Natural rubber, also called China rubber or caoutchouc, is an elastomer (an elastic hydrocarbon polymer) that was originally derived from latex, a milky colloid produced by some trees.
The trees would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined into a usable rubber.
The original tapped latex contains 36% rubber hydrocarbon, 60% water, 1.8% acetone extract (natural anti- oxidant), 1.8% proteins and 0.4% minerals.
The latex must be stabilized once retained from the tree as it otherwise will coagulate (solidify; sticking together) immediately (known as the Brownian movement). Stabilization of the retained latex will be done by adding ammonia or potassium hydroxide.
Because the tapped latex contains so much water it would be a very expensive way to transport the material.
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There are several techniques to decrease the water content and higher the rubber content from the tapped and stabilized latex:
Roaming: ammonia conserved latex will be left for months; the rubber particles (which are lighter than the water) will float to the top. This floating to the top can be stimulated by adding chemicals like PVA, methylcellulose etc. as the rubber particles will stick together. This roam will be diluted in low concentrations of water and solids.
Centrifuging: roaming method with a machine called the Laval. It is roaming by help of machinery.
Evaporation: letting the water evaporate from the latex. Compared to centrifuging no rubber particles will get lost in this process. To avoid coagulation you need to use a stabilizing soap and the rubber content can go up to 73% various with centrifuging is will be app. 60%.
Electrodecantation: roaming by electrodes up to 60%.
Centrifuging and Evaporation are the most commonly used.
The stabilized high-rubber content latex can be delivered pre-vulcanized or post-vulcanized.
All rubber products must at the end be vulcanized to achieve elastic properties and temperature stability. The vulcanization process consists of: heating and adding of sulfur, peroxide or bisphenol to improve resistance and elasticity, and to prevent it from perishing.