## 4 Applications of Cellulose Nanomaterials in Cultural Heritage  
Cultural heritage is an inestimable patrimony of society: it encloses potentially all of the artifacts, artworks, objects, and intangible assets designated by each state as fundamental, containing values of archaeology, literature, art, science, folklore, ethnology, or anthropology. Therefore, cultural heritage constitutes a priceless good; thus, it is mandatory to protect it from degradation mechanisms and the course of time in order to continue cultural and intellectual progress while preserving and transferring the ancient traditions and knowledge to future generations [1,4]. In the last few years, new technological and innovative materials based on nanotechnology science have been designed and synthesized to enhance the performance and technical sustainability of materials used in the field of cultural heritage conservation and, therefore, to obtain non-destructive and non-invasive cleaning treatments, a reliable consolidation, or long-lasting selective conservation [63,64]. At the same time, new sophisticated techniques for the characterization of these materials are optimized to understand the chemical and physical properties and the interaction between the nanostructures and artworks [1]. The collections of objects and artifacts that belong to our world artistic patrimony are largely made of cellulosic-based materials, such as paper, painting canvases, archeological fabrics, and wood, and all of the world historical memory and anthropological values are associated to them; for these reasons, the preservation of cellulose-based artworks is a crucial topic in the conservation science of cultural heritage [4]. The variety of the degradation phenomena that concern artworks reflects the vast range of materials used in humankind heritage, and their prevention results in being advantageous for different artworks, such as books, manuscripts, maps, drawings, and textiles, as well as wooden artifacts such as sculptures or shipwrecks. A significant amount of these artworks requires an urgent intervention of restoration due to several factors to which they are subjected; moreover, those situated outside are particularly irreparably exposed to several agents of degradation, such as humidity, temperature, microorganisms, and air contaminants, all of which are responsible for the natural aging of art materials [4,24,63]. Among these, the acidity mechanism causes a decrease in the polymerization degree and, consequently, the loss of the mechanical properties; the degradation by sulfur dioxide and nitric oxides from air pollution makes cellulosic fibers increasingly brittle; another problem is the thermal degradation due to photolysis, microorganisms, and fungi [24]. Moreover, almost all of the materials used in the past restoration treatments are acidic or may develop acidic products upon aging, thus degrading the works of art; they also must be removable or must at least leave the object retractable, but this is not always possible with traditional consolidation products [18]. Therefore, due to the variety of artistic substrates, conservation science has explored different pathways, developing several technical approaches for solving conservation problems, and nanocellulose-based materials are one of these solutions [63]. Recently, efforts are being made to develop ecological and green approaches to address the above problems, which are also thanks to nanotechnology. For example, [PERSON] et al. [65] proposed a sustainable alternative approach for designing new nano-based consolidants in order to support the development of safer nanostructures for conservation whilst preserving their functionality. This very innovative flowsheet consists of several consequential steps, where each affect one aspect of the process, such as the study of the state-of-the-art, the initial formulation of the consolidant, the screening of the hazard assessments and, therefore, the eventual optimization of the product, and, finally, the evaluation of its safety and sustainability [65].