Remarkable increase of paper strength by combining enzymatic cellulose nanofibers in bulk and TEMPO-oxidized nanofibers as coating

Cellulose nanofibers (CNF) have been proposed by several authors as a reinforcing additive for papermaking pulps; their use allows one to avoid mechanical refining of pulp fibers, which damages the fibers and reduces their lifespan and consequently recycling cycles. In the present work, use of CNF obtained through enzymatic pretreatment as a bulk pulp additive is studied versus traditional (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized CNF. Results indicate that enzymatic CNF improves the overall paper properties in a similar way to TEMPO-oxidized CNF; however, the enzymatic pretreatment is supposed to be significantly cheaper and environmentally friendly compared with the chemical treatment. Paper reinforced with enzymatic CNF was later surface-coated with solution containing TEMPO nanofibers oxidized with 15 mmol NaClO to further promote the mechanical strength. The results indicate that the combination of bulk addition of enzymatic CNF to the papermaking pulp followed by surface application of TEMPO-oxidized CNF induced significant improvement in the mechanical properties of the paper at lower cost than sole use of TEMPO-oxidized CNF as bulk additive. To the best of our knowledge, this is the first work in which enzymatic and TEMPO-oxidized CNF are combined as paper additives for bulk and surface application to improve overall paper properties