A Comparative study of “green” and synthetic gels as tools for the cleaning of artifacts

Prior to conservation interventions, cleaning of any undesired matter (aged coatings, degraded materials, deposits of pollutants, graffiti, dust and dirt) from the surfaces of artifacts is essential and needs a delicate approach. The challenge is to remove foreign matter without affecting the original properties of artifacts. Different kinds of gels have been used as suitable tools (transporting medium of solvents or emulsions) for cleaning purpose over the last decades. Among the gel materials used in this field, both physical (e.g. xanthan gum, gellan gum, agar, and chitosan) and chemical gels (e.g. acrylamide and bisacrylamide hydrogels), the ones made with synthetic polymers have shown better performance than the others [1-2]. However, there is a strong necessity to elaborate new cleaning systems for water sensitive artifacts with eco-friendly gel materials. For this purpose, a new bio-degradable gel material was prepared by combining the natural polymer (konjac glucomannan) with two different synthetic polymers (Polyvinyl alcohol, PVA, and Polyvinylpyrrolidone, PVP). The performances of the investigated gel were compared with the traditional materials, i.e konjac glucomannan (reacted with borax) and hydrogel obtained from HEMA-MBA (2-hydroxyethyl methacrylate/N,N-methylenebisacrylamide) copolymer and PVP. All the considered gel materials were characterized using different techniques in order to comparatively assess their properties that are relevant for cleaning purpose: gel content, equilibrium water content, retention capability, morphology, tensile strength, hardness, and durability. Gels were loaded with appropriate amounts of nano-structured emulsions containing different concentrations of cleaning agent (eco-friendly surfactant and/or organic solvents) and their performances tested after application on the surface of laboratory biocalcarenite (e.g. Lecce stone) specimens. In particular, a comparative study of the nanoemulsion-loaded gels was carried out in order to evaluate their ability to remove old acrylic polymer coatings (e.g. Paraloid B-72), graffiti, soil, and organic pollutant from the stone surface. Different analytical techniques were used to investigate the performances: chromatic variations and contact angle measurements, optical microscopy, iodine vapour staining test, SEM-EDS, FTIR and micro-FTIR (in ATR mode). The newly synthesized gel material showed better performances than the considered traditional gels in cleaning approach of soiled stone surface. Moreover, it is mainly based on a natural polymer and is more affordable compared to completely synthetic hydrogel's. Therefore, it can be considered as a promising tool for cleaning procedures applied to artifacts.