How Is Rubber Processed?
Regardless of whether the rubber is natural or synthetic, the processing options are generally the same. Additional processing compounds the rubber so it can be used for a variety of industrial purposes. These are the four main steps.
1. Compounding (Formulating)
Adding chemicals to a rubber base creates rubber compounds. Chemicals can stabilize the polymers or reinforce the strength of the rubbers. Sometimes, compounding can also stretch the rubber, which reduces the final cost.
2. Mixing
Similar to compounding, this step includes additives that are mixed in with the rubber. To improve ingredient dispersion and avoid raising the temperature too high, professional mixers complete this in two steps. First they create a masterbatch that includes additives, such as carbon black. After cooling the rubber, they then add the chemicals necessary for vulcanization.
3. Shaping
Some of the common shaping techniques include coating, extrusion, casting, calendering, and molding. Depending on the final product, manufacturers could rely on several shaping techniques.
4. Vulcanization
Vulcanization is a chemical process in which the rubber, natural or synthetic, is heated with sulfur, accelerator, and activator. This process forms cross-links between long rubber molecules, which improves elasticity, resilience, tensile strength, viscosity, hardness, and weather resistance. This is the final step of the process. In the past, this took up to five hours. Due to modern-day advancements, vulcanization can be completed in 15 to 20 minutes.
Natural rubber is strong and flexible and protects against wear and tear, such as abrasion, fatigue, and exposure to water and certain chemicals. Natural rubber also adheres well to other materials, ideal for making enforced products, such as tires.
Natural rubber has a decent service temperature range, but there may be better choices for extreme heat, harsh lighting, or ozone exposure. Additionally, natural rubber is not highly resistant to fuel, oil, and other substances.
Natural rubber can be found in thousands of products, from industrial components to everyday consumer items. These products may include hoses and belts, medical devices, protective gloves, and children’s toys.
The tire industry consumes a significant portion of the world’s natural rubber supply. Natural rubber is often found in high-performance vehicle tires because of its excellent tear strength, even at high temperatures caused by friction. Aircraft, heavy truck, and race car tires are often made from natural rubber.
The tire isn’t the only vehicle part that contains natural rubber. Brake pads, airbags, seals, and other automotive components also rely on rubber’s desirable properties to serve essential functions while the vehicle is in service.
Every natural rubber product will have a slightly different composition profile based on its service environment. An essential natural rubber recipe includes:
Most of today’s natural rubber supply comes from a single species of rubber tree, Hevea brasiliensis. Hevea brasiliensis is native to South America, but Hevea brasiliensis plantations can be found all over Southeast Asia. Some major companies are experimenting with making rubber from other plants, but Hevea brasiliensis remains the primary source.
How is rubber made? The first step of the natural rubber production process is harvesting. Rubber trees must be at least six years old before being tapped. Once the tree reaches maturity, a tapper peels back a carefully cut section of the tree’s bark, which disrupts the plant ducts and releases latex, a milky white substance. The latex flows along the grooves of the peeled-back panel and is collected in cups or bags. Rubber tappers then contain all the harvested latex and transport it for processing.
The freshly harvested latex is filtered and packaged into drums. At this stage, acid is added to the latex, which forms clumps. This clumpy fluid is rolled into sheets at a mill, which removes water and prepares the material for drying and smoking.
Next, the latex sheets are treated with chemicals and low, gentle heating, a process called prevulcanization. Stabilizers and other ingredients may be introduced at this stage, depending on the desired final properties of the rubber. Further heating transforms the sheets into a firm, black material that most people recognize as rubber. At this stage, the rubber can be molded, shaped, or otherwise processed into a final product.
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