Retention and capillary flow dynamics assessment of Fatty Acid Methyl Esters (FAMEs) in Carrara marble

The conservation of cultural heritage often involves the use of solvents for cleaning porous substrates like marble, but traditional solvents pose environmental and health risks. Fatty Acid Methyl Esters (FAMEs) are potential green alternatives due to their low toxicity and biodegradability, yet their interactions with heritage materials are not well understood. This study explores the retention behavior of FAMEs with varying chain lengths in Carrara marble using Nuclear Magnetic Resonance (NMR) relaxometry, as well as their perfusion and diffusion behaviors using Mercury Intrusion Porosimetry (MIP), contact angle measurements, and the Lucas-Washburn equation. NMR relaxometry performed by a single-sided portable instrument showed that FAMEs are retained in marble pores, with spin-spin relaxation times increasing upon imbibition and varying with solvent chain length over time. Shorter-chain FAMEs demonstrated faster penetration but lower retention, indicating a reduced long-term impact on the substrate. The NMR relaxometry findings were corroborated by mercury intrusion porosimetry, contact angle measurements, and the Lucas-Washburn equation. These results highlight the potential of NMR relaxometry as a non-destructive method for investigating solvent interactions and flow dynamics of FAMEs within porous substrates.