Natural rubber is a sap obtained from some trees, better known as latex. It is actually the original form of rubber, which is later processed by various methods to get the form that we are so well acquainted with. Latex is a white milky sap, with high viscosity and density. In case of natural rubber, it is the latex that is directly collected from the trees.
Chemically, natural rubber is a hydrocarbon polymer. It contains several units of isoprene polymerically united to form the stringy form of rubber. In its natural form, rubber is much more elastic, soft, and sticky.
There are processes to make this rubber hard and tough, one of the most common being vulcanization. When vulcanized, rubber loses most of its elastomer properties and becomes almost inelastic.
Hevea brasiliensis is a native Brazilian plant, as its name indicates. But in the later part of the nineteenth century, this tree was implanted to the Far East, where it showed a much better propensity for growth. Countries like Indonesia, Malaysia, Thailand, Sri Lanka, Singapore, and India, showed a great crop of the tree in a very short time.
Today, Malaysia ranks as the number one producer of rubber in the world, and about three fourths of all the latex used in the world comes from the three countries of Malaysia, Indonesia, and Thailand.
In India, the state of Kerala is also a major producer of latex in the world, along with the southern country of Sri Lanka. Some rubber production is also obtained from the two African countries of Nigeria and Liberia, but that is about all.
Latex is important in rubber requirement of the world. Today there are methods of preparing the rubber isomer with synthetic methods, but due to the abundance of natural rubber sources, synthetic methods are not quite vastly used. For high-end purposes like making tires, almost half of the rubber requirement across the world is obtained from natural sources.
In ordinary practice, the incision is made sometime in the afternoon and the latex is allowed to flow into the receptacle. By the next morning, a cupful of latex is usually obtained. This is collected and mixed with formic acid, which gives it some of its hardness. From there on, the latex is sent to the factories for further processing.
Once an incision is made, the latex in the tree is allowed to build up for a time period, before an incision can be made on the tree again. A new incision will always be made at a new place on the tree. Typically, rubber trees will show multiple incisions indicating that latex has been extracted several times from them.
Vulcanization of rubber, the method perfected by Charles Goodyear, is a method to transform the soft, sticky natural rubber mass into a hard, tough substance that is suitable for commercial use. Depending on the requirement, the procedure can be adjusted.
Generally, a mass of latex is mixed with some amount of sulfur and then heated for a specific time, at a specific temperature, according to the requirements. This makes the polymer chains shorter (due to the incorporation of the disulfide units in them) and the rubber becomes harder.