Sugar-rubber tyre inches closer to the road

15:00 29 March 2010 by MacGregor Campbell

Even the most clapped-out jalopy could get a green upgrade thanks to a process that can turn plants into synthetic rubber for tyres – usually, the stuff is made from petroleum.

Isoprene is a synthetic version of natural rubber that is used primarily in tyres: it makes up as much as 27 per cent of new tyres, says Ilana Aldor, a chemist at Genencor, a company based in Silicon Valley. Because supplies of natural rubber cannot meet our demand for tyres, most isoprene is collected as a by-product of petroleum refining – and those supplies are under threat, says Aldor, because refining is getting better.

Now Genencor, working with tyre giant Goodyear, has found an alternative source. "We are successfully producing large amounts of bio-isoprene," says Aldor. Some has even been made into tyres to demonstrate the concept.

Engineered organisms

Aldor and colleagues took gene sequences for an enzyme that allows vines and trees like kudzu and poplar to synthesise isoprene, and inserted them into strains of the bacterium Escherichia coli and a fungus. The genetically engineered micro-organisms were able to feed on plant products such as glucose, sucrose, glycerol or plant oils to produce isoprene gas, which was then collected, condensed and purified.

Different combinations of micro-organism strain and feedstock are being tried to find the best yield. So far the set-up has produced 60 grams of isoprene gas per litre of feedstock broth in under 40 hours, says Aldor.

Proof of concept

Her colleague Joseph McAuliffe told New Scientist that although the technology won't be hitting the road for several years, there seems to be no reason why it can't be used to make tyres commercially.

"I think it's definitely feasible," says Adam Meadows, a chemist at green chemistry firm Amyris, based in Emeryville, California, who works on similar biochemical methods for making diesel from plant feedstocks. "They've demonstrated a nice proof-of-concept."

Although the production of bio-isoprene may be more sustainable than that of the petroleum-based version, bio-isoprene isn't free of environmental problems: neither compound is biodegradable.

(newscientist.com)