Novel Microemulsions with Essential Oils for Environmentally Friendly Cleaning of Copper Cultural Heritage Artifacts

Abstract

Cleaning represents an important and challenging operation in the conservation of cultural heritage, and at present, a key issue consists in the development of more sustainable, “green” materials and methods to perform it. In the present work, a novel xylene-in-water microemulsion based on nonionic surfactants with low toxicity was obtained, designed as low-impact cleaning agent for metallic historic objects. Phase diagram of the mixtures containing polyoxyethylene-polyoxypropilene triblock copolymer Pluronic P84 and D-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) as surfactants, water, ethanol and xylene was studied, and a microemulsion with low surfactant content was selected as suitable cleaning nanosystem. Essential oils (EOs) from thyme and cinnamon leaf were added to the selected microemulsion in order to include other beneficial properties such as anticorrosive and antifungal protection. The microemulsions with or without EOs were characterized by size, size distribution and zeta potential. The cleaning efficacy of the tested microemulsions was assessed based on their ability to remove two types of artificial dirt by using X-ray energy dispersion spectrometry (EDX), scanning electron microscopy (SEM), contact angle measurements and color analysis. Microemulsions exhibit high capacity to remove artificial dirt from model copper coupons in spite of very low content of the organic solvent. Both thyme and cinnamon oil loading microemulsions prove to significantly reduce the corrosion rate of treated metallic plates compared to those of bare copper. The antifungal activity of the novel type of microemulsion was evaluated against Aspergillus niger, reported as main treat in biocorrosion of historic copper artifacts. Application of microemulsion with small amounts of EOs on Cu plates inhibits the growth of fungi, providing a good fungicidal effect.

Cinnamon Bark Oil as an Effective Fungicide in Protecting the Surface of Wood-Based Softboards against the Development of Mold Fungi

“…An ethanol solution of cinnamon bark oil can be used for preventive, short-term protection of surfaces against molds. The obtained test results confirm the reports of other authors about the biocidal effectiveness of cinnamon oil against mold fungi [41,42]. Substances with fungicide properties can be obtained from various parts of plants.…”

Stealing from Phytotherapy—Heritage Conservation with Essential Oils: A Review, from Remedy to Sustainable Restoration Product

“…Thyme and cinnamon EOs have also been added to microemulsion systems as anticorrosive and antifungal agents for copper artworks [205]. This application method seems to reduce the corrosion rate of treated metallic plates, a small amount of EO (approximately 1%) being enough to inhibit the growth of fungi.…”