## 4 Applications of Cellulose Nanomaterials in Cultural Heritage
### Wood
Despite this, nanocellulose does not improve the adhesion properties of the adhesive resins, but this problem is easily overcome with the crosslinking approach and functionalization of this nanomaterial, possibly thanks to the availability of free hydroxyl groups on the surface of nanocellulose [73]. Usually, in order to improveseveral properties of wood adhesives, a small amount of nanocellulose is required as reported in the literature [74; 75]. Another work that involves a different use of nanocellulose for the treatment of wood is the one proposed by [PERSON] et al. [52], who describe the synthesis of new green protective coatings, trying in this way to extend the lifetime of the artistic objects without affecting their original integrity. The use of CNF for these coatings allows us to obtain several advantages, such as transparency, flexibility, and tensile strength, but also the disadvantage of a possible deformation of these films after drying. On the other hand, the use of CNC provides a high crystallinity and chemical stability of these coatings, but more brittle and shiny films. Consequently, a blend of CNF and CNC turned out to be the better solution to overcome these problems and to obtain new stable composite coatings, with a high compatibility with wood, able to preserve the roughness and the morphology of the treated material and prevent the degradation of wooden artworks. Moreover, IR-analysis showed another important characteristic of these coatings: their reversibility by means of water-loaded cleaning hydrogels. Regarding the consolidating coatings for wood, [PERSON] et al. [76] also suggested the addition of CNC to improve the mechanical properties of these films without a significant modification of their optical characteristics, such as their color, optical transparency, and sheen. Shipwrecks and waterlogged wood from land waterlogged sites or from submerged archaeological sites are often among the most common wooden archaeological findings. In these cases, the water fills the pore spaces, including capillaries and microcapillaries, changing the dimension and shape of wood [77]. Subsequently, many chemical and biological factors can cause the decay of the wooden artworks; for example, the salinity of sea water or a biological attack of degraders, such as the erosion or tunnelling bacteria, lead to a loss of mass and an increase in the porosity and permeability of the wood, thus weakening the material [78]. Also in the case of waterlogged wood, the consolidation treatments should provide integrity and stabilization of the wood after the drying procedures, required for the musealization of these wooden objects. Moreover, the consolidants should be stable, resistant to the biotic and environmental attacks, eco-friendly, and, where possible, reversible. Historically, the most used chemical methods provided alum treatment [79] and polyethylene glycol [80]; otherwise, most recent studies showed the use of several materials able to consolidate the decayed wood, such as natural resins [81], sugars [82], and polysaccharides [21], therefore also including nanocellulose. In fact, different kinds of nanocellulose-based materials were recently investigated by [PERSON] et al. [18], such as bacterial nanocellulose (BNC) and cellulose nanocrystals (CNC), for the consolidation of the degraded cell walls of waterlogged wooden artifacts, obtaining successful results in terms of consolidation and interactions with the wood ultrastructure, although the two types of consolidants acted differently, one penetrating little into the wood in the case of CNC, and the other forming a compact layer on the surface in the case of BNC. Regardless, the best result can be obtained by combining the use of the two types of nanocellulose, one more filamentous and the other composed of more spherical nanoparticles, to increase the adhesion of nanofillers with the cell walls of the wood ultrastructure.