Sustainable Materials for Liquid Repellent Coatings

A modern environmental safety approach requires the implementation of green or sustainable strategies, such as banning or significantly lowering the presence of harmful substances on the market or in the industrial environment. To date, the majority of highly performing solutions are still based on fluorine chemistry, even with a growing effort to lower its impact. Economic costs, but also persistence, long-term degradation, and transformation in the environment can raise issues about medium- and long-term effects on human health and wildlife. Coatings with high water and oil repellence are used worldwide in daily life and in industrial and research fields, such as self-cleansing, anti-icing, and anti-biofouling. The combination of a particular geometry or surface structure and low-energy materials results in unique properties related to a range of materials in natural or synthetic categories aiming to build, when possible, a fluorine-free world. This work revises recent and key literature to propose valid alternatives to fluoro compounds in terms of water and oil repellence, as well as stability and resistance to physico-chemical agents. In this paper, natural compounds like fatty acids and waxes are addressed together with more synthetic systems like silicon-based solutions, and polymeric and inorganic nanostructured coatings. Most of the revised papers deal with topics fulfilling environmental requirements but are mainly restricted to highly repellent water and aqueous systems. Nevertheless, new and sustainable strategies for providing suitable, highly oleophobic surfaces to lower fluorine presence have been reported from a small but growing body of literature.