Rubber

Definition

Any of a number of natural or synthetic high polymers having unique properties of defor- mation (elongation or yield under stress) and elas- tic recovery after vulcanization with sulfur or other cross-linking agent, which in effect changes the polymer fro

Definition

A natural or synthetic polymeric elastic material. Natural rubber is a polymer of methylbuta-1,3-diene (isoprene). Various synthetic rubbers are made by polymerization; for example chloroprene rubber (from 2-chlorobuta-1,3-diene) and silicone rubbers. See also vulcanization.

Definition

rubber: polymeric substance obtainedfrom the sap of the tree Heveabrasiliensis. Crude natural rubber isobtained by coagulating and dryingthe sap (latex), and is then modifiedby vulcanization and compoundingwith fillers. It is a polymerof isoprene containing the unit–CH₂C(CH₃):CHCH₂-. Various syntheticrubbers can also be made.

Agricultural Uses

Rubber is a naturally occurring elastic substance. It is found in the latex of many plant species belonging to about 311 genera. Rubber quickly restores itself to its original size after it has been stretched or compressed. The yield or stretch of the vulcanized material ranges from a few hundred to over l000 percent.
Natural rubber is obtained from many plants and commercially from Huvea brusiliensis, a tree native to Brazil. The tree is now grown in the tropical regions of Asia, Africa and America. Havea is propagated through seeds and by adopting vegetative methods. Planting is done in specially prepared nursery beds. The soil is dug up and mixed with fertilizers. The germinated seeds are planted with a spacing of 30 cm x 30 cm. The seedlings are grown in the nursery till they attain a diameter of 20 to 25 mm above the collar.
The seedlings are usually transplanted in June-July into pits made in the field about 4.5 m apart to accommodate a stand of about 500 plants per hectare. Sometimes the seeds are sown in situ in the fields. Rubber trees should be regularly manured with balanced fertilizer mixtures from the time of planting to the age of economic production for ensuring maximum production. The recommended dose varies according to the age of the plant. During the first year of planting, a single dose of 225 g of a 10: 10:4: 1.5 NPKMg mixture is applied to each plant. The dosage increases to 900 g and 100 g in two split doses during the second and third years respectively. From the fourth year till the plants in the area become ready for tapping, the application of 900 g of the mixture per plant in two split doses, one in April- May and the other in September-October is recommended. For trees under tapping, an NPK 10: 10: 10 mixture at the rate of 900 g per tree is applied annually during April-May
Latex is obtained from the bark of the rubber tree by tapping. Tapping is a process of controlled wounding, during which thin shavings of the bark are removed to induce the flow of latex. Normally a rubber tree can be tapped economically for 25 to 30 years. A slanted cut is made in the bark and the milky fluid latex, occurring in the inner bark, is tapped off. The latex, an aqueous colloid of rubber and other particles, is coagulated with dilute acid and creped or sheeted and smoked. Natural rubber is a polymer of isoprene. Its elasticity is due to the chains being randomly coiled but tending to straighten when the rubber is stretched.