ZEIN-BASED HYDROPHOBIC COATING: FROM PROMISING PROPERTIES TO FIELD APPLICATION

The research project illustrated in the thesis deals with the development of a new zein-based hydrophobic coating for the protection of exposed architectural stone surfaces. Zein, the amphiphilic protein extracted from corn endosperm, was chosen thanks to its biodegradability, natural origin, solubility in non-toxic and environmentally friendly solvents and ability to give origin to hydrophobic surfaces. The protein was deeply studied with the aim to reach the formation of a hydrophobic layer onto stone surfaces, tuning several parameters, which are known to drive the formation of either hydrophilic or hydrophobic, surfaces depending on the exposed chemical moieties. Thus, several solvents were tested such as ethanol/water mixtures, dimethyl sulfoxide (DMSO) and benzyl alcohol (BA), whereas the tested zein concentration was taken between 5 and 20 % (w/v). Spray coating was chosen as application method after demonstrating that a fast evaporation of the solvent significantly contributes to the formation of a hydrophobic surface. The highest degree of hydrophobicity was obtained using the 5% (w/v) of zein in dimethyl sulfoxide, where a WCA of 121 ° ± 3 was measured with the application of the coating. Several techniques were used for the evaluation of the water-linked properties of the obtained coatings, such as static contact angle measurements, water vapor permeability and water vapor uptake tests. A reduction in water absorption was observed after coating deposition and, despite the slight decrease in water vapor permeability, the reduction (%) was maintained under the threshold of 20%. The study of coating-stone interactions was carried out through morphological and chemical analyses (profilometer, SEM analysis, adhesion test, XPS and ATR-FTIR analysis). Coating stability was evaluated through ageing tests and resistance to biodeterioration, while its applicability in CH field was evaluated through biodegradability and removability tests, giving promising results. The need of using more green materials is becoming more and more urgent in CH field, but only a limited number of solutions have been proposed up to now. The here proposed materials demonstrated to fulfill the requirements for its application in CH field and therefore it may represent a suitable alternative to the available synthetic materials. Moreover, thanks to its biodegradability it also responds to the need of more eco-friendly materials with low impact on the environment.