Foam polystyrene is a major environmental concern. It is used as a protective packaging for all sorts of products, but it is not biodegradable. Various manufacturers have experimented in making it more environmentally friendly, for example by incorporating cellulose and starch which microbes can break down, or by adding light-sensitive polymers that degrade in sunlight.
But Shanpu Ya and colleagues at the Polymer Science & Engineering College of Quingdao University of Science & Technology in China say these methods all have serious disadvantages. In particular, it takes too long time for polymers to break down in these ways, they claim.
Instead, they have developed a new approach that involves embedding water-absorbing resin particles about 5 micrometres in diameter throughout a chemical like styrene before it is polymerised to form a polystyrene-like material.
When the resulting solid comes into contact with water, the resin particles expand, reducing the polymer structure to a powder that should then biodegrade. The team says the rate of disintegration can even be controlled by altering the ratio of ingredients.
But a crucial factor, says the team, is that the resulting foamed polystyrene is cheaper than conventional materials and should therefore be readily adopted by cost-conscious companies that also want to be environmentally responsible.
Faster biodiesel production
Making biodiesel involves a reaction called transesterification in which the triglycerides and free fatty acids in oils from plants such as corn or linseed react with methanol to form methyl esters of 16-18 carbon atoms in length. Purified methyl esters can then be used in place of diesel fuel.
The problem is that transesterification is a slow process and currently the only way to speed it up is to cook chemicals in batch reactors at high temperatures and pressures. But having to produce fuel in batches also limits the rate at which biodiesel can be made.
Now Christian Fleisher and colleagues at Cornell University have developed a way of making biodiesel continuously, without the need to fill and empty batch reactors.
The trick is to produce the transesterification reaction as the necessary chemicals mix and flow through a pipe. The result is a system – known as a “plug flow” reactor – in which plant oil and methanol is added continuously at one end, while biodiesel flows out of the other.
Fleisher achieves this speed increase by using a catalyst, such as sodium hydroxide. So, instead of taking hours, the transesterification reaction then takes place in under three minutes. Fleisher has even set up a company called Biodiesel Technologies to commercialise the idea.
Plenty of RFID tags do not need a battery. Instead, each tag has an antenna connected to a circuit that converts an AC signal to a DC voltage when zapped with radio waves from a tag reader. The tag then uses this voltage to transmit a signal of its own. Essentially, the tags harvest energy from ambient radio waves.
But, since there is no shortage of radio signals on the airwaves, might it be possible to harvest a little of this too?
Marlin Mickle, an electrical engineer at the University of Pittsburgh, thinks so. His idea is to make tags with numerous antenna circuits, each tuned to absorb energy from a different radio frequency.
The antenna should thus harvest juice from commercial radio stations, public service transmitters, and anything else on the airwaves, producing clean and free energy from an as-yet untapped source. This method could be used to power other devices than RFID tags too.
Shuguang Zhang and colleagues at the Laboratory of Molecular Self Assembly at the Massachusetts Institute of Technology in the US want to use biologically-derived molecules to harvest light instead.
The plan is to isolate active light-harvesting molecules called chlorophyll from extremophile bacteria. These bacteria can withstand very high temperatures, so the resulting solar cells should be able to withstand high temperatures too.
The chlorophyll is attached to peptide molecules that can stick to zinc oxide nanowires on a semiconducting substrate. The entire assembly is then coated in a transparent polymer for protection. Energy is produced as electrons in the pigment are excited to higher energy levels.
The idea raises a number of questions: how efficiently can these bio-solar cells convert sunlight into electricity, how long would they last, and above all how cheaply can they be made? Zhang does not address these issues in his patent application but, since its early days for bio-solar cells, you can bet they’ll get better in the near future.