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Rubber

Tapping and coagulation

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When the bark of the Hevea tree is partially cut through (tapped), a milky liquid exudes from the wound and dries to yield a rubbery film. The biological function of this latex is still obscure: it may help wound-healing by protecting the inner bark, or it may serve other biochemical functions. The latex consists of an aqueous suspension of small particles, about 0.5 micrometer in diameter, of cis-polyisoprene, a linear rubbery polymer of high molecular weight. The rubber content of the suspension is about 30 percent.

Rubber trees are tapped about once every two days, yielding a cupful of latex, containing approximately100 grams of solid rubber ,under the favorable conditions of the environment by a healthy hybrid RRII-105 adult plant /tree. The standard method of tapping is to score the tree with a knife for half the circumference of the trunk, slanting the cut down from left to right at an angle of 30° starting at the highest point convenient to the tapper. Each subsequent cut is made immediately below its predecessor. Trees are often rested for a period after heavy tapping. Production commences when a tree is 5 or 6 years old; with care, the tree's useful life may extend to more than 20 years. With trees cultivated at a density of 375 to 450 per hectare (150 to 200 per acre), approximately from hybrid verity rubber 3,500 to 4,500 kilograms of rubber can be produced per hectare per year (that is, approximately ).

After collection of the tapped latex, rubber is recovered from emulsion by coagulation with formic acid, creating crumbs that resemble curds of milk. The crumbs are washed, dried between rolls, and compacted into blocks 67 by 33 by 18 centimeters (26 by 13 by 7.5 inches) in size and weighing 33.3 kilograms (73 pounds). The blocks are then wrapped in polyethylene sheets and packed into one-ton crates for shipping. Other productions as smoked sheet, where the coagulum is pressed into thin sheets that are washed and then dried over a smoky wood fire . The smoke contains natural fungicides that protect against mold growth and impart a characteristic amber colour. Dried sheets are packed into 110-kilogram (250-pound) bales for shipping.About 10 percent of all natural rubber is shipped as latex, concentrated by centrifugation to a rubber content of approximately 60 percent and used for making dipped goods such as surgical gloves, prophylactics, and toys.

 


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Rubber Cultivation

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Rubber can be grown from sea level up to an altitude of 500 m in areas of well distributed annual rainfall of not less than 200 cm and a warm, humid equatorial climate (21-35ºC). The soils of main rubber tracts in India, confined to a narrow belt on the west of the Western Ghats, running parallel to it for about 400 km, are mostly laterite in nature. Well-drained alluvial and red loam soils are also suitable for rubber cultivation.

Propagation

(i) By clonal seeds collected from approved poly-clonal seed gardens in the country and abroad.
(ii) By budded plants.
(iii) By tissue culture plants.

The clones may be planted as follows:

Category 1
Budded clone of RRII 105 and PB 260 may be planted to cover only 50% of the total area of any estate or small holding.

Category 2
Budded clones of RRIM 600, Gl 1, PB 28/59, PB 217 and RRIM 703. Three or more of these may be planted to cover up to 50% of the total area of any estate or small holding.

Category 3
Budded clones of RRII 5, RRII 203, PR 255, PR 261, PB 235, PB 280, PB 311 Tjir 1, PB 86, GL 1, PR 107, RRIM 605, RRIM 623, RRIM 628, RRIM 701, PB 6/9, PB 5/51, RRII 118, RRII 208 and polyclonal seeds of approved sources may be planted in very small scale not to exceed 15% of the total area in aggregate.

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