The Use of Chemical Additives to Protect SBS Rubbers Against Ozone Attack

SBS thermoplastic elastomers offer an inexpensive alternative to vulcanised rubbers for many undemanding applications. They are, however, particularly susceptible to attack from atmospheric ozone leading to cracking as soon as any strain is applied. In most rubber applications some strain is unavoidable. In this paper a compounding approach to protecting SBS thermoplastic rubbers against ozone is described. An explanation is offered for why a protective effect Is observed only when certain combinations of additive are used. SBS elastomers are the most affordable class of thermoplastic rubbers. To achieve finished products resistant to ozone and without compromising the light colours often demanded, recourse must be made to blending with other saturated elastomers or replacement by hydrogenated (SEBS) types. The latter is a significantly more expensive alternative. Under laboratory conditions where the rate of ozone attack is increased by several decades, unprotected SBS begins to crack within a few hours. Several different protective agents are examined here, the best of which, a cyclic enol ether, $Vulkazon^{(R)}$ AFD, can extend the resistance to any cracking to several weeks by the use of a few percent by weight of additive. The systems reported neither discolour the polymer nor stain other materials with which it may be in contact. Use of the protective systems described here could enable SBS elastomers to compete in many applications with the more expensive SEBS polymers.