The Swiss Federal Laboratories for Materials Science and Technology, known as Empa, has developed a physically and chemically independent network of flame retardants inside cotton fibers, circumventing a problem often found in flame retardant cotton textiles that can release formaldehyde and be uncomfortable to wear.
Empa said the process retains the positive properties of cotton fibers of creating a favorable microclimate and softness on the skin, as well as being absorbent. Empa, an interdisciplinary Swiss research institute for applied materials sciences and technology, said for firefighters and other emergency service personnel, protective clothing provides a critical safety barrier. For such purposes, cotton is mainly used as an inner textile layer that needs additional properties such as being fireproof or protective against biological contaminants.
However, it should not be hydrophobic, which would create an uncomfortable microclimate, Empa noted. These additional properties can be built into the cotton fibers via chemical modifications.
“Until now, it has always taken a compromise to make cotton fireproof,” Sabyasachi Gaan, a chemist and polymer expert who works at Empa’s Advanced Fibers lab, said. “Wash-durable flame retardant cotton in industry is produced by treating the fabric with flame retardants, which chemically links to the cellulose in the cotton. Currently, the textile industry has no other choice than to utilize formaldehyde-based chemicals–and formaldehyde is classified as a carcinogen. This has been an unsolved problem for decades.”
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Gaan said while formaldehyde-based flame retardant treatments are durable, they have additional drawbacks–certain groups of cellulose are chemically blocked, which considerably reduces the capability of cotton to absorb water and results in an uncomfortable textile.
Gaan and his colleagues, Rashid Nazir, Dambarudhar Parida and Joel Borgstädt, utilized a tri-functional phosphorous compound that has the capability of reacting only with specifically added molecules to form its own network inside cotton. This makes the cotton permanently fire-resistant without blocking the favorable components that allow the positive attributes.
This flame retardant treatment does not include carcinogenic formaldehyde, which would endanger textile workers during manufacturing. The phosphine oxide networks formed do not wash out–after 50 launderings, 95 percent of the flame retardant network is still present in the fabric.
To render additional protective functionalities to the flame retardant cotton developed at Empa, the researchers also incorporated in silver nanoparticles inside the fabric. Silver nanoparticles provide the fiber with antimicrobial properties and also survive 50 laundry cycles.
Gaan added that two important hurdles remain.
“For future commercialization, we need to find a suitable chemical manufacturer who can produce and supply trivinylphosphine oxide,” he said. “In addition, trivinylphosphine oxide has to be REACH-registered in Europe.”