PFAS-free with silicone: Three coating solutions for anti-ice, barrier and non-stick applications

The Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM) has been developing PFAS-free coatings for several years. One research focus lies on polysiloxane-based formulations, which can achieve performance levels similar to PFAS-containing systems in non-stick, sliding and barrier coatings. Polysiloxanes offer advantages such as chemical resistance, weatherability and outstanding high-temperature stability due to their Si–O–Si backbone, combined with a low surface energy of around 20–24 mN/m.

The article introduces three functional high-performance coatings designed to eliminate fluorine chemistry: anti-ice coatings based on silanised polyurethanes, barrier systems combining polyimide and layered silicates, and non-stick powder coatings based on low-melting PAEK polymers modified with silicone oils. The goal is to provide durable functionality with viable industrial processing conditions.

Anti-ice: Silanised PUR systems with reduced ice adhesion

To assess ice-repellent properties, water contact angle alone is not a reliable indicator. Fraunhofer IFAM therefore uses a dedicated ice chamber (for clear and rime ice) and a standardised centrifugal test (ISO/TS 19392-6:2023) to quantify ice adhesion. Building on earlier work with fluorinated polyurethane coatings, the researchers developed silanised PUR binders in which siloxane groups are covalently incorporated.

The resulting coating features a smooth surface (Rz = 0.29 µm) and a surface energy of 18.0 mN/m. Compared with a PTFE tape (OFE 15.1 mN/m; Rz = 0.69 µm), water droplet roll-off is slightly reduced, but the ice adhesion is significantly lower: 40 kPa compared to 130 kPa. This value is well below the commonly referenced 100 kPa threshold for ice-repellent surfaces and approaches the < 20 kPa range required for passive de-icing systems.

Barrier: Polyimide with organically modified layered silicates

For sealing and barrier applications, the IFAM team employs a multi-material concept. At its core is a PFAS-free functional layer made of polyimide (PI), reinforced with organically modified layered silicates. The barrier effect relies on extending the diffusion path of permeating molecules: plate-shaped pigments with a high aspect ratio reduce free volume and block diffusion routes.

Permeation tests for oxygen and water vapour confirm that the polyimide/silicate layer system provides improved barrier performance compared with pure PI. Such hybrid structures are already in use as protective coatings for electronic components and are suited for demanding chemical and thermal environments.

Non-stick: PAEK powder plus silicone oil as PTFE alternative

In cookware, PTFE coatings remain the standard non-stick solution – but they rely on fluorochemicals. As an alternative, the research team investigated low-melting polyaryletherketones (PAEK, Victrex FG 900 series), which melt around 40 °C below PEEK. This allows curing conditions suitable for incorporating silicone additives.

A two-layer powder coating system was developed, consisting of a PAEK primer and a modified PAEK topcoat containing silicone oil (900-O). Tests performed in accordance with DIN EN ISO 2178/2360/2409/1518-2, as well as impact (DIN EN ISO 6272-2), egg-frying and soak tests, revealed good adhesion, scratch and impact resistance, and improved non-stick properties through silicone modification. While commercial PTFE or sol-gel coatings still perform slightly better in egg-frying tests, the PAEK/silicone system maintained its non-stick effect even after soaking at 70 °C in dishwasher detergent solution. Ongoing testing is evaluating long-term performance and dishwasher resistance.

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