Natural rubber comes from the Havea brasiliensis tree, which grows in tropical regions. They typically reach 20-30 metres in height on rubber plantations, and are able to produce commercial quantities of latex at about 7 years of age, depending on climate and location. Economical life span of a rubber tree is between 10 to 20 years, but may extend past 25 years in the hands of a skilled tapper and bark consumption.
It should be noted that latex is different to tree sap.
Havea trees are not tapped any more often than once per day, with 2 or 3 days being the norm. In countries such as Thailand, tapping usually takes place in the early hours of the morning, prior to dawn due to the high day time temperatures and the protective clothing worn to protect against snakes etc. Also flow rates are increased due to higher turgor pressures at these times.
A tapper uses a sharp hook shaped knife to shave a thin layer of fresh bark from the tree. This exposes the latex vesicles. The cut is typically done at 25-30° to the horizontal, as this exposes the maximum number of vesicles. The same incision is re-opened the next time (typically the next day) by shaving off a small amount of bark. Virgin bark is exposed first working around in panels. The same area may be exploited again after about 7 years.
Figure 1. Tapping a rubber tree using angular, semi-spiral incisions.
The thickness of the layer is important as too thick a slice will damage the tree and reduce its productivity and life, while too thin a slice will not produce sufficient latex. Bark is removed in a localised area for a period of time, and then a new area is tapped allowing the tree to repair itself.
The latex runs down and is collected in a cup. Each tree usually produces about half a cup of latex per day and is collected later in the day. Latex will flow for approximately 1 to 3 hours after which time the vesicles become plugged with coagulum.
Processing of natural rubber involves the addition of a dilute acid such as formic acid. The coagulated rubber is then rolled to remove excess water.
Figure 2. Rolling the latex into thin sheets.
Then a final rolling is performed using a textured roller and the resultant rubber sheet is dried. Following this, the rubber is ready for export of further processing. This type of natural rubber accounts for about 90% of natural rubber production.
Figure 3. Final rolling of the latex sheets using a textured roller.
Figure 4. The dried sheet of latex.
Natural rubber is used in a pure form in some applications. In this case, the latex tapped from trees is concentrated using centriguges, removing water and proteinaceous materials. It is then preserved using a chemical such as ammonia.
The natural rubber is used for making products such as:
· Some medical tubing
· Elastic thread
At the end of a rubber trees’ useful life, the wood is used to make furniture and souvenirs.