During the initial period of rubber manufacturing, the raw material was procured almost entirely from South America. Rubber occurs in the ‘Hevea Brasilienses’ tree as latex, a milky liquid exuded when the tree is wounded or cut. As early as 1834, Hancock from Brazil, suggested the possibility of growing rubber tree under more controlled conditions in the similar tropical climate of the Far East. In 1876, an alternate was made by Sir Henry Wikham. Some 70,000 seeds brought by himself from Brazil were planted at Kew and about 2,000 young plants were obtained. Most of these were sent to Sri Lanka where they were successfully established. It was principally from Sri Lanka that the Hevea tree was established in other parts of the Far East like Malaysia, Indonesia, Thailand, India and other places.
Types of Rubber
There are two types of rubber which are described in the following paragraphs:
Natural Rubber – It is obtained from the rubber tree by tapping process when it exudes out in the form of milky liquid called latex. This is a colloidal solution of natural rubber in water. Rubber latex is present in the latex vessels contained in the cortex in the layer 2-3 mm thick nearest to the cambium. It is produced all around the year, however, the yield decrease during winter. A tree is tapped for latex when it is 4-6 years old. Tapping is carried out without damaging the tree by removing bark with a special knife and making a cut at an angle of 25-30C to the horizontal. Tapping is done before sun rise when the yield of latex is maximum. Latex is collected in cups made of glazed earthenware. Tapping is carried out at regular interval. The examples of natural rubbers are Oil Extended Natural Rubber, Superior Process rubber (SP), Epoxidised Natural Rubber, Chlorinated Rubber, etc.
Synthetic Rubber – It is the product of chemicals having similar physical properties as natural rubber, but it can be produced at large scale. USA was the first country to manufacture synthetic rubber at large scale. Today, a wide range of synthetic rubber is available to meet many varied applications. It can be broadly classified into following categories:
- General purpose rubber
- Weather resistant rubber
- Oil resistant rubber
- Heat resistant rubber