# Comparative Studies on Nanocellulose as a Bio-Based Consolidating Agent for Ancient Wood
## 1 Introduction  
Recently, one of the most important tasks of nanotechnology has been to develop new materials with a high added value and low environmental impact, starting with renewable and green resources [1; 2; 3]. In this regard, nanocellulose, thanks to its enormous availability from various natural primary sources and its numerous applications, has turned out to be one of the most interesting innovative materials to enable this technological revolution [4]. Through the mechanical or chemical treatment of wood pulp or vegetable cellulose, it is possible to obtain both cellulose nanocrystals and cellulose nanofibrils with different degrees of crystallinity [5; 6; 7]. In particular, crystalline nanocellulose (CNC), consisting of cylindrical, elongated, less-flexible, and rod-like nanoparticles 4-70 nm in width, 100-6000 nm in length, and with a 54-88% crystallinity index, is usually produced by acid hydrolysis [4]. The numerous properties of cellulose nanocrystals, such as their nanometric scale, non-toxicity, light weight (1.5 g/cm\({}^{3}\)), high specific surface area, easy processing,high elastic modulus (140-150 GPa), high aspect ratio and stiffness, gas impermeability, interesting mechanical characteristics, and good thermal stability, suggest the utility of developing novel nanocellulose-based systems [8; 9; 10]. As well as its other applications, nanocellulose is also used in the conservation and recovery of Cultural Heritage [11; 12; 13; 14; 15]. In fact, the collections of objects and artifacts that belong to our artistic patrimony are largely made of cellulosic-based materials, such as paper, painting canvas, and wood. Very often, all these cellulosic materials require consolidation and restoration interventions due to the processes of decay and aging, mainly caused by acidity, which originates from primers, paints, glues, and the absorption of acidic gases from the environment, as well as from the poor conservation conditions to which they are subjected. Usually, the degradation of cellulose-based works of art occurs by the acid-catalyzed hydrolysis of \(\beta\)-1,4-glycoside bonds, resulting in the loss of their original mechanical properties. This acidification mechanism can be caused by the same materials used in the past for recovery and conservation. For all these reasons, many times, cellulose-based artistic materials require synergistic reinforcement and deacidification interventions [16; 17]. In addition, cellulose-based materials can also be subject to biological attacks due to the action of insects and microorganisms that carry out excavator activity [18]. Usually, to preserve a lignocellulosic artefact, chemical consolidants are used; among these, we find the synthetic resins Paraloid B-72 and Regalrez 1126, which can also be used, for example, with the addition of nanoparticles of ZnO for the consolidation of degraded fir wood, thus increasing its resin retention values [12]. Paraloid B-72 is a copolymer of ethyl methacrylate-methyl acrylate that is soluble in various types of solvents--for example, ethanol, acetone, and butyl acetate--that can also be defined as an acrylic resin, with excellent characteristics of hardness, brilliance, and adhesion on a variety of substrates. It is used in the field of restoration as a final varnish or as a consolidator of works of art in wood, marble, stone, metal, etc., at low concentrations (2-4%), and rarely as an adhesive in higher concentrations. Regalrez 1126 is a low molecular-weight aliphatic resin characterized by high resistance to aging and optical properties close to those of natural resins; it is ideal as a mild consolidating agent for wooden artifacts. It is soluble in medium and low-polarity solvents (white spirit, petroleum essence, butyl acetate) and insoluble in water and polar solvents. Another usual approach is based on the use of colloidal systems, as reported by [PERSON] et al.