Fluorinated compounds under scrutiny: PFAS – best left to toothpaste?

In the coatings industry, fluorosurfactants and other fluorinated additives are used for their strong influence on the surface tension and energy of paints and coatings. By lowering the surface tension, coatings can wet substrates more evenly, improving both appearance and performance. They can also enhance resistance to water, oil and dirt, which increases durability and protective function.

What makes fluorosurfactants special?

Fluorosurfactants can be cationic, anionic or non-ionic. Their fluorine content and structure vary, and in some cases, the fluorine component serves as a modifier for other polymers. This results in a broad product portfolio offering a range of effects in both liquid coatings and dried films. Thanks to the unique characteristics of fluorine, such as its low intermolecular interactions and highly stable covalent C-F bonds, even small amounts of fluorosurfactants can significantly reduce surface tension and impart pronounced hydrophobicity, which helps reduce dirt pick-up on surfaces.

Driven by sustainability and regulatory developments, many companies are seeking environmentally friendly alternatives. Silicone-based additives are a promising option, offering similar benefits to fluorosurfactants, particularly in reducing surface tension and improving surface energy. The key lies in the careful selection and combination of these silicone-based additives.

Recommendations for PFAS-free surface additives

PFAS-based additives are used globally in many coatings and applications. The first step in replacing them is to understand the function of the additive in the specific system. Depending on the desired property, different chemical strategies can be applied. With a clear target and awareness of limitations, effective alternatives can be found.

Event tip: PFAS

The next EC Conference on PFAS will take place on 3–4 December 2025 in Cologne – and it’s more relevant than ever: from 2026, a Europe-wide ban on fluorinated substances could come into force. How far along is the industry in reformulating PFAS-free coatings? Which substance groups are in focus? And what functional alternatives are already available? International experts will present the latest developments in materials, regulatory challenges and strategies for fluorine-free formulations. Topics include: PFAS materials, substitution strategies, regulatory impact and industry implications.

Reducing static surface tension

Good substrate wetting occurs when the surface tension of the coating is equal to or slightly lower than the surface energy of the substrate. Waterborne systems often pose challenges, as their surface tension is significantly higher than solvent-based systems. When silicone compatibility is given, polysiloxanes can be used for moderate surface tension reduction. For strong reductions in waterborne systems, silicone surfactants are often employed.

To find PFAS-free alternatives, it is essential to define the product requirements. A comparison of available fluorinated additives shows varying degrees of surface tension reduction, which is also true for fluorine-free options. As shown in Fig. 1, 0.02% active matter of fluorosurfactants 1 and 2 results in only slight surface tension reduction (from 72.8 to approx. 45 mN/m). A similar effect can be achieved with a silicone- and solvent-free surfactant based on modified succinic acid and esters. Fluorosurfactants 3–7 also reduce surface tension moderately, by around 44 to 49 mN/m. Comparable reductions can be achieved with polyether-modified polydimethylsiloxanes or other modified polysiloxanes. Fluorosurfactant 8 is highly effective in lowering surface tension, but equivalent performance is possible with appropriately modified silicone alternatives.

All effects were measured at 0.02% active matter. In practice, dosage series are advisable for optimal performance. Similar behaviour is seen in a waterborne 2K PU clearcoat (Fig. 2), where surface tension drops from 34.2 to below 30.0 mN/m with just 0.1% fluorine-free surfactant. This improves both wetting and flow. Fluorosurfactants often lower surface tension excessively and influence other properties, such as foam stabilisation. A foam test (scale 1 = no foam to 5 = high foam stability) reveals significantly lower foam stabilisation with fluorine-free surfactants. Almost all fluorosurfactants strongly stabilise foam.

Spreading behaviour of liquids

Another aspect is how additives influence solvent spreading on various substrates – critical for achieving good coating flow and wetting. In spreading tests, additives are blended into solvents and applied (after 24 hours conditioning) to non-polar substrates like PE, PP, PET and PVC. A drop of 0.01 ml is applied without pressure, and the spread is measured after 10 and 30 seconds. Pure water does not wet the substrate, but surfactant-added water spreads immediately. Timing accuracy is essential. Fluorosurfactants show little effect on spreading. Only fluorosurfactants 6 and 10 yield marginal improvements. Similarly, fluoromodified acrylates like BYK-3440 and BYK-3441 show limited spreading. In contrast, polyether-modified polysiloxanes significantly increase drop diameter, enhancing wetting on all substrates.

Wetting performance without fluorosurfactants

Wetting is closely linked to flow and surface tension. While fluorosurfactants affect surface tension, they often have minimal impact on spreading. Thus, direct wetting behaviour should be assessed when replacing additives. Fig. 3 shows a PU dispersion without surfactant failing to wet PU leather. A 0.02% fluorosurfactant improves this but remains suboptimal. At 0.2%, the result is much better. This effect can be matched using fluorine-free polyether-modified polysiloxanes. Here, a fluorosurfactant must lower surface tension to 22.9 mN/m, while the silicone surfactant achieves similar wetting at 29.2 mN/m. For difficult substrates, the dosage may need adjustment.

Flow performance without fluorosurfactants

Even with good wetting, flow and appearance must be optimised for a smooth finish. Fig. 4 illustrates a floor coating applied in a crosshatch pattern. Despite reduced surface tension with a fluorosurfactant, full substrate wetting is not achieved. Compared to the surfactant-free version, the improvement is visible but insufficient. For optimal flow, surface tension should approach that of the substrate, and polar/dispersive fractions must align. Polyether-modified polysiloxanes offer benefits here. They improve wetting without overly lowering surface tension or altering the polarity balance. This enables better flow, fewer application marks, full coverage and a more homogeneous surface.

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