Study of menthol sublimation kinetics to deliver essential oil for the disinfection of stone monuments

The biodeterioration of stone substrates represents a major issue in cultural heritage conservation, as microbial colonization – driven by environmental factors and stone bioreceptivity – can induce irreversible surface and structural damage over time. Chemical biocides remain widely used, but their environmental and toxicological drawbacks have prompted the search for sustainable and eco-compatible alternatives. Within this context, Essential Oils (EOs) are increasingly studied for their antimicrobial activity and low environmental impact, although their high volatility strongly limits persistence and long-term performance on stone surfaces. This study introduces an innovative approach based on the use of menthol as a film-forming, volatile binding medium for EOs, aimed at modulating its evaporation kinetics and enhancing coating stability. Oregano EO ( Origanum vulgare L.), one of the most frequently employed natural biocides against stone-colonizing microorganisms, was selected and combined with menthol at different ratios. The mixtures were characterized by ATR-FTIR spectroscopy, while sublimation kinetics were investigated on both non-porous glass slides and porous stone substrates (Carrara marble and Peperino). Gravimetric monitoring was performed under controlled conditions, and additional morphological and optical surface assessments were carried out using Optical Coherence Tomography and Fiber Optics Reflectance Spectroscopy. The results demonstrate that menthol affects the sublimation dynamics, film morphology, and evaporation rate of oregano EO. These findings highlight the potential of EO–menthol systems as sustainable and adaptable surface treatments. By addressing the intrinsic limitations of EO volatility, this work provides new insights into the design of next-generation, eco-compatible biocidal formulations specifically tailored to the preventive conservation of stone cultural heritage.