Mix of graphene nanoribbons, polymer has potential for cars, soda, beer

Mix of graphene nanoribbons, polymer has potential for cars, soda, beer
A composite material created at Rice University is nearly impervious to gas and may lead to efficient storage of compressed natural gas for vehicles. A 65-micrometer-wide polymer film, photographed edge-on with an electron microscope, contains a tiny amount of enhanced graphene nanoribbons that present gas molecules a "tortuous path" to escape. Credit: Changsheng Xiang/Rice University

A discovery at Rice University aims to make vehicles that run on compressed natural gas more practical. It might also prolong the shelf life of bottled beer and soda.

The Rice lab of chemist James Tour has enhanced a polymer material to make it far more impermeable to pressurized and far lighter than the metal in tanks now used to contain the gas.

The combination could be a boon for an auto industry under pressure to market consumer cars that use cheaper . It could also find a market in food and beverage packaging.

Tour and his colleagues at Rice and in Hungary, Slovenia and India reported their results this week in the online edition of the American Chemistry Society journal ACS Nano.

By adding modified, single-atom-thick graphene nanoribbons (GNRs) to thermoplastic polyurethane (TPU), the Rice lab made it 1,000 times harder for to escape, Tour said. That's due to the ribbons' even dispersion through the material. Because gas molecules cannot penetrate GNRs, they are faced with a "tortuous path" to freedom, he said.

The researchers acknowledged that a solid, two-dimensional sheet of graphene might be the perfect barrier to gas, but the production of graphene in such bulk quantities is not yet practical, Tour said.

Mix of graphene nanoribbons, polymer has potential for cars, soda, beer
A close-up cross section of graphene nanoribbon-enhanced polymer shows the ribbons as white dots dispersed through the material, where they effectively block gas molecules from passing through. The material created at Rice University could be useful for storing compressed gas in a lighter, stronger vessel and for food packaging. Credit: Changsheng Xiang/Rice University

But graphene nanoribbons are already there. Tour's breakthrough "unzipping" technique for turning multiwalled carbon nanotubes into GNRs, first revealed in Nature in 2009, has been licensed for industrial production. "These are being produced in bulk, which should also make containers cheaper," he said.

The researchers led by Rice graduate student Changsheng Xiang produced thin films of the composite material by solution casting GNRs treated with hexadecane and TPU, a block copolymer of polyurethane that combines hard and soft . The tiny amount of treated GNRs accounted for no more than 0.5 percent of the composite's weight. But the overlapping 200- to 300-nanometer-wide ribbons dispersed so well that they were nearly as effective as large-sheet graphene in containing gas molecules. The GNRs' geometry makes them far better than sheets for processing into composites, Tour said.

They tested GNR/TPU films by putting pressurized nitrogen on one side and a vacuum on the other side. For films with no GNRs, the pressure dropped to zero in about 100 seconds as nitrogen escaped into the vacuum chamber. With GNRs at 0.5 percent, the pressure didn't budge over 1,000 seconds, and it dropped only slightly over more than 18 hours.

Stress and strain tests also found that the 0.5 percent ratio was optimal for enhancing the polymer's strength.

"The idea is to increase the toughness of the tank and make it impermeable to gas," Tour said. "This becomes increasingly important as automakers think about powering cars with natural gas. Metal tanks that can handle natural gas under pressure are often much heavier than the automakers would like."

Mix of graphene nanoribbons, polymer has potential for cars, soda, beer
An electron microscope image shows graphene nanoribbons embedded in a block copolymer. The composite material created at Rice University shows promise for containing compressed natural gas and for food packaging. Credit: Tour Group/Rice University

He said the material could help to solve long-standing problems in food packaging, too.

"Remember when you were a kid, you'd get a balloon and it would be wilted the next day? That's because gas molecules go through rubber or plastic," Tour said. "It took years for scientists to figure out how to make a plastic bottle for soda. Once, you couldn't get a carbonated drink in anything but a glass bottle, until they figured out how to modify plastic to contain the carbon dioxide bubbles. And even now, bottled soda goes flat after a period of months.

"Beer has a bigger problem and, in some ways, it's the reverse problem," he said. "Oxygen molecules get in through plastic and make the beer go bad." Bottles that are effectively impermeable could lead to brew that stays fresh on the shelf for far longer, Tour said.

Explore further

Unzipped nanotubes unlock potential for batteries

More information: pubs.acs.org/doi/abs/10.1021/nn404843n
Journal information: ACS Nano

Provided by Rice University
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Oct 10, 2013
NASA's replacement of the Space Shuttle was ultimately scrapped since it was based on composite fuel tanks that were evidently too far ahead of their time, so this is important work indeed.

Oct 11, 2013
Nice way to up the gas barrier.
Would this be applicable for hydrogen tanks as well? IIRC graphene is also impermeable to hydrogen, so the nanoribbons should also force the 'tortuous path' on hydrogen molecules
It will certainly be less effective than for nitrogen but it might be worth looking into.

On the down side I'm not sure I'd want this in plastic bottles. The micromechanical effects of crabon nanotubes in the body aren't well studied yet.

Oct 11, 2013
Recyclable? Biodegradable? Something to be considered if this is used in a way that ultimately leads to it being discarded. Particularly if it replaces something that is.

Oct 11, 2013
You got my attention!

Oct 11, 2013
Would this be applicable for hydrogen tanks as well?

To what ends though? Hydrogen has such a poor volumetric energy density that there's no real point in storing it in small tanks, and large tanks have to be built much thicker for structural reasons anyhow so the benefit of the graphene layer is diminished below its cost.

Oct 11, 2013
Graphene: carsinogen

Low-molecular-weight and carcinogenic compounds are known to be generated during the thermal reduction/exfoliation of graphite oxide. Such compounds are readsorbed onto the reduced material during the cooling process.

It's not the graphene, but the impurities from the process.

Oct 11, 2013
To what ends though?

Besides tanks there are pipe systems that need to convey hydrogen in various industrial sectors. If that coating can limit loss (and/or corrosion) that's a big boon.

Low-molecular-weight and carcinogenic compounds are known to be generated during the thermal reduction/exfoliation of graphite oxide.

I wouldn't be so much worried about the chemically toxic compounds. Nanotubes are pretty stable and I'd rather want some studies done on whether we'd be facing an 'asbestos'-like problem.

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