Wednesday, November 16, 2011

New process for manufacturing nanocellulose: Using nanocellulose to create novel composite materials

For some time now nanocellulose has been at the focus of a good deal of industrial and scientific interest as a novel biomaterial. Potential applications range from the creation of new kinds of commercially useful materials and uses in medical technology all the way to the food and pharmaceutical industries. Researchers with Switzerland's Empa research institute have now developed a manufacturing process for nanocellulose powder, the raw material for creating polymer composites which can be used, for example, in lightweight structures for the car industry or as membrane and filter material for biomedicinal applications.

Cellulose is a biopolymer consisting of long chains of glucose with unique structural properties whose supply is practically inexhaustible. It is found in the cell walls of plants where it serves to provide a supporting framework -- a sort of skeleton. Cellulose is extremely strong in tension and can be chemically modified in many ways, thereby changing its characteristics. It is also biodegradable. In the search for novel polymer materials with certain desirable characteristics material scientists have developed such substances as high performance composites in which nanofibers of cellulose are embedded. In the form of lightweight structural material, these composites have similar mechanical properties to steel, while as nanoporous "bio"-foam they provide an alternative to conventional insulating materials.

The ideal lightweight structural material

Classical cellulose chemistry on the industrial scale is primarily used in the wood pulp, paper and fiber industry. Commercial research is currently focused on isolating and characterizing cellulose in the form of nanofibers. So-called nanocellulose consists of fibers or crystals with a diameter of less than 100 nm. Material scientists hope to be able to use nanocellulose to create new lightweight materials boasting high mechanical strength -- in short the ideal material for creating lightweight structures.

The cellulose experts in Empa's Wood Laboratory isolated cellulose nanofibers from wood pulp. These are several micrometers long but only a few nanometers thick and are closely interlinked. The fibers have an extremely large surface area on which chemical-physical reactions with substances such as water, organic and inorganic chemicals and polymer compounds can occur. Cellulose nanofibers can therefore be used as stable, extremely reactive raw materials for technical applications while boasting the additional advantages of being biologically produced and biodegradable. Such applications include reinforcing (bio-)polymers to create very promising, environmentally safe, lightweight construction material for the car industry, as well as membrane or filter materials for applications in packaging and biomedicine.

The solution lies in chemical modification

Nanocellulose isolated from wood pulp is initially in the form of a water-based suspension. If the material dries out the cellulose fibers stick together forming rough clumps and it loses its outstanding mechanical properties. For this reason the Empa researchers sought to develop a process which allowed them to dry nanocellulose without it clumping and becoming rough. To achieve this, the cellulose was treated using a technique which is easily implemented on a large scale and is also completely harmless, even being suitable for applications in the food industry. The method prevents the cellulose fibrils from forming clumps and sticking together

The results are worth looking at: after being re-dispersed in water the dried nanocellulose powder boasts the same outstanding properties as undried, unmodified cellulose. This makes the new product an attractive alternative to conventional cellulose suspensions for the synthesis of bio-nanocomposite materials. Suspensions currently in use consists of over 90% water which causes the transport costs to explode and increases the danger of degradation by bacteria or fungi. In addition aquatic cellulose suspensions are laborious to work with since usually in the course of chemical processing solvents must be exchanged.

Empa Research Prize 2011 goes to Christian Eyholzer

The work on developing the new manufacturing process and identifying applications for nanocellulose in various biopolymers was recently recognized with the award of the Empa Research Prize 2011. In a collaborative project with the "Lulea University of Technology," Sweden, Empa researcher and PhD student Christian Eyholzer and his co-workers used the novel nanocellulose powder to reinforce adhesives, hydrogels and biodegradable synthetics. After completing his doctoral dissertation Eyholzer left Empa and is currently employed by Sika as project leader in the product development department.

Story Source:

The above story is reprinted from materials provided by Empa. The original article was written by Nina Baiker.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Chiral metal surfaces may help to manufacture pharmaceuticals

New research shows how that lack mirror symmetry could provide a novel approach towards manufacturing pharmaceuticals.

These ‘intrinsically chiral’ metal surfaces offer potential new ways to control chiral chemistry, pointing to the intriguing possibility of using heterogeneous catalysis in drug synthesis. Such surfaces could also become the basis of new biosensor technologies.

A chiral object, such as your hand, is one that cannot be superposed on its mirror image. Chirality is fundamental in biochemistry. The building blocks of life – amino acids and sugars – are chiral molecules: their molecular structures can exist in either “left-handed” or “right-handed” forms (or “enantiomers”).

A living organism may respond differently to the two enantiomers of a chiral substance. This is crucially important in the case of pharmaceutical drugs, where the therapeutic effect is often tied strongly to just one enantiomer of the drug molecule. Controlling chirality is therefore vital in pharmaceutical synthesis.

Research into controlling chiral synthesis focuses mainly on using homogeneous catalysts, where the catalyst is in the same phase as the reactants and products, such as a liquid added to a liquid-phase reaction. However, this poses significant practical challenges in recovering the valuable catalyst material from the mixture. To avoid this problem, an attractive alternative would be heterogeneous catalysis over a solid – the type of catalysis used in catalytic converters in car exhaust systems, as well as in industrial Haber-Bosch synthesis of ammonia and Fischer-Tropsch synthesis of synthetic fuel, for example. The question then is how to achieve enantiomer-specific effects at a surface.

To help answer this question, scientists at the University of Cambridge have been probing the spontaneous self-organization of a simple chiral amino acid, alanine, into regular molecular arrays on copper single-crystal surfaces. Thanks to a powerful scanning tunnelling microscope, capable of resolving individual atoms and molecules, their work is revealing the various manifestations of chirality that occur, giving important clues to how they arise, and how they might be controlled and exploited.

Dr Stephen Driver, of the Department of Chemistry at the University of Cambridge, who led the experimental work, said: “We set out to investigate two distinct scenarios. In one scenario, the surface is non-chiral, so any chirality that we see can only arise from the chirality of the alanine molecule. In the other scenario, we move to a surface that is intrinsically chiral. Now the question becomes: do the two enantiomers of alanine behave differently on this chiral surface?”

On the non-chiral surface, the researchers found that alanine can self-organise into either of two patterns. In one of these, the self-organisation is driven by hydrogen bonding between the molecules, while the chiral centre has no discernable impact on the regular array. In the other structure, a network of long-range chiral boundaries punctuates the array, and the boundary chirality switches with molecular chirality.

Driver explained: “The implication is that the chiral centre is having a direct influence on the packing of two alanine neighbours at the boundary, and that the chirality of this pair propagates to the next pair and the next and so on, so that the chiral boundary is built up over a long range.”

The chiral surface is created simply by choosing a surface orientation that lies away from any of the bulk planes of the metal crystal. When the researchers added alanine, they found that the surface changes its local orientation, forming nanometre-scale facets. The two enantiomers of alanine self-organise into different chiral patterns: a strong, enantiomer-specific structural effect. This “proof of principle” could potentially be exploited in chiral recognition, in chiral synthesis (forming a chiral product from non-chiral reactants), and in chiral separations.

Driver added: “It looks like alanine can shape a comfortable, chiral bonding site for itself. The copper surface has the flexibility to adapt itself to the shape of the alanine molecule, and this shape is different for the two different molecular enantiomers.”

The results imply that certain surface orientations will form stable, ordered structures with one molecular enantiomer but not the other: exactly the right conditions to promote chiral chemical effects.

Professor Sir David King, former Chief Scientific Advisor to the UK Government and current Director of the Smith School of Enterprise and the Environment at Oxford, brought together the team carrying out this research. “These results are very exciting,” said King. “Tailoring the right surface to the right molecule should lead to strong enantiospecific effects. We see a real basis here for a breakthrough technology in the pharmaceuticals sector. It’s something that pharma companies should be taking a close interest in.”

The Cambridge team’s findings are published in Topics in Catalysis.

More information: Image credit: Steve Driver

Provided by University of Cambridge (news : web)

Graphene grows better on certain copper crystals

New observations could improve industrial production of high-quality graphene, hastening the era of graphene-based consumer electronics, thanks to University of Illinois engineers.

By combining data from several imaging techniques, the team found that the quality of graphene depends on the crystal structure of the copper substrate it grows on. Led by electrical and computer engineering professors Joseph Lyding and Eric Pop, the researchers published their findings in the journal Nano Letters.

"Graphene is a very important material," Lyding said. "The future of electronics may depend on it. The quality of its production is one of the key unsolved problems in nanotechnology. This is a step in the direction of solving that problem."

To produce large sheets of graphene, methane gas is piped into a furnace containing a sheet of copper foil. When the methane strikes the copper, the carbon-hydrogen bonds crack. Hydrogen escapes as gas, while the carbon sticks to the copper surface. The carbon atoms move around until they find each other and bond to make graphene. Copper is an appealing substrate because it is relatively cheap and promotes single-layer graphene growth, which is important for electronics applications.

"It's a very cost-effective, straightforward way to make graphene on a large scale," said Joshua Wood, a graduate student and the lead author of the paper.

"However, this does not take into consideration the subtleties of growing graphene," he said. "Understanding these subtleties is important for making high-quality, high-performance electronics."

While graphene grown on copper tends to be better than graphene grown on other substrates, it remains riddled with defects and multi-layer sections, precluding high-performance applications. Researchers have speculated that the roughness of the copper surface may affect graphene growth, but the Illinois group found that the copper's crystal structure is more important.

Copper foils are a patchwork of different crystal structures. As the methane falls onto the foil surface, the shapes of the copper crystals it encounters affect how well the carbon atoms form graphene.

Different crystal shapes are assigned index numbers. Using several advanced imaging techniques, the Illinois team found that patches of copper with higher index numbers tend to have lower-quality graphene growth. They also found that two common crystal structures, numbered (100) and (111), have the worst and the best growth, respectively. The (100) crystals have a cubic shape, with wide gaps between atoms. Meanwhile, (111) has a densely packed hexagonal structure.

"In the (100) configuration the carbon atoms are more likely to stick in the holes in the copper on the atomic level, and then they stack vertically rather than diffusing out and growing laterally," Wood said. "The (111) surface is hexagonal, and graphene is also hexagonal. It's not to say there's a perfect match, but that there's a preferred match between the surfaces."

Researchers now are faced with balancing the cost of all (111) copper and the value of high-quality, defect-free graphene. It is possible to produce single-crystal copper, but it is difficult and prohibitively expensive.

The U. of I. team speculates that it may be possible to improve copper foil manufacturing so that it has a higher percentage of (111) crystals. Graphene grown on such foil would not be ideal, but may be "good enough" for most applications.

"The question is, how do you optimize it while still maintaining cost effectiveness for technological applications?" said Pop, a co-author of the paper. "As a community, we're still writing the cookbook for graphene. We're constantly refining our techniques, trying out new recipes. As with any technology in its infancy, we are still exploring what works and what doesn't."

Next, the researchers hope to use their methodology to study the growth of other two-dimensional materials, including insulators to improve graphene device performance. They also plan to follow up on their observations by growing graphene on single-crystal copper.

"There's a lot of confusion in the graphene business right now," Lyding said. "The fact that there is a clear observational difference between these different growth indices helps steer the research and will probably lead to more quantitative experiments as well as better modeling. This paper is funneling things in that direction."

Lyding and Pop are affiliated with the Beckman Institute for Advanced Science and Technology at the U. of I. The Office of Naval Research, the Air Force Office of Scientific Research, and the Army Research Office supported this research.

Story Source:

The above story is reprinted from materials provided by University of Illinois at Urbana-Champaign.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Joshua D. Wood, Scott W. Schmucker, Austin S. Lyons, Eric Pop, Joseph W. Lyding. Effects of Polycrystalline Cu Substrate on Graphene Growth by Chemical Vapor Deposition. Nano Letters, 2011; : 111004083339002 DOI: 10.1021/nl201566c

Recycling thermal cash register receipts contaminates paper products with BPA

Kurunthachalam Kannan and Chunyang Liao explain that manufacturers produce more than 8 billion pounds of BPA worldwide every year. Research links BPA with a variety of harmful health effects. BPA has been used in plastic water bottles, the lining of food cans and a variety of other products. But how much do non-food sources contribute to humans' daily BPA exposure? BPA coats the surfaces of thermal receipts, where it acts as a developer for the printing dye. To see whether this source of BPA was a concern, the researchers analyzed hundreds of samples of thermal cash register receipts and 14 other types of paper products from the U.S., Japan, Korea and Vietnam.

They found BPA on 94 percent of the receipts. The only receipts with that were BPA-free were those from Japan, which phased out this use of BPA in 2001. BPA was in most of the other types of paper products, with tickets, newspapers and flyers having the highest concentrations. But these levels still paled in comparison to BPA on receipts, which the study said are responsible for more than 98 percent of consumer exposure to BPA from paper. The researchers estimate that receipts contribute about 33.5 tons of BPA to the environment every year in the U.S. and Canada. They note that handling of paper products can contribute up to 2 percent of the total daily BPA exposures in the general population, and that fraction can be much higher in occupationally exposed individuals.

More information: Widespread Occurrence of Bisphenol A in Paper and Paper Products: Implications for Human Exposure, Environ. Sci. Technol., Article ASAP. DOI: 10.1021/es202507f

Bisphenol A (BPA) is used in a variety of consumer products, including some paper products, particularly thermal receipt papers, for which it is used as a color developer. Nevertheless, little is known about the magnitude of BPA contamination or human exposure to BPA as a result of contact with paper and paper products. In this study, concentrations of BPA were determined in 15 types of paper products (n = 202), including thermal receipts, flyers, magazines, tickets, mailing envelopes, newspapers, food contact papers, food cartons, airplane boarding passes, luggage tags, printing papers, business cards, napkins, paper towels, and toilet paper, collected from several cities in the USA. Thermal receipt papers also were collected from Japan, Korea, and Vietnam. BPA was found in 94% of thermal receipt papers (n = 103) at concentrations ranging from below the limit of quantitation (LOQ, 1 ng/g) to 13.9 mg/g (geometric mean: 0.211 mg/g). The majority (81%) of other paper products (n = 99) contained BPA at concentrations ranging from below the LOQ to 14.4 µg/g (geometric mean: 0.016 µg/g). Whereas thermal receipt papers contained the highest concentrations of BPA (milligram-per-gram), some paper products, including napkins and toilet paper, made from recycled papers contained microgram-per-gram concentrations of BPA. Contamination during the paper recycling process is a source of BPA in paper products. Daily intake (DI) of BPA through dermal absorption was estimated based on the measured BPA concentrations and handling frequency of paper products. The daily intake of BPA (calculated from median concentrations) through dermal absorption from handling of papers was 17.5 and 1300 ng/day for the general population and occupationally exposed individuals, respectively; these values are minor compared with exposure through diet. Among paper products, thermal receipt papers contributed to the majority (>98%) of the exposures.

Provided by American Chemical Society (news : web)

Industrial by-products upgraded into fuel

Researchers have achieved good results in using waste and other excess products from industry to develop new and innovative fuels for transport. Working within the Academy of Finland's research programme Sustainable Energy (SusEn), researchers have studied the processing of both biobutanol and biogas into transport fuels. Biobutanol can be produced from by-products of the food industry and the pulp and paper industry, which makes it a suitable candidate for replacing petrol as a fuel. Methane derived from biogas is also a top candidate for a fuel substitute, as shown in life-cycle assessment, which measures the entire production chain.

"Butanol is a very energy-efficient alternative and, like ethanol, lends itself well for industrial-scale production," says Professor Ulla Lassi from the University of Oulu, who has been working on a research project investigating the use of biobutanol as a transport fuel. Butanol production is a microbiological process where raw material is converted into sugars and further processed using microbes. The microbes efficiently turn carbon compounds into butanol. Butanol contains more carbon than ethanol does and is therefore also more energy-efficient.

Lassi's project has also studied the production of butanol via chemical synthesis, which uses novel catalyst materials to convert compounds such as glycerol, methanol or ethanol into alcohols such as butanol, pentanol and alcohol mixes. These are directly suitable as liquid fuels. According to Lassi, using glycerol in fuel production could be quite cost-efficient, as it is a by-product of biodiesel.

There are a number of challenges in the microbiological production of butanol. One of the main challenges concerns the digestion of the raw material to fermentable sugars. In addition, the multi-stage fermentation is in itself a very complex process. Another major challenge is that the fermentation process is inhibited by high solvent contents, which combined with instability in solvent production may also cause a drop in microbial activity.

Lassi explains: "Recent breakthroughs in butanol fermentation techniques have partly solved these problems. However, if we want to produce new liquid fuels, we need completely new chemical synthesis routes and catalyst development."

The research project investigating the production of biobutanol involves researchers from the University of Oulu and Abo Akademi University.

Once landfill gas, now fuel

Another research project within the SusEn research programme has looked at the use of biogas as a transport fuel. As a joint Finnish-Chilean effort, the researchers studied the upgrading of landfill gas into fuel. "In recent years, interest in using biogas technology in the utilisation of industrial by-products for energy purposes has increased considerably. Some countries have already introduced this technology on a large scale," says Professor Jukka Rintala, the principal investigator of the project.

Biogas can be produced from many different materials ranging from biodegradable waste to energy crops. "The biogas produced in this process is a versatile source of energy. It can be used for heat and electricity, be processed into vehicle fuel or fed into the natural gas grid. In addition, the residual material, the so-called digestate, from the process can be used as fertilizer or soil conditioner," Rintala explains.

Methane derived from biogas has been shown to be one of the most suitable candidates for use as biofuel, thanks to its sustainable production chain. Methane also meets the EU's criteria for sustainable biofuels, which will take effect in a few years' time.

The experiments in Rintala's project were carried out at the Mustankorkea Waste Treatment Facility in Jyväskylä and they particularly focused on the fate and removal of trace compounds of biogas. "Biogas can be used as a biofuel once its methane content is raised above 95 per cent. In our research, we used water absorption, which yielded a methane content of 80-90 per cent. The rest is carbon dioxide and nitrogen."

Nitrogen does not cause any damage to car engines, but it does lower the energy content of biogas. "To reach a higher methane content through this process, we should prevent the access of nitrogen in the gas collection system in the landfill. Carbon dioxide does not damage engines either, but it lowers the energy value of biogas," says Rintala.

Rintala would like to see more research on the effects of process parameters on the costs of biogas upgrading and the effects of pressurisation on compound removal. "As a rule, the only criterion for biomass is that it can be broken down by microbes under oxygen-free conditions. Of course, the composition of feedstocks does affect the composition of the biogas produced and also the chosen method of purification. Landfill gases are generally thought of as being the most difficult ones to upgrade into fuel."

Story Source:

The above story is reprinted from materials provided by Suomen Akatemia (Academy of Finland), via AlphaGalileo.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.