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.