20 dec 2019
The use of natural and synthetic forms of rubber is essential to the well-being of humanity.
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Stuff of Progress, Pt. 6: Rubber
By Tony Morley
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Approximately 10 percent of all flowering plants produce a small amount of latex when punctured or cut. Latex is a complex chemical mixture of proteins, alkaloids, starches, sugars, oils, tannins, resins, and gums that coagulate upon exposure to air. As the latex polymer hardens, it begins to resemble a crude form of rubber recognizable to anyone acquainted with modern rubber.

 

While there are a vast number of plants which produce at least some latex, it is the Pará rubber tree (Hevea brasiliensis) that is the world's primary source of the latex feedstock needed in the production of natural rubber. The Pará rubber tree is native to the Amazon rainforests spanning the width of South America and has been tapped for its latex by the native inhabitants of the region since at least 1000 CE.

 

The first natives of the Amazon utilized latex in a number of highly innovative artisan products. Wet latex was brushed into clothing and foot coverings to improve durability and provide an effective method of waterproofing. Latex was poured over or into earthen molds and allowed to evaporate forming durable and flexible bowls, water containers and baskets.

 

The French explorer Charles-Marie de la Condamine was the first European to encounter latex producing plants in Peru in 1735 and to send specimens to Europe in 1736. The agricultural cultivation of latex-producing plants, and the industrial use of latex and rubber in Europe, was slow in gaining traction until the early 1800s. The dawn of the Industrial Revolution was simultaneously the dawn of rubber as a material of prominent importance.

 

Demand for natural rubber became unquenchable. A growing number of rubber plantations across South American and, later, Asia, India and Africa struggled to meet the demand of Europe and, to a lesser degree, North America. Scientists, entrepreneurs and industrialists swiftly found thousands of applications for rubber. The material became invaluable in the manufacture of belts, gaskets, waterproofing, clothing, boots, early tires and much more.

 

However, the use of natural rubber was limited by two key flaws: strength and durability. Natural rubber tends to stiffen dramatically in cold environments, and lose all strength and melt when subjected to relatively modest heating. These limits were overcome through a combination of experimentation and serendipity in 1839, when American Charles Goodyear (he of modern tire fame) developed a process for heating natural rubber in the presence of sulfur. Once perfected, the process would come to be called rubber vulcanization.

 

Vulcanization was no incremental upgrade to the material. The procedure dramatically improved the strength, and heat- and cold-resistance of rubber. Over the following hundred years, the vulcanization process vaulted rubber into a mainstay of the rapidly industrializing West. The use of rubber in passenger vehicles, bicycles, trucks, aircraft, boats, ships, factories, and homes transformed and enriched civilization.

 

However, demand for natural rubber continued to outstrip supply and World War II, in particular, created a substantial shortage of natural rubber – especially among the allied forces. Synthetic rubber produced from naturally-occurring hydrocarbons was first synthesized in a series of experiments between 1875 and 1882. Still, the production of synthetic rubber remained largely in the laboratory until the early 1940s.

 

Synthetic rubber had the distinct advantage of utilizing naturally-occurring hydrocarbons as opposed to extensive tropical plantations and logistically arduous supply chains. Shortly after the close of World War II, improving synthetic rubber chemistry, and increasing manufacturing sophistication and efficiency, led to major breakthroughs in rubber technologies and applications. Improvements to the chemistry and manufacture of rubber continued through the 1960s into the modern era – with the world consuming truly prodigious volumes of both natural and synthetic rubber.

 

In 2019, humanity produced and used a little more than 29 million metric tons of natural and synthetic rubber. Almost 14 million of those metric tons were natural rubber and 15.2 million metric tons were synthetic. The extensive use of both natural and synthetic rubber has an enormous impact on modern life. Nearly every car and truck on the planet rides atop reinforced vulcanized rubber tires, transporting families, food and materials. And nearly every aircraft lands on high-performance rubber tires.

 

The transport industry is perhaps the most prominent user of rubber. However, the material continues to serve civilization across hundreds of thousands of applications, from modern prophylaxis in the form of latex condoms, to waterproofing, vibration dampening and the truly enormous tires that allow mining loaders and trucks to furnish humanity with the minerals and metals of progress. Looking toward to the future, sustainably sourced rubber, both natural and synthetic, will continue to play a key role in the prosperity of developed countries, while aiding in the economic growth of developing countries. 

Tony Morley is a freelance science writer, and human progress and economic growth exponent. He is based in Australia.
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