New elastic polymer self-heals in just one minute

By Yun Xie
From http://arstechnica.com/

Dominique Bersier and Gina Fiore for Adolphe Merkle Institute, Case Western Reserve University, US Army Research Laboratory.

Self-healing polymers are extremely sought after by scientists, as they have many useful—not to mention lucrative—applications. Back in 2009, we reported a polyurethane-based polymeric material that heals itself in roughly an hour when exposed to UV light. That particular polymer, made by Biswajit Ghosh and Marek W. Urban, would be useful as a protective coating for phones, cars, etc. It worked based on the principle of having a reactive chemical component that would split open when physically damaged to create two reactive ends that can then covalently link together under UV light to repair itself.

In a recent issue of Nature, Mark Burnworth and his colleagues report a different type of self-healing material, one that can repair itself in about a minute under UV light. Burnworth’s polymeric material also doesn’t function on the basis of forming chemical bonds between organic compounds for repair. Instead, it relies on localized heating and metal-ligand interactions.

Burnworth and his team used rubbery oligomers, poly(ethylene-co-butylene), as the core of their material. They attached ligands, 2,6-bis(1’-methylbenzimidazolyl)pyridine (Mebip), that can bind to metals at the ends of the oligomers. To form long polymers, the researchers added either zinc (Zn²⁺) or lanthanum (La³⁺) ions to the solution of oligomers. The metal ions form metal-ligand complexes with the Mebip, linking the oligomers with one another.

For their self-healing tests, Burnworth and his team shaped the polymers into films that were 350 to 400 µM thick. They purposefully cut the polymer to about 50 to 70 percent of the overall thickness of the film. When the cuts were exposed to two consecutive 30-second rounds of UV light (320 to 390 nm wavelength at an intensity of 950 mW cm^-2), the cuts sealed up. The healed material was comparable in toughness to the original polymeric film, and images from atomic force spectroscopy show that the cuts essentially disappeared.

This process works because complexes of Mebip with metals are chromophoric, so they can absorb light of a specific wavelength, such as light in the UV range. Once they absorb light, they get into a higher energetic state and then lose that energy by giving off heat. Thus, when the researchers exposed the cuts to UV light, there was heating at the surface of the polymeric film—enough heating to reach over 220°C in 30 seconds. The heat quickly depolymerizes the area around the cut. Once the UV light is turned off, the liquidized area cools, reforms the ligand-metal complexes, and seals up the cut.

The healing process can be localized, as you only need to hit damaged areas with UV light. The researchers also show that the healing process would still work if the polymer was under a load of about 8 kPa. They suggest that different ligands could be used to cover a range of absorbable wavelengths. Thus, you could selectively tailor the wavelength of light to heal different types of damaged materials.

Burnworth and his colleagues have made a significant step in getting us closer to having self-healing polymers on the market. Their approach is quite different than that of Ghosh and Urban, which we described previously. While Burnworth’s method certainly heals quicker, it also produces a dramatic increase in surface temperature during healing. Such a huge temperature surge could be disadvantageous for certain applications.

Nature, 2011. DOI: 10.1038/nature09963 (About DOIs)

Rubber Made from Chewed Gum Could Replace Plastic

From: http://www.treehugger.com/

by Jaymi Heimbuch, San Francisco, California

Image via The Gumdrop Bin

It's not news that chewing gum is the scourge of city sidewalks. Nor that it takes a lot of money and energy to clear gum off walkways, shortening the lifespan of the surfaces at the same time. Designer Anna Bullus read the statistics of the gum problem in London -- that the government spends £150 million annually to clean up gum, over 30,000 pieces of which end up stuck to Oxford street alone each day -- and she decided there must be a better way to deal with the problem. So, she headed to the laboratory and came up with a way to transform chewed gum into a useful rubber that can be made into anything from toys to boots. But she's starting out by making chewed gum into discrete but identifiable waste bins for used gum.

The Gumdrop Bin by Anna Bullus is potentially a perfect solution to the problem of chewed gum. She cites that over 3.5 billion pieces of gum are discarded every year, too many of which end up on sidewalks, but by posting small repositories like the Gumdrop, they can be collected and transformed into something new.

The Guardian writes that Bullus "spent eight months working in a lab, trying to turn old gum into a new material...From getting it to make a foam, Bullus was able to make a used-gum pellet; then, adding ingredients (these remain secret), she extracted a polymer that she calls BRGP (Bullus Recycled Gum Polymer). This is the substance she uses to make the pink bubble bins now dotted around Orpington College, where they're being trialled as gum-specific litter bins. When the bins are full, both bin and innards are recycled into new BRGP, which in turn become more bins and possibly other products, too."

There are a few inherent problems, such as keeping the Gumdrop bins empty of anything except gum, when and who collects the gum from the bins, and getting people to use them instead of spitting out their gum wherever they feel like. Getting people to notice, and understand what the pink orbs are for is a big part of the challenge. But if it becomes a useful service, then it could save cities millions in clean up efforts, and save citizens hours of cleaning shoes.

Speaking of shoes, that's exactly what Bullus hopes to make out of chewed-gum-turned-rubber: "The amazing thing is you can use it for any plastic product," says Bullus. "I'd love to do some Wellington boots, for example. Gum boots, in fact."

Chewed gum as a substitute for plastics, at least on a small scale? We'll take it.

So far the repositories are popping up around London and even in a Six Flags in New Jersey. We'll watch and see if, and how, the idea takes off.

Grease? New Coating Comes Clean With Water

Jessica Marshall, Discovery News

Oil-Resistant | Discovery News Video

Aug. 21, 2009 -- Removing oily smudges from mirrors, countertops or fabrics usually requires some elbow grease... and a strong soap or solvent.

A new coating developed by Jeffrey Youngblood and colleagues at Purdue University promises that grease stains can be wiped away with plain old water.

Incorporating this material into cleaning products, paints or sealants could reduce the need for environmentally damaging solvents and phosphate-containing detergents, the researchers say.

Phosphate detergents can kill aquatic life by allowing algae and microbes to overgrow bodies of water, suffocating other animals by consuming the dissolved oxygen.

The new coating is made by binding a water-loving molecule to a Teflon-like molecule that repels oil. This pairing makes for a surface that prevents oil from sticking to it, while also allowing it to be wet by water.

"Most surfaces that repel oils are inherently very water repellent as well. This works great for making something 'non-stick', but when the surface does get dirty, it's basically impossible to clean the oil off without using soap," said polymer scientist Ryan Hayward of the University of Massachusetts Amherst.

"Youngblood's group has introduced a clever twist to this picture by directly incorporating soap-like components in their polymer coatings," he added.

"These materials are resistant to oils but at the same time can be easily wet by water, meaning that an oil-coated surface can be cleaned simply by rinsing with water. If these polymers can be made into robust coatings or fabrics, they could have real potential for reducing the amount of detergent that we use."

The first generation of the material was complicated and expensive to make. It took a graduate student about a week under stringent conditions to coat a piece of glass, Youngblood said.

The latest work simplifies the process, creating a compound that can be mixed straight into a window cleaner, for instance.

"We are learning that our [new products] are not as good as our original technology, but add other benefits in terms of ease of use," Youngblood said. "One might have to make a tradeoff. "

The best quality coating might be worth the effort to apply to a telescope or camera lens (the coating also has anti-fog properties), he explained. "For consumer products, we would have another system. It doesn't work as well, maybe doesn't last as long, but it's much cheaper to produce."

While the team continues to experiment with coating formulas, a product with a shorter lifetime might be good enough for use in a window cleaner where a consumer would apply it periodically, anyway, he suggested. "Every time people clean their windows, it's going to redeposit itself. "

Purdue Scientists Develop 'Self-Cleaning' Coatings that Repel Oil

By GreenerDesign Staff

WASHINGTON, DC — Purdue scientists working with polymers say they've developed "eco-friendly coatings" that can be applied in industrial and household settings to create surfaces that resist oil and can be cleaned with plain water, reducing the need for heavy duty detergents or solvents.

Jeffrey Youngblood, an assistant professor of Materials Engineering at Purdue University, provided a media briefing on the project yesterday at the 238th National Meeting of the American Chemical Society in Washington, D.C.

The polymer coatings, which can be applied to surfaces including glass and concrete, are 20,000 times thinner than a human hair and have two key layers: A bottom layer of polyethylene glycol, which attracts water, and an upper layer of a Teflon-like molecule that repels oil.

So when oil, whether in a machine shop or a kitchen, comes in contact with a concrete floor or a countertop coated with the substance, the surface resists the oil while attracting the water, said Youngblood in his presentation, which was videotaped.

"Water will just completely remove the oil, you don't need any soap," he said. "You prevent soaps from getting into the environment."

The substance can also be used to prevent fogging either by coating a surface with it or adding it to a product.

A graduate student added the substance to a glass cleaner and sprayed it on half his bathroom mirror, then the researchers turned on the shower taps and left the room. When they returned about 20 minutes later, half the mirror was fogged over, the other half was clear, said Youngblood, who also applied an early version of the stuff to his dive mask.

"It worked better than the commercial defogger, but not as good as spit," he said, adding that the formula has improved since.

So far the team has used glass, metals, ceramics, aluminum and cement as substrates. Youngblood said the researchers are also interested in the substance's application with plastics, nylon, resins and wood. In addition, they're looking into use of the material and fabrics to make the textiles stain resistant.

Youngblood said the coatings may be commercially available in a few years.

The role of polymers in the cleaning process is also being developed by scientists in the United Kingdom.

Earlier this year at the international Clean Show 2009 in New Orleans, researchers from the University of Leeds, who formed a cleaning company startup called Xeros Ltd., and Cambridge Consultants rolled out a proof-of-concept washing machine that launders clothes with reusable nylon polymer beads and cuts water consumption by as much as 90 percent.

In the Xeros model, the nylon polymer beads are released into a load of wash that has been slightly dampened to create steam, which in turn activates polarizing properties in the polymer beads that then bind to -- or capture -- dirt and stains.

^{Image by Aldridged, Dreamstime.com, via the American Chemical Society}

I've Seen The Future, And It’s Made of Mushrooms

Posted by Garret Ohm

I hate mushrooms. As a general rule, I don’t like any form of fungus, and absolutely detest the thought of ingesting it. But a pair of mechanical engineering students from Rensselaer Polytechnic Institute have come up with a killer technology that is making me rethink my disdain for shrooms. They’ve created Greensulate, a strong, low-cost biomaterial that replaces the expensive, non-biodegradable plastics and styrofoam used in modern packaging and wall insulation (two HUGE pollutants).

Here’s the short version of how the stuff works:

In a lab, workers grow mycelia, the roots of mushrooms that look like gobs of white and brown fiber. In place of dirt, the roots grow in agricultural by-products, which creates a series of intertwining fibers which give the product its rigidity. Then, they simply place the mixture in a mold and let it grow for a couple of weeks until it’s super dense (1 cubic inch has 8 MILES of fibers). After that they shove them in an oven to dry and presto, you’ve got a finished product.

The inventors have started a company called Ecovative Design to market the technology, and I think they’re really onto something. Just imagine if they’re able to form this product into low-cost, biodegradable auto body panels and other automotive components. Or counter tops. Or flooring. They could even conceivably figure out a way to make children’s toys out of the material. For my sake, I hope they stop short of making dishes and kitchen utensils out of them, though. I don’t eat ANYTHING that touches mushrooms. Blech.

Keep an eye on Ecovative on Twitter HERE.

Garret Ohm is a hybrid marketing/business development director. He loves cars, dogs, golf and has a strange fascination with helicopters. He blogs here.