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