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(The Gist of Science Reporter) Green Flame Retardants – Keeping out Fires [JUNE-2019]

Green Flame Retardants – Keeping out Fires

Flame Retardant Polyester Textiles

Polyester fabrics and blends have re-emerged with improvements in weaving quality, finishing, strength and durability. Currently they meet the increasing demand for aesthetic finishing at a cheap price, and their demand is continuously growing in the fashion, interior furnishings, sportswear and protective clothing industries.
But polyester is not characteristically a good flame suppressing material because it melts and drips when it burns due to its simple linear structures. It can be made flame retardant, however, by using either co-monomeric modifications or by introducing additives during polymerisation or fibre extrusion stages.
Fabrics are treated with additives based on their chemical composition and their thermal characteristics to make them flame retardant.
The conventional flame retardant additives are Borax and Boric acid and its hydrated salts, Al2O3, Ca2O3, Na2SiO3, calcium carbonate, thiourea, etc.
They are either added at the time of spinning processes performed on synthetic fibers or are deposited on the synthetic or natural fabric surfaces.
Their insulating layer brings the temperature below the pyrolysis temperature and prevents combustion as it releases water vapour and produces a foamed glassy coating on the fibre surface.
However, these additives are generally toxic pollutants and direct or indirect exposure to them can have adverse effects on the health of children, pregnant women and workers in particular.

Eco-friendly Flame Retardants

Common Halogenated flame retardants release toxic dioxins and furans during the burning process. Some escape into the atmosphere, mix with dust and causes indoor air pollution.
There are others that cause cancer, reproductive problems, impaired foetal brain development, as well as decreased fertility.
So, alternative eco-friendly phosphorus-based chemicals are now being developed. They do not accumulate in the food chain, have a low toxicity profile and eventually mineralize in nature posing no harm to the environment. Phosphorus-based flame retardants are made of inorganic or organic compounds.
They can be reactive products which are chemically hound into the polymer or can be additive products. The reactive products are used in polyester fibres and also as coatings on textiles with water-resistant flame-retardant finishing.
Phosphorus containing flame retardants are quite versatile in their flame retardant action. They follow condensed phase mechanisms by disrupting the combustion cycle.
This process involves thermal decomposition which produces phosphoric acid that cross links with hydroxyl containing polymers thereby altering the pyrolysis temperature to yield less flammable by-products.
Phosphorus-containing polyesters behave as flame retardants by removing heal from the flame zone during melt dripping. But, serious melt dripping can lead to immediate burning, secondary damage, and can increase the risk of fire.
Therefore, phosphorus based flame retardants require high add-on percentage on the textile surface for which larger quantities of toxic chemicals have to be used.