Vulcanized rubber is an incredibly versatile and useful material, but how is it manufactured?
Vulcanization is a chemical process that converts natural rubber into a tougher, more durable form. It achieves this through the addition of numerous curatives – substances that can enhance a material from its organic state – including sulphur, peroxides and acetoxysilane.
These curatives work by modifying rubber’s structural form, adding numerous strengthening crosslinks between its individual polymer chains. This transforms rubber and similar materials from sticky, easily deformable substances into materials that, while still pliable, are far more resistant to wear.
Focusing on the most common curative, sulphur, the vulcanization process works as follows in the creation of a typical car tyre. First natural rubber compounds are harvested and combined with sulphur and a variety of additives. These additives include accelerators, such as vulcafor, as well as antidegradants, such as paraffin waxes. The accelerators act both to speed up the crosslink creation process and also improve the quality and number of crosslinks between the rubber’s polymer strains. Antidegradants, meanwhile, prevent the rubber breaking down during the intense vulcanization process.
Next, the mixture is dumped into a compression mould, which in this case is tyre-shaped. The mould is then ‘cooked’ in a pressurised oven for about ten minutes at 170 degrees Celsius (338 degrees Fahrenheit).
The heat and pressure, in combination with the mixture’s composition, catalyse the crosslink process and sustain it at a rapid level. Once cooled, the mould is removed, releasing the base tyre for further processing.