The sap from the Hevea brasiliensis, or rubber tree, flows as a white milky liquid. Workers who harvest this liquid, known as latex, begin when the tree is six to 10 years old. The workers, or rubber tappers, make a diagonal cut into the bark. The latex slowly drips into buckets, with each tree yielding around 1 3/4 ounces per cut. A new cut can be made every two or three days until the tree needs to rest. With careful harvesting, the tree will continue to produce latex for up to 25 years.
Workers filter the sap to remove debris. They preserve the filtered liquid with ammonia before exporting it for processing. At other times, the rubber tappers pour the filtered latex into long rectangular forms and mix it with water and acid. After several hours, when the latex has thickened, it is fed through heated rollers to remove excess water and acid. The latex then is shredded and heated in large ovens for a few minutes. When it is removed, it is compressed into blocks. These blocks usually are exported to manufacturing companies to be made into tires, balloons, tubing, rubber bands and other products.
Many factories use a process known as vulcanization, in which the latex is once again heated and sulfur and other ingredients added. Sulfur causes the rubber to become much stronger. The vulcanization process also increases the rubber's elasticity and its ability to tolerate weather extremes. Vulcanized rubber does not conduct electricity, and gases cannot penetrate it; but it gradually breaks down when exposed to sunlight.
When the rubber product no longer is useful, it can be recycled to make new products. In developing countries, workers dismantle tires by removing the rubber tread or sidewalls from the steel bands. The rubber is used to make sandals and other items. A recycling process whereby the old rubber goes through a grinder and is treated with acid to reclaim the latex sometimes is used but is very costly. Since 2000, patents have been issued for other processes that are more efficient in recovering the various elements of a tire.