Natural Rubber is an elastic substance originally obtained from the latex sap of trees belonging to the genera Hevea and Ficus. Natural rubber is an elastomer or an elastic hydrocarbon polymer.
The rubber plants are tapped for collecting the rubber latex. For this, an incision is made into the bark of the rubber tree and the latex sap is collected in cups. After collecting the latex sap, the raw natural rubber is refined to convert it into a usable rubber. Initially an acid was added to the latex which used to make the sap set like a jelly. The latex jelly thus obtained was then flattened and rolled into rubber sheets and hung out to dry. In the year 1839, Charles Goodyear invented a more sophisticated way of making rubber stronger and more elastic. This was the process of rubber vulcanising. The unprocessed natural rubber is sticky, deforms easily when warm, and is brittle when cold. In such a state, it cannot be used to make products having a good level of elasticity. Vulcanization prevents the polymer chains from moving independently. As a result, when stress is applied the vulcanized rubber deforms, but upon release of the stress, the product reverts to its original shape.
The natural rubber is produced from hundreds of different plant species. However, the most important source is from a tropical tree known as Hevea brasiliensis, which is native to the tropical Americas. This tree grows best in areas with an annual rainfall of just under 2000mm and at temperatures of 21-28 degrees. Due to these features and the preferred altitude of the tree around 600 metres, the prime growing area is around 10 degrees on either side of the equator. However it is also cultivated further north in China, Mexico, and Guatemala.
In 1876, Sir Henry Wickham collected some 70,000 Hevea tree seeds from Brazil. These seeds were germinated and shipped to the East Indies, where they began today's rubber plantations. Today Malaysia, Indonesia, and Thailand produces around 90% of the world's natural rubber. New plantations have also been started in Africa, The Phillipines, and Europe to make up for insufficient rubber output in Indonesia.
- Natural rubber combines high strength (tensile and tear) with outstanding resistance to fatigue.
- It has moderate resistance to environmental damage by heat, light and ozone.
- The natural rubber has excellent adhesion to brass-plated steel cord, which is ideal in rubber tyres.
- It has low hysteresis which leads to low heat generation, and this in turn maintains new tyre service integrity and extends retreadability.
- It has high resistance to cutting and tearing.
- Natural rubber forms an excellent barrier to water.
- Natural rubber is an excellent spring material and used for elastic band production