analysis of acrylic coatings aged 72 h at 80 °C and treated with the methyl-β-cyclodextrin/AEDTA complex (A) and with uncomplexed AEDTA (B). The arrow highlights the AEDTA peak in the coating containing the inclusion complex.
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