Nav: Home

New coatings make natural fabrics waterproof

June 29, 2018

CAMBRIDGE, Mass. -- Fabrics that resist water are essential for everything from rainwear to military tents, but conventional water-repellent coatings have been shown to persist in the environment and accumulate in our bodies, and so are likely to be phased out for safety reasons. That leaves a big gap to be filled if researchers can find safe substitutes.

Now, a team at MIT has come up with a promising solution: a coating that not only adds water-repellency to natural fabrics such as cotton and silk, but is also more effective than the existing coatings. The new findings are described in the journal Advanced Functional Materials, in a paper by MIT professors Kripa Varanasi and Karen Gleason, former MIT postdoc Dan Soto, and two others.

"The challenge has been driven by the environmental regulators" because of the phaseout of the existing waterproofing chemicals, Varanasi explains. But it turns out his team's alternative actually outperforms the conventional materials.

"Most fabrics that say 'water-repellent' are actually water-resistant," says Varanasi, who is an associate professor of mechanical engineering. "If you're standing out in the rain, eventually water will get through." Ultimately, "the goal is to be repellent -- to have the drops just bounce back." The new coating comes closer to that goal, he says.

Because of the way they accumulate in the environment and in body tissue, the EPA is in the process of revising regulations on the long-chain polymers that have been the industry standard for decades. "They're everywhere, and they don't degrade easily," Varanasi says.

The coatings currently used to make fabrics water repellent generally consist of long polymers with perfluorinated side-chains. The trouble is, shorter-chain polymers that have been studied do not have as much of a water-repelling (or hydrophobic) effect as the longer-chain versions. Another problem with existing coatings is that they are liquid-based, so the fabric has to be immersed in the liquid and then dried out. This tends to clog all the pores in the fabric, Varanasi says, so the fabrics no longer can breathe as they otherwise would. That requires a second manufacturing step in which air is blown through the fabric to reopen those pores, adding to the manufacturing cost and undoing some of the water protection.

Research has shown that polymers with fewer than eight perfluorinated carbon groups do not persist and bioaccumulate nearly as much as those with eight or more -- the ones most in use. What this MIT team did, Varanasi explains, is to combine two things: a shorter-chain polymer that, by itself, confers some hydrophobic properties and has been enhanced with some extra chemical processing; and a different coating process, called initiated chemical vapor deposition (iCVD), which was developed in recent years by co-author Karen Gleason and her co-workers. Gleason is the Alexander and I. Michael Kasser Professor of Chemical Engineering and associate provost at MIT. Credit for coming up with the best short-chain polymer and making it possible to deposit the polymer with iCVD, Varanasi says, goes primarily to Soto, who is the paper's lead author.

Using the iCVD coating process, which does not involve any liquids and can be done at low temperature, produces a very thin, uniform coating that follows the contours of the fibers and does not lead to any clogging of the pores, thus eliminating the need for the second processing stage to reopen the pores. Then, an additional step, a kind of sandblasting of the surface, can be added as an optional process to increase the water repellency even more. "The biggest challenge was finding the sweet spot where performance, durability, and iCVD compatibility could work together and deliver the best performance," says Soto.

The process works on many different kinds of fabrics, Varanasi says, including cotton, nylon, and linen, and even on nonfabric materials such as paper, opening up a variety of potential applications. The system has been tested on different types of fabric, as well as on different weave patterns of those fabrics. "Many fabrics can benefit from this technology," he says. "There's a lot of potential here."

The coated fabrics have been subjected to a barrage of tests in the lab, including a standard rain test used by industry. The materials have been bombarded not only with water but with various other liquids including coffee, ketchup, sodium hydroxide, and various acids and bases -- and have repelled all of them well.

The coated materials have been subjected to repeated washings with no degradation of the coatings, and also have passed severe abrasion tests, with no damage to the coatings after 10,000 repetitions. Eventually, under severe abrasion, "the fiber will be damaged, but the coating won't," he says.

The team, which also includes former postdoc Asli Ugur and Taylor Farnham '14, SM '16, plans to continue working on optimizing the chemical formula for the best possible water-repellency, and hopes to license the patent-pending technology to existing fabric and clothing companies. The work was supported by MIT's Deshpande Center for Technological Innovation.
-end-
Written by David L. Chandler, MIT News Office

ADDITIONAL BACKGROUND

ARCHIVE: A new way to mix oil and water

http://news.mit.edu/2017/new-way-mix-oil-and-water-1108

ARCHIVE: Stick, peel, or bounce: Controlling a freezing droplet's fate

http://news.mit.edu/2017/stick-peel-bounce-controlling-freezing-droplets-0911

Massachusetts Institute of Technology

Related Polymers Articles:

Oyster shells inspire new method to make superstrong, flexible polymers
Columbia Engineers developed a method inspired by the nacre of oyster shells, a composite material with extraordinary mechanical properties, including great strength and resilience.
The brighter side of twisted polymers
A strategy to produce highly fluorescent nanoparticles through careful molecular design of conjugated polymers has been developed by KAUST researchers.
New strategy produces stronger polymers
MIT researchers have found a way to reduce the number of loops in polymer networks such as gels, plastics, and rubber.
Team highlights work on tuning block polymers for nanostructured systems
High-performance materials are enabling major advances in a wide range of applications from energy generation and digital information storage to disease screening and medical devices.
Estimating the glass transition temperature for polymers in 'confined geometries'
Polystyrene has a glass transition temperature of about 100 C -- at room temperature it behaves like a solid material.
Rapid Imaging of Polymers Could Lead to Better Bioimaging
A recent study by researchers at the Beckman Institute for Advanced Science and Technology at the University of Illinois identifies a method of Quantum Cascade Laser-based (QCL) infrared spectroscopic imaging that provides a more rapid method than conventional Fourier transform infrared imaging (FT-IR) to examine spherulites, large semicrystalline polymer samples, in order to identify chemical and structural properties.
Macromolecules: Light to design precision polymers
Chemists of Karlsruhe Institute of Technology have succeeded in specifically controlling the setup of precision polymers by light-induced chemical reactions.
International engineering team develop self-powered mobile polymers
n international group involving Inha University, University of Pittsburgh and the Air Force Research Laboratory has built upon their previous research and identified new materials that directly convert ultraviolet light into motion without the need for electronics or other traditional methods.
'Bottlebrush' polymers make dielectric elastomers increasingly viable for use in devices
A multi-institutional research team has developed a new electroactive polymer material that can change shape and size when exposed to a relatively small electric field.
NIST-made 'sun and rain' used to study nanoparticle release from polymers
In a recently published paper, researchers from the National Institute of Standards and Technology (NIST) describe how they subjected a commercial nanoparticle-infused coating to NIST-developed methods for accelerating the effects of weathering from ultraviolet (UV) radiation and simulated washings of rainwater.

Related Polymers Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Digital Manipulation
Technology has reshaped our lives in amazing ways. But at what cost? This hour, TED speakers reveal how what we see, read, believe — even how we vote — can be manipulated by the technology we use. Guests include journalist Carole Cadwalladr, consumer advocate Finn Myrstad, writer and marketing professor Scott Galloway, behavioral designer Nir Eyal, and computer graphics researcher Doug Roble.
Now Playing: Science for the People

#529 Do You Really Want to Find Out Who's Your Daddy?
At least some of you by now have probably spit into a tube and mailed it off to find out who your closest relatives are, where you might be from, and what terrible diseases might await you. But what exactly did you find out? And what did you give away? In this live panel at Awesome Con we bring in science writer Tina Saey to talk about all her DNA testing, and bioethicist Debra Mathews, to determine whether Tina should have done it at all. Related links: What FamilyTreeDNA sharing genetic data with police means for you Crime solvers embraced...