Recombinant hydrophobic protein acts as toxin-free fire retardant on textiles

Researchers have discovered that recombinant hydrophobic protein can act as a fire retardant when applied to textiles, eliminating the need for toxic chemicals.

The team at the Hub for Biotechnology in the Built Environment at University of Northumbria revealed their findings in the paper’ ’Innovating fire safety with recombinant hydrophobic proteins for textile fire retardancy’ which has been accepted by Microbial Biotechnology, an Applied Microbiology International publication.

This process of inferring fire retardancy could make the manufacturing of textiles for furnishings more sustainable by eliminating the need for toxic chemicals which can be economically and environmentally costly, said corresponding author Professor Meng Zhang.

Flammable materials

“A lot of textile furnishings in the built environment, like sofas, need to be flame retardant - however, they are made from materials which are flammable such as synthetic nylon, or cotton,” she said.

“In order to make these materials flame retardant they are coated with chemicals which can cause pollution and are in some cases toxic. 

“We had previously discovered that we could stick a hydrophobic (water-repellent) protein from bacteria onto cellulosic material using a cellulose binding module.

“Now we have shown that this same protein can also stop flames spreading across textiles to a level passable by current British Standards. By using the same cellulose binding module, we showed that this protein can evenly coat nylon, cotton, linen and bacterial cellulose.”

Cell-free extract

The team used E coli to produce the hydrophobic protein with cellulose binding module recombinantly and collected it as cell-free extract. It was then used to coat swatches of different textiles including wool (which is naturally fire retardant), acrylic, nylon, bacterial cellulose, linen and cotton. They also included a control experiment of cell free extract from cells that do not have this hydrophobic protein.

“These coated swatches were mounted on metal frames and were set alight on a dry day in ambient temperatures and little wind, in keeping with official testing guidelines,” said Professor Zhang.

“We then recorded how long the material burned, and what area was affected. We found that the wool was not affected with or without our protein as it is naturally fire retardant. All other textiles, with the exception of acrylic, had significantly reduced flame damage, and the fire went out quicker when the hydrophobic protein was applied.

Protein on samples

“It was suspected that the acrylic would not perform well as it is not very absorbent and, as previous tests had shown, it had very little protein on it. The amount of protein on each sample was assessed in two ways, by measuring the concentration and volume of protein applied, and visually, by using a green fluorescent protein as a proxy for the colourless hydrophobic protein.”

One surprise was that this method worked for a synthetic textile (nylon), as cotton, linen and bacterial cellulose are all cellulosic, allowing the binding module to attach. 

“The structure of nylon means that this binding module also helps to increase the amount of protein that can remain on this textile,” Professor Zhang said.

“It was also a surprise to see how well this protein worked - the coating would pass current guidelines for fire retardancy.

Other species

“There are numerous proteins from bacteria or fungi which could be candidates for water-repellency and fire-retardancy, and it is possible that some may perform even better than the protein used here. 

“In addition, through the protein engineering approach, we could manipulate protein sequence and enhance the fire retardancy.  It would also be beneficial to test out some other binding modules to make this kind of coating applicable to acrylic materials.”

This study was led by Prof Meng Zhang with postdoc Dr Katie Gilmour and support from researchers from the Hub for Biotechnology in the Built Environment at Newcastle and Northumbria University, including textile expert Dr Jane Scott, engineering biologist Dr Paul James, materials scientist Dr Yunhong Jiang, architect Prof Martyn Dade-Robertson. Additional support carrying out the experiments was provided by postdoc Dr Thora Arnardottir and technician Oliver Perry.

’Innovating fire safety with recombinant hydrophobic proteins for textile fire retardancy’ appears in Microbial Biotechnology, an Applied Microbiology International publication.