Self-sealing Breathable Membranes

A layer of an amphiphilic polymer conetworks on a breathable membrane seales punctures and allows water to evaporate

Companies supplying outerwear for the general public have a holy grail: find a textile membrane that will keep out the heaviest of downpours while remaining breathable and comfortable during a physical effort. Over the past few years, textiles have been continuously improved, but these improvements come with a hefty sticker price that only some customers can really afford. And to make matters worse, these same textiles are often easily damaged or punctured once they are taken out into the great outdoors, the environment the outerwear was designed for. Even the tiniest of holes can cause a leak. 

Nico Bruns and his colleagues at the Adolphe Merkle Institute (AMI), the University of Basel and University of Applied Sciences and Arts Northwestern Switzerland have developed a composite membrane to overcome at least part of these problems, one that remains water-tight even if punctured with a sharp item.

Their idea was to take a thin breathable membrane and then add to it a so-called amphiphilic polymer co-network (APCN). APCNs are rubbery materials that swell when they come into contact with water. “The nanostructure of hydrophilic and hydrophobic domains allows for efficient water transport across the material, while at the same time rendering them exceptional durable,” says AMI Prof. Nico Bruns, lead researcher on the project.

If the membrane is punctured, the APCN layer immediately seals the hole, withstanding water pressure of at least 1.6 bar, or around half of what comes out of a garden hose. This pressure is the same as a water column of 16,000 mm, which is high for textiles. A membrane is considered waterproof at just 1,300 mm. Despite the high level of waterproofness, the extra layer does not stop liquid evaporating through the membrane though.

Bruns and his colleagues chose to test their concept in the context of medical cooling garments, such as those used to alleviate multiple sclerosis (MS) symptoms. Up to 80 per cent of MS patients are affected by heat sensitivity, which is strongly correlated with disabling symptoms such as fatigue, pain, and difficulty concentrating according to a Swedish 2011 study.

Measurements showed that the new membrane could be an alternative to current materials used for these devices.

Self-sealing materials are not a new concept. They were used for self-repairing tires and for bulletproof aircraft fuel tanks during the Second World War. Nature also uses self-sealing mechanisms. A liana found in the eastern United States, pipevine, has its own system to close off defects. However none of these concepts combines self-sealing properties of the new material with the ability for water to permeate through the sealing layer, which is essential for the evaporation of moisture.

“We are now going to work with industrial partners and with the financial support of the Swiss Commission for Technology and Innovation to take our research from the lab to scalable production,” says Bruns. “The aim is that that self-sealing membranes for medical cooling textiles and for outdoor garments enter the consumer market.”

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