Strategies to mitigate the synergistic effects of moist-heat aging on TEMPO-oxidized nanocellulose

Abstract

Cellulose oxidation catalyzed by TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl) is a trending methodology to enable the fibrillation and production of large amounts of cellulose nanofibrils (CNF) in a cost-effective and energy-saving manner. However, TEMPO-oxidized CNF lack colorimetric, thermal, and physicochemical stability due to intrinsic structural characteristics, i.e., the presence of sodium carboxylate functional groups and anhydroglucuronate units of low molecular weight. The susceptibility of CNF to deterioration at moist-heat conditions can negatively impact the use of these promising nanomaterials in long-term applications, such as protective coatings and electronic devices. Herein, we showed that the incorporation of lignin nanoparticles (LNP) enhanced the resistance to degradation of nanocomposite films based on nanocelluloses (CNF and cellulose nanocrystals). The improvement of the aging performance in nanolignin-containing films was attributed to the higher antioxidant capacity provided by lignin, which also imparted UV-protection. Alternatively, the removal of unstable functional groups and residues in TEMPO-oxidized CNF by an alkali-acid post-treatment was also proven effective in imparting higher thermal, physicochemical, and colorimetric stability to CNF and nanocomposite films. Therefore, the incorporation of LNP or the implementation of a post-treatment protocol into CNF are diverse, yet simple and efficient strategies to enable the application of these bio-based green nanomaterials into durable products.