The surface functionalisation of wood and cellulosic fibres using natural components

Abstract

This work focused on developing surface treatments for various cellulosic materials, including wood, cellulose nanofibrils (CNF), and natural textiles (cotton and linen). For this purpose, several approaches were developed, aiming at various improvements depending on the type of substrate. Some components were created specifically for this work, including amphiphilic galactoglucomannan (GGM) derivatives and an aqueous carnauba wax dispersion. On wood, non-continuous coatings were assembled, made of natural wax particles alone or combined with UV-absorbing additives. When wax particles were used alone, the performance of the coated wood was compared to a continuous wax film and commercially available coatings (lacquer, linseed oil). The treatment with particles enhanced the hydrophobicity of the wooden surface and its moisture buffering performance. Additionally, it is known that protection from the degrading effect of UV light is as important as protection against water. Therefore, zinc oxide nanoparticles were incorporated together with wax particles into multilayer coatings through layer-by-layer (LbL) deposition. The multilayers increased the roughness of the wooden surface and provided UV-absorbing properties. Moreover, the coated wood was superhydrophobic, yet the moisture buffering was preserved and even enhanced. On CNF, galactoglucomannan derivatives with different hydrophobic tails were adsorbed. The derivatives were synthesised using naturally occurring fatty acids or polydimethylsiloxane as hydrophobic blocks. The hydrophobic moieties did not hinder the adsorption on cellulose, and all GGM-derived materials were found to adsorb irreversibly. However, the use of hydrophobic blocks with high molar mass was required in order to overcome the inherent hydrophilicity of the GGM molecule, and increase the hydrophobicity of the surface. Moreover, inspired by the promising results achieved on wood, wax-containing multilayers were assembled on CNF and textiles. Here poly-L-lysine (PLL) was utilised instead of zinc oxide as the cationic counterpart. Two bilayers were sufficient to reduce the sensitivity towards water and switch surfaces from being highly hydrophilic to hydrophobic, or superhydrophobic. In addition, studying the LbL assembly with quartz crystal microbalance revealed that the adsorption of the wax particles increased with the pH of the PLL solution. Nevertheless, the oxygen permeability of the CNF films and moisture sorption of textiles were preserved in all cases. Having these properties, the enhanced cellulosic materials could be used in advanced applications, like smart packaging, passive climate control systems, and breathable superhydrophobic clothing for sports and outdoors.