Investigation of hydrophobic coatings on cellulose-fiber substrates with in-situ polymerization of silane/siloxane mixtures

The purpose of this study was to investigate the interfacial interactions of SilRes BS290, a mixture of silanes and siloxanes, upon in-situ polymerization and curing over cellulose substrates (40 and 110 °C), and to further investigate the influence of these chemical interactions with hydrophobic development of the film. SilRes solutions (7 wt%) were prepared in n-heptane and roll-coated over pure cellulose substrates (Whatman). The bond development with time was monitored with FTIR, and was compared with surface hydrophobic development, monitored with contact angle analysis using deionized water droplets. It was found that the bond development was completed well before the onset of surface hydrophobicity in both the low and high temperature curing cases, with superhydrophobicity being observed for the high temperature preparations. Hydrophobic development tended to be influenced more strongly by surface topology resulting from the appearance of 300 nm-size polysiloxane beads on the fiber surface. Film porosity was also observed in some cases which additionally improved the hydrophobic outcome of the surface. While the hydrophobic behavior did not appear to coincide with the interfacial bond development of the in-situ polymerized film, damage to the surface hydrophobic layer via mechanical action decreased the hydrophobic performance in some cases. This was mainly due to a reduction in vibrational activity of the surface hydrophobic groups. High temperature curing maintained hydrophobic performance despite similar damage to chemical bonding, perhaps as a result of higher levels of covalent bonding to the substrate. Therefore, although the hydrophobic surface requires roughness and porosity to fully form, the chemical hydrophobicity created from polymerization also ultimately contributes to the overall hydrophobicity observed.