RECYCLING RUBBER
Introduction
Rubber is produced from natural or synthetic sources. Natural rubber is obtained from the
milky white fluid called latex, found in many plants; synthetic rubbers are produced from
unsaturated hydrocarbons.
Long before Colombus arrived in the Americas, the native South Americans were using rubber
to produce a number of water-resistant products. The Spaniards tried in vain to copy these
products (shoes, coats and capes), and it was not until the 18th century that European
scientists and manufacturers began to use rubber successfully on a commercial basis. The
British inventor and chemist Charles Macintosh, in 1823, established a plant in Glasgow for
the manufacture of waterproof cloth and the rainproof garments with which his name has
become synonymous.
A major breakthrough came in the mid 19th century with the development of the process of
vulcanisation. This process gives increased strength, elasticity, and resistance to changes in
temperature. It also renders rubber impermeable to gases and resistant to heat, electricity,
chemical action and abrasion. Vulcanised rubber also exhibits frictional properties highly
desired for pneumatic tyre application.
Crude latex rubber has few uses. The major uses for vulcanised rubber are for vehicle tyres
and conveyor belts, shock absorbers and anti-vibration mountings, pipes and hoses. It also
serves some other specialist applications such as in pump housings and pipes for handling of
abrasive sludges, power transmission belting, diving gear, water lubricated bearings, etc.
In this brief, we will be looking primarily at the reclamation and reuse of scrap tyres. This is
simply due to the fact that this is the major source of waste rubber in developing countries.
What is rubber?
Natural rubber is extracted from rubber producing plants, most notably the tree Hevea
brasiliensis, which originates from South America. Nowadays, more than 90% of all natural
rubber comes from these trees in the rubber plantations of Indonesia, the Malay Peninsula
and Sri Lanka. The common name for this type of rubber is Para rubber.
The rubber is extracted from the trees in the form of latex. The tree is ‘tapped’; that is, a
diagonal incision is made in the bark of the tree and as the latex exudes from the cut it is
collected in a small cup. The average annual yield is approximately 2 ½ kg per tree or 450kg
per hectare, although special high-yield trees can yield as much as 3000kg per hectare each
year.
The gathered latex is strained, diluted with water, and treated with acid to cause the
suspended rubber particles within the latex to coagulate. After being pressed between rollers
to form thin sheets, the rubber is air (or smoke) dried and is then ready for shipment.
Synthetic Rubber
There are several synthetic rubbers in production. These are produced in a similar way to
plastics, by a chemical process known as polymerisation. They include neoprene, Buna
rubbers, and butyl rubber. Synthetic rubbers have usually been developed with specific
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