Natural rubber: an exotic material
Today, we take modern materials very much for granted, without realising that many are relatively recent discoveries or inventions. Rubber for example, is a vital component of cars, supplying traction between the wheels and the road, as well as sealing oil and fuel from leakage and absorbing unwanted vibrations from the engine.
Rubber also supplies us with many domestic items (toy balloons, water bottles, condoms, carpet underlay, mattresses and cushioning); office products (rubber bands, erasers) and articles of entertainment and recreation (footballs, golf balls, tennis balls etc.). So when was it first introduced?
Europeans' first encounter with rubber
Natural rubber was discovered during the various invasions of South America by the Spanish conquistadors in the 15th and 16th centuries. The material - made by simply drying out the sap of a native tree, Hevea Brasiliensis - was indeed first spotted by Columbus in the West Indies in the 1490s, where it was used for play balls.
It was also made into bags for carrying liquids by moulding flexible sheet into the desired shape. Rubber was clearly a material well known to native cultures, and it is hardly surprising that earlier knowledge of the material has come to light about its use in sacred ceremonies.
The Mexican Ball Game
One such ceremony was the Mexican Ball Game, a game played between two teams with a solid rubber ball (6 inches in diameter) in a rectangular enclosure. Played by the Olmecs and Aztecs with teams of nobles and some professional players, the object was to pass the ball through hoops at the side of the court, somewhat like basketball.
Once in play, the ball had to be kept moving by the team who gained possession in their half. If lost to the other side of the court, it counted against them. The ball could be struck only with hips, elbows or legs, requiring protective apparel like American football players.
According to one Spanish chronicler, bets were laid by spectators in "gold, turquoises, slaves, rich mantles or even cornfields and houses".
Such gambling fever has, of course, modern parallels, but who would guess that the religious omens were read from the movement of the ball or the nature of the final victory?
It appears that some players (presumably cheaters or poor performers) may also have paid the final sacrifice, judging by the skulls at the side of the court.
Finding a use
Despite the early "discovery" by the Spanish, it was not until about 1730 that rubber (or caoutchouc) was introduced into Britain, and not until 1791 that its use for the Mackintosh (the rubberised raincoat) was introduced.
In 1770 Joseph Priestley (the discoverer of oxygen) mentions its use for erasing pencil marks. Perhaps this was a serendipitous discovery, but it still took some time before the material was to find widespread application.
One reason for this was its deterioration with time, degrading in air to a sticky unmanageable mess. That was to change dramatically with the invention of "vulcanization", when, in 1834, Goodyear found that cooking the material with raw sulphur stabilised it, and also stiffened products manufactured from the substance.
The discovery opened the way to pneumatic tyres for early vehicles such as carriages (travel in which was rather painful owing to the rigid wheels and rough roads then in existence).
The first patent for a tyre dates from 1846, when Thompson announced the pneumatic tyre, a great advance for wheeled traffic. The key to the idea is the cushion provided by the air pocket, the pressure of which can be varied to suit the user.
The invention languished, perhaps because of problems with containing the inevitable leaks of air from the many inner tubes. However, solid rubber tyres were adopted, with much reduced cushioning. An idea before its time?
However, vulcanized rubber came to be used for an increasing number of products, such as galoshes or Wellington boots, and improved Mackintoshes, where rubber and textile were combined to make a waterproof fabric.
The growing demand for natural rubber made it a commodity product, yet only supplied by one area in the world: Brazil. As a result, the price soared, creating rich entrepreneurs, who essentially exploited native Indians to collect the raw latex from the rain forest.
Spreading rubber around the world
But since the tree could potentially be grown in any tropical climate, why not collect seedlings and transplant to other countries? The path was open because other commodity monopolies had already been broken with coffee (1767) and tea (1834), let alone more exotic plants like the opium poppy (1832), or even the mulberry tree for feeding silkworms.
The route taken was however a little more scientific with Hevea Brasiliensis. Like the mulberry tree and the opium poppy, there is only one species of plant involved and so intensive efforts were made at Kew Gardens to raise healthy plants from seeds collected by Sir Henry Wickham in Brazil (1876).
The young trees raised in the tropical greenhouse at Kew were shipped to Ceylon and Malaysia to form the nucleus of large plantations. Those countries were able to meet the rising demands of the rubber industry, and the price of raw rubber fell dramatically.
Dunlop reinvents the wheel
Over 40 years after Thompson's invention of the pneumatic tyre, in 1888, a Belfast vet, John Dunlop, responded to a request from his young son for better tyres for his trike. When ridden over the rough cobbles of Belfast's streets, solid rubber tyres just could not give a comfortable ride.
Various rubber tubes were used by vets, and Dunlop re-invented the pneumatic tyre by fitting a wheel with an inflated rubber tube protected by a heavier outer cover. After much experimentation, the world's first bike tyre emerged.
Dunlop's first patent to protect the invention was inevitably invalid because of Thompson's prior patent, but he went on to invent the valve and numerous other components which were proved valid.
Those inventions were the base on which he and others built the bike tyre industry, which brought cycling into a new era for everyone. It was an era when industrial progress had created new-found wealth and leisure time for millions.
As with any new and fundamental invention, the idea was taken up by others, especially by Michelin in France (1896) to develop a much heavier duty device, the car tyre.
The outbreak of the Second World War saw the loss of much of the world’s natural rubber (NR) production to the Japanese, and led directly to synthetic rubber, of which there are many types, made from gas or oil.
These new materials replaced NR where different properties were needed, such as the tyre inner (butyl rubber), polybutadiene for the sidewall and SBR (tread).
Indeed, many different types of synthetic rubber are available to designers today, many for specialty tasks requiring (for example) very high or low temperatures.
Yet NR is still a valuable international commodity, helping many developing countries earn useful hard currency. The technology of processing the raw rubber has improved greatly over the years, but the basics still remain the same as they were when Kew Gardens selected the best plants for cloning and transplanting.