Surface hydrophobization of CNF films by roll-to-roll HMDSO plasma deposition

Cellulosic films are typically sensitive towards moisture which limits their industrial applicability. In this study the films made from cellulose nanofibrils (CNF) were surface silylated with hexamethyldisiloxane (HMDSO) by roll-to-roll plasma deposition. The effects on surface hydrophobicity were clear and indisputable. Water contact angles of non-modified and plasma-deposited CNF films were 23 degrees and 103 degrees, respectively. As a result of surface silylation the relative polarity decreased from 46.8% to 0.6%. Surface hydrophobicity correlated well with the plasma deposition line speeds (0.5, 5, and 10 m/min) and the water vapor barrier properties. Silylation also decreased the oxygen transmission rates both at 50% and 80% relative humidity as compared to non-modified CNF films. All films were completely impermeable to olive oil and intact in contact with castor oil, toluene, and n-heptane or mixtures of them. The developed surface hydrophobization method can be exploited in strengthening the position of cellulosic films in high performance film applications.