Monday, October 24, 2011

No need for old tyres to be an environmental hazard thanks to new recycling technology

A new recycling process could be the answer to alleviating the environmental burden of old tyres.

Researchers with Deakin University’s Institute for Technology Research and Innovation worked with industry partner VR TEK Global to develop a new cost-effective and environmentally friendly solution for turning old tyres into high quality ingredients for the manufacture of new rubber products.

“What we have developed is a significant breakthrough in tyre that is superior to the current practices of shredding and burying tyres in landfill, burning tyres or recycling them into low quality materials of limited use,” explained Deakin research engineer Chris Skourtis.

“Our process does not rely on chemicals and uses less power—making it more environmentally friendly. It also results in high quality ingredients that can replace virgin and synthetic rubbers in the manufacture of products such as new tyres, car parts, insulation materials, conveyor belts and ashphalt additive for roads.”

Each year more than 20 million tyres in Australia, and one billion world-wide, reach the end of their working lives. Only a small percentage of these tyres are recycled with most making their way into landfill; placing a burden on the environment and human health.

“There is a world-wide need to address the issue of disposing of end-of-life tyres in a responsible, manner,” Mr Skourtis said.

“Tyres simply dumped or placed in landfill are known to leach harmful chemicals into the environment; cause fires; and provide a perfect breeding ground for pests like mosquitoes and rats.

“We have come up with a way of giving new life to old tyres that should eliminate the need for them to end up in landfill.”

The Deakin researchers, led by Professor Qipeng Guo, developed a small scale facility at the University’s Waurn Ponds Campus to test and refine the recycling technology developed and patented by VR TEK Global.

“We now have a technology that is far better than any other tyre recycling processes,” Mr Skourtis explained.

“First, the tyres are segmented in a way that allows for each part to be treated differently which eliminates impurities and results in a higher quality end product. For example, the steel reinforcement in the tyre is separated without fragmenting, which is not common in current tyre recycling.
“We have then created an efficient means of devulcanising and activating the tyres into rubber powders for recycling into rubber products.

“Devulcanisation essentially reverses the chemical process used to create the tyres. This is normally done using environmentally harmful chemicals. We have developed a mechanical method that requires no chemicals.

“We have also developed a way of using ozone gas to activate the rubber powder which makes it more compatible with other materials. This extends the usability of the powder for producing a wider range of rubber and plastic products than currently possible.”

Provided by Deakin University

Two early stages of carbon nanotube growth discovered

 Boston College researchers have discovered two early-stage phases of carbon nanotube growth during plasma enhanced chemical vapor deposition, finding a disorderly tangle of tube growth that ultimately yields to orderly rows of the nanoscopic tubes, according to a report in the latest edition of the journal Nanotechnology.

By using a thin layer of catalyst, Professor of Physics Zhifeng Ren and researcher Dr. Hengzhi Wang discovered two previously overlooked stages of carbon nanotube growth, they report. The method yields a first stage where budding tubes appear randomly entangled, then a second stage of partially aligned tubes, then a third and final stage of tubes in full alignment, which is the standard used by researchers who produce carbon nanotubes for use in a range of materials and biomedical research.

"These growth phases are controlled by the thickness of the catalyst in use," said Wang. "Each stage, it turns out, has its own merit. Each stage has its own purpose."

In plasma enhanced chemical vapor deposition, carbon nanotubes are grown through the repeated accumulation of carbon atoms from the decomposition of gasses upon a catalyst particle, which creates multilayered carbon material on a substrate. Researchers have sought to create neatly aligned rows of millions of carbon nanotubes upon the substrates.

"We didn't know why we were seeing these nanotube configurations," said Ren, among the pioneers in the development of aligned carbon nanotubes. "This is really why you are a scientist. You see a new phenomenon and then you try to understand it."

Ren and Wang say that in the process of achieving the third stage of nanotube growth, the two earlier phases of growth have gone overlooked as each stage is etched away by the next application of plasma. Further masking these early-stage carbon nanotubes is the fact that they are not present when a thick catalyst is used, according to their findings.

The first stage tubes, produced in zero to four minutes, are described as a tangle of random large and small diameter carbon nanotubes. The second stage tubes, created in four to ten minutes, are generally smaller in diameter, but taller and only partially aligned.

Wang says that while these nanotubes are not in neat, orderly rows, they do have the advantage of offer a larger volumetric density and create a larger surface area, which could be an important development in the use of carbon nanotubes in heat transfer in thermal management. A potential application could involve in applying a thin coating of carbon nanotubes to an integrated circuit in order to draw away heat and efficiently cool the device.

After ten minutes of plasma etching, the early stage nanotubes have been washed away and the third stage tubes begin to emerge in tall, ordered rows upon the substrate. At this stage, the tubes themselves are shielded by makeshift "helmets" of catalyst particles, which effectively protect them during the last part of the growth process. Eventually, these last bits of catalyst are etched away as well.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Boston College.

Green discovery uses waste glass to clean up water

 A simple method to convert waste glass into a material which can be used to remove pollutants from contaminated water has been developed by Dr Nichola Coleman from the University of Greenwich's School of Science.

Nichola Coleman, a Senior Lecturer in Materials Chemistry at the university's Medway campus says: "The novelty of the research is that the glass can be recycled into something useful -- nobody has previously thought to use waste glass in this way."

She is finding a new use for the large quantities of coloured glass which are being stockpiled in the UK as there is less recycling demand for green and brown bottles than there is for clear bottles.

Her simple processing method creates tobermorite, a naturally occurring mineral, by combining waste glass with other basic materials.

A mixture of ground glass, lime and caustic soda is heated to 100 Celsius in a sealed stainless steel container to produce the tobermorite. The mineral, which can be produced as a powder or granules, can be used to absorb toxic heavy metals from water located beneath the ground or waste water streams.

Nichola is now looking at creating other types of filter and forming barriers that could prevent pollutants spreading from contaminated areas.

Details of the research have been published in the International Journal of Environment and Waste Management.

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The above story is reprinted (with editorial adaptations by ) from materials provided by University of Greenwich, via AlphaGalileo.

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Guidelines set out for obtaining more efficient latex

 Chemical engineer Ms Ines Mariz has presented guidelines for obtaining better quality and more efficient latex, in a PhD thesis defended at the University of the Basque Country (UPV/EHU). This involves a strategy which facilitates obtaining a more concentrated material without it losing its handling properties. In this way it is able to cover the substrate in question with fewer layers than is usual, it dries quicker, its formulation is more flexible and enables savings in storage and in transport.

The thesis is entitled High solids content low viscosity latexes with small particle size. A number of articles have also been published based on the research, including the one in Polymer Journal.

The research by Ms Mariz is based on the synthesis of latex with a high solid content. Latex is an aqueous emulsion and so, with this synthesis, the idea is to concentrate the greatest percentage of solid material possible within this emulsion, in order to obtain a more efficient and better quality material. Nevertheless, this concentration has to be limited as, otherwise, the latex will be too viscous and difficult to handle. Viscosity can be reduced by increasing the size of the particles used for the synthesis, but previous studies show that the largest ones are not those most propitious for forming films. As a consequence, the objective of this thesis was to set out a strategy for producing latex with high solid content and low viscosity, but with particles of a size less than 350 nanometres.

Unimodal and bimodal

Ms Mariz undertook several trials before obtaining the desired particle size distribution (PSD); i.e. that which maximises the packing (the compacted organisation) of the particles, always respecting the determined range of sizes.

In the first place, this mentioned synthesis with unimodal PSD (all particles of equal size) was investigated. Provoking polymerisation in a semi-continuous reactor, acrylic latexes were obtained which, with particles less than 350 nanometres, had a 61 wt% (concentration index) of solids content and with a reasonable viscosity. It was also verified that this type of latex stays stable with an ionic surfactant concentration (substance that facilitates and stabilises emulsions) less than 1 wt% with respect to the compound.

Subsequently, the synthesis of latex with high solids content with bimodal PSDs was tackled, i.e. those with particles of different sizes. In this way, the smallest particles cover spaces that are left between the largest particles, thus increasing the solids content and maximising packing.

The synthesis of unimodal latex is easier because the growth of the particles is known a priori. But, as regards bimodal particles, Ms Mariz had to design a strategy that would make this equally predictable. Thanks to this strategy, it was known a priori what polymerisation reaction (initiated in semi-continuous reactor) formula was required for obtaining the desired result: that is, a bimodal latex which, with particle sizes less than 350 nanometres, has high solid content (up to 70 wt%) and the lowest possible viscosity.

Practical application

Finally, water-based paints with latex of different PSDs have been formulated and it has been shown that particles sized less than 350 nanometres produce better results. Concretely, the latex with high solids content and small particle size has given rise to paints with enhanced properties, such as higher brilliance and elasticity and less drying time. They also show a low content in volatile organic components, given that a greater concentration of solids in the aqueous emulsion of the latex means, at the same time, a lower content of solvents.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Elhuyar Fundazioa.