The purpose of this article is to review the developments in antioxidants for rubber over the past 25 years since the publication of Davis and Blake's “Chemistry and Technology of Rubber”. The intent is to provide a guide for rational use and further development. Accordingly, the organization of the material is as follows: a) Outline of the mechanism of oxidative attack and antioxidant action. b) Critical review of methods of evaluation. c) Survey of antioxidants in the literature. Numerous reviews of antioxidants in one or more aspects have been published. These have been duplicated only so far as necessary to form a complete outline. Patent references are included only when the specification cites experimental data in support of the claims of antioxidant action. Usage divides rubber antioxidants into four categories: 1) Polymer stabilizers, which are added in the polymerization plant to repress the action of oxygen during drying and storage of the uncured rubber. 2) Antioxidants, which are added in compounding to prolong the useful life of the vulcanizate by retarding the oxidative changes that occur over a long period of service. 3) Flex-crack inhibitors, antioxidants which retard crack initiation or crack growth under conditions of cyclic deformation. 4) Antiozonants, substances which by chemical action (or by a combination of physical and chemical processes) delay the onset or growth of cracks resulting from ozone attack. (This definition is written to exclude waxes, which protect from ozone by forming a chemically nonreactive surface film.) There is a closer fundamental connection between polymer stabilizers and vulcanizate antioxidants than among other classes. The discussion of mechanisms of oxidation and antioxidant action will introduce the first two. Evaluation of the two classes of materials are operationally different and will be discussed separately. The present discussion is limited to “general purpose” elastomers of the present time; namely, NR, IR, SBR and BR.

Calculation of the complete temperature cycle in a tire cure has not been published although the digital method here presented was suggested by Gehman. This general method, attributed to Schmidt, consists in dividing the article into cubical volume elements and calculating the heat flow from contiguous surrounding cubes to obtain the temperature for a given element in the next time interval. Vostroknutov reviewed the classical differential equations in a study of retreading cures but his solutions were specific rather than general and utilized the usual graphical methods.

250 in molecular weight gave breaking loads averaging 1.5 pounds over the control. Sodium sulfonates of the lower homologs had little effect.

Four different laboratory machines for the evaluation of tire treadwear have been described which used concrete, steel, and tungsten carbide abrasion surfaces at variable speed and slip, but none has satisfactorily replaced highway testing. Predominant sources of wear on passenger tires appear to be cutting and frictional fatigue, the rates of which are influenced differently by temperature and load. Thus, seasonal or climatic, topographical, and geographical effects are evidenced. Treadwear cannot be expressed solely as a property of the tire since it is the resultant of the interaction of the tire with multivariate environmental conditions.

The time to first visible crack of ozone sensitive vulcanizates appeared to be short and replicable 3–5 h at 25 pphm ozone, 2 h at 50 pphm. For antiozonant protected OE-SBR below the critical strain, the time to first visible crack was found to be a stochastic value with a normal or log normal distribution.