The
curing of rubber has been carried out since prehistoric times. The name of the first major civilization in Guatemala and Mexico, the
Olmec, means 'rubber people' in the
Aztec language. Ancient
Mesoamericans, spanning from ancient Olmecs to Aztecs, extracted
latex from
Castilla elastica, a type of
rubber tree in the area. The juice of a local vine,
Ipomoea alba, was then mixed with this latex to create processed rubber as early as 1600 BCE. In the Western world, rubber remained a curiosity, although it was eventually used to produce waterproofed products, such as
Mackintosh rainwear, beginning in the early 1800s.
Modern developments In 1832–1834
Nathaniel Hayward and Friedrich Ludersdorf discovered that rubber treated with sulfur lost its stickiness. It is likely Hayward shared his discovery with
Charles Goodyear, possibly inspiring him to make the discovery of vulcanization.
Charles Goodyear (1800–1860), a scientist and engineer, was the first to patent vulcanization of rubber, through "
combining of sulphur and white lead with the indie-rubber, and in the submitting of the compound thus formed to the action of heat at a regulated temperature". He was awarded a patent on June 15, 1844.
William Brockedon coined term 'vulcanization', in 1845, and first appeared in the 1847 patent of John Tyrell. In 1847, Thomas Hancock was awarded a British Patent for a process to vulcanize rubber; this was court granted after he asserted his formula for vulcanizing rubber was developed independently. Goodyear claimed that he had discovered vulcanization earlier, in 1839. He wrote the story of the discovery in 1853 in his autobiographical book
Gum-Elastica. Here is Goodyear's account of the
invention, taken from
Gum-Elastica. Although the book is an
autobiography, Goodyear chose to write it in the
third person so that and referred to in the text are the author. He describes the scene in a rubber
factory where his brother worked: The inventor made experiments to ascertain the effect of heat on the same compound that had decomposed in the mail-bags and other articles. He was surprised to find that the specimen, being carelessly brought into contact with a hot stove, charred like leather. Goodyear goes on to describe how his discovery was not readily accepted. He directly inferred that if the process of charring could be stopped at the right point, it might divest the gum of its native adhesiveness throughout, which would make it better than the native gum. Upon further trial with heat, he was further convinced of the correctness of this inference, by finding that the India rubber could not be melted in boiling sulfur at any heat, but always charred. He made another trial of heating a similar fabric before an open fire. The same effect, that of charring the gum, followed. There were further indications of success in producing the desired result, as upon the edge of the charred portion appeared a line or border, that was not charred, but perfectly cured. Goodyear then goes on to describe how he moved to
Woburn, Massachusetts and carried out a series of systematic experiments to optimize the curing of rubber, collaborating with
Nathaniel Hayward. On ascertaining to a certainty that he had found the object of his search and much more, and that the new substance was proof against cold and the solvent of the native gum, he felt himself amply repaid for the past, and quite indifferent to the trials of the future.
Later developments The discovery of the rubber-sulfur reaction revolutionized the use and applications of rubber, changing the face of the industrial world. Formerly, the only way to seal a small gap between moving machine parts was to use
leather soaked in oil. This practice was acceptable only at moderate pressures, but above a certain point, machine designers were forced to compromise between the extra
friction generated by tighter packing and greater leakage of steam. Vulcanized rubber solved this problem. It could be formed to precise shapes and dimensions, it accepted moderate to large deformations under load and recovered quickly to its original dimensions once the load is removed. These exceptional qualities, combined with good durability and lack of stickiness, were critical for an effective sealing material. Further experiments in the processing and compounding of rubber by Hancock and his colleagues led to a more reliable process. Around 1900,
disulfiram was introduced as a vulcanizing agent, and became widely used. In 1905
George Oenslager discovered that a derivative of
aniline called
thiocarbanilide accelerated the reaction of sulfur with rubber, leading to shorter cure times and
reducing energy consumption. This breakthrough was almost as fundamental to the rubber industry as Goodyear's sulfur cure. Accelerators made the cure process faster, improved the reliability of the process and enabled vulcanization to be applied to synthetic polymers. One year after his discovery, Oenslager had found hundreds of applications for his additive. Thus, the science of accelerators and retarders was born. An accelerator speeds up the cure reaction, while a retarder delays it. A typical retarder is
cyclohexylthiophthalimide. In the subsequent century chemists developed other accelerators and ultra-accelerators, which are used in the manufacture of most modern rubber goods. ==See also==