Natural rubber finds its use in thousands of different products that people used almost on a daily basis. Some examples of these include car tires, waterproof shoes, water hoses, wetsuits, and latex gloves. The making of these rubber products requires an industrial manufacturing process to transform rubber from its natural form to a usable product.
Sourcing Natural Rubber
Rubber in its natural form looks very different from the rubber products made and used regularly. Natural rubber comes from an important long-chain chemical compound or polymer known as latex. Latex is produced in over 2,500 plants. When extracted from these plants, the latex appears as a milky sap. The latex that is used for most commercial applications is extracted from the tropical rubber tree that is known as Hevea brasiliensis. This tree has its origins in South America.
Natural rubber has a long history spanning back as many as 3,000 years ago. The Mesoamerican people in South America at that time made rubber using latex from the Hevea brasiliensis tree mixed together with morning glory juice. As they played around with the proportions of latex and morning glory, they were able to create different types of rubber for different purposes and functions.
The Modern Manufacturing Process
The rubber manufacturing process has seen changes and improvement over the centuries. The method of manufacturing used in modern applications is carefully monitored to produce rubber with the right quality and the right properties.
The first stage in rubber manufacturing is harvesting latex from rubber trees. The trees that are ready for harvest must have their bark cut or scored. Once that is done, the sap-like latex can then be collected into a container placed near the cut. These containers placed under different rubber trees are then combined into large collection tanks.
There are various methods of extracting rubber from latex. The most common method used is coagulation. For this, formic acid or a different acid must be added to the latex. Coagulation then takes place over a period of about 12 hours. This involves the thickening or curdling of the polyisoprene polymer, which forms rubber, in the mass of latex. After coagulation, separation must take place. The thickened rubber is squeezed using a roller mechanism to remove the water. After this process, thin sheets of the polymer can be dried over wood in smokehouses. It takes several days for the drying to be completed.
An alternative to the smoke drying is air drying. This produces air-dried sheets that are used to produce a higher grade of rubber. Even higher quality rubber can be produced from using two stages of coagulation followed by the air-drying stage.
After drying in the smokehouses, the result is a ribbed smoked sheet. This dark-brown rubber is folded up and transported to the next stage for processing.
The final and very important stage is the processing stage. This is used whether the rubber is obtained from a natural latex source or whether the polymer comes from a synthetic process. the rubber processor takes the rubber bales through four processing stages. These are compounding, mixing, shaping, and finally vulcanizing. Depending on the type of rubber required, different formulations and methods can be used in the compound stage in particular.
Compounding involves adding chemicals and additives to the rubber to adjust its properties and make it fit for its intended purpose. Mixing is used to mix in the added chemical to the entire batch. After this, the rubber must be shaped using different methods to produce the final product. The last stage of rubber manufacturing is vulcanization. This involved heating the rubber with sulfur at about 280 F for about five hours to form strong bonds.