CompoPFAS - Compounding without PFAS in flame retardant formulations

In the course of the current PFAS restriction procedure of the European Chemicals Agency (ECHA), poly- and perfluorinated alkyl substances (PFAS), also known as “forever chemicals”, are coming under increasing pressure. The outcome of possible restrictions is not yet fully foreseeable. However, many users and compounders increasingly wish to develop and offer “PFAS-free” compounds. Today, PFAS-containing additives are mainly used in the field of processing aids as well as tribological and flame-retardant compounds. In these applications, the fluorine-containing additives fulfill certain functions and are often difficult to substitute today; compromises are essential.

Taking flame-retardant compounds as an example, one function is as the anti-dripping mode. Here, PTFE is often used for polyamides, polycarbonates, PC/ABS and polybutylene terephthalate. On the other hand, highly efficient flame retardants such as perfluorobutane sulfonate in polycarbonates or fluorine-containing pigments are used to color compounds. The latter ones are mostly low-molecular PFAS compounds, which are likely to be even more critical than high-molecular PFAS such as PTFE. Regardless of whether the PFAS are low or high molecular weight, substitutes are required. In many cases, these substitutions are not possible on a 1:1 basis, as the special property portfolio or the chemical-physical behavior of the fluorine compounds is responsible for the corresponding mode of action. Therefore, the aim of this joint industrial project proposed here is to better understand the mode of action of fluoropolymers and their possible substitutes using the example of flame-retardant compounds. It further compiles the necessary theoretical and practical fundamentals for the development of novel flame-retardant compounds.

Project Focus & Approach

First of all, the main priorities of the participants are taken. The most relevant plastics or polymer types (e.g. PA, PC, PBT) for the participants are defined and the focal points (anti-dripping agents, flame retardants and/or pigments) for the project are specified and focused. On the basis of this information, known interactions of the fluorine-containing representatives to be substituted (anti-dripping agents, flame retardants, pigments) are compiled from the literature and evaluated. Subsequently, the open and patent literature is searched and classified with regard to reported fluorine-free alternative materials. Where available, reported correlations between structure and mode of action or mechanism are compiled and evaluated for both the fluorine-containing compositions and for possible reported substitutes.

Promising approaches and formulations are derived and proposed from this literature and market research. The formulations are made on lab-scale extruders and iteratively tested for effectiveness in the subsequent project phase. In addition, investigations are carried out regarding the mode of action of the substitutes found in comparison to their fluorine-containing counterparts. Structure-property relationships are derived from these findings.

In up to four consecutive compounding and injection moulding campaigns (12 compounds each), possible compositions are produced and characterized in comparison to fluorine-containing references. The focus is primarily on the fire behavior according to UL-94, LOI, supplemented if necessary by cone calorimetry on selected compounds and tensile elongation tests from selected samples (depending on the initially set and agreed focal points, possibly also color and gloss). Further tests such as thermogravimetric analysis (TGA) or microscopy (e.g. scanning electron microscopy) are used to clarify the mode of action of the flame retardants.

Finally, the participants are given recommendations on possible substitutes, their components, their mode of action and possible restrictions.