Wetenschap - 13 september 2012

Flower power

At first sight, it looks like any other black rubber car tyre by Dutch tyre manufacturer Vredestein. Nothing revolutionary about that. But you look at it with fresh eyes when you hear that it is made of rubber obtained from dandelions. Made in Wageningen.

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Foto: .

The tyre rolled out of the laboratory at Apollo Vredestein in Enschede at the beginning of July: the first car tyre made of dandelion rubber in western Europe. This tyre is the tangible result of a big European project led by Hans Mooibroek of Biobased Products.
Natural rubber comes from the rubber tree Hevea brasiliensis and is a polymer of isoprene, a fairly simple hydrocarbon. Rubber consists of chains of more than 5000 of these building blocks. But the rubber tree is not the only plant that makes this stuff; the dandelion does it too. More precisely, the Russian dandelion Taraxacum koksaghyz, a relative of the dandelion common in the Netherlands. The roots of this plant contain rubber in the form of latex.
The Russians made tyres out of this latex during the second world war, when the import of hevea rubber was disrupted. The Americans made comparable efforts to extract rubber from the guayule plant. After the war, producers quickly reverted to using the cheaper and better quality hevea rubber.
Crisis
There are several reasons for the current renewed interest in alternative sources of rubber, explains project leader Mooibroek. Demand for rubber has soared in recent decades due to fast-growing economies such as China and India. And the price of rubber has kept pace. 'Through the economic crisis, though, the price has now dropped to less than three euros per kilo', says Mooibroek. 'But there is still a threat of a shortage.' The supply of rubber is therefore under constant pressure. The rubber tree originally comes from South America, until fungal infections wiped out the plantations there. Today's plantations in South-east Asia have hitherto been spared this fate. But the danger is never far away, according to Mooibroek. 'Manufacturers want a guaranteed supply. And they are quite prepared to pay a bit extra for that.'
Mooibroek's own interest in the dandelion as an alternative source of rubber dates back to 1996 when, together with an American colleague, he wrote an article giving an overview of the situation in the rubber industry. The conclusion was that if Europe wanted to do something with natural rubber, its best bets would be the Russian dandelion and guayule. Seven years later, Mooibroek was asked to lead a long-term international EU project that is now due to end in a couple of months, and culminates with a natural rubber conference in Wageningen this month as a summit. Vredestein's tyre rolled up just on time.
Fiddling with the genes
But it is the product of a great deal of work, some of which took place in Wageningen. Biobased products developed a way of extracting the rubber from the dandelion (see box). PRI concentrated on field tests with guayule in Spain and on the latex proteins in dandelions. The Wageningen company KeyGene collaborated on figuring out the biosynthesis of rubber and which genes play a key role in the production and the quality of rubber. 'The synthesis route is well known in itself,' explains Mooibroek, 'but can you upscale that processing of isoprene into rubber by fiddling around with the genes or by being quick to select the right cross-breed? And which genes and proteins play a role in this? We also try to find this out using micro-organisms.
In short, everything possible is being done to spur the dandelion on to higher production levels. One approach is to improve the plant by cross-breeding until its production of biomass and rubber is maximized. This process is far from finalized. Mooibroek: 'We still get too little out of it now. Getting about ten percent of rubber should be viable; that is the amount we get out of guayule too. But to achieve that we need to do further breeding. At the moment we do not have a readymade marketable line.'
Sustainable materials
So what about Vredestein's tyres? 'To be precise, there are two of them. They are made of 502 grams of rubber', says the head of materials development at Apollo Vredestein, Nico Gevers. This is the entire harvest of a German test plot 100-square metres in size, planted with wild Russian dandelion and guayule rubber. That is rather different to the thousand kilos of rubber expected at the start of the project. 'In the end we made the tyres in the lab instead of on the production line.'
Nevertheless, Gevers is very enthusiastic about the project. 'We are very interested in sustainable materials. We are always on the lookout for them and we spend some of our R&D budget on that. We see a future for this project.'
Of the two tyres that have been produced, one is intended as a demo sample. The other one was tested last week for rolling friction, braking performance in wet weather, and speed. Gevers is keeping the results under his hat until the rubber conference in Wageningen, when the sample tyre will be on display.
The evidence is there now that rubber can be produced from dandelions grown on European soil. But it is far from economically viable at present, agrees Mooibroek. 'We cannot compete with the price of hevea rubber at the moment.' Upscaling the process is the next step, he says. But that costs money. A lot of money. 'To set up a large-scale extraction facility, a factory, you need about 25 million euros. Plus thousands of hectares of land. The question is: where is such an injection of funding to come from? It has to come from companies and governments.' One plus in this respect is that the dandelion also provides other useful materials. Mooibroek is very keen to set up a follow-up to the EU project. 'We have made a very good start but we are certainly not there yet.' Vredestein is eager to participate too, says Gevers. 'A second project would be most welcome.'

The slow road to a car tyre
If you want to extract rubber from the Russian dandelion, it is the root you need. Rubber is found there in the form of latex in a tailor-made circulation system. Frans Kappen (Biobased Products) developed a method of extracting the rubber from the roots and refining it. This is done in just a couple of steps, he explains. The roots are first boiled in water, and then pushed into a ball mill that separates the rubber from the rest of the root. Kappen: 'The balls break down the cellulose fibres and at the same time the rubber gets squashed together. This creates bigger and bigger balls of rubber, and then you filter the rubber from the fibre.' Lastly, the raw rubber is washed in ethanol to remove impurities (resin).

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