## 1 Introduction
If nanocellulose is used to realize composite materials for the electronic industry, it is able to enhance flexibility and conductivity. As an example, polyaniline nanocellulose composite film is widely used as conductive adhesives, paper-based sensors, flexible electrodes, and in electronic device fabrication [10]. Focusing on cultural heritage, it should be emphasized that many collections of objects and artifacts of world artistic patrimony are made of cellulose-based materials such as wood, paper, archaeological fabrics, and painting canvases, and a large part of these requires an intervention of recovery and restoration due to the chemical acidification processes caused by primers, paints, and glues; the absorption of acid gases present in the atmosphere to which they are subjected; or the biological attacks by xylophagous insects and microorganisms that digest cellulosic substances, deteriorating the material [18]. For these reasons, nanocellulose-based innovative materials with many fascinating characteristics, such as a high specific surface area, non-toxicity, light weight, high elastic modulus (140-150 GPa), gas impermeability, high aspect ratio, high stiffness, and interesting mechanical properties, are very important for the recovery and conservation of cultural heritage, because an intervention with these materials certainly gives better results compared to synthetic products, and, moreover, they do not alter the optic effect of artistic surfaces. In fact, beyond the similar chemical nature of the consolidant and the treated materials, the nanometric dimension of cellulose enhances the physicochemical interaction between the consolidant and the substrates, providing more effective actions than the synthetic consolidants that are usually used [19]. In this context, nanocellulose can not only be used as a consolidating agent or structural reinforcement, which are actions related to its penetrating power, but also as an antibacterial agent due to the possibility of being functionalized thanks to the availability of numerous free hydroxyl groups. For all of these reasons, scientists and art curators all over the world believe that nanocellulose will be one of the most important materials for the entire technology and engineering world [10; 13; 20]. In this review paper, the description of different types of nanocellulose is first reported, and then several characterization methods used to analyze them. Finally, the most recent applications of these innovative nanomaterials in the artistic context have been collected; nanocellulose has proved to be useful for several purposes, such as: ancient and degraded wood consolidation, wood reinforcement coating, the consolidation of waterlogged wooden artifacts, and structural reinforcement for canvases degraded by aging [18; 19; 21; 22; 23; 24; 25]. The novelty of this review, which aims to offer an interesting overview about the use of nanocellulose for the recovery and conservation of cultural heritage, lies in having collected the latest applications of this bio-nanomaterial for the treatment of several artworks in a single paper. To achieve this, Scopus and WOS databases were used. The information collected and mentioned in this paper about nanocellulose applications was selected in a timeframe ranging from 2013 to 2022, focusing on the last five years. Earlier articles, dating from 1985 to 2012, have been mentioned in the more theoretical paragraphs in relation to nanocellulose extraction processes, its classification, and the recovery and conservation methods used in the past.