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

Abstract

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.

From Nanoparticles to Gels: A Breakthrough in Art Conservation Science

“…Finally, colloids are being increasingly developed and proposed for the protection of works of art, i.e., preventing damage and alterations by either acting on the works’ surfaces (remedial conservation) or devising tools to neutralize environmental degradation agents before they reach the artifacts (preventive conservation). , Among the latest applications, we mention here multifunctional halloysite nanotubes, the use of graphene veils to prevent the fading of colors, colloidal semiconductor photocatalyst or nanocrystals for self-cleaning and degradation prevention, , soil colloids as templates to protect jade, antioxidant bionanocomposites or antifouling coatings, , sol–gel or nanocarriers to protect bronze from corrosion, , mesoporous silica nanoparticles for the controlled release of antimicrobials, cellulose nanocrystals or lignin nanoparticles as UV absorbers, and organic–inorganic composites or metal organic frameworks to absorb volatile acids in enclosures. − These are all key studies to show the vast potential impact of nanoparticles and nanocomposites in cultural heritage conservation, thanks to properties that surpass those of conventional restoration materials. Current challenges involve scaling up the production of these innovative systems, implementing green synthetic processes, transferring the best products to the conservation market, and linking with transversal sectors that can benefit from the new materials.…”

Modified Lignin Nanoparticles as Potential Conservation Materials for Waterlogged Archaeological Wood

“…In addition to consolidating wooden cultural heritage, it is expected that the hydrogen bonding between consolidants and wood cell can prevent and slow down the degradation process of wood carbohydrates (cellulose and hemicellulose), which is crucial for extending the lifespan of heritage objects and maintaining their original integrity. 22 In this work, model waterlogged wood samples were degraded by an alkali solution. Three LNPs [original, aminated (hydrophilic), and esterified (hydrophobic)] were prepared and characterized.…”

“…Additionally, microbial degradation and heating can also have adverse impacts. ,− Over the past decade, there has been increasing interest in developing new materials to replace PEG, such as keratin (hydrolyzed feather keratin and keratin-metal/magnesium), organosilicons (methyltrimethoxysilane, organosilicon compounds, and ethyl orthosilicate), and halloysite nanotubes. , However, finding a sustainable consolidation agent with satisfactory compatibility and reinforcement effect for waterlogged archaeological wood remains challenging. Therefore, the idea of using the original composition of wood (cellulose, hemicellulose, and lignin) as sources of consolidation materials for wooden cultural heritage has been proposed. − …”

“…As an alternative, lignin nanoparticles (LNPs) were prepared as a consolidant for waterlogged archaeological wood . These particles, with much smaller size, can more easily penetrate the wood structure due to the anatomical characteristics of wood. , In addition, LNPs show a lighter color appearance than the bulk lignin and are more stable in neutral aqueous solutions . However, their consolidation efficiency in wood is limited because their penetration depth in waterlogged archaeological wood is only about 1.2 mm. , …”

“…Hydrophilic LNPs have more hydroxyl groups and tend to bind to the remaining cellulose and hemicellulose in archaeological wood, which may allow the particles to retain more in the wood. In addition to consolidating wooden cultural heritage, it is expected that the hydrogen bonding between consolidants and wood cell can prevent and slow down the degradation process of wood carbohydrates (cellulose and hemicellulose), which is crucial for extending the lifespan of heritage objects and maintaining their original integrity …”