Background
Hydrophobicity is a desirable quality for many types of cellulosic materials, including paper, cotton textiles, cardboard, and wood. There are large existing markets for waterproofing fabrics and building materials that are exposed to the elements as well as emerging applications that rely on creating precise hydrophobic surface patterns to direct fluid flow, as is required for microfluidic paper-based analytical devices. A critical aspect of achieving broad use of these emerging applications is the availability of scalable processes for their manufacture. Existing technologies for rendering cellulosic surface hydrophobic generally require undesirable processing conditions, including high temperatures or extensive use of volatile organic solvents that limit applications. It would be desirable to have additional methods and compositions for imparting hydrophobic barriers on these materials, and for these devices to be less expensive than what is obtained using currently available technologies.
Technology Overview
Researchers found that paper, cotton cloth, and other cellulose-containing substrates can be made hydrophobic upon exposure to silicone polymers containing boronic acid groups. This new type of functional silicone polymer offers unique advantages when applied to cellulose. Boronic acid has a strong and specific interaction with vicinal diol groups on the surface of cellulose. By targeted adsorption/chemisorption of boronic acid onto vicinal diols, the functionalized silicone polymer efficiently renders the cellulose hydrophobic (water contact angle greater than 90°), and in some cases superhydrophobic (contact angle greater than 150°). The polymer can be applied to cellulose from a dilute solution using a variety of different solvents. Depending on the polymer composition (overall molecular weight and weight fraction boronic acid), it can be dissolved in common hydrocarbon solvents or alcohols. In addition, the boronic acid groups stabilize polymer colloids in water, allowing hydrophobic coatings to be formed from waterborne dispersions without added emulsifiers. The hydrophobic properties are obtained after solvent evaporation at room temperature, or after an optional moderate temperature drying step.
Benefits
Boronic acid-containing polymers offer several unique advantages in creating hydrophobic coatings on cellulose, namely that a) coatings can be applied using polar and non-toxic solvents, including water and ethanol, b) the hydrophobic properties rapidly develop upon drying the cellulose at room temperature, and c) the mild solvents used for applying the coating are compatible with standard inkjet printing hardware and with many biomaterials.
Applications
Hydrophobic coatings