Published: Jan 1958
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The problem of obtaining rubber products having adequate resistance to ozone has become more difficult in recent years principally because of the increased use of ozone-susceptible synthetic rubber, increasing use of oil extended and plasticized rubber, and the higher atmospheric ozone concentrations existing around many industrial centers. While the problem is common to all users of rubber items, it is believed to be especially acute in the case of the military, since this usage involves long periods of storage under a variety of conditions, with the mandatory requirement that the material be at all times in a state of immediate combat readiness. During these periods of uncertain global conditions, the time-consuming processes of manufacture and procurement cannot be relied upon to provide the necessary rubber for operation of a modern military machine. A typical example depicting ozone cracking resulting from static storage of a truck tire and the enlargement of these cracks after a short period of service is shown in Fig. 1. The means presently available for obtaining ozone resistance in rubber items may be classified as follows: A. Proper selection of polymer: (1) Chemically saturated type, and (2) Sterically hindered type; B. Application of physical barrier: (1) Wrappers—paper or plastic films, (2) Paint film—flexible films of ozone resistant rubber or plastic, and (3) Chemical film—antiozonant in solvent; C. Proper compounding and use: (1) Chemical antiozonants, (2) Waxes, (3) High set and low modulus compounds, and (4) Storage of items in unstressed state. With the notable exception of the use of chemical antiozonants (1), these methods are practically identical to those listed in Chemistry and Technology of Rubber (2) over 20 years ago. Of course, during this interval many additional ozone-resistant rubbers have become available, providing the compounder a much greater latitude in choice of starting material from which to prepare ozone-resistant compounds.
Ossefort, Z. T.
Chemist, Rock Island Arsenal Laboratory, Rock Island, Ill.