Surface engineering of wood fiber/filler networks

The hydrophilic property of cellulose substrates and their sensitivity to moisture limits their use in certain applications. The aim of this study is to enhance the barrier properties of cellulosic and lignocellulosic paper by utilizing environmentaly benign techniques. Chemical Vapor Deposition (CVD), Plasma Enhanced Chemical Vapor Deposition (PECVD), and Atomic Layer Deposition (ALD) techniques were employed to deposit Dichlorodimethylsilane (DCDMS), tetrafluoromethane (CF₄), and aluminum oxide (Al₂O₃) on cellulosic and lignocellulosic papers, respectively. A wide range of fiber sizes from unrefined, 927 µm, to highly refined, 177 µm, were employed to make handsheets and the effect of the chemicals and the deposition techniques, mentioned above, on wettability and gas permeability of the handsheets was investigated. In this regard, the contact angles on handsheets prepared with unrefined fibers are significantly higher (140°-153°) than those of the refined ones (95°-120°) due to their higher surface roughness. However, on handsheets formed with refined fibers, although the treatments resulted in a hydrophobic surface, the water droplets absorb to the handsheets over time. It is also shown that at certain fiber size (561 µm) the water vapor transmission rate (WVTR) reaches its minimum value and further decrease of the fiber size does not significantly affect the WVTR. In terms of wettability, the cellulosic and lignocellulosic substrates coated by deposition of CF₄ resulted in the highest contact angles (120°-153°). However, regarding moisture barrier properties, the Al₂O₃ deposited substrates resulted in the lowest WVTRs (2.1 g·m-²·day-¹). Moreover, the impact of fabrication method was studied and the fiber drying mechanism during sheet formation was also elucidated. It was found that casting of a Micro Fiber (MF) suspension on hydrophobic substrates results in formation of optically translucent films with mechanical and barrier properties similar to micro and nano fibrillated cellulose films. The manufacturing of the latter is energy intensive and hence the new method has potential advantage. Finally, Janus (hydrophilic-hydrophobic) fillers were fabricated and the effect of filler’s dual functionality on barrier properties of handsheets loaded with Janus fillers was investigated. Silanization of handsheets substrates in conjunction with dual functionality of fillers results in formation of a superhydrophobic handsheet.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat