Poly and Per Fluoro Alkyl Substances (PFAS or “forever” chemicals) are a large chemical class characterized by having compounds with the Carbon-Fluorine bond. It is estimated that this class contains more than 12,000 compounds listed in the Toxic Substances Control Act database of the EPA. This class contains compounds that are gases, liquids and solids and are used in thousands of applications due to their unique set of desirable properties that are brought by the extreme stability and strength of the carbon-fluorine bond. These properties including high Thermal, Oxidative, Chemical and Environmental resistance and low surface energy. High temperature and chemical resistance polymers like Teflon and elastomers like Viton are examples of solid PFAS materials that are widely used in many industries. Many PFAS liquids have unique surface activity in that they can be used to create surfaces that are both hydrophobic and oleophobic. This property is particularly useful for making stain resistant textiles and carpeting as well as unique surfactant performance that is used for emulsion polymerization of PFAS polymers and for applications like self-healing fire-fighting foams for hydrocarbon (Class B) fires. The stability of the carbon-fluorine bond however, has a very serious downside in that it has an extremely long lifetime in the natural environment leading to the popular term “forever” chemicals. In the language of chemical regulation this is termed “persistence” and this property alone is cited by some regulatory bodies (mainly in the EU) as reason enough for limiting production and use. In the US the EPA has taken a somewhat different approach in that PFAS materials are not restricted just due to persistence but are restricted once data is presented to show harm or potential harm to human health. This has been the case for some surfactants used for fluorinated polymer production, fire-fighting foams and treating paper for hydrophobic/oleophobic food packaging. Many companies are now seeking alternatives for PFAS compounds in these and many other applications that may not be currently restricted but can pose an unreasonable future risk for producers.
Looking to nature as inspiration for PFAS replacements is not an unreasonable approach. There are several examples in nature for materials that can mimic some of the desirable properties of PFAS, especially in the surface-active area. Some natural surfaces like lotus leaves and waterfowl feathers have extreme hydrophobicity. Proteins like wool and soy protein isolate (SPI) have natural fire retardant properties and some natural materials like cellulose can withstand decades of weather exposure with minimal degradation. Nature has proven to offer a wealth of materials with properties chemists have been attempting to replicate for many years. An entire area of chemistry termed “biomimetics” takes inspiration from nature for materials that can supercede the performance of existing synthetics. A good example of this is development of adhesives that perform well underwater using chemical approaches found in mussels for attachment to rocks and wood. Bioproducts have already shown that they can be a part of the solution in replacing PFAS in several applications like fire-fighting foam and hydrophobic wood and paper coatings. Exploration of new biomaterials based on hybrid silicone and long chain fatty acids is a promising area to further expand the toolchest for PFAS replacement in surface treatments.
