A green chemistry approach for the functionalization of oxidized cellulose nanofilms for the improvement of hydrophobic properties

Due to the constant increase in society's interest in the realization of ecological transition highlighted by EU Directive 2019/904, the scientific community has increased the focus on the valorization of biomass. Thanks to its abundance in nature and its biodegradability, cellulose is one of the most studied biopolymers, however it also has some disadvantages, which limit its potential: it is insoluble in water, hydrophilic and the defibrillation process are energy intensive. For these reasons, the scientific community has focused attention on the possibility of obtaining more processable nanoscale cellulose derivatives Among others, Isogai et al. in 2011 proposed a method to obtain a stable suspension of C6-oxidated cellulose nanofibers by treatment of cellulose in the presence of the TEMPO/NaBr/NaClO system (TEMPO-oxidized-cellulose nanofibrils TEMPO-ox-CNF)1. TEMPO-ox-CNF has carboxyl groups on its surface which can be modified into ester or amide groups to improve its properties2 or impart new ones3. In this contribution, the chemical grafting of TEMPO-ox-CNF by amidation with amines and diamines is proposed using 4-(4,6-Dimethoxy-1,3,5-triazin- 2-yl)-4-methylmorpholinium chloride (DMTMM) as a condensing agent. The amidation reaction promoted by DMTMM has various advantages such as the use of water as a solvent and low temperatures. Its effectiveness has already been successfully demonstrated for obtaining high performance films4. The material obtained has been characterized by spectroscopic, thermal, and physical-mechanical investigations. Chemical grafting impacts various properties such as hydrophobicity with a significative improvement of contact angle from 40° to 90°.