Natural Rubber Latex

Hevea Brasiliensis

Botanically known as Hevea Brasiliensis rubber seedlings ‘smuggled’ out of its native Amazon in 1876 planted in the nurseries at Henaratgoda botanical gardens in Sri Lanka became progenitors of the great rubber plantations of Asia.

Rubber Latex

The word latex generically means a stable dispersion (emulsion) of polymer micro particles in an aqueous medium. Latex may be natural or synthetic. Latex as found in nature is the milky sap of many plants that coagulates on exposure to air. The term latex is attributed to Charles Marie de la Condamine and derived from lac, the Latin word for milk and often used to refer to natural rubber, the milky white sap from the rubber tree.

Natural rubber is a thixotropic neutral milky fluid with a density of around 0.975 g/cc. The rubber hydrocarbon, chemically called cis 1,4 polyisoprene, is in colloidal suspension in water of molecular aggregates of 0.5 to 1.0 micron (1/100 of a mm) diameter. In addition, latex contains proteninaceous and nigrogenous substances, carbohydrates, lipids, mineral salts, carotenoid resins and enzymes.

Tapping

The farmer starts the day before dawn, as the cool morning air encourages the latex flow and improves yield.

The latex is collected by cutting a channel into the bark of the tree with a special tapping knife. The angle of the channel is critical: if it is too steep, the life and yield of the tree is reduced and contamination is increased. If it is too shallow, the yield is reduced. The cut must also be neither too deep nor too thick. Either will reduce the productive life of the tree. The channel is re-cut every morning to revive the latex flow. Contrary to common belief, the latex does not drop out of the channel, but is pumped up into the channel, before being directed into a spout attached to the end of the channel. The spout allows the latex to be directed away from the bark into the collection cup.

Coconut shells are commonly used for collecting latex in Sri Lanka due to their low cost and ready availability. Firstlight provides its rubber farmers with plastic cups as these are easier to clean and hence hygienic. This results in minimal scrap and increased yield. Firtslight is funding research to develop a coated paper collection cup - a step in the green direction.

Latex should be collected as soon as possible after the flow has ceased, which may be 3 to 4 hours after tapping. Latex is then transferred into galvanized iron buckets. Unclean buckets are a source of bacterial contamination which would induce premature coagulation.

To preserve the latex from putrefaction and coagulation, the tapper should add stabilising agents - a dispersion of Zincoxide and Tetramethylthiutamdisulphide (TMTD) followed by liquid Ammonia. Firstlight provides these preservatives free of charge.

The farmer takes the latex to collection centres located close to his land where it is weighed and accepted.