Development, characterization and assessment of innovative materials for ancient and modern paper artifacts conservation

The work described in this PhD thesis acquires greater significance when framed within a broader vision. Indeed, 2018 was the First European Year of Cultural Heritage and it has considerably educated citizens and policy makers about the importance of culture and heritage in Europe. This initiative aims to raise awareness of European history and values and to strengthen the sense of European identity; moreover it draws attention to the opportunities offered by our Cultural Heritage, but also to the challenges it faces. Indeed, Cultural Heritage has universal value for each of us, for communities and societies. It is important to keep it and pass it on to future generations. Heritage can be thought of as "something of the past" or static, but in reality it develops through the way we relate to it. Furthermore, Italian Cultural Heritage has an important role to play in building the future of Europe, and it should not be left to decline, deterioration and destruction. For this reason, in 2018, this initiative was established and the EU has funded projects in support of Cultural Heritage preservation. In this thesis, the theme concerning the safeguarding of paper material, a field as delicate as it is unexplored, will be addressed and suitable “green” strategies will be proposed. Research relating to cleaning and/or consolidating materials and restoration techniques is very recent in this area. Suffice it consider that the first extensive treatment on restoration and the conservation of paper artifacts took place in Italy only in 1981. Preserving the testimony of own past is fundamental, as memory is what we are made of. It is what constitutes the way we speak and think; therefore an ancient manuscript is an asset of civilization and it must be saved. In the present work, exploiting the expertise gained by the research group of the Department of Chemical Sciences and Technologies of “Tor Vergata” University, Rome, in collaboration with restorers of ICRPAL (Rome), about an innovative method to perform wet treatments on paper artifacts using rigid Gellan gum hydrogels, an improvement of paper cleaning systems has been proposed. These “green” innovative materials have been developed, characterized, from a physico-chemical point of view, and their effectiveness assessed for ancient and modern paper artifacts conservation. Their chemical compatibility with paper, differing in composition, age and resistance to wet treatments, has been studied in detail in order to prevent any alteration of the support. In detail, Gellan gum microgels have been proposed, because they could offer several advantages compared to their macroscopic counterpart, hydrogels, in terms of reduced size, comparable with the average pore size of the paper, and softness, therefore adaptable even to irregular surfaces. These features contribute to a more efficient and faster cleaning method than traditional ones. These experimental evidences led the work towards the development of systems that could accommodate the benefits of Gellan gum microsized systems, but overcoming their drawbacks. Hence, the use of synthetic polyvinyl alcohol polymer to obtain hydrogels and microbubbles has been pointed out; this material ensures long-lasting stability, higher reproducibility, and allow to have greater control over the final properties of the system compared to natural ones. In the form of hydrogel, polyvinyl alcohol shows excellent compatibility with cellulosebased supports, and cleaning efficiency comparable to that of Gellan gum hydrogel, but with a lower release of water amount and therefore usable for treating delicate materials. While, polyvinyl alcohol based microbubbles, combined with ultrasounds (US), are able to exploit a mechanical action, without damaging the artifact, but removing both cellulose degradation byproducts and fragments of aged adhesive, without the use of solvents dangerous for operator and artwork. The whole work was validated using a multidisciplinary approach, in order to shed light on every aspect of the problem. Future perspectives concern the improvement of the systems listed above, in order to implement their cleaning power, make them more selective for a single paper component or even apply them on materials of different nature. Moreover, a problem that will be addressed in detail is studying the use of aerogels, in this work characterized from a physical-chemical point of view, as possible absorptions for volatile organic components, inside museum display cases, and/or antimicrobial treatment of contaminated paper surfaces.