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.
Rubber is an incredibly common and versatile material, used for making many items such as elastic bands, footwear, swimming caps and hoses. Indeed, half of all rubber produced goes towards making vehicle tyres. As such a vital material, how is rubber made and where does it come from?
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Humans have been exploiting the durable and elastic nature of rubber for making products for over 1,000 years. Although early forms of rubber were made from natural sources, as demand increased for this material, scientists developed artificial or synthetic rubber in laboratories that mimicked the natural material. These days, most rubber produced is of the synthetic kind.
Natural rubber is made by extracting a liquid sap, called latex, from certain types of tree. There are over 2,500 types of tree that produce this sap (including plants like dandelions), but the overwhelming majority of latex for rubber production stems from the Hevea brasiliensis tree, or the aptly named rubber tree. These trees are native to South America but are today commonly found in Southeast Asia.
Latex is gathered from the trees by making a cut in the bark and collecting the runny sap in cups. This process is called tapping. In order to prevent the sap from solidifying, ammonia is added. Acid is then added to the mix to extract the rubber, in a process called coagulation. This can take about 12 hours.
The mixture is then passed through rollers to remove excess water. Once this is complete, the layers of rubber are hung over racks in smokehouses or left to air dry. Several days later, they will then be folded into bales ready for processing.
It was when natural rubber sources became scarce during World War I that German scientists developed artificial rubber. Although these early forms of rubber were inferior in quality to natural rubber, as research developed, synthetic rubber improved. Today, synthetic rubber is as strong and reliable as natural rubber.
Synthetic rubber differs from natural rubber in that it is made by linking polymer molecules together in a laboratory.
Both natural and synthetic rubber need to undergo a series of processes to turn it into a usable product. These stages can be adapted slightly according to the intended use of the final product.
Firstly, chemicals are added to the rubber to make it stable. Without this, the rubber would get brittle if it got cold or become sticky during high temperatures. Commonly, a carbon black filler is added to the rubber mix, to improve its strength and durability.
The rubber is then carefully mixed and allowed to cool, before being shaped. It can be shaped by pushing it into rollers, called calendering, or by squeezing it through holes to make hollow tubes, known as extrusion.
In order to make rubber strong and durable, it finally goes through a heat-treatment phase known as vulcanisation. This is where the rubber is cooked (often with sulphur) to create extra bonds or cross-links between the molecules of the rubber, so they don’t easily fall apart. Charles Goodyear accidentally discovered this process, when he dropped some rubber onto a hot stove and noticed how the heat made the rubber harder and more durable.
After vulcanisation, any imperfections are removed from the rubber and it is then shaped or moulded into the final product.
As one of the most important inventions ever, rubber continues to enjoy versatile use today.
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