Rubber tree, Hevea brasiliensis

70 percent of the rubber harvest goes into the production of car, bicycle and aircraft tyres. Half of all car tyres and all aircraft tyres are made from natural rubber, which is superior to synthetic rubber due to its better mechanical properties. The remaining 30 percent is used in around 50,000 products – from rubber boots, inflatable boats and doorstops to balloons, erasers, chewing gum, condoms and medical products such as protective gloves and infusion tubes.

White sap from huge trees

The evergreen rubber tree, with its spirally arranged leaves and inconspicuous greenish-yellow flowers, belongs to the spurge (euphorbia) family. It grows to a remarkable height of twenty to forty meters. In plantations, the trunk reaches a diameter of 35 cm. Its heartwood is yellowish, the bark light grey. Tubes run through the trunk, through which the milky sap flows, a fluid consisting of a watery solution of 30-40 percent latex, the natural constituent of rubber.

The rubber tree prefers to grow on soils that can drain excess water well, i.e. ideally on hills and mountain slopes. After five to six years, it has matured enough to have the latex extracted, which is collected in small buckets after the bark has been scored and scratched. At the age of 25 to 30 years, the tree stops producing latex and is felled. Until then, it yields around 1.5 kilograms of natural rubber per year – there are around 800 to 900 trees per hectare in a typical plantation.

When the tree stops producing latex, it is felled and yields a light-colored wood, known as rubberwood, which is processed into furniture and toys. Thanks to its hardness and humidity resistance, it is also used in the construction of musical instruments.

History of the weeping wood

Indigenous peoples in Mexico and Central America used the latex of Hevea brasiliensis for medicines, rituals and painting as long as 3,600 years ago. The dried latex was made into shoes and rubber balls for ceremonial games.

In the 15th century, Portuguese conquistadors reported on latex and its benefits, for example for making waterproof clothing by coating the material with the viscous milky sap. In 1736, the Frenchman Charles-Marie de La Condamine sent dried latex to Europe during an expedition. He coined the term ‘caoutchouc’, which is derived from the Quechua word ‘kwachu’ and means ‘weeping wood’. A little later, the Briton Joseph Priestley discovered that you can erase pencil marks with dried latex. This is where the word ‘rubber’ comes from. It was not until 1839 that the American Charles Goodyear invented the technique of vulcanisation, which is used to create natural rubber from latex. With the invention of the bicycle in 1817, the automobile in 1886 and the pneumatic tyre in 1888 (Dunlop), the demand for rubber increased rapidly. Brazilian rubber barons such as Fitzcarraldo became immensely wealthy thanks to the white gold.

After several unsuccessful attempts, an Englishman succeeded in smuggling rubber tree seeds from Brazil on behalf of the British government in 1876. The British used the seeds to establish the first plantations on the Malaysian peninsula they occupied after various setbacks in the 1890s, bringing their products to the world market from 1905. Soon afterwards, Great Britain enjoyed a monopoly position in the global rubber trade. Hevea brasiliensis was not originally found in Asia and many of the rubber trees that exist in Asia today can be traced back to the few specimens from the Englishman. As a result, they are all genetically very similar, which is why they are susceptible to disease. Currently, the Brazilian populations are also threatened by a parasitic fungus that causes leaf drop disease.

Currently, 94 percent of rubber is grown in the so-called rubber belt (approximately 30° north latitude to 30° south latitude) with a focus on Southeast Asia, with Thailand and Indonesia being the most important growing countries, producing more than 60 percent of the natural rubber traded worldwide. They are followed by Malaysia, China and India, with some West African countries further behind. Only around two percent of global production comes from South America. China and India produce exclusively for their own needs. The demand for natural rubber has continued to rise into the 21st century. While global production in the 1960s was still at 2 million tons per year, it already exceeded 6 million tons in the early 1990s and reached more than 15 million tons in 2022 according to the FAO.

From juice to rubber

Natural rubber is a high-molecular, unsaturated secondary plant substance that occurs in the milky sap (latex) of the milk tubes of numerous plants such as cassava, ficus, lettuce, sow thistle and dandelion. It is believed to be important in the healing of wounds in the plant.

After harvesting, the emulsified rubber in the latex is precipitated with the help of diluted acids and then passed through heated presses and formed into films, occasionally also smoked to prevent bacterial infestation or treated to protect against fermentation. To produce rubber with high elasticity, tensile strength and resistance to ageing, the raw rubber is vulcanized, i.e. brought back into a plastic form by heating and kneading under atmospheric oxygen, before being mixed with vulcanization aids. This mixture is pressed into molds and heated to 120 °C. If blowing agents are added during vulcanization, foam rubber is produced. To meet the huge demand, synthetic rubber is also produced alongside natural rubber, although it is more expensive to produce and has different properties.

Natural rubber: sustainable or a climate offender?

Between 1985 and 2022, the area under rubber cultivation more than doubled. While the trees in Indonesia are mainly planted in agricultural forests, in Thailand and Malaysia they are mainly grown on plantations. Large areas of rainforest have been cleared for this purpose. This deforestation has a serious impact on the ecosystem. Deforestation releases large quantities of greenhouse gases and habitats for numerous animal and plant species are lost. Cultivation in monocultures is also accompanied by a high use of pesticides, which has a negative impact on soil, water and biodiversity. The intensive use of synthetic fertilizers is increasingly degrading the soil, and the uncovered ground encourages erosion.

However, it is not only nature that is suffering, but also the people – especially those who are being driven from their land for the establishment of large plantations. The rubber boom led to the awarding of large-scale concessions for larger plantations, which deprived small farmers of their land. However, the workers on the plantations are also often exposed to undignified working conditions, and child labor is sometimes used. Smallholders are also dependent on the highly fluctuating prices of the global market.

Nevertheless, many consider a product made from natural rubber to be sustainable as, unlike synthetic rubber, it is not obtained from crude oil. In order to ensure that rubber does not come from deforested areas and that social grievances can be uncovered, it is therefore important to have complete traceability of raw materials along the entire supply chain.

If the trees are cultivated by small farmers in near-natural agroforestry systems, they can bind a comparatively large amount of carbon dioxide and do not contribute to the restriction of animal and plant habitats. The prerequisite for this is that no forests or other natural ecosystems such as peat soils or savannahs are destroyed for the cultivation of rubber. In agroforestry systems, rubber trees are combined with other tree species such as fruit and timber trees. Various crops such as coffee, cocoa and vegetables grow underneath them. Trees and plants provide each other with shade and enrich the soil with nutrients. Diversification means that pests cannot spread as quickly, which is why the use of pesticides can be significantly reduced or eliminated altogether. Yields can also be increased through sustainable expertise around healthy trees without the use of artificial fertilizers. The livelihoods of farmers can also be significantly improved by this diversification of cultivation systems. If rubber prices fall, they still have other crops that they can sell on the local or international market.

Sources

Fascination rainforest: Rubber – the white gold
Spectrum: Rubber
Encyclopedia of the agricultural world: Rubber tree
Encyclopedia of the agricultural world: Natural rubber in the supply chain