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One of the main issues in the cultural heritage field of restoration chemistry is the identification of greener and more effective methods for the wet cleaning of paper artefacts, which serve as witnesses to human history and custodians of cultural values. In this context, we propose a biocompatible method to perform wet cleaning on paper based on the use of 1 MHz ultrasound in combination with water-dispersed polyvinyl alcohol microbubbles (PVAMBs), followed by dabbing with PVA-based hydrogel. This method can be applied to both old and new papers. FTIR spectroscopy, X-ray diffraction, HPLC analysis, pH measurements and tensile tests were performed on paper samples, to assess the efficacy of the cleaning system. According to the results, ultrasound-activated PVAMB application allows for an efficient interaction with rough and porous cellulose paper profiles, promoting the removal of cellulose degradation byproducts, while the following hydrogel dabbing treatment guarantees the removal of cleaning materials residues. Moreover, the results also pointed out that after the treatment no thermal or mechanical damages had affected the paper. In conclusion, the readability of these kinds of artifacts can be improved without causing an alteration of their structural properties, while mitigating the risk of ink diffusion. [ABSTRACT FROM AUTHOR]

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The gellan hydrogel is used as a cleaning agent for paper artworks. The purposes of this work were to give the gellan hydrogel both a microbial resistance and a cytocidal action against the biodeteriogens using hydrolates. Broth microdilution assays were performed to identify the fungicidal action of 16 hydrolatesvs3 fungal strains. The study concerned the Minimal Fungicidal Concentration and pH, colour, and ultra-structural variations on all paper samples, by placing them in contact with GELYD (GELlan + hYDrolat). Thein vitrotests showed that eight out of 16 hydrolates strongly inhibited fungal growth, but only two of them (Monarda fistulosa,Citrus aurantiumsubspamara) showedin situfungicidal action. Data indicate a new and interesting eco-innovative use of hydrolates, since GELYD is able not only to clean paper artworks, but also to kill the fungal cells present on paper that are potentially harmful for paper and operators. [ABSTRACT FROM AUTHOR]

Hypothesis Due to their highly retentive properties, innovative recently developed, semi-interpenetrated hydrogels made up of poly(vinyl pyrrolidone) (PVP) chains embedded in a poly(2-hydroxyethyl methacrylate) (p(HEMA)) network should be efficiently used as cleaning material for fragile and degraded paper artworks. In restoration practice, indeed the wet cleaning of these artworks is usually performed by immersion of paper in water, a procedure which may lead to several drawbacks, including paper fibers swelling and dissolution of water-soluble original components. Experiments This class of gels were yet presented in literature, but their interactions with paper materials and ability to be spiked with active enzymes (as cleaning agents), have not been analyzed. To establish the suitability of these hydrogels as paper cleaning materials, first, a rheological and microstructural characterization of the gels was performed. Moreover, diffusion of macromolecules inside gels was studied using fluorescence microscopy, to check if these innovative hydrogels can be used as carriers for hydrolytic enzymes. Indeed, pastes and glues are usually found in old paper artworks, and their removal is a very delicate operation that requires a selective action, which is granted by specific hydrolytic enzymes. At the same time, spectroscopic analyses on paper samples under investigation before and after cleaning treatment has been performed, thus assessing the capabilty of these gels as cleaning materials. Findings With the aim of demonstrating the versatility of these hydrogels, several case studies, i.e., the removal of grime and water-soluble cellulose degradation byproducts, the removal of animal glue and the removal of starch paste from real samples, are presented. Results obtained with these gels have been compared to those obtained by using another gel used for paper artworks cleaning, i.e., Gellan gel. [ABSTRACT FROM AUTHOR]

Wet cleaning of ancient papers is one of the most delicate and important steps in a restoration process. It allows to improve the optical quality of a graphic work as the removal of pollution and of organic substances resulting from cellulose degradation. Nevertheless, washing by immersion – the traditional process – usually involves a substantial impact on the original morphological structure of paper and could be dangerous for water sensitive inks and pigments. Furthermore it is very important that the time of the cleaning process is optimized in order to remove all contaminants, thus minimizing invasive treatments and time costs. In this contest, we have developed an innovative and non-invasive cleaning and diagnostic tools, based on a hydrogels combined with electrochemical sensor, suitable to verify in situ and in a simple way the paper degradation progress, and the efficiency of cleaning treatment. More in detail, the wet cleaning technique is based on the use of a rigid hydrogel of Gellan gum. This gel is able to gradually release the water and also to absorb the water-soluble degradation products present on the paper. Moreover, it is rigid and therefore its application and removal are fairly simple, not leaving residues on the paper surface after treatment. It could be easily combined with selective electrochemical biosensors, suitable to monitor the cleaning process. Using this new tool (a biocompatible hydrogel and an electrochemical sensor) it is possible to know when the cleanup process is completed, avoiding lengthy and sometimes unnecessary cleaning material applications. Here we report the results obtained by applying the proposed system to the “ Breviarium Romanum ad usum Fratrum Minorum ”, a breviary of the 18th century, highlighting the advantage and the potentiality of this new tool with respect to the traditional old paper cleaning methodology. To perform a complete characterization of the proposed system, several invasive and non-invasive techniques, such as spectroscopy, scanning electron microscopy, high-performance liquid chromatography analysis and pH measurements have been used. [ABSTRACT FROM AUTHOR]

Highlights: [•] Gellan hydrogel is proposed as a new method for wet cleaning of paper artworks. [•] Gellan hydrogel has been used to clean four different paper samples. [•] Every sample has been fully characterized before and after cleaning. [•] For our studies a multitechnique approach has been used. [Copyright &y& Elsevier]

• PVA based chemical hydrogels can be formulated with controlled architectures. • Characterization of the hydrogels shows their compatibility with paper artworks. • The hydrogels show different paper cleaning abilities depending on their structure. Hydrogel-based cleaning of paper artworks is an increasingly widespread process in the cultural heritage field. However, the search for tuned (compatible, highly retentive and not perishable) hydrogels is a challenging open question. In this paper, a complete characterization of chemical hydrogels based on polyvinyl alcohol (PVA) crosslinked with telechelic PVA and their remarkable performances as gels for cleaning paper artworks are reported. The rheological properties, porosity, water content of these gels were determined and analyzed as a function of the components concentration during synthesis. Due mechanical and retentive properties, the reported gels are optimum candidates for paper cleaning applications. The efficacy of these PVA-based gels has been demonstrated applying them on the surface of the sheets of several paper artworks, and characterizing the samples before and after the cleaning process by means of a multidisciplinary approach involving spectroscopic and chromatographic tests. [ABSTRACT FROM AUTHOR]