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EMPA researchers have 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.
According to EMPA, 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. They say 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 nanofibres 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.
EMPA explain that classical cellulose chemistry on the industrial scale is primarily used in the wood pulp, paper and fibre industry. Commercial research is currently focused on isolating and characterising cellulose in the form of nanofibres. They say material scientists hope to be able to use nanocellulose to create new lightweight materials boasting high mechanical strength.
EMPA say that cellulose nanofibres can 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.
They say that nanocellulose isolated from wood pulp is initially in the form of a water-based suspension. If the material dries out the cellulose fibres 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
Results found that 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.
The work on developing the new manufacturing process and identifying applications for nanocellulose in various biopolymers was recently recognised 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.
Fraunhofer IWM Researchers Set Out to Develop Green EV Charging Stations
Researchers at the Fraunhofer Institute for Mechanics of Materials IWM in Halle, Germany, want to improve the green credentials of EV charging points, which usually feature a steel- or aluminum-clad housing by developing an alternative in wood-plastic composites (WPC).
In collaboration with their industrial partner, Bosecker Verteilerbau Sachsen, Fraunhofer are developing an alternative solution based on eco-friendly materials. Their idea is to replace the steel cladding that protects cables, power outlets and electronic switchgear with honeycomb panels made of a wood-plastic composite (WPC). They say that, at present, the main application for this type of reconstituted wood product is weather-resistant decking for patios.
WPC is a natural fibre composite made up of 70 parts of cellulosic wood fibre derived from sustainable resources to 30 parts of thermoplastic polypropylene. Fraunhofer explain that its advantages, apart from the high proportion of sustainable raw materials, are that it is 100% recyclable and contains no tropical timber. Wood-plastic composites can be repeatedly recycled into new products and have a neutral carbon footprint. As Sven Wüstenhagen, one of the IWM researchers in Halle, explains “Trees extract huge quantities of carbon dioxide from the atmosphere as they grow, and sequester carbon in their ligneous Fibres. It is therefore probable that the use of WPC in this new application will result in lower CO2 emissions compared with the use of steel.”
Another advantage of the composite material, according to Wüstenhagen, is that its production is more energy-efficient than that of steel or other metal cladding materials. WPC is produced using an extrusion process that involves melting a mixture of wood fibres and thermoplastic resin under high pressure and at high temperature and feeding the resulting viscous product into a continuous mould. Fraunhofer say that with modern processing technologies, the fibres can be added to the mixture in their natural state, without first being transformed into granulate, thus eliminating an energy-intensive intermediate stage and preserving the quality of the fibres. Because wood has a high thermal sensitivity, it has to be processed at temperatures below 200 degrees Celsius.
The housings are manufactured in the form of modular components that can be clipped together as required to create a wide variety of different designs, thus allowing them to blend in with the surrounding architecture. Their modular structure also enables the composite panels to be removed easily during repairs. Industrial design expert Wüstenhagen is already thinking about other possible new applications for the WPC components “They could be used, for instance, to construct street furniture such as park benches or bus shelters. That’s one of our next objectives. Another of our ideas is to integrate functional elements such as cable holders and cable management systems in the components for EV charging stations. This is a viable proposition because WPC can be formed into almost any shape, unlike the metal sheeting used in currently available housings.”
The WPC cladding must be shatterproof and sufficiently elastic to withstand impact without damage, and it must be capable of resisting wide variations in temperature, high levels of humidity and prolonged UV exposure. The researchers are therefore testing samples of the material in a climate chamber to assess its resistance to extreme temperature conditions and determine which additives or types of coating provide the best weather protection. The Fraunhofer researchers have almost completed their first prototype of the new WPC housing and are about to start outdoor testing. Sven Wüstenhagen and his team are confident that it won’t be long before the first “all-green” EV charging stations appear on our streets.
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