Flame retardants – chemicals that open new possibilities for the industry…

Published: 26-06-2017

Plastics are contained in the majority of everyday life objects. As such, polymer materials intended for the construction, transportation, furniture and electronics industries are subject to strict fire resistance criteria. These requirements are aimed at reducing the risk of fire and extending the time for evacuation from the site of the incident. Flammability tests take into account flame spread rating, heat emission, smoke production, and the toxicity of the resulting gases. The intended application of the material determines the individual weighting which each of these parameters carry for the purposes of security assessment.

The flammability of plastics can be limited, for instance, through the addition of special chemicals – flame retardants (FRs).­­ Their structure contains atoms of elements such as chlorine, bromine, phosphorus, nitrogen, boron or aluminium, which improve the fire resistant properties of the material. Combining various types of flame retardants, e.g. chlorine compounds with antimony compounds or phosphorus compounds with nitrogen compounds, helps enhance their performance due to the synergy effect.

The action of a particular FR depends on its chemical structure. The impact of flammability-reducing agents on the mechanism of combustion may be chemical and/or physical in nature, and may take place in the gas phase and/or the solid phase. The chemical action involves the deactivation of reactive radicals that support the combustion process (gas phase) and the creation of a charred layer on the surface of the material (solid phase). In contrast, the physical action involves the dilution of the reaction mixture (gas phase), absorption of the heat of the combustion reaction (gas phase), and the protection of the material against the access of oxygen and the heat from the combustion zone (solid phase).

There are several primary factors which determine the application of a specific flame retardant. The aspects under consideration include the processing conditions of the material to which the chemical is to be added. Depending on the type of plastic, the FR can be either solid or liquid. For instance, polyethylene processing involves primarily flame retardant powders (bromine compounds, mineral additives), while the polyurethane industry favours mainly liquid forms (phosphorus compounds, chlorine compounds). Another factor of tremendous importance is the compatibility of the flame retardant with the material (for example, mineral fillers cannot be used for transparent applications). Nonetheless, the effectiveness of an FR is the fundamental argument for its application. Halogen compounds and phosphorus compounds are considered the two most effective groups of flame retardants. Another significant selection criterion involves economic considerations. Mineral compounds are the most common (about 40% of materials with flame retardants) due to their low price. Unfortunately, these FRs are not very effective – they must be used in large quantities for the assumed flame retardant effect to be achieved. This in turn adversely affects the functional properties of the material. Furthermore, it is becoming increasingly important to ensure that the compounds added to a material have no negative environmental impact. As a result, the current trend is to abandon halogen flame retardants, with the application of halogen-free phosphorus compounds forecast to increase in forthcoming years.

The product portfolio of the PCC Group includes a range of phosphorus flame retardants marketed under the brand name Roflam. These chemicals play a key role in residential and industrial construction as components of structural and insulation materials. They are used to make spray insulation for floors, foundations, lofts and roofs, as well as insulation boards for the walls of residential buildings, warehouses and industrial facilities. Roflam products are found in assembly foams and in adhesives for polystyrene foam and plaster cardboard. Insulation materials are also an integral element in cooling devices, such as chill cabinets, refrigerators and freezers, which is why manufacturers from the refrigeration and household appliance industries reach for flame retardants as well. One of the most critical areas of FR application is transport, where high resistance of materials to combustion is of particular importance. As a result, flame retardants are widely used in materials making up fittings in cars, trains and airplanes, such as armchairs, armrests, headrests, dashboards, bumper fillings and ceiling linings. The furniture industry is yet another important market for phosphorus flame retardants, which are used in the production of armchairs, sofas, mattresses and artificial leather. Roflam products also have other specialised applications, for example as a component of mining adhesives and coating materials.

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