Flame Retardants: Answers to 7 Most Common Questions on Selection, Testing, and Legislation

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Flame retardants are critical components in many industrial sectors – from construction and electronics to the automotive industry. Their proper selection and application can significantly impact the safety of the final product and its compliance with legislative requirements. However, manufacturers often face uncertainty: Which type of flame retardant should be chosen for a specific material? How is fire resistance testing conducted? And how can it be ensured that raw materials meet REACH and CLP requirements? In this article, we answer seven of the most common questions our clients address – from technical specifications to practical aspects of handling and storage.

1. What types of flame retardants exist, and how to choose the right one?

Flame retardants are divided into several basic categories based on their chemical composition and mechanism of action. The most common are inorganic compounds (e.g., aluminium hydroxide or magnesium hydroxide), which release water when heated, cooling the material. Organophosphate compounds, on the other hand, form a protective layer that prevents oxygen access. Halogenated flame retardants (e.g., brominated or chlorinated) disrupt combustion chemical reactions, but their use is declining due to legislative restrictions. There are also nitrogen-based compounds that promote the formation of an insulating layer, or synergistic mixtures combining multiple mechanisms.

The selection of the right type depends on the material into which the flame retardant is added and the desired properties of the final product. For plastics, phosphorus or brominated compounds are often used, while inorganic hydroxides are more suitable for textiles or wood. It is also important to consider the thermal stability of the flame retardant – some decompose at 200 °C, while others can withstand up to 300 °C. Compatibility with the polymer and the impact on mechanical properties, such as strength or flexibility, must always be verified. For sensitive applications (e.g., electronics), halogen-free variants are recommended.

2. How is the effectiveness of flame retardants tested?

The effectiveness of flame retardants is tested using standardised test methods that simulate real fire conditions. The basic test is flammability testing according to standardised procedures, where the rate of flame spread, burning time after removal of the ignition source, or smoke formation is measured. For plastics, the UL-94 test is often used, which evaluates the material's behaviour during vertical or horizontal burning. Another important test is the determination of the Limiting Oxygen Index (LOI), which indicates the minimum oxygen concentration required to sustain combustion – a higher value means better fire resistance.

For a more comprehensive evaluation, tests are conducted in a calorimetric chamber, where heat release, heat release rate (HRR), and the production of toxic gases are measured. These parameters are key for assessing the safety of the material in real conditions. For building materials, the reaction to fire is also evaluated according to the European classification (classes A1 to F), which includes smoke formation and the dripping of burning particles. Test results must be supported by a certificate from an accredited laboratory to meet legislative requirements.

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3. What legislation regulates the use of flame retardants?

The use of flame retardants is strictly regulated at both European and national levels, primarily by the REACH and CLP regulations. REACH restricts or prohibits certain hazardous substances, such as polybrominated diphenyl ethers (PBDEs) or hexabromocyclododecane (HBCD), which were previously commonly used. CLP sets rules for the classification, labelling, and packaging of chemical substances, including flame retardants that may be toxic, ecotoxic, or persistent in the environment.

In addition to REACH and CLP, manufacturers must comply with sector-specific regulations. For example, in electrical engineering, the RoHS directive restricts the use of certain hazardous substances, including some halogenated flame retardants. Building materials must meet fire safety requirements according to national standards, which are based on the European classification of reaction to fire. It is also important to monitor legislative updates, as limits for hazardous substances are regularly tightened, and lists of prohibited compounds are expanded.

4. What are the most common mistakes when selecting and applying flame retardants?

One of the most common mistakes is underestimating the compatibility of the flame retardant with the polymer or other material. For example, some inorganic hydroxides can impair the mechanical properties of plastics, such as strength or elongation, if not properly dispersed. Another issue arises from incorrect dosing – too low a concentration does not provide the required protection, while too high a concentration can lead to material degradation or increased smoke formation. It is also important to consider the thermal stability of the flame retardant during material processing to prevent premature decomposition.

Another mistake is ignoring legislative requirements, especially for export products. Some countries have stricter limits for hazardous substances than the EU, and the product may be rejected at the border. Synergistic effects are also often overlooked – combining different types of flame retardants can significantly increase effectiveness, but an incorrect mixture can reduce fire resistance. Thorough testing of the final product is always necessary, as laboratory results may differ from behaviour in real conditions.

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5. How do flame retardants affect the mechanical properties of materials?

Flame retardants can significantly impact the mechanical properties of processed materials, which is a key factor when selecting the appropriate additive. For example, halogenated flame retardants often increase the stiffness of plastics but simultaneously reduce their impact strength. This can be problematic in applications where impact resistance is required, such as in electronic enclosures or automotive components. Conversely, halogen-free alternatives, such as phosphorus or nitrogen-based compounds, usually have less impact on mechanical properties, but their effectiveness may be lower or require higher dosing.

When optimising the formulation, the compatibility of the flame retardant with the polymer matrix must be considered. Some additives can cause migration to the material's surface, leading to undesirable "blooming" and deterioration of surface properties. Testing of mechanical properties, such as tensile strength, modulus of elasticity, or resistance to cracking, should be conducted using standardised test methods. In practice, different types of flame retardants are often combined to achieve the desired balance between fire resistance and mechanical parameters.

6. What are the ecological and health aspects of using flame retardants?

The ecological and health impacts of flame retardants are an increasingly frequent topic in industrial applications. Halogenated flame retardants, particularly brominated compounds, are under scrutiny due to their persistence in the environment and potential toxicity. Some of them are already regulated by the REACH regulation, and their use is restricted or prohibited. For example, polybrominated diphenyl ethers (PBDEs) have been phased out in many countries due to the risk of bioaccumulation and negative effects on the endocrine system.

Halogen-free alternatives, such as phosphorus or nitrogen-based flame retardants, are generally considered more environmentally friendly, but their overall impact must also be assessed. For example, some phosphorus compounds can release toxic gases, such as phosgene, during combustion. When selecting a flame retardant, it is therefore important to consider not only its effectiveness but also the entire life cycle of the product – from production and use to recycling or disposal. Certifications such as EcoLabel or adherence to circular economy principles can help reduce environmental impact.

7. How to properly store and handle flame retardants?

Proper storage and handling of flame retardants are essential to maintain their effectiveness and safety. Most of these substances are sensitive to moisture, temperature, or light, which can lead to degradation or loss of functional properties. For example, some phosphorus-based flame retardants are hygroscopic and, if stored improperly, can absorb moisture, reducing their effectiveness. It is recommended to store them in sealed, original packaging, in a dry and cool environment, ideally at temperatures between 15 and 25 °C.

When handling, it is necessary to follow occupational safety principles, especially for powder forms, which can create explosive mixtures with air. The use of personal protective equipment, such as gloves, safety goggles, and respirators, is essential. It is also important to ensure good ventilation of the workspace and prevent contamination of other materials. In case of spillage, procedures according to the safety data sheet should be followed, and suitable absorbent materials should be used. Adhering to these principles not only extends the lifespan of flame retardants but also minimises risks to workers' health and the environment.

Do you have specific requirements for flame retardants?

Every application requires an individual approach. GCG Group provides detailed safety and technical data sheets for each raw material and advises on selecting the optimal solution for your needs – whether it involves halogen-free systems, synergistic mixtures, or certified products for demanding conditions. Contact us – or explore our catalogue of over 1,300 products.