Preparation and characterization of TEMPO-oxidized cellulose nanofibrils with ammonium carboxylate groups

Fibrous TEMPO-oxidized celluloses with 100% ammonium carboxylate groups (TOC-COONH4) were prepared by adding aqueous ammonia to fibrous TOC-COOH/water slurries. Using a gentle mechanical disintegration treatment in water, the obtained never-dried TOC-COONH4/water slurries could be converted to highly viscous and transparent gels consisting of mostly individualized TEMPO-oxidized cellulose nanofibrils. The self-standing TOCN-COONH4 film prepared from the aqueous TOCN-COONH4 dispersion via casting and drying had high optical transparency. When the self-standing TOCN-COONH4 film was heated at 105°C for 1 day, clear yellowing was observed on the film. FT-IR analysis of the heated TOCN-COONH4 films indicated the partial formation of TOCN-COOH type structures from the TOCN-COONH4 due to evaporation of NH3 gas from the films during heating. The heated TOCN-COONH4 films had lower moisture contents, higher film densities, and higher Young's moduli than the unheated TOCN-COONH4 films.