Natural rubber
The latex is a sticky, milky and white colloid drawn off by making incisions in the bark and collecting the fluid in vessels in a process called "tapping".
[8] In 2013, by inhibiting one key enzyme and using modern cultivation methods and optimization techniques, scientists in the Fraunhofer Institute for Molecular Biology and Applied Ecology (IME) in Germany developed a cultivar of the Kazakh dandelion (Taraxacum kok-saghyz) that is suitable for commercial production of natural rubber.
The earliest archeological evidence of the use of natural latex from the Hevea tree comes from the Olmec culture, in which rubber was first used for making balls for the Mesoamerican ballgame.
[13][14] Charles Marie de La Condamine is credited with introducing samples of rubber to the Académie Royale des Sciences of France in 1736.
[15] In England, Joseph Priestley, in 1770, observed that a piece of the material was extremely good for rubbing off pencil marks on paper, hence the name "rubber".
The rubber trade was heavily controlled by business interests but no laws expressly prohibited the export of seeds or plants.
In 1876, Henry Wickham smuggled 70,000 Amazonian rubber tree seeds from Brazil and delivered them to Kew Gardens, England.
[20] In the early 1900s, the Congo Free State in Africa was also a significant source of natural rubber latex, mostly gathered by forced labor.
[21] King Leopold II's colonial state brutally enforced production quotas due to the high price of natural rubber at the time.
Days before entering Iquitos by boat Casement wrote "'Caoutchouc was first called 'india rubber,' because it came from the Indies, and the earliest European use of it was to rub out or erase.
[28] Before World War II significant uses included door and window profiles, hoses, belts, gaskets, matting, flooring, and dampeners (antivibration mounts) for the automotive industry.
Rubber produced as a fiber, sometimes called 'elastic', had significant value to the textile industry because of its excellent elongation and recovery properties.
While rubber is still used in textile manufacturing, its low tenacity limits its use in lightweight garments because latex lacks resistance to oxidizing agents and is damaged by aging, sunlight, oil and perspiration.
Because there are weakened allylic C–H bonds in each repeat unit, natural rubber is susceptible to vulcanisation as well as being sensitive to ozone cracking.
Cooling below the glass transition temperature permits local conformational changes but a reordering is practically impossible because of the larger energy barrier for the concerted movement of longer chains.
"Frozen" rubber's elasticity is low and strain results from small changes of bond lengths and angles: this caused the Challenger disaster, when the American Space Shuttle's flattened o-rings failed to relax to fill a widening gap.
Crystallization has occurred, for example, when, after days, an inflated toy balloon is found withered at a relatively large remaining volume.
The final properties of a rubber item depend not just on the polymer, but also on modifiers and fillers, such as carbon black, factice, whiting and others.
Though rubber is known to be produced by only one enzyme, extracts of latex host numerous small molecular weight proteins with unknown function.
These slanting cuts allowed latex to flow from ducts located on the exterior or the inner layer of bark (cambium) of the tree.
Tappers usually rest and have a meal after finishing their tapping work and then start collecting the liquid "field latex" at about midday.
Some smallholders use small containers, buckets etc., but often the latex is coagulated in holes in the ground, which are usually lined with plastic sheeting.
Vulcanization is a process by which the rubber is heated and sulfur, peroxide, or bisphenol are added to improve resistance and elasticity and to prevent it from oxidizing.
Carbon black, which can be derived from a petroleum refinery or other natural incineration processes, is sometimes used as an additive to rubber to improve its strength, especially in vehicle tires.
[47][48] During vulcanization, rubber's polyisoprene molecules (long chains of isoprene) are heated and cross-linked with molecular bonds to sulfur, forming a 3-D matrix.
Natural rubber latex is shipped from factories in Southeast Asia, South America, and West and Central Africa to destinations around the world.
In addition to the pandemic, demand exceeded supply in part because long term plantations had been torn out and replaced with other crops over the previous 5–10 years, and other areas were affected by climate-fueled natural disasters.
The flexibility of rubber is appealing in hoses, tires and rollers for devices ranging from domestic clothes wringers to printing presses; its elasticity makes it suitable for various kinds of shock absorbers and for specialized machinery mountings designed to reduce vibration.
The mid-range which comes from the technically specified natural rubber materials ends up largely in tires but also in conveyor belts, marine products, windshield wipers, and miscellaneous goods.
Although this may be confused with an allergy to latex, it is distinct from it, typically taking the form of Type IV hypersensitivity in the presence of traces of specific processing chemicals.
