How is Natural Rubber Made?

Humans have been using rubber to create products for hundreds of years. The earliest evidence of rubber use comes from the Olmec culture of Mesoamerica, who used natural rubber materials to create balls for ball games. Today, rubber is an incredibly common and versatile material that is used in the creation of thousands of products, ranging from cookware to rubber gloves to tires and more. While most rubber products today are made from synthetic rubber, natural rubber was considered the superior option for a significant time. 

In this two part series, we’ll be taking a look at how both natural and synthetic rubber are created and how they’re used. Read on for our discussion on the creation of natural rubber.

Uses Prior to World War II

Prior to World War II, significant uses of natural rubber included door and window profiles, hoses, belts, gaskets, matting, flooring, and automotive dampeners. The use of rubber in car tires consumed a significant amount of rubber, as did gloves and toy balloons. Rubber was used as an adhesive in many manufacturing industries and products, the two most significant of which were the paper and the carpet industries. Rubber was also commonly used to make rubber bands and pencil erasers.

The production of synthetic rubber greatly expanded during World War II, which we will discuss in the second part of this series. 

Where does natural rubber come from?

Natural rubber is made by extracting latex – the liquid sap – from certain types of trees and other plants. While most latex is sourced from the Hevea brasiliensis tree, aka the rubber tree, over 2,500 varieties of trees and plants (including dandelions) produce the right kind of sap.

Latex is harvested through a process called tapping. It is done by making a cut in the bark of a tree and collecting the runny sap that comes out in cups. 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 mixture is then passed through rollers to remove excess water. Once rolling is complete, the layers of rubber are hung over racks in smokehouses or left out to air dry. Several days later, they will be ready for processing.

Processing natural rubber

Even natural rubber needs to undergo a series of processes in order to turn it into a usable product.

Firstly, chemicals are added to the rubber to make it stable. These chemicals may vary depending on the intended use of the rubber. Without this process, the rubber would become brittle in cold or sticky in high heat. A carbon black filler is often added to the rubber mix at this stage to improve its strength and durability. The rubber is mixed, cooled, and shaped.

Vulcanization

In order to make rubber strong and durable, it goes through a heat-treatment phase known as vulcanization. Essentially, the rubber is cooked to create extra bonds or cross-links between the molecules of the rubber so they don’t easily fall apart. After vulcanization, the rubber is harder and more durable. The process of vulcanization was an accidental discovery of engineer Charles Goodyear in 1839. Having accidentally dropped a piece of sulfur-coated rubber onto a hot stove, causing it to char and metamorphose into a leather-like substance, the American inventor uncovered the secret to stabilizing the latex of the rubber tree.

Limitations

Natural rubber was considered superior to synthetic rubber alternatives for a significant part of history. However, developments during World War II, which we will discuss in more detail in part two of this series, changed this. It’s important to note that while natural rubber has a great many applications, like tires, and dampening applications, it is no longer considered a good option for the sealing industry, especially when there is a chance of oil contact. Natural rubber will absorb oil until the rubber itself has disintegrated, meaning that it cannot be used to seal against oil. Another consideration is ozone, which causes natural rubber to break down over time. 
For more information about rubber, natural or synthetic, contact the engineers at Apple Rubber!

How is Natural Rubber Made?

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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Origins of rubber

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

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.

Synthetic rubber

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.

Processing rubber

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.

Vulcanisation

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.

If you require a wide variety of high-quality rubber products, ranging from matting to seals and extrusions, look no further than Coruba.