Natural rubber
latex (NRL) is the milky fluid secreted in the latex ducts of a number of trees and plants. By far the most economically important such plant is
Hevea Brasiliensis.
The material is obtained from the tree by a process known as tapping, in which a worker uses a sharp knife to make a thin cut in the trunk of the tree. The cut penetrates the bark and the latex ducts, but should leave the underlying cambium untouched. If the cambium is damaged, the tree is scarred for life, and may well die if the damage is severe.
When the fluid comes out of the tree, it typically comprises:
* 40 percent natural rubber (cis 1,4 polyisoprene)
* 2 percent proteins and other biological material
* The remainder is water
NRL is coloured white, and has a milky feel to it. The latex is naturally unstable. If left untreated, the rubber content of the material will spontaneously coagulate, to form a solid material known as cup lump. Cup lump can be further processed to make solid natural rubber.
If plantation managers prefer to collect latex, as opposed to cup lump, either the latex collection cups must be collected shortly after they are filled, or the latex must be made alkaline, to prevent coagulation. The alkali of choice is ammonia.
Once the latex from a large number of trees has been collected together, it is passed to a factory where it is stabilised with more ammonia, strained to remove any solid impurities, and then passed to a centrifuge, where some of the water is removed, and the solids content is increased to 60 percent. Latex concentrate, as the resulting material is known, is white, and has a creamy feel. If left on the hands, or any other part of the body, the water quickly evaporates, leaving a thin layer of unvulcanised polyisoprene on the skin. The smell is pungent because of the ammonia used to stabilise the latex.
At this point the latex concentrate can be used to make goods using the dipping process. Such products include condoms, balloons, and especially, examination gloves, used in the medical industry.
Latex concentrate can be made to coagulate by changing its pH (acidity). Adding small amounts of formic acid (used in the industry), or lemon juice, vinegar or other acid (in the home) will cause the rubber molecules to clump together into a solid mass, very similar to cup lump. It is important to note that this is not a curing process, or vulcanization, but simply the coagulation of a lot of large, organic molecules.
The resulting material is very similar to the material used for balls used by the Mayans in their ritual ball games.
Although the protein content of the latex is small, the proteins can trigger severe reactions in humans. Some people can become sensitised to one or more of these proteins, resulting in a debilitating condition known correctly as natural rubber latex protein allergy (NRLPA), but more commonly abbreviated to latex allergy. It is an IgE-mediated allergic response, and can lead to death by anaphylactic shock. Although death is rare, the condition, is extremely debilitating for those who suffer from it.
Other plants which secrete NRL include the desert shrub Guayule and the dandelion plant. However, these are not economically important in any part of the world.