Synthesis of amino-functionalized nanocellulose by guanidine based deep eutectic solvent and its application in fine fibers retention

A guanidine-based Deep Eutectic Solvent (DES) consisting of 1,3-diaminoguanidine monohydrochloride and glycerol was utilized to prepare C-CNC from dissolving pulp. The pulp fibers were oxidized to dialdehyde cellulose by periodate, then fibrillated through the hydrogen bonds shear of DES and aminocationized through Schiff base effect of the amino groups in the DES solvent to obtain C-CNC. The results revealed that the characterization of the DES (such as viscosity, polarity, and pH) was related to the molar ratio of glycerol/guanidine-salts. The hydrogen bond network structure of DES solvent with optimal system was simulated by DFT and its damage to fiber hydrogen bond network was predicted. The C-CNC produced under the optimal reaction conditions (molar ratio of 1:2, 90 °C for 2 h) was highly dispersible with an average length and diameter of 85 ± 35 nm and 5.0 ± 1.2 nm, a charge density of 2.916 mol/g. C-CNC exhibited excellent flocculation when added to fine fiber suspensions of chemomechanical slurries, achieving rapid flocculation and settling onto fibers in <1 min. The DES solvent maintained its reactivity after 5 cycles. This study lays the foundation for the batch preparation of nanocellulose in an environmentally friendly manner and its application as a green additive in paper industry.