One-step superhydrophobic coating using hydrophobized cellulose nanofibrils

Superhydrophobic surfaces have high potential in self-cleaning and anti-fouling applications. We developed a one-step superhydrophobic coating formulation containing sodium oleate (NaOl), hydrophobized precipitated calcium carbonate and biobased cellulose nanofibrils (CNFs) hydrophobized with either alkyl ketene dimer (AKD) or amino propyl trimethoxy silane (APMS) as a binder to fix and distribute the particles. Coatings were made on paperboard and the wetting behavior of the surface was assessed. Static, advancing and receding contact angles with water as well as roll-off and water shedding angle were compared to coatings made with styrene butadiene latex as binder instead of CNFs. Modifications with alkyl ketene dimer showed most promising results for a viable process in achieving superhydrophobic paperboard but required reformulation of the coating with optimized and reduced amount of NaOl to avoid surfactant-induced wetting via excess NaOl. A static water contact angle of 150 degrees was reached for the CNF-AKD. The use of CNFs enables the improvement of coating quality avoiding cracking with the use of nanocellulose as a renewable binder.