4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholinium chloride-assisted amide crosslinking of carboxymethyl cellulose for high-performing films

This study reports the first example of crosslinking of carboxymethyl cellulose (CMC) and aliphatic diamines (CMCA) using a condensation agent, (4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholinium chloride (DMTMM)), to prepare highly functional films for food packaging application. The novelty of this work lies in the combination of diamine crosslinking and DMTMM activation to produce films with enhanced barrier and mechanical properties. Products were analysed by mono-/bi-dimensional NMR to prove the amide linkage and by the modification degree (MoD) for diamine quantification. The physical-chemical characteristics of the CMCA films were further determined by DSC, TGA, SEM, and ATR-FTIR, and the moisture content (MC%), moisture uptake (MU%), water vapour permeability (WVP), oil absorption ratio (OAR), and tensile strength (TS) evidenced the key role of DMTMM in the formation of strong covalent bonds between the carboxylate groups of CMC and the diamine, influencing the properties of CMCA films. When a COONa/ethylenediamine/DMTMM molar ratio of 6/1/2 was employed, the best WVP (2.63 ± 0.24 × 10^-10 g m^-1 s^-1 Pa^-1), OAR (7.4 ± 0.5 × 10^-2%), and transparency were obtained, along with an exceptionally high UVC barrier and one of the highest TS values ever reported for CMC films (75.90 ± 2.90 MPa). Results clearly highlight that the presence of the diamine hydrophobic alkyl chain plays a key role in improving the physical-mechanical characteristics of CMCA, making it superior to the best-performing CMC films reported in the literature and as a sustainable alternative for food packaging applications.