Vulcanisation

Chemical process, discovered by Charles Goodyear (1839), by which the physical properties of natural or synthetic rubber are improved.

It consists principally of heating rubber with sulfur; other substances (accelerators, carbon black, antioxidants, etc.) are also added. The sulfur does not simply dissolve or disperse in the rubber, but rather combines chemically, mostly in the form of cross-links (bridges) between the long-chain molecules; however, the reactions are not fully understood. Vulcanized rubber has higher tensile strength and resistance to swelling and abrasion, and is elastic over a greater range of temperatures.

The molecular behaviour outlined above is sufficient to give polymers the properties of extensibility and elasticity, but in many cases the properties of elastomers must be modified in order to turn them into useful rubbery materials. The necessity for such modification was first demonstrated by natural rubber (polymer designation cis-polyisoprene) when…

Chemically, the process involves the formation of cross-linkages between the polymer chains of the rubber's molecules. Vulcanization is accomplished usually by a process invented by Charles Goodyear in 1839, involving combination with sulfur and heating. A method of cold vulcanization (treating rubber with a bath or vapors of a sulfur compound) was developed by Alexander Parkes in 1846. Rubber for almost all ordinary purposes is vulcanized; exceptions are rubber cement, crepe-rubber soles, and adhesive tape. Hard rubber is vulcanized rubber in which 30% to 50% of sulfur has been mixed before heating; soft rubber contains usually less than 5% of sulfur. After the sulfur and rubber (and usually an organic accelerator, e.g., an aniline compound, to shorten the time or lower the heat necessary for vulcanization) are mixed, the compound is usually placed in molds and subjected to heat and pressure. The heat may be applied directly by steam, by steam-heated molds, by hot air, or by hot water. Vulcanization can also be accomplished with certain peroxides, gamma radiation, and several other organic compounds. The finished product is not sticky like raw rubber, does not harden with cold or soften much except with great heat, is elastic, springing back into shape when deformed instead of remaining deformed as unvulcanized rubber does, is highly resistant to abrasion and to gasoline and most chemicals, and is a good insulator against electricity and heat. Many synthetic rubbers undergo processes of vulcanization, some of which are similar to that applied to natural rubber. The invention of vulcanization made possible the wide use of rubber and aided the development of such industries as the automobile industry.

  Vulcanisation Agents& Accelarators