Antimony Oxide As Flame Retardant – Efficient But Also Dangerous?

Flame-retardant coated fabrics typically contain flame retardants in the coating. The following applies: The thinner the fabric and the coating, the more efficient flame retardant finishes are required. Antimony oxide is a so-called synergist which, in combination with halogen-containing flame retardants in plastics, is a very efficient flame retardant. Specks of dust of antimony oxide that can enter the body via the lungs are generally classified as carcinogenic.

Therefore, investigations are currently being carried out to determine whether coated textiles equipped with antimony oxide can pose a health hazard, reports Sebastian Eibl of the ‘Wehrwissenschaftliches Institut für Werk- und Betriebsstoffe’ in Erding.

The special aspect here is the fact that a harmful effect on health is not known by an absorption through the skin. This raises the question of whether a health hazard from antimony oxide is possible at all if it is present as a flame retardant embedded in the material of the coating and is not permanently released.

In order to take into account the influence of moisture and the ageing state of the tissues, ageing tests were carried out which lasted up to twelve weeks. It turned out that antimony oxide is exposed on the surface by ageing in humid air at simultaneously increased temperatures.

To predict the release behaviour over longer periods of time at room temperature from laboratory data, a ‘Arrhenius’ method was used (quantitative temperature dependence in physical and above all chemical processes in which activation energy has to be overcome at the molecular level). Here it can be concluded that the influence of humidity is critical with regard to antimony oxide exposure under typical environmental conditions - ten per cent of the total antimony oxide contained escapes at 20°C after a few years.

Health hazard – Yes Or No?

For the assessment of a possible health hazard from antimony oxide, specks of dust that enter the lungs when inhaled are particularly relevant. However, the investigations presented here only examine the basic possibility of superficial exposure. Explicit investigations on the release of dust were not carried out. As long as the material is embedded in the polymer, no relevant exposure of a user can be assumed.

However, it is not sufficient to evaluate the tissue only in its new condition. A possible exposure or release of antimony oxide must also be excluded during use. In the sense of a risk-benefit assessment, the use of antimony oxide as a flame retardant synergist can be quite sensible in the case of a justified need for efficient flame retardancy in fabrics with thin coatings.

At present, further efforts are being made to evaluate and classify the health-endangering potential. A possible regulation by "REACH" (an EU regulation) is not to be expected in an estimated period of about ten years, according to the „Bundesinstitut für Risikobewertung“ (Federal Institute for Risk Assessment).

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