Sustainable, Safe, and Effective (Super)Hydrophobic Coatings for Cellulosic Fiber Material via Alkyl Ketene Dimer and Polysaccharide Integration

In light of increasing environmental and regulatory restrictions on per- and polyfluoroalkyl substances (PFAS), silicones, and other persistent synthetic hydrophobic agents, we report the development of novel biodegradable, water-based hydrophobic coatings for cellulosic fiber materials based on alkyl ketene dimer (AKD) and naturally derived polysaccharides alginate, cellulose nanofibers, starch, and agar as matrices. Coatings on the cellulosic fiber material were applied through screen printing and cured at low temperatures. The prepared coatings transformed the initially (super)-hydrophilic cellulosic fibers into a hydrophobic material, with static water contact angles ranging from 126° to 153°. Application of the coatings extended water drop absorption times from immediate uptake to as long as up to 5 h, exhibiting rolling-off behavior consistent with lotus-leaf-like hydrophobicity. SEM-EDX analysis revealed well-defined microstructuring and uniform elemental distribution, confirming complete coverage of the cellulosic fibers. FTIR spectroscopy and sequential organic solvent extraction provided evidence of covalent AKD-cellulose bonding, confirming successful chemical surface modification of the substrate. The coatings demonstrated excellent durability, maintaining hydrophobic performance even after 30 laundering cycles and exhibiting resistance to chemical and mechanical stress. A synergistic effect between AKD and polysaccharides was observed and explained: while AKD imparts intrinsic hydrophobicity, the polysaccharides act as functional stabilizers and physical barriers, improving coating uniformity, adhesion, and long-term performance.