Wet strength improvement of TEMPO-oxidized cellulose sheets prepared with cationic polymers

Cellulose fibers were oxidized with a catalytic amount of 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) in water, and these TEMPO-oxidized cellulose fibers were subjected to sheet making with cationic polymers such as cationic poly(acrylamide) (C-PAM) and poly(vinylamine) (PVAm). The wet strength of the sheets thus prepared was evaluated in terms of the cationic polymer used. It was found that wet tensile strength of the sheets was clearly improved by the cationic polymer addition to the cellulose slurries. Especially, the C-PAM addition was effective in wet strength improvement of the sheets, when the TEMPO-oxidized cellulose fibers were used. The results obtained using the TEMPO-oxidized and then NaBH4-reduced cellulose fibers showed that aldehyde groups present in the TEMPO-oxidized cellulose fibers have some interactions with the cationic polymers in the sheets, contributing to their wet strength improvements. Hemiacetals, N-acylcarbinolamines, carbinolamines, and Schiff bases are the possible structures formed at the interfaces between the TEMPO-oxidized cellulose fibers and cationic polymers in the sheets. Repulping behavior of the once-dried sheets was studied as well.