Textiles with ‘water shield’ nano-coating can be cleaned without detergent

Stained and dirty clothes could one day be washed by simply rinsing them with water thanks to a new self-cleaning coating for textiles. The researchers say it could make doing laundry more convenient and more environmentally friendly by reducing water use and limiting wastewater contaminated with detergents and microplastic fibres.

Self-cleaning coatings are nothing new and they are usually based on three kinds of materials. Superhydrophobic ones work against water-based contaminants but struggle with oily residues. Photocatalytic self-cleaning surfaces can degrade contaminants under light but they don’t prevent dirt attaching in the first place. Meanwhile, lubricant-based self-cleaning coatings allow contaminants to slide off but they lack long-term stability and durability on flexible fabrics.

Now, Chinese researchers have made a new kind of self-cleaning coating for textiles that instead relies on molecular interactions in a polyelectrolyte multilayer, which creates a ‘nano-shield’ of water molecules. This effectively prevents contaminants from latching on to fibres, making it easier to remove stains, oily residues, bacteria and mould when rinsed with just water.

‘What first inspired us was not laundry itself, but a more fundamental question in interfacial chemistry: what kind of surface can prevent contaminants from sticking tightly enough that they can be removed with water alone?’ says Chongling Cheng at Southeast University, China.

The team had previously investigated surfaces comprising sulfonate groups, which strongly attract water. The researchers found that when arranged at high density these groups sustained a stable and continuous nanoscopic layer of tightly bound water molecules that effectively shielded the solid surface from external contaminants.

Applying this concept to textiles, the researchers sprayed polyester, cotton and silk with two oppositely charged polyelectrolyte materials. The process – akin to nanoscale painting or brushing – was done repeatedly to make a continuous and uniform coating across the textile surface. This ensured the protective layer of water molecules was dense enough to stop contaminants from finding gaps and reaching the underlying fibres.

The coated textiles were then stained with ketchup, soy sauce and engine oil, as well as exposed to bacteria and mould. When given a single rinse cycle in a washing machine, the results either matched or outperformed uncoated textiles that received one conventional wash cycle with detergent and four rinse cycles.

The team calculated that the overall water and electricity use and time taken was reduced by approximately 82%. Meanwhile, the use and discharge of detergent was eliminated and the release of microplastics in wastewater was vastly reduced. ‘Without the assistance of detergent, it becomes much more difficult for microplastics to enter the water,’ explains Cheng. ‘Therefore, this approach may help reduce microplastic release in two ways at the same time: by reducing fibre generation and by reducing fibre dispersion.’

‘This work presents an elegant shift in how we think about laundry,’ comments Rajesh Ramanathan, a nanomaterials chemist at The Royal Melbourne Institute of Technology, Australia. ‘What is particularly interesting is that the mechanism is non-catalytic and non-biocidal, relying purely on interfacial physics rather than chemical degradation.’

‘It is certainly an interesting approach and offers some impressive results in terms of cleaning performance,’ says Richard Blackburn, who researches sustainable materials and textiles at the University of Leeds, UK. However, he says user comfort, especially breathability of the coated fabrics, as well as their biodegradation and end of life are not addressed. ‘Certain textile coatings, some with similar chemistry, significantly reduce biodegradation rates of treated textiles. If such treatments are hard to remove they also significantly reduce recyclability of fabrics.’

‘Of course, these results should only be taken as preliminary and encouraging signs,’ says Cheng. ‘Environmental evaluation, integration into manufacturing workflows, and long-term durability under practical conditions all still need further study.’