A new chemical process developed by Empa turns cotton into a fire-resistant fabric that nevertheless retains the skin-friendly properties of cotton. Researchers utilized a tri-functional phosphorous compound, which can react only with specifically added molecules (nitrogen compounds like piperazine) to form its network inside cotton. This makes the cotton permanently fire-resistant without blocking the favorable -OH groups. In addition, the physical phosphine oxide network also likes water. The flame retardant treatment does not include carcinogenic formaldehyde, which would endanger textile workers during textile manufacturing. The phosphine oxide networks, thus formed, do not wash out: After 50 launderings, 95 percent of the flame retardant network is still present in the fabric.
“Until now, it has always taken a compromise to make cotton fireproof,” says Sabyasachi Gaan, a chemist and polymer expert who works at Empa’s Advanced Fibers lab. Wash-durable flame retardant cotton in the industry is produced by treating the fabric with flame retardants, which chemically link 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. While formaldehyde-based flame retardant treatments are durable, they have additional drawbacks: The -OH groups of cellulose are chemically blocked, which considerably reduces the capability of cotton to absorb water, which results in an uncomfortable textile.
Gaan said, “We have used a simple approach to fix the phosphine oxide networks inside the cellulose. We first treated the cotton with an aqueous solution of phosphorus and nitrogen compounds for our lab experiments. We then steamed it in a readily available pressure cooker to facilitate the crosslinking reaction of the phosphorus and the nitrogen molecules. Steaming textiles after dyeing, printing, and finishing is a normal step in the textile industry. So it does not require additional investment to apply our process.”
A patent application protects the newly developed phosphorus chemistry and its application.
