Stone sustainable protection and preservation using a zein-based hydrophobic coating

• Published in: Progress in organic coatings Vol. 159; p. 106434
• Main Authors: Zucchelli, Margherita, Mazzon, Giulia, Bertolacci, Laura, Carzino, Riccardo, Zendri, Elisabetta, Athanassiou, Athanassia
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01-10-2021; Elsevier BV
• Subjects: Accelerated aging tests; Bio-based coating; Coating; Hydrophobic performance; Hydrophobicity; Natural stone protection; Profilometers; Roughness; Sandstone; Spray coating; X ray photoelectron spectroscopy; Zein; Hydrophobic performance; Zein; Bio-based coating; Natural stone protection; Spray coating
• ISSN: 0300-9440; 1873-331X
• DOI: 10.1016/j.porgcoat.2021.106434

In the present work, the efficiency of an ecofriendly 5% (w/v) solution of zein in DMSO was evaluated as protective material for stone. The solution was sprayed on 5 × 5 × 1 cm slabs of Serena stone, a sandstone widely used in Florentine architecture, in order to create a hydrophobic coating. The obtained coating turned out to be hydrophobic, showing WCA of around 120°, while a reduction of 8.4% in water uptake was observed during 15 days. SEM and profilometer analyses stated that the zein coating application resulted in the formation of a compact film on the stone's surface with a continuous structure characterized by micro-scale roughness. XPS analysis confirmed the presence of the thin conformal layer over the stone. A mechanism of hydrophobic surface formation, in which both the roughness and the solvent's evaporation style are believed to play a significant role, was finally proposed. Accelerated aging tests indicated a good resistance to aging in terms of hydrophobicity and color variations, where the overall color parameter of ΔE < 2.0 was maintained, indicating invisible color changes to the naked eye. This sustainable approach can be easily scaled and may represent a valuable alternative to the most common synthetic treatments used nowadays in stone protection.
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•An environmental-friendly zein-based protective coating for stone was developed.•Good hydrophobicity and breathability were reached without evident color changes.•Spray coating technique and intrinsic stone roughness influenced the hydrophobicity.•A mechanism of hydrophobic surface formation was proposed.•High resistance to accelerated aging test was observed.