Wood pulp extract stronger than carbon fiber or Kevlar

 

Underlying structure of the wall of a wood cell, showing the substructure of load-bearing cellulose microfibrils

The Forest Products Laboratory of the US Forest Service has opened a US$1.7 million pilot plant for the production of cellulose nanocrystals (CNC) from wood by-products materials such as wood chips and sawdust. Prepared properly, CNCs are stronger and stiffer than Kevlar or carbon fibers, so that putting CNC into composite materials results in high strength, low weight products. In addition, the cost of CNCs is less than ten percent of the cost of Kevlar fiber or carbon fiber. These qualities have attracted the interest of the military for use in lightweight armor and ballistic glass (CNCs are transparent), as well as companies in the automotive, aerospace, electronics, consumer products, and medical industries.
Cellulose is the most abundant biological polymer on the planet and it is found in the cell walls of plant and bacterial cells. Composed of long chains of glucose molecules, cellulose fibers are arranged in an intricate web that provides both structure and support for plant cells. The primary commercial source for cellulose is wood, which is essentially a network of cellulose fibers held together by a matrix of lignin, another natural polymer which is easily degraded and removed.

Cellulose structures in trees from logs to molecules

Wood pulp is produced in a variety of processes, all of which break down and wash away the lignin, leaving behind a suspension of cellulose fibers in water. A typical cellulose wood fiber is only tens of microns wide and about a millimeter long.

Micrographs of cellulose fibers from wood pulp

The cellulose in wood pulp, when dry, has the consistency of fluff or lint - a layer of wood pulp cellulose has mechanical properties reminiscent of a wet paper towel. Not what you might expect to be the source of one of the strongest materials known to Man. After all, paper is made from the cellulose in wood pulp, and doesn't show extraordinary strength or stiffness.

Cellulose fibers and the smaller structures within them - a) fiber from wood pulp; b) microcrystalline cellulose; c) microfibrils of cellulose; d) nanofibrils of cellulose; e) cellulose nanocrystals from wood pulp; f) CNCs from sea squirts (the only animal source of cellulose microfibrils); and g,h) cellulose nanofibrils from other sources

Further processing breaks the cellulose fibers down into nanofibrils, which are about a thousand times smaller than the fibers. In the nanofibrils, cellulose takes the form of three-dimensional stacks of unbranched, long strands of glucose molecules, which are held together by hydrogen bonding. While not being "real" chemical bonds, hydrogen bonds between cellulose molecules are rather strong, adding to the strength and stiffness of cellulose nanocrystals.

The upper figure shows the structure of the cellulose polymer; the middle figure shows a nanofibril containing both crystalline and amorphous cellulose; the lower figure shows the cellulose nanocrystals after the amorphous cellulose is removed by acid hydrolysis

Within these nanofibrils are regions which are very well ordered, in which cellulose chains are closely packed in parallel with one another. Typically, several of these crystalline regions appear along a single nanofibril, and are separated by amorphous regions which do not exhibit a large degree of order. Individual cellulose nanocrystals are then produced by dissolving the amorphous regions using a strong acid.
At present the yield for separating CNCs from wood pulp is about 30 percent. There are prospects for minor improvements, but the limiting factor is the ratio of crystalline to amorphous cellulose in the source material. A near-term goal for the cost of CNCs is $10 per kilogram, but large-scale production should reduce that figure to one or two dollars a kilo.

Cross-sectional structure of various types of cellulose nanocrystals showing various crystalline arrangements of the individual cellulose polymer molecules (the rectangular boxes)

CNCs separated from wood pulp are typically a fraction of a micron long and have a square cross-section a few nanometers on a side. Their bulk density is low at 1.6 g/cc, but they exhibit incredible strength. An elastic modulus of nearly 150 GPa, and a tensile strength of nearly 10 GPa. Here's how its strength to compares to some better-known materials:

• Material...........................Elastic Modulus................Tensile Strength
• CNC......................................150 GPa.............................7.5 GPa
• Kevlar 49..............................125 GPa.............................3.5 GPa
• Carbon fiber.........................150 GPa.............................3.5 GPa
• Carbon nanotubes..............300 GPa............................20 GPa
• Stainless steel.....................200 GPa............................0.5 GPa
• Oak..........................................10 GPa.............................0.1 GPa

The only reinforcing material that is stronger than cellulose nanocrystals is a carbon nanotube, which costs about 100 times as much. Stainless steel is included solely as a comparison to conventional materials. The relatively very low strength and modulus of oak points out how much the structure of a composite material can degrade the mechanical properties of reinforcing materials.
As with most things, cellulose nanocrystals are not a perfect material. Their greatest nemesis is water. Cellulose is not soluble in water, nor does it depolymerize. The ether bonds between the glucose units of the cellulose molecule are not easily broken apart, requiring strong acids to enable cleavage reactions.
The hydrogen bonds between the cellulose molecules are also too strong in aggregate to be broken by encroaching water molecules. Indeed, crystalline cellulose requires treatment by water at 320° C and 250 atmospheres of pressure before enough water intercalates between the cellulose molecules to cause them to become amorphous in structure. The cellulose is still not soluble, just disordered from their near-perfect stacking in the crystalline structure.
But cellulose contains hydroxyl (OH) groups which protrude laterally along the cellulose molecule. These can form hydrogen bonds with water molecules, resulting in cellulose being hydrophilic (a drop of water will tend to spread across the cellulose surface). Given enough water, cellulose will become engorged with water, swelling to nearly double its dry volume.
Swelling introduces a large number of nano-defects in the cellulose structure. Although there is little swelling of a single CNC, water can penetrate into amorphous cellulose with ease, pushing apart the individual cellulose molecules in those regions. In addition, the bonds and interfaces between neighboring CNC will be disrupted, thereby significantly reducing the strength of any material reinforced with CNCs. To make matters worse, water can move easily over the surface/interfaces of the CNCs, thereby allowing water to penetrate far into a composite containing CNCs.
There are several approaches to make CNC composite materials viable choices for real world applications. The simplest, but most limited, is to choose applications in which the composite will not be exposed to water. Another is to alter the surface chemistry of the cellulose so that it becomes hydrophobic, or water-repelling. This is easy enough to do, but will likely substantially degrade the mechanical properties of the altered CNCs. A third approach is to choose a matrix material which is hydrophobic, and preferably that forms a hydrophobic interface with CNCs. While not particularly difficult from a purely chemical viewpoint, there is the practical difficulty that interfaces between hydrophobic and hydrophilic materials are usually severely lacking in strength.
Perhaps the most practical approach will simply be to paint or otherwise coat CNC composite materials in some material that keeps water away. For such a prize - inexpensive strong and rigid materials - we can be sure that innovations will follow to make the theoretical practical.
Source: US Forest Service

Graphene paper anodes pave way for faster charging Li-ion batteries

A scanning electron microscope image of the treated graphene oxide paper

While the lithium-ion batteries commonly used in electric cars are capable of storing a fairly large amount of energy, they’re not able to accept or discharge that energy very quickly. That’s why electric vehicles require supercapacitors, to speedily deliver energy when accelerating, or to store it when braking. Recently, however, researchers from New York’s Rensselaer Polytechnic Institute created a new anode material, that allows Li-ion batteries to charge and discharge ten times faster than those using regular graphite anodes. It could make EV supercapacitors unnecessary, and vastly shorten the charging time required by electronic devices.
The team, led by Prof. Nikhil Koratkar, started by creating a large sheet of graphene oxide paper. About the thickness of a piece of printer paper, it was made up of layered sheets of graphene (each graphene sheet being composed of a one one-atom thick layer of linked carbon atoms).
That paper was cut into smaller pieces, which were then subjected either to a laser, or the flash from a compact camera. In either case, the resulting flash of heat caused “mini explosions” to take place throughout the thickness of the paper, as oxygen atoms were expelled from its structure. The result of this carnage was graphene sheets that were full of flaws such as cracks, pores and voids. Additionally, the pressure exerted by the escaping oxygen forced the stacked layers of graphene apart from one another, resulting in a five-fold increase in the thickness of the paper.
When samples of this paper were tested for use as anodes, however, the marked decrease in charge and discharge times was noted. This was due to the fact that the lithium ions could enter (or exit) the anode at almost any point, using its imperfections as points of entry – by contrast, on graphite anodes, the ions can only enter at the sides and then slowly work their way into the middle.
The graphene oxide paper anodes were found to still work perfectly after more than 1,000 charge/discharge cycles. According to Koratkar, the sheets can be easily and inexpensively made in just about any shape or size, and the production process should be easy to scale up. His team’s next order of business is to match the anodes up with a high-power cathode, within a full Li-ion battery.
A paper on the research was recently published in the journal ACS Nano.
Source: Rensselaer Polytechnic Institute

Cryogenic treatment could cut coal-fired power plant emissions by 90%

   

Cooling the emissions from coal-fired power plants would significantly reduce the levels of dangerous chemicals entering the atmosphere

A team of physicists from the University of Oregon (UO) has calculated that cooling the emissions from coal-fired power plants would result in a reduction of the levels of dangerous chemicals entering the atmosphere, including CO2, by 90 percent. While cryogenic treatment would also see a 25 percent drop in efficiency, and therefore result in electricity costs increasing around a quarter, the researchers believe these would be offset by benefits to society, such as reductions in health-care and climate-change costs.
Previous studies, including one conducted in the 1970s by the Bechtel Corp. of San Francisco, have shown that cryogenic treatment of flue gases from coal-fired power plants can work. While the Bechtel study was looking at its effectiveness in capturing sulfur dioxide emissions, it also noted that large quantities of CO2 would also be condensed – something that didn’t warrant much attention back in the 70s but is of tremendous interest now.
Building on previous research he carried out in the 1960s into using cryogenic treatment technology as a way to remove odor-causing gases being emitted from a paper mill in Springfield, Oregon, UO physicist Russell J. Donnelly and his team have now composed a math-driven formula on an electronic spreadsheet that could be used by industry to weigh up the potential benefits of the technology.

UO physicist Russell J. Donnelly

The team’s paper says that CO2 condensed and captured as a solid would then be warmed and compressed into a gas that could be delivered via pipeline at near ambient temperatures to dedicated storage facilities that could be located hundreds of miles away. Additionally, other chemicals including sulfur dioxide, some nitrogen oxides and mercury would also be condensed so they could be safely removed from the gases emitted by the power plants.
The team’s calculations show that a cryogenic system would capture at least 90 percent on CO2, 98 percent of sulfur dioxide, and virtually 100 percent of mercury emissions. This is more than the capturing of 41 percent of sulfur dioxide and 90 percent of mercury emissions called for by the new mercury and air toxic standards (MATS) issued by the EPA in December 2011.
The team’s formula doesn’t take into account the cost of construction or retrofitting of the cooling machinery to existing power plants, which would be much larger than existing systems that use scrubbers – potentially as large as a football stadium. Nor does it take into account the cost of disposing of the captured pollutants. However, Donnelly thinks such systems are affordable, “especially with respect to the total societal costs of burning coal.”
“In the U.S., we have about 1,400 electric-generating unit(s) powered by coal, operated at about 600 power plants," Donnelly said. “That energy, he added, is sold at about 5.6 cents per kilowatt-hour, according to a 2006 Congressional Budget Office estimate. "The estimated health costs of burning coal in the U.S. are in the range of $150 billion to $380 billion, including 18,000-46,000 premature deaths, 540,000 asthma attacks, 13,000 emergency room visits and two million missed work or school days each year."
A separate, unpublished and preliminary economic analysis carried out by the team estimates that implementing large-scale cryogenic systems into coal-fired plants would see an overall reduction in costs to society of 38 percent through a sharp cut in associated health-care and climate-change costs.
The team’s paper appears in the journal Physical Review E.
Source: University of Oregon

   

A chemical engineer has created a 'food biorefinery' that converts used coffee grounds and other food waste into succinic acid

Every year, the individual stores that make up Starbucks Hong Kong produce almost 5,000 tons (4,536 tonnes) of used coffee grounds and unconsumed bakery items. As it stands now, all of that waste is incinerated, dumped in a landfill, or composted. In the future, however, it may be used to produce a key ingredient in laundry detergents, plastics, and many other items. A recent experiment showed that it can indeed be done.
The project began when the non-profit organization The Climate Group approached Dr. Carol S. K. Lin, a chemical engineer at the City University of Hong Kong. Lin’s team was already developing biorefineries, which are used to convert plant-based materials such as corn and sugar cane into biofuel or other products. In this case, The Climate Group was hoping that she could adapt the technology to process food waste from one of its corporate members, Starbucks Hong Kong.
In the resulting “food biorefinery,” the coffee grounds and baked goods are blended with a mixture of fungi. These fungi excrete enzymes, which break the carbohydrates in the food down into simple sugars. The food/fungi mixture is then transferred into a fermenting vat, where Actinobacillus succinogenes bacteria convert the sugars into succinic acid. It is that acid which is used in products such as detergents, plastics and medicines.
Potentially, the technology could greatly reduce the amount of food waste going into landfills and incinerators, plus it might also provide a more eco-friendly, sustainable alternative to the petroleum products currently used for plastic production. It could also provide the suppliers of the food waste with a source of income, and reduce the need for crops that are currently grown specifically to be biorefined.
Lin is now working on scaling up the process, and plans to test it in a pilot plant in Germany.
Source: American Chemical Society

New nanocrystals let solar panels generate electricity and hydrogen gas

   

Scientists have developed new nanocrystals that allow solar panels to generate both electricity and hydrogen gas

At first glance, photovoltaic solar panels are brilliant. They’re self-contained, need no fuel and so long as the sun is shining, they make lots of lovely electricity. The trouble is, they’re expensive to make, batteries are poor storage systems for cloudy days, and the panels have a very short service life. Now, Dr. Mikhail Zamkov of Ohio's Bowling Green State University and his team have used synthetic nanocrystals to make solar panels more durable as well as capable of producing hydrogen gas.
Solar panels using inorganic molecules as part of their construction have a short service life. The effects of UV radiation and heat degrade them, and they end up with a life of only about 20 years. Given how expensive it is to make solar panels, it’s not surprising that the cost per kilowatt is so much higher than conventional energy sources. In a video paper published in the Journal of Visualized Experiments (JoVE), Zamkov outlines his team’s process that involves replacing the organic molecules with two inorganic nanocrystals made from zinc selenide and cadmium sulfide, with a platinum catalyst added.

Structure of the nanocrystal (Image: Bowling Green State University)

According to Zamkov, "The main advantage of this technique is that it allows for direct, all inorganic coupling of the light absorber and the catalyst." In other words, these are very durable crystals compared to their organic counterparts. Not only are they less susceptible to heat and UV radiation, they also don’t suffer from degradation problems that plague their organic counterparts – where those are often irreversibly “poisoned” while in service, the nanocrystals can be recharged with a methanol wash.
The other advantage is that the nanocrystals don’t just generate electricity, they produce hydrogen gas as well. When immersed in water and exposed to light, the rod-shaped cadmium sulfide nanocrystal breaks down the water into hydrogen and oxygen.
Meanwhile, the nanocrystal – that is composed of stacked layers of zinc selenide – is photovoltaic and generates electricity. With this dual capacity, a panel made with the nanocrystals would not only generate power during the day, but also hydrogen to run a fuel cell at night.
Source: Journal of Visualized Experiments

Bioengineered bacteria could produce fuel from CO2

In the near future, genetically-altered Ralstonia eutropha bacteria could be used to convert carbon dioxide gas into fuel

Scientists at the Massachusetts Institute of Technology (MIT) have succeeded in genetically altering Ralstonia eutropha soil bacteria in such a way that they are able to convert carbon into isobutanol, an alcohol that can be blended with or even substituted for gasoline. It is hoped that once developed further, this technology could help reduce our reliance on fossil fuels, and lessen the amount of carbon dioxide released into the atmosphere by smoke stacks.
When their regular carbon food sources become scarce, R. eutropha ordinarily respond by synthesizing a type of polymer, in which they store whatever carbon they’re able to find. By “knocking out a few genes, inserting a gene from another organism and tinkering with the expression of other genes,” the team of MIT biologists were able to get the bacteria to produce isobutanol instead of that polymer.
Unlike certain other biofuels, isobutanol can be used directly as is, requiring no refining. The bacteria produce the alcohol continuously, releasing it into their fluid environment, from which it can be filtered. This differs from experiments conducted at other institutions, in which various types of bacteria have had to be destroyed in order to harvest the desired biofuel byproducts from their bodies.
Currently, the genetically modified microbes are getting their carbon from fructose. It is expected that with further alterations, however, they should be able to draw it from industrial carbon dioxide gas emissions. In fact, the scientists believe that properly bioengineered R. eutropha should be able to feed on carbon from almost any source, such as agricultural or municipal waste.
The team is now looking into increasing the bacteria’s isobutanol production levels, and scaling the technology up for use in industrial-scale bioreactors. If successful, such facilities should lessen the need for biofuel-dedicated crops such as corn, that compete with food crops for land and water.
In fact, MIT isn’t the first place to experience success in this area of research. In 2009, scientists from UCLA announced that they had been able to harvest isobutanol from CO2-consuming Synechoccus elongatus bacteria.
A paper on the Massachusetts research was published this month in the journal Applied Microbiology and Biotechnology.
Source: MIT

Scientists develop material that's harder than diamonds

Simulated structure of buckyballs and new super-hard material (Image: Lin Wang, Carnegie Institution of Washington)

Diamonds may be forever, but they aren’t what they were. True, they shine just as brightly and they’re as hard as ever, but scientists from the Carnegie Institution of Washington are giving them some competition. An international team led by Carnegie’s Lin Wang has discovered a new substance that is not quite crystalline and not quite non-crystalline, yet is hard enough to dent diamonds.
The new substance, which has yet to be named, is described by Wendy Mao, a Stanford University professor, as a “hybridization of crystalline and amorphous structures at an atomic level.” It was also something of a surprise to the Carnegie team.
The super-hard material started out as clusters of carbon-60 – the soccer-ball shaped molecules of carbon commonly known as "“buckyballs." These were mixed with m-xylene solvent, which is used in the manufacture of soft drink bottles. The mixture was then placed in a diamond cell anvil at the Argonne National Laboratory's Advanced Photon Source in Argonne, Illinois.

The diamond cell anvil was key to the experiment. This is a super high-pressure chamber made of two flat-faced diamonds. The buckyball/solvent mixture is placed in a cell between the diamonds and pressure is applied. As the diamonds squeeze together, the mixture is subjected to a pressure of, in this case, 600,000 atmospheres. Not surprisingly, the buckyballs were crushed. What was mildly surprising was that properties of the former buckyballs were altered until they became hard enough to dent the diamonds. That is not unprecedented, but what was very surprising was that the new substance retained its structure once the incredible pressure was removed. What was even more surprising was that it turned out to be a substance that no one had seen before.
All solid matter comes in one of two forms. Either it has an ordered, crystalline structure, like quartz or iron or diamonds, or it is non-crystalline or amorphous, like glass or gels. What this new substance has is both. If you apply massive pressure to buckyballs, you should get mashed buckyballs, but the m-xylene reacted with the carbon in some manner so that it retained a long-range, regular molecular structure. In other words, it retained the order of a crystal despite its crystalline structure being destroyed.
According to Wang, there is more here than a laboratory curiosity. “We created a new type of carbon material, one that is comparable to diamond in its inability to be compressed,” Wang said. “Once created under extreme pressures, this material can exist at normal conditions, meaning it could be used for a wide array of practical applications.”
Exactly what these applications are remain unknown, though it could be as a protective coating or find mechanical, electronic, and electrochemical uses.
Sources: Carnegie Institution for Science Stanford University

Mobile machine can make biofuel for military and humanitarian operations

A diagram of the process utilized by the Endurance Bioenergy Reactor 

 

Researchers at the U.S. Department of Energy's Argonne National Laboratory (ANL) have created a device called the Endurance Bioenergy Reactor (EBR) that can produce bioenergy on location, using waste from kitchens and latrines. The fuel can go directly into engines and generators without any need for refining, avoiding the complications of distribution and supply chains associated with fuel production. The researchers say the EBR can produce 25 to 50 gallons (94.6 to 189.2 liters) of biofuel a day from waste streams or processed cellulosic materials.
The EBR is based on an engineered photosynthetic bacterium, an organism that divides itself quickly. The technology combines plant enzymes with an efficient light-harvesting system that is found in abundance within these cells. The reactions from the combination of enzymes and bacteria result in fuel molecules that are foreign to the bacterium, which then expels them into a culture medium where they can be sequestered and separated from the fermentation broth. When it gets to that stage, the molecules can be used, without refining, as diesel surrogates in engines or generators.
Because of its inherent mobility, the system would be ideal for military settings, humanitarian activities in emergency zones, native peoples' villages, and in any other remote setting. The same version of the system can be used for military and civilian purposes. It is estimated that one EBR can fuel a generator that can charge up to 60 light- to medium-duty electric vehicles per day, with an estimated daily range of 50 miles (80.4 km).
The EBR is past its development phase, so all the team needs to do now is to deal with integration and scale-up issues. The researchers anticipate only a small investment will be necessary, somewhere between US$2 and $3 million.
The Argonne National Laboratory is part of the US Department of Energy. It’s a multidisplinary project that works on pressing national issues related to science and technology.
In the video below Argonne bioscientist Phil Laible talks about the EBR and its applications.
Source: ANL