Amidated carboxymethylcellulose: synthesis, characterization and evaluation of their performance in paper coating application

This work reports the first example of the use of octylamine for the functionalization of carboxymethylcellulose (CMC-Oct) to produce highly hydrophobic and oil-resistant paper. CMC functionalization was carried out in water, in the presence of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholinium chloride (DMTMM) as condensing agent. Different DMTMM/carboxymethylated glucose residues (GlcCOONa) molar ratios (0.5, 1, 2.0) were employed to evaluate the efficiency of DMTMM in terms of degree of amidation, measured by 1H NMR (DANMR) and Elemental Analysis (DAEA). CMC-Oct with DANMR of 0.07, 0.14 and 0.24 were obtained and used to prepare films, which were characterised by ATR-FTIR, TGA/DSC, UV–Vis, colour, moisture uptake (MU%) and water vapor permeability (WVP). Best performing film (F2, DANMR = 0.24), was obtained with a DMTMM/GlcCOONa molar ratio of 2, giving a reduction in MU% and WVP of 64% and 60% compared to CMC. This formulation (2 wt% in water) was employed for up to three layers of paper coatings. Grammage, thickness, scanning electron microscopy images, contact angle, water vapor permeability (WVP), oil absorption ratio (OAR%), mechanical properties, and surface energy were evaluated and compared among uncoated paper, paper coated with unmodified CMC, and paper coated with CMC-Oct. Data show that three applications of CMC-Oct coating on paper significantly improved the hydrophobicity, barrier, mechanical properties and surface energy of the paper. Contact angles of up to 105 ± 8°, significant reduction in WVP and OAR% (up to 56% and 99.8%, respectively), and increase in EB% and TS (+ 32% and 47%, respectively), supporting its potentials as a sustainable alternative to fossil-based coatings for packaging applications.