Swiss Federal Laboratories for Materials Science and Technology (EMPA) scientists have developed a new way to create cotton fire-resistant which preserves its skin-friendly properties. Advanced flame retardant cotton textiles release formaldehyde and are rough to wear as these decrease ability of cotton to absorb water.
EMPA scientists produced a physically and chemically sovereign network of flame retardants inside the cotton fibres. This method keeps the integrally positive properties of cotton fibres, which account for three-quarters of the world’s plea for natural fibres in clothing and home textiles.
Cotton is wear-friendly as it can absorb large amounts of water and maintain a promising microclimate on the skin.
For firefighters and other emergency service workers, protective clothing offers the most vital barrier. For such purposes, cotton is mostly used as an inner textile layer that needs additional properties.
For instance, it must be fireproof or protect against biological contaminants. It should also not be hydrophobic, which would create an uncomfortable microclimate. These additional properties can be built into the cotton fibres by suitable chemical modifications.
“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 Fibres lab.
Wash-durable flame retardant cotton in 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.
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 – these treatments chemically block the -OH groups of cellulose, which reduces the capability of cotton to absorb water, resulting in an uncomfortable textile.
Gaan, who knows the chemistry of cotton fibres well and has spent many years at EMPA developing flame retardants based on phosphorus chemistry that are already used in many industrial applications, found an easy way to anchor phosphorous in form of an independent network inside the cotton.
This flame retardant treatment does not include carcinogenic formaldehyde, which would endanger textile workers during textile manufacturing. The phosphine oxide networks do not wash out. After 50 launderings, 95 percent of the flame retardant network was still present in the fabric.
To add more protective properties to the flame retardant cotton, the team incorporated in situ generated silver nanoparticles inside the fabric. This works in a one-step process together with generating the phosphine oxide networks. Silver nanoparticles provide the fibre with antimicrobial properties and survive 50 laundry cycles.
“We have used a simple approach to fix the phosphine oxide networks inside the cellulose,” Gaan says.
“For our lab experiments, we first treated the cotton with an aqueous solution of phosphorus and nitrogen compounds and then steamed it in a readily available pressure cooker to facilitate the crosslinking reaction of the phosphorus and the nitrogen molecules.”
The application process is compatible with equipment used in the textile industry. “Steaming textiles after dyeing, printing and finishing is a normal step in the textile industry. So, it doesn’t require additional investment to apply our process,” Gaan adds.
The newly developed phosphorus chemistry and its application are being patented. “Two important hurdles remain,” Gaan says.
“For future commercialization, we need to find a suitable chemical manufacturer who can produce and supply trivinylphosphine oxide. In addition, trivinylphosphine oxide has to be REACH-registered in Europe.”
