A species of dandelion is leading the way towards sustainable rubber. Find out how, by growing this unusual plant yourself and extracting the rubber from the roots.
Look around you: what objects can you see that are made from rubber? You might spot an elastic band, a pencil eraser, or perhaps one of the biggest users of rubber – car tyres. In fact, over 40 000 everyday products are produced from natural and synthetic rubber. With this material in such high demand, scientists are exploring an alternative source of rubber from a particular species of the familiar, but underestimated, dandelion: Taraxacum kok-saghyz, commonly known as the Russian dandelion.
To help students understand more about sustainability and this unusual source of rubber, we developed two simple methods to extract the rubber from the dried roots of the Russian dandelion. In the first method, students grind the roots into a powder to extract the rubber particles and create their own eraser. In the second method, sodium hydroxide is used to erode the woody parts of the root, and students can stretch out the fine strands of rubber that remain. The activities can be carried out by students aged 11–14 or older, in small groups of three or four, and will take about two hours.
The majority of the world’s natural rubber comes from plantations of the tropical rubber tree Hevea brasiliensis – over 90% of which are cultivated in Southeast Asia. Natural rubber production is responsible for widespread deforestation, and most of this rubber is used to make tyres. Relying on natural rubber to meet rising demands is not only unsustainable, but also risky: yields of natural rubber are falling due to a decline in prices, which has resulted in farmers switching to more profitable plantations such as palm oil. Climate change and crop diseases pose additional threats. These challenges make the future of natural rubber production uncertain. Producing rubber synthetically can help, but it requires the use of crude oil – so it is important to find an environmentally friendly and sustainable alternative.
The Russian dandelion, Taraxacum kok-saghyz, was discovered in Eastern Kazakhstan in 1931. The plant has the yellow flowers characteristic of the dandelion genus, but the roots contain a higher percentage of rubber than the familiar species of dandelion found in Europe. Soon after its discovery, the Soviet Union began large-scale cultivation of T. kok-saghyz to extract the rubber and end the country’s dependence on imports (see Göbel & Gröger, 2016). When the Japanese seized rubber plantations in Southeast Asia during World War II, other countries, including the USA and Germany, started farming the dandelion as an alternative. When the war ended and supplies from the rubber tree, H. brasiliensis, became available again, research on the Russian dandelion ceased – until recently.
Today, research into the Russian dandelion is growing. The Fraunhofer Institute for Molecular Biology and Applied Ecologyw1, based at the University of Münster, and the tyre company Continentalw2 are just two of the organisations working on using Russian dandelion as an alternative source of rubber.
Compared to tree-sourced rubber, the Russian dandelion is extremely resilient and can be grown in moderate climates on poor soils. This means that it can be grown locally, reducing dependence on imports. It is also much quicker to grow dandelions than trees – Russian dandelions can be harvested twice a year, whereas natural rubber trees take 7–10 years to mature before the sap, which is processed into rubber, can first be collected. What’s more, the Russian dandelion produces inulin (a sugar substitute and potential biofuel) as a by-product.
Rubber is used in so many products because of its unique chemical and physical characteristics. An elastomer (a polymer with elastic properties, such as rubber) can be stretched to over 100% of its original length without breaking. Natural rubber consists of long chains of cis-1,4-polyisoprene (figure 1), each comprising up to 30 000 isoprene monomers. The chains are interwoven with one another like a plate of cooked spaghetti. When you stretch rubber, the chains are pulled apart but do not break, due to the linkages between the entangled chains (figure 2).
In preparation for the following activities, you will need to grow the Russian dandelion plant and harvest the roots to dry. The whole preparation process will take approximately seven months from February to September, but teachers could use this opportunity to teach students about plants and the requirements for growing them. Seeds can be purchased onlinew3 and should be sown in February in a window-sill greenhouse. After two months, transfer the plants into flower boxes. You can harvest the roots from August onwards. To dry them, place the roots on paper towels and leave them at room temperature for 3–4 weeks.
Before carrying out the two main activities, spark your students’ interest with this starter activity introducing the topic of rubber and the Russian dandelion.
In this activity, students physically extract rubber from dried Russian dandelion roots to produce a small eraser.
Each group of 3–4 students will need:
The rubber from fresh dandelion roots is an emulsion of polymer micro-particles, similar to the sap from a rubber tree. In the dried roots, however, the rubber is a solid aggregate. In this activity, students dissolve the outer, woody material of the dried roots to gain access to the inner net of rubber.
Each group of 3–4 students will need:
This procedure involves the use of sodium hydroxide solution. Students should wear lab coats and safety goggles. See also the general safety note on the Science in School website.
Alongside the activities, discuss the following questions with your students to teach them about different types of rubber, the properties of rubber, and the importance of sustainability.
Seeing and experiencing the elasticity of rubber from the Russian dandelion is sufficient proof of natural rubber. To extend the activities, however, you could chemically detect the double bonds in polyisoprene, for example using bromine, potassium permanganate (Baeyer test) or the Burchfield colour reaction (see Göbel & Gröger, 2017).