Solvent-free cellulose fatty amide synthesis aided by enzymatic oxidation

While cellulose is hydrophilic, it is amenable to hydrophobic modification via grafting of its hydroxyl groups. Increased material hydrophobicity could deliver renewable materials with good water barrier properties. This study explores an enzymatic pathway for cellulose fatty amides synthesis. Firstly, we employed the commercially available, low cost enzyme formulation, Cellic^® CTec2, to oxidize cellulose under conditions which restricted its hydrolytic enzyme activity. The resulting carboxylated cellulose was reacted with tetradecylamine at 50 °C for 48 h, washed thoroughly with ethanol to give grafted cellulose fatty amides at Degrees of Substitution of 0.57. The formation of cellulose fatty amides was verified by analysis including FT-IR, solid state ¹³C CP/MAS NMR and Optical Photothermal Infrared Spectroscopy. The hydrophobicity of synthesized cellulose amides was determined by water contact angle (WCA) measurements of disc-compressed fibers; these were significantly increased to 124.3 ± 12° compared with cellulose WCA of 28 ± 5°. Additionally, cellulose amide fibers were incorporated into cellulose paper sheets at 10 wt% and gave a remarkable 92% reduction in water droplet area spread compared to plain cellulose sheets. These findings demonstrate the feasibility of enzymatic cellulose oxidation and amidation, and the materials benefits of highly functional cellulose amides which avoid chemical oxidants and reaction solvents.