Ancient Mesoamerican peoples manufactured rubber from latex some 3,500 years before the modern invention of vulcanization and even compounded it for different applications, says new research from a Massachusetts Institute of Technology research team.
According to archaeology professor Dorothy Hosler and technical instructor Michael Tarkanian of MITâ€™s Department of Materials Science and Engineering, pre-Hispanic peoples not only invented rubber, but they perfected a system of chemical processing to enhanceÂ rubberâ€™s properties.
The result was strong, wear-resistant rubber for sandal soles, resilient, bouncy rubber for game balls, and rubber optimized for resilience and strength for wide bands used to attach handles to axe heads.
The research follows a 1999 study which demonstrated that these people predated development of Charles Goodyearâ€™s vulcanization process by 3,500 years.
Flourishing from at least 2,000 B.C. to the Spanish invasion in 1521 in what is now parts of Mexico and Central America, the Mesoamerican civilization engineered the properties of latex from the native Castilla elastica tree.
A sticky liquid that dries to a brittle solid, natural latex, which contains an oily chemical called isoprene, was mixed with juice from the morning glory species Ipomoea alba.
As the first polymer scientists, the Mesoamerican people stirred the liquid until it solidified into a white mass which they shaped by hand into rubber balls, hollow rubber figurines, and other rubber artifacts.
The process relies on chemistry similar to that of modern vulcanization: The juice of the morning glory vine causes cross-linking of polymer molecules, making the rubber elastic and removing compounds that turn latex brittle.
In the new research, Tarkanian and Hosler set up their own processing facility at MIT, and experimented using raw materials collected during field trips to Mexico.
They noted that by varying the proportions in the mixture made of Castilla tree sap and morning-glory vine juice, a different kind of rubber could be obtained.
A 50-50 blend of the latex and morning glory produced maximum bounciness, perfect for the rubber balls. Pure latex worked best for rubber bands and adhesives, while a three-to-one mix of latex to morning glory provided the most durable material, perfect for sandals.
The Mesoamericans had plenty of time to work out these properties through trial and error. By the time the Spanish arrived, there was â€œa large rubber industry in the region, producing 16,000 rubber balls each year, and large numbers of rubber statues, sandals, bands and other products,â€ Tarkanian said in a MIT statement.
A few such balls, which ranged in size from a few inches to a foot across, have been found in archeological digs in the region — the oldest dating back to 1600 B.C.
They were used in ceremonial ball games, which were played on stone-walled ball courts. Sixteenth century Spanish invaders reported that the ball game, a central ritual element in all ancient Mesoamerican societies, also involved gambling for land, slaves and other valuables.
The high-stakes games may have even ended in human sacrifices.