Contents lists available at ScienceDirect International Journal of Adhesion and Adhesives journal homepage: www.elsevier.com/locate/ijadhadh Investigation of hydrophobic coatings on cellulose-fiber substrates with in- situ polymerization of silane/siloxane mixtures Taylor Rutter, Brenda Hutton-Prager ⁎ University of Mississippi, Chemical Engineering Department, 140 Anderson Hall, University, MS 38677, USA ARTICLE INFO Keywords: Cellulose Micro-roughness Silanization Contact angles Hydrophobicity ABSTRACT 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 in- vestigate 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 de- velopment 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 develop- ment 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 im- proved 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 per- formance 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. 1. Introduction Organosilanes, first discovered in the 1940s [1], are frequently used as coupling agents to adhere polymeric substances with specific prop- erties to inorganic substrates, such as metals, glass, or other inorganic minerals [2–4].The general form of silanes is R’-Si-(OR) 3 , and the R’ group is often a functional organic group (e.g. amino, chloro, etc.) that can react with a polymer identified for attachment to a substrate. The OR groups are often methoxy or ethoxy groups, and are easily hydro- lysed to form silanols [1,2]. The silanols may react with themselves, forming a siloxane oligomer, with a characteristic -Si-O-Si- linkage [1,2,5–7], and can also attach to the substrate in one of two methods, depending on conditions and the balance between hydrolysis and condensation. Covalent bonding of polysiloxanes onto the substrate is often observed at high thermal curing temperatures (at least 110 °C) where a condensation reaction occurs. At lower temperatures (room or 40 °C), it is more likely hydrogen-bonding that occurs between the polysiloxanes and substrate [6]. This has been confirmed with FTIR studies [8–10] and soxhlet extraction methods [11]. While the polysiloxanes may be used as a bridge between polymeric substances and a given substrate, silanes themselves have useful hy- drophobic properties if the R’ group is a hydrocarbon chain, and these may be exploited without the need for attaching additional polymeric content. Silane coupling agents were initially applied to inorganic substrates, however more recent research has focused on opportunities to modify cellulose fibers with polymeric substances for added strength, primarily for applications in reinforced fiber materials [7–13]. Fewer studies have exploited the hydrophobic properties of stand-alone silanes on paper substrates as coating applications. One study by Karapanagiotis et al. [5] utilized silica nanoparticles dissolved in silane/siloxane mixtures that were brushed onto paper substrates. The silane/siloxane mixture polymerized in-situ over the substrate forming a film, and the resulting surface was superhydrophobic, confirmed with contact angle (CA) https://doi.org/10.1016/j.ijadhadh.2018.07.008 Accepted 17 July 2018 ⁎ Corresponding author. E-mail addresses: trutter@go.olemiss.edu (T. Rutter), bhprager@olemiss.edu (B. Hutton-Prager). International Journal of Adhesion and Adhesives 86 (2018) 13–21 Available online 04 August 2018 0143-7496/ © 2018 Elsevier Ltd. All rights reserved. T