Protective Coatings Based on Cellulose Nanofibrils, Cellulose Nanocrystals, and Lignin Nanoparticles for the Conservation of Cellulosic Artifacts

Green nanocomposites combining cellulose nanofibrils (CNFs), cellulose nanocrystals (CNCs), and lignin nanoparticles (LNPs) were designed and applied for the first time as ternary protective coatings on cellulosic materials, i.e., substrates mainly composed of cellulose. All the nanostructures were obtained from elephant grass biomass. CNFs and CNCs are less than 10 nm thick and present a filament-like morphology, while LNPs are spheres with an average diameter of less than 100 nm. The use of water-based nanoparticle dispersions is a facile and greener alternative to synthetic varnishes usually based on toxic organic solvents. Moreover, the coatings from renewable sources were chemically stable; showed high compatibility with wood, paper, and fabric; and preserved the roughness and surface morphology of the substrates after application. Moist-heat accelerated aging and UV-shielding assays revealed that the nanocellulose/nanolignin coatings were able to protect the coated cellulosic substrates against degradation. The wettability of nanocomposite-coated substrates could be tailored and reduced to produce hydrophobic surfaces by applying additional layers of water-based carnauba wax nanoparticles, which are also sustainable. Additionally, two-dimensional infrared spectroscopy mapping confirmed the reversibility of the coating application, as the nanocomposite layers could be easily removed from the cellulosic substrates by water-loaded cleaning hydrogels. Therefore, the functional protective coating introduced here represents an environmentally friendly and nontoxic approach for the conservation of cellulosic artifacts in general, including cultural heritage objects based on paper, wood, and fabric.