In search of the PFAS substitute

The impending PFAS ban is not only unsettling the industry, consumers are also alarmed. After all, Teflon coatings in frying pans can be harmful to health - if they are handled incorrectly. It is therefore only logical that PFAS alternatives are very popular.

The plastic polytetrafluoroethylene (PTFE), better known under the brand name Teflon, is popular as a non-stick coating for frying pans, baking tins and kitchen appliances such as baking machines, sandwich makers, waffle irons and raclette grills. The reason: food does not stick to the cooking utensil, making it easier to use even for inexperienced users. However, PTFE surfaces scratch relatively easily. And the past has also tarnished the reputation of this coating:

Perfluorooctanoic acid (PFOA), which has since been banned, was used in its production; ADONA or HFPO-DA are now used as substitutes. In principle, residues of these substances from production could still be present in the pan.

Some manufacturers therefore recommend rinsing and boiling the Teflon-coated pan with water before using it for the first time. Finally, toxic fumes can also be released if pans with a PTFE coating are overheated. According to the Federal Institute for Risk Assessment, this can happen above 360 degrees Celsius. Last but not least, PTFE is a per- and polyfluoroalkyl substance (PFAS), which the EU wants to restrict.

Industry committed to PFAS replacement

However, other coating materials for frying pans also have their weaknesses. Ceramic coatings, for example, can quickly lose their non-stick effect. However, the impending PFAS ban by the EU is spurring coating suppliers on - not only for frying pans, but also for other applications.

ACS Coating Systems GmbH from Wilhelmshaven, for example, has developed two special non-stick coatings for frying pans. The first coating is called Duraquarz and combines quartz ceramic (SiO2) with the plastic polyaryletherketone (PAEK). This plastic does not contain fluorine and therefore does not fall under the PFAS group of substances. A special property of PAEK, as well as the other polyetherketones, is that it retains its strength even at higher temperatures.

ACS therefore states that the Duraquarz coating has a short-term temperature resistance of up to 450 degrees Celsius. It is twice as thick as conventional pan coatings and is therefore more robust, durable and dishwasher-safe. It also offers very good corrosion protection. Compared to an enamel coating, Duraquarz is not as brittle and offers a non-stick effect comparable to PTFE.

For the second coating called Durapek nonstick, ACS uses the plastic polyetherketone (PEK), which is related to PAEK. According to the company, the material is applied in four layers and, at 70 micrometers, is twice as thick as conventional Teflon coatings and correspondingly more robust. However, it is also five times more expensive than PTFE, as the manufacturer admits. It is suitable for permanent temperatures of up to 300 degrees Celsius, which means that Durapek-coated pans can also be used in the oven. Compared to Duraquarz, Durapek has a higher wear resistance and is resistant to most acids and alkalis.

According to ACS, both coating systems are applied in several layers using a powder process. The manufacturer has developed the powders for this itself and also produces compounds and powders itself. Both coatings are also used in industrial environments, for example for tools, machine parts, in mechanical engineering or in vehicle construction. The first predecessor of today's Durapek coating was developed and patented over 20 years ago for new, single-layer cylinder-head gaskets.

Different application methods for ceramic coating

Ilag Industrielack AG from Wangen in Switzerland takes a different approach. Its Xeradur 3 coating is a one- or two-layer system based on xerogels. Xerogels are porous solids with a net-like structure resulting from the drying of a lyogel. Ilag uses this process to apply the ceramic to the frying pan substrates made of pressed and forged aluminum, die-cast aluminum or stainless steel. A large layer thickness range of 35 to 60 micrometers makes the product more flexible and at the same time stable in performance. The manufacturer specifies a stoving temperature of 270 degrees Celsius and a service temperature of 250 degrees Celsius. The PFAS-free coating offers very good abrasion resistance and does not crack or stain.

The Spanish manufacturer Umbrella Coating S.L. in Las Rozas uses a sol-gel process to apply the ceramic coating. The company uses a simplified, two-stage process in which a primer and a top coat are applied and cured at 250 degrees Celsius for 60 minutes each. This reduces the complexity and cost of the coating, as well as the risk of errors during the coating process. As a result, the ceramic coating called Umbrella Metal offers higher thermal conductivity than fluoropolymer coatings, which saves energy during application. At the same time, it is more resistant to scratches and abrasion; in specific tests, the coatings achieved a hardness of 6H at 200 degrees Celsius. In addition, there is a corrosion resistance of 400 hours in the NSS salt spray test.

The development project for Umbrella Metal was also launched with clear requirements: Priorities were ease of application, cost reduction in material recovery and better durability than traditional non-stick coatings. A detailed report on the Umbrella Metal coating system can be found in MO issue 5-6/2024 on pages 18-21.

Researchers also committed to PFAS replacement

Researchers at the Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM) in Bremen have taken a different approach. Their newly developed coating called Plaslon is applied using a cold plasma process. One advantage of this procedure is that only a very small amount of fluorine-free chemicals (siloxane chemistry) are used during the coating process - fluorine-containing chemicals are completely replaced. In addition, energy consumption is low. In everyday use of the frying pans, the non-stick coating offers uninhibited heat transfer and a long service life. As the Plaslon coating is designed as a gradient layer, it provides excellent adhesion to the product body on the one hand and optimum non-stick properties to the food on the other. It is also easy to clean and similar in hardness to enamel with a Mohs hardness of between 4.5 and 5.5 - making it resistant to cutting and abrasion. The coating is non-porous and tasteless as it is highly cross-linked, as the research institute reports.

It is also food-safe and exhibits oleophilic behavior in relation to edible oils and fats when wetting with oil. Last but not least, the coating can be structured and coated very well with the laser. The institute specifies a temperature resistance of up to 230 degrees Celsius.

There is also a large selection of possible substrates. According to the Fraunhofer IFAM, tool steel, stainless steel, enamel, glass, earthenware, stoneware and porcelain can all be coated. This gives Plaslon an advantage over other non-stick coatings, as products made of enamel, glass, stoneware or porcelain are very scratch-resistant but have a poor non-stick effect. Coating aluminum, iron and copper is also technically possible, they say. However, the researchers recommend testing this in each individual case.

For practical implementation, the scientists at the institute have the know-how to be able to economically refine products in large quantities. Depending on customer requirements, different concepts such as XXL systems or continuous systems are available.

ACS Coating Systems GmbH
acs-coating.de

Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM)
www.ifam.fraunhofer.de

Ilag Industrielack AG
www.ilag.ch

Josef Schulte-Ufer KG Metallwarenfabrik
www.schulteufer.de

Umbrella Coating S.L.
www.umbrella-coating.com