Effect of EPDM Structure on the Properties of Babylon Tire Black Sidewall Compound

Abstract

The tire black sidewall is the outer surface that protects the casing against
weathering. It is formulated for resistance to weathering, ozone aging, abrasion,
tearing and cracking, and for good fatigue life by using blends of natural rubber and
cis-1.4- butadiene rubber.
The tire black sidewall uses blends of natural rubber and cis-1.4-butadiene
rubber are used to achieve desired physical properties; however, use of these
elastomers requires protection against ozone aging in order to maintain desirable
properties over the lifetime of the tire. Protection against ozone aging is of particular
interest since reaction with these olefinically unsaturated elastomers results in
polymer decomposition via chain scission. Ethylene propylene diene terpolymer has
proved most effective. However, its use also results in a surface discoloration, and
thus it can be used in sidewall compound when the tire appearance is also an
important factor.
The best formulations are obtained in the presence of 40,50 phr EPDM to achieve
desired physical properties. Improved ozone resistance was obtained by using 40 and
50 phr of EPDM rubber in the compound there is no cracking throughout the life of
the black sidewall compound. Blends of NR/BR/ EPDM with up to 50 phr of EPDM
rubber afforded adhesion levels greater than that of a natural rubber model sidewall.
Compounds containing NR /BR/ EPDM blends with 2 phr of the 6PPD antiozonant
provided the best dynamic ozone resistance.
Blending of EPDM with NR and BR enhances the abrasion resistance.
However, elongation at break and tear strength values are highest for those
compounds having high contents of NR and Butadiene rubber.