White cotton can normally only be made fire resistant by adding toxic flame retardants, but a new form could enable us to make inherently non-flammable cotton fabrics
18 January 2023
A form of cotton that is able to resist flames has been created by breeding parent strains that had no similar characteristics themselves. This could let us make fire-resistant fabrics without having to add toxic chemicals.
The spread of fires through people’s homes often involve textiles catching alight, so many countries now require the fabrics used in furniture to have a certain level of resistance. Some workers and soldiers also need to wear flame-resistant clothing. There are synthetic fibres that are inherently resistant to fire, such as aramid, but they aren’t as comfortable or as sought-after as natural fibres like cotton.
While a few varieties of brown cotton do have some fire resistance, at present, the only way to make white cotton resistant is to add flame-retarding chemicals. These typically release toxic substances, such as formaldehyde, and the fire-resisting qualities can also be lost when fabrics are cleaned.
Previous studies of the brown cotton varieties suggested that their flame resistance is due to the presence of a colourless compound of a kind known as a flavonoid, hinting that it could occur in white cotton too. So, Gregory Thyssen at the Agricultural Research Service of the US Department of Agriculture (USDA-ARS) and his colleagues decided to look for flame resistance in hundreds of lines of white cotton previously created by USDA-ARS for developing improved varieties, in case any also had this characteristic.
These lines were created from 11 diverse parent strains using a breeding technique designed to generate a lot of variety in the offspring.
The researchers burned tiny quantities of each cotton line and picked the five that produced the least heat as they burned. They then made nonwoven fabric from these five lines and did a standard flammability test involving putting a strip of fabric on a 45-degree incline and exposing it to a flame for a few seconds (see video, above). Four of the five fabrics self-extinguished after the flame was removed, whereas strips of normal cotton burned up entirely.
“The fibre quality was not affected by the new self-extinguishing trait,” says Thyssen. “Since these new lines were developed from already cultivated white cotton varieties, they do possess desirable traits for growers and consumers.”
Thyssen and his colleagues were surprised to find this level of flame resistance given that none of the 11 parent strains had this trait. They have identified some gene variants involved in flavonoid synthesis that might be responsible, but haven’t yet been able to pinpoint any specific compound involved. Whether the flame resistance is retained after washing isn’t yet known, says Thyssen.
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