Optimization of preparation of thermally stable cellulose nanofibrils via heat‐induced conversion of ionic bonds to amide bonds
Résumé
Improving the thermal stability of nanocelluloses is important for practical applications such as melt compounded nanocellulose-reinforced polymer composites and flexible substrates for nanocellulose-containing electronic devices. Here, we report optimum conditions for a straightforward surface modification strategy for improving the thermal stability of 2,2,6,6-tetramethypiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNs); the heat-induced conversion of TOCN alkyl ammonium carboxylates to amides. Different amine-terminated compounds (R-NH2) were grafted onto the surface of TOCNs under aqueous conditions. The influences of R-NH2 molecular weight, R-NH2/TOCN-COOH molar ratio, and thermal stability of R-NH2 on the properties of the grafted TOCN films were investigated through infrared spectroscopy and thermogravimetric analysis. For maximum thermal improvement of up to 90 °C, complete ionic bonding of TOCN carboxy groups with R-NH2 was required, as well as proper selection of the R-NH2 compound. A controlled heating process was also needed to achieve effective ionic-to-amide bond conversion.