IN A classic episode of The Simpsons, Bart and his schoolmates watch an educational film called . For reasons unexplained, a man called Jimmy wants to live without zinc. His wish is granted, but he soon regrets it: he can’t go on a date because his car won’t start, and he can’t call his girlfriend because his telephone won’t work. Horrified at what he has done, he tries to shoot himself. But his gun won’t fire, because the firing pin is made of zinc.
A real-life world without zinc would probably be survivable. But there are some commodities we would struggle without. Many are obvious: steel, oil, aluminium. But others are less so. In A World Without Zinc, Jimmy wakes up to find it was all a bad dream. In A World Without Rubber, however, the nightmare threatens to become all too real.
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Rubber is one of industrial civilisation’s great unsung heroes. Apart from its obvious uses in tyres, wellies, condoms and underwear elastic, it is a crucial ingredient in some 40,000 products, including shock absorbers, transmission belts, gaskets, hoses, medical devices, sports equipment, cement, paints, plastics and pharmaceuticals. According to agricultural scientist , rubber is “essential to the enjoyment of the conveniences and amenities of modern life”.
Unfortunately, the prospect of a rubber crisis isn’t the stuff of fiction. Demand keeps growing, but supply isn’t keeping pace. With a deadly fungus threatening to wipe out rubber trees, and the rubber industry, the hunt is on for new sources of the stuff.
Right now, the world has two of those sources: oil and trees. For many applications, the tree version – called natural rubber – is considered superior to the synthetic version made from petrochemicals. It is stronger, more elastic, better at absorbing impacts and more resistant to heat and friction. In other words, rubberier. To connoisseurs, the difference is like that between Madagascar vanilla and its synthetic substitute.
“The supply of natural rubber is a security issue. A shortage could destabilise global trade”
The key to good rubber is very long polymer molecules and a property called “spontaneous self-reinforcement” – reversible stiffening under mechanical stress. Think of a car cornering: the tyre deforms a bit, which causes it to stiffen in response. What enables natural rubber to be either elastic or hard is a process mediated by proteins and fats at the end of its long, polymer molecules. These have proved hard to create in the synthetic form.
For some applications – everything from engine parts to silicone cooking utensils – synthetic rubber, or a blend of synthetic and natural, is superior. But for many, natural rubber is indispensable. For instance, aircraft tyres must be 100 per cent natural rubber or the heat and friction would make them explode on landing, says , a rubber expert at Ohio State Universsity.
For the past 70 years or so, the world’s major source of natural rubber has been the Pará rubber tree (Hevea brasiliensis), a native of Brazil that is now grown all over the tropics. It is tapped for its latex, a white gunk that oozes out after the tree’s bark has been carefully sliced. This is processed to make rubber as we know it. The total area under cultivation is about , mostly in South-East Asia. The Pará produces excellent rubber, but grows slowly and is extremely fussy about temperature, rainfall, altitude and soil, which restricts its range to just a few degrees north and south of the equator. Extracting the latex is labour-intensive and scaling up production almost impossible, meaning that supply is extremely – and ironically – inelastic. Recycling is notoriously difficult too (see “Reclaimed rubber”).
In 2017, global demand for rubber was close to . The natural rubber industry could only satisfy about 45 per cent of that. And that proportion will only diminish. “Up until the recession of 2008, the price of natural rubber went up about tenfold over a decade because of the expanding economies in Asia,” says David Wolyn, a plant breeder and geneticist at the University of Guelph in Canada. “The recession tempered that increase, but people are still very ,” he says.
Black death
But as countries in South-East Asia develop economically, landowners are shifting away from rubber. “They cut down their rubber trees and put oil palm in instead, which is less labour-intensive and you get your harvest sooner,” says Cornish.
The shift to palm oil is a threat to supply, but it isn’t the worst. A much bigger one is the lack of genetic diversity of the Pará tree crop, which makes it frighteningly susceptible to disease – especially a fungus called South American leaf blight, the “black death” of rubber. It can’t be treated: it killed off the rubber industry in South America in the 1930s. As yet, it hasn’t spread to Asia thanks to strict quarantine measures, but if it does, the world economy is in big trouble. “If the blight ever got to South-East Asia, it would wreak havoc on our rubber supply,” says Wolyn. The industry could be wiped out in a year, says Cornish.
Because of this, leading agronomists have warned that . A sudden shortage of aircraft tyres, for example, could destabilise global trade. The threat is so great that the United Nations lists the leaf blight as a potential biological weapon.
All of which has spurred a decades-long, global search for alternative sources of natural rubber. Dozens of plants have been tried, yet most have failed. The Panama rubber tree, Castilla elastica, for example, produces good rubber, but usually dies after being tapped, while the India rubber plant, Ficus elastica, is hardy, but produces poor-quality rubber. Now, however, two unlikely candidates – a feeble northern weed and a scrubby desert shrub – may put the spring back into the rubber industry’s step.
It is rarely possible to pinpoint the exact time and place of a crop’s domestication, but the Pará rubber tree is an exception: 1876, where the Amazon and TapajÓs rivers meet in Pará state. That was where British explorer Henry Wickham collected some 70,000 H. brasiliensis seeds, which he took back to Kew Gardens in London on a falsified export licence. Kew germinated the seeds and dispatched seedlings to parts of what are now Sri Lanka, Malaysia, Singapore and Indonesia, where they were used to establish plantations. These quickly outcompeted the South American industry, which relied on smallholders tapping latex from wild trees.
Today, about 90 per cent of all natural rubber comes from the descendants of Wickham’s contraband trees, mostly in Indonesia, Thailand and Malaysia. According to Nair, every tree in these nations is a clone of one of just 1919 seedlings. “Some of the largest rubber-producing countries have miles of virtually genetically identical trees with their roots and canopies intermingled,” says Cornish. That is a blight epidemic waiting to happen.
The industry has tried to increase genetic diversity by cross-breeding with other strains, but none appears to be resistant to the black death. It is only a matter of time before the fungus makes landfall in Asia and rips through the plantations. Two small outbreaks are rumoured to have happened already. On both occasions, it took a scorched earth policy to stop the spread.
Beating the blockade
Although the world as a whole has yet to endure a rubber famine, it has happened in some regions. One was , when South-East Asian exports were blockaded by the Japanese. Luckily, the USSR had already sown the seeds of a domestic rubber industry. In the early 1930s, Soviet agronomists tested more than 1000 species of indigenous plant as sources of rubber. The rubberiest was the Siberian dandelion, a native of the Tian Shan mountains of Kazakhstan. This close relative of the common-or-garden patio weed produces large amounts of high-quality rubber in its roots. Local people had long used it as a kind of chewing gum and the second half of its scientific name, Taraxacum kok-saghyz, means “root rubber” in Kazakh.
Throughout the decade, the Soviets developed ways to cultivate and process the dandelion. By the time of the Nazi invasion in 1941, the USSR had 67,000 hectares of it, and domestic rubber was meeting 30 per cent of its needs. Production continued after the war, but was halted in 1951 as cheaper South-East Asian rubber bounced back onto the market.
The Japanese blockade also hit the US. In 1942, it set up the Emergency Rubber Project, employing more than 1000 scientists to find alternatives. They too experimented with Siberian dandelions, and also a desert shrub, Parthenium argentatum, better known as guayule (pronounced why-oolie). This had already been commercialised as a rubber crop in the early 20th century, although that industry died out in the Great Depression. The project cultivated wild guayule plants from Mexico and Texas, but the war ended before it could make much headway.
Now, however, both plants are back in the frame. “They would go a long way to solving our problems,” says Cornish.
On the dandelion side, German tyre giant Continental has set up a research centre with the Fraunhofer Institute for Molecular Biology and Applied Ecology in MĂĽnster. Its US competitor Bridgestone runs a pilot plant in Arizona that makes guayule rubber. Both firms recently unveiled demonstration tyres proving that the alternative rubber is high-enough quality, although neither is yet commercially available. Dandelion rubber is also being developed in China, India and the US and there are guayule projects in Spain, Australia and South Africa.
Team dandelion recently stole a march on the competition when a team at the Chinese Academy of Sciences published , a critical step towards rapid crop improvement. “It helps tremendously to understand the genetic traits the breeders are after,” says plant geneticist Kenneth Olsen of Washington University in St Louis, Missouri. “That allows you to have a more informed breeding strategy.”
There are still hurdles to overcome, says Cornish, who has commercial interests in both plants. The dandelion isn’t a strong plant, she says. “It grows slowly to start with and we don’t have chemical weed control. It’s not going to be a commercially viable crop until that is achieved.”
There is also the challenge of scaling up to the millions of hectares needed to meet demand – a problem for both contenders.
Ultimately, the world needs all three crops, says Cornish. Demand for natural rubber is so high that nobody is going to put anyone else out of business. “We could have the rubber tree in the tropics, dandelion in northern temperate regions and guayule in semi-arid areas. They complement each other,” she says.
For now, maybe we should show more appreciation for this essential stuff – and hope we don’t live to see a world without rubber.
Reclaimed rubber
It is extremely difficult to recycle rubber. To be reused as a raw material it has to be “devulcanised”, which means reversing the chemical process used to strengthen it. Various methods exist, but they degrade a key polymer, so the quality of the recycled rubber is low. Consequently, about half of the 1.6 billion tyres made every year – accounting for 70 per cent of global rubber consumption – aren’t recycled or repurposed. Those that are mostly end up being shredded for applications such as flooring, road surfaces and insulation.
