Background

Rubber is a material, derived both naturally and synthetically, that the world uses in abundance. Every year, around 4 million tons of natural rubber is produced, which pales in comparison to the 7 million tons of man-made rubber produced. About 70% of this rubber goes to the automobile industry, while the remainder is used for rubber products such as the soles and heels of shoes; the backing of carpet; raincoats; gumboots; rubber bands; rubber balls; rubber erasers; and rubber adhesive. In excess of 50,000 products are made from rubber. You probably can't go through a day without encountering a rubber product.

Natural Rubber Production

Natural rubber is an elastomer, polymerized by the drying and coagulation of the latex (milky juice) found in the sap of some plants. The major constituent of natural rubber, polyisoprene, a thermoplastic polymer, (C₅H₈)_n, can also be synthetically produced.

The Para rubber tree (Hevea brasiliensis) is the world's primary commercial source of natural rubber latex. This rubber tree, which is a member of the spurge family, Euphorbiaceae, sources latex well because when damaged, the tree produces more latex. Other plants that provide latex besides Para rubber trees include Guayule (Parthenium argentatum), Russian dandelion (Taraxacum kok-saghyz), Gutta-Percha (Palaquium gutta), Panama rubber tree (Castilla elastica), rubber fig (Ficus elastica), common dandelion (Taraxacum officinale), and Scorzonera (tau-saghyz).

Natural rubber can be ideal for dynamic or static engineering applications. It has excellent dynamic properties, with a low hysteresis loss, and good low temperature properties, it can be bonded well to metal parts, has high resistance to tear and abrasion and it is relatively easy to process. It also has excellent low temperature properties. Natural rubber, does, however, have a relatively high reactivity with its environment, especially in the cases of oxygen and particularly ozone. Ozone causes surface cracking that can rapidly penetrate the component when even a low threshold value of tensile stress is applied. It should be noted that in these cases the actual penetration of the oxygen and ozone can be low, with the inside being protected by the degraded exterior.

Synthetic Rubber Production

Although Natural Rubber, with the benefit of modern compounding, is very satisfactory for many applications, it is also a strategically important material, a natural crop only produced in tropical countries and has relatively poor aging properties. Scientists in the 20th century, therefore, set out to answer the question of how to make rubber using synthetic materials. Numerous synthetics are now produced to withstand high and low temperatures; corrosive environments; and contact with fluids of various types at varying pressures.

Synthetic rubber is produced through the the polymerization of various monomers. These monomers can be mixed in various desirable proportions to be copolymerized for a wide range of physical, mechanical, and chemical properties. The primary synthetic rubbers include Styrene Butadiene Rubber (SBR), Butadiene Rubber (BR), Chloroprene Rubber (CR), (Acrylo) Nitrile Butadiene Rubber (NBR), Iso Butylene Isoprene (Butyl) Rubber (IIR), Ethylene Propylene Rubber (EPDM or EPR), Silicone Rubber, and Chloroprene Rubber.