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20 November 2014

New Materials, in the Trash

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With the growing public awareness that the world that we inhabit does not have infinite resources for exploitation, the incentives are increasing for research into new ways to recycle products previously thought of as waste, in some cases replacing raw materials that can be put to other uses.

An example of this can be found in a recent study on the manufacture of bioplastics from vegetable waste. With the intention of eliminating  dependence oil in the manufacture of plastics, and also to enhance biodegradation, the chemical industry has been developing new compounds from vegetable material. Starch, cellulose and other biopolymers are used as starting points in the chemical processes that will result in bioplastics, and these base substances are obtained from corn, peas, potatoes, cotton, hemp and wood, with the consequent negative impact of diverting raw materials to other uses and the necessary increase in the land area devoted to cultivating these crops.

Bioplastics produced from cocoa beans. Italian Institute of Technology

Ilker Bayer of the Italian Institute of Technology in Genoa (Italy) has developed a method of producing bioplastics from plant waste such as rice husks, cocoa pods and the stems of spinach or parsley. The researcher was working on a modification of a method for producing cellophane from cellulose cotton and hemp and found he could obtain a moldable plastic mass by dissolving plant material in trifluoroacetic acid, without the treatment normally used.

This gave him the idea of investigating the characteristics of bioplastics using alternative cellulose sources and found that the material had different properties depending on the source material. Thus, the bioplastic obtained from the stems of spinach was more flexible than that derived from rice, for example. In this way, Bayer suggests, there may be a new use for the parts “that we don’t want to eat”, although much research remains to make this technology an economically viable substitute to the use of refined vegetable products.

The US company Newlight Technologies also manufactures plastics from recycled materials, with the particularity that the material they reuse is a greenhouse gas: the methane produced by bovine flatulence on farms or by the decomposition of organic matter in covered landfills. They call it AirCarbon and the computer maker Dell has already adopted it for their packaging. The technology in this case is to use the carbon present in the methane and combine it in a series of chemical processes, thanks to a biocatalyst developed by Newlight, to form a thermoplastic that is 60% composed of elements from the methane and 40% by oxygen from the air. According to the manufacturers, the properties are the same as those that are made from petroleum.

Dell uses plastic Newlight AirCarbon

Obsolescence recycled

If technology can provide new forms of recycling, technological development can also make objects now in use become obsolete and start piling up in landfills. An example of this may be that of car batteries, which nowadays are recycled. 90% of the lead recovered from the processing of spent batteries is used in the manufacture of new batteries of the same type. However, the automotive industry is moving in the direction of replacing these lead batteries with more efficient lithium ion ones, meaning that the previously recycled lead will become a potential environmental pollutant.

Angela Belcher, professor in the departments of Energy and Materials Science and Biological Engineering at the Massachusetts Institute of Technology (USA) estimates that over 200 million of these lead acid batteries will be accumulated only in the United States. And it will be partly their fault because this research group is dedicated to obtaining better and more efficient lithium batteries, including through genetic engineering. Fortunately, they are also working on the solution. In an article published in July, they detail how to use lead batteries to manufacture solar panels.

A new experimental type of photovoltaic cell uses a lead compound with a perovskite crystal structure as a material that absorbs light rays. This material is undergoing further development in terms of improved efficiency, and has already surpassed the established technologies based on solar cells with a thin film of silicon. Apart from its potential, the main advantage of perovskite solar cells is the reduced manufacturing cost, but they have the drawback of requiring lead, itself a highly contaminating metal and with an environmentally damaging extraction.

Christine Daniloff / MIT

Belcher’s work demonstrates that it is feasible to take the lead from used car batteries and use it for manufacturing such solar cells. According to his analysis, the lead from a single battery can be used to manufacture enough solar energy to supply 30 houses. And when these solar panels need to be replaced at the end of their life, the lead they contain can be recycled again.

From being partly responsible for climate change, to helping to mitigate it. This is the virtuous circle of new recycling technologies.

 Ventana al Conocimiento (Knowledge Window)

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