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Sci Tech
Tyre colour
PHOTO: V.V. KRISHNAN
What is the reason for making tyres black in colour?
R.VAISHAKH
Chennai
The tyres of different vehicles, starting from bicycles to aeroplanes are all made up of synthetic rubbers, which are polymer blends designed to meet very severe conditions of wear and abrasion on the road, stringent requirements of strength and elasticity apart from resistance and stability in moderately hot conditions.
Halo-butyl polymers have been found to meet most of the mechanical performance requirements. However, the wear resistance and further mechanical strength are achieved by impregnation of the rubber with elemental sulphur and carbon in finely divided powder form.
The carbon powder, also known as carbon black or lamp black, is prepared by incomplete combustion of oil. These powders are best suited for the purpose, because they aggregate into strong, rather linear, clusters which bind the polymer strands to a strong mass but allow the extension necessary during running. This also imparts good rolling friction resulting in good grip on the road.
The other benefit of using carbon black is the superior ability of such tyres in transferring heat generated by abrasion with the road to the atmosphere.
In modern tyres, as much as 25 per cent of their weight comes from carbon black. The use of such a large amount of carbon black makes the tyres look black.
H. K. SAHU
Scientific Officer, IGCAR,
Kalpakkam
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