Say no to repellent fabrics

Materials World magazine
,
27 Feb 2019

Waterproof outerwear is over-engineered using chemicals that should be phased out, say researchers. Ceri Jones looks at the alternatives.

Protective coatings designed to repel hazardous liquids should not be used in clothing for the general public, according to researchers who claim they are unnecessary and environmentally unsound.

The team based in Leeds, UK, and Stockholm, Sweden, deemed the manufacturing process of performance textiles as harmful to the environment due to the need for large amounts of fluorochemicals, including polymeric perfluoroalkyl and polyfluoroalkyl (PFASs).

These highly chlorinated substances are essential for producing fabrics that protect against oils and bodily fluids, but the researchers say these should be restricted to biohazard use only as while most waterproof outerwear is designed to repel dangerous liquids, they only really need to protect against rain.

The study, led by the University of Leeds, UK, Highly fluorinated chemicals in functional textiles can be replaced by re-evaluating liquid repellency and end-user requirements, argues for industries to invest in more eco-friendly durable water repellents (DWR) as standard, with fluorinated chemicals used on a fit-for-purpose basis.

On the surface

Textile production has come under fire in recent years due to unsustainable practices, such as its use of 25% of global chemical production.

Aiming to design out some of the problems, the team at Leeds tested non-fluorinated DWRs against fluorinated substances, to demonstrate the performance of alternatives and to distinguish nice-to-have functionalities from occupational health and safety requirements.

The team tested common fluorinated and novel non-fluorinated alternative DWR polymers. PET fabric samples were coated with non and fluorinated DWRs and cured. Liquids were chosen for different surface tensions and polarities, but all with low viscosity to heighten the chance of them penetrating the fabrics. The general purpose apparel was exposed to water, orange juice, red wine and olive oil, while the functional ones were subjected to simulated blood, gastric fluid and cough medicine.

This was done by spray and Bundesmann rain-shower methods, to account for angles of movement in clothing. Droplet roll-off, level of absorption, and liquid penetration was observed and measured.

As expected, fluorinated substances with long side-chain fluorinated polymers (SFP) had the lowest absorption levels, at less than 1%, and roll-off angles of 11 degrees. Shorter chain variations didn’t perform as well, but all repelled water, stopped wetting, and had high oleophobicity and droplet roll-off which would prevent stains.

The best of the non-fluorinated coatings performed similarly to the short-chain SFPs, with relatively low liquid absorption and no water absorption, but having low repellency. Particularly successful were a polymer based on polydimethylsiloxane, a wax-based encapsulated polymer, a fatty acid-modified saccharide, and a silicone-modified saccharide, Head of Sustainable Materials Research Group at the University of Leeds, and Co-author of the paper, Dr Richard Blackburn told Materials World. He added that the latter three are also biodegradable, without breaking down into toxic substances.

Fit for purpose

While some alternatives were resistant to droplets with high surface tensions, none prevented oil absorption.

‘Certain non-fluorinated, biodegradable DWRs are likely to be sustainable alternatives for water repellency – and certain stain repellency – meeting consumer requirements and expectations for most outdoor apparel. Green chemistry solutions are therefore available, but are being resisted by some manufacturers and retailers,’ the paper reads.

‘Non-fluorinated alternatives are a viable option in all cases where stain repellency is not an essential textile function. Non-fluorinated alternatives provide excellent rain protection and their lack of stain protection should be balanced with the long-term ecological benefits of phasing out PFASs.

‘Substitution of PFAS-based DWRs [for biohazards] cannot be considered as an option at this time. These occupational textiles need to be rethought in terms of product design to make non-fluorinated alternatives viable in these use categories.

The team is now seeking funding and research support to further this work. The study was published in The Journal of Cleaner Production, and for more information on DWR substances and testing results, you can read it here: bit.ly/2Su903P