Innovative two-phase air plasma activation approach for green and efficient functionalization of nanofibrillated cellulose surfaces from wheat straw

ABSTRACT A green, facile two-phase air plasma/mild alkaline (TPAP/MA) pretreatment approach was developed for efficient production of carboxyl- and amino-functionalized nanofibrillated cellulose derivatives (TO-NFC and NFC-Amine, respectively) from wheat straw (WS). Herein, TPAP activation was performed stepwise through two-scissions at the level of WS fibers and, subsequently, WS-cellulosic fibers combined with mild NaOH pretreatment. The pretreated substrates showed altered surface-characterizations with a gradual-additional aldehyde, carboxyl, and reactive hydroxyl groups according to activation time, all of which promoted the subsequent cellulose isolation, nanofibrillation, and functionalization reactions. TPAP/MA pretreatment accompanied by TEMPO-oxidization and protecting-group-free amidation revealed high carboxyl and amine contents of TO-NFC and NFC-Amine (up to 2.55 mmol COO-/g and 2.20 mmol NH2+/g, DSs=1.02 and 1.42, respectively), leading to a 5.9- and 6.5-fold increase in pH-responsive swelling ratios of their nanohydrogels compared to the conventional alkaline pretreated substrates. Considering feasibility and green aspects, the 90 s-TPAP/MA produced high cellulose and nanofibrillation yields of 73.4% and 97.6%, respectively. Furthermore, this pretreatment consumed only 158.5 kWh/t and showed a 90.4 % reduction in the total energy consumption of the relative functionalized NFC production process compared to the baseline process, demonstrating an efficient and energetically friendly pretreatment route with significant potential to be scaled to industrial-level.