September 1, 1921 



THE INDIA RUBBER WORLD 



887 



plications to all forms of pneumatic, solid, cushion, or other rub- 

 ber or rubber substitute tires, or tires containing springs or other 

 mechanical devices to afford resilience. 



Electric Tire. A term early applied to a tire built up of 

 parallel cords laid in two plies transverse to each other and re- 

 garded as more "electric" or resilient than a fabric tire. See Cord 

 Tire. 



Emergency Strap. A leather strip wound about a damaged 

 tire as temporary repair. See Boot. 



Enameling Duck. A medium-weight, plain-woven cotton duck 



with laid warp and plied yarn weft, suitable for enameling and 

 used for spare tire covers. 



Endless Inner Tubes. Air-containing tubes of the all-circle, 

 continuous type. See Molded Inner Tubes. 



Exceptions. A repair term applying to tires not of standard 

 construction. 



Extensible Beads. Semi-hard, stretchable, projecting flanges 

 on the inner periphery of a tire casing, adapted for fitting into 

 the upraised, incurving edges of a clincher wheel rim. See 

 Clincher Tire. 



Ten Years' Experience With Aging Tests* 



By William C. Geer, Vice-President, and Waller W. Evans, Development Manager, The B. F. Goodrich Co., Akron, Ohio. 



INTRODUCTION 



THE most prominent problem that has confronted the rubber 

 chemist is the prevention of deterioration of vulcanized rub- 

 ber with age. We deal with a perishable vegetable mate- 

 rial, and there is no problem quite so important to manufacturer 

 and consumer as the too rapid change in physical properties on 

 simple standing. On account of this change in vulcanized rub- 

 ber it has become common practice to build into our composi- 

 tions excess properties beyond the real needs of service, in order 

 to make allowance and leave after a period of time sufficient 

 quality to withstand the service for which the articles were 

 designed. 



In dealing with this problem some years ago the writer 

 analyzed the situation and determined that the first step in its 

 solution, and the most necessary one for immediate use, was a 

 means by which the rate of decay could be predicted. Even, 

 therefore, if a knowledge of means of preservation was lacking 

 it would at least be possible to so handle materials that the 

 maximum life with present knowledge could be determined. 

 This led to a study of accelerated aging tests, and the develop- 

 ment of the one described in this paper. 



Let me assure you that there has not been and there is not 

 now any attempt to claim perfection, or even near perfection. 

 This paper attempts to describe simply an experience good, bad, 

 or indifferent, as that may happen to be to those who may wish 

 to use it. The facts are that this experiment has proved to be 

 a valuable means of approximately predicting the relative rate of 

 deterioration of a variety of rubber compounds. The proof of 

 the value has been determined over a period of ten years, and I 

 thought that it might be interesting if the experience were to be 

 written and the conclusions presented to the International Rub- 

 ber Congress. I do not doubt that you will find many flaws in 

 the method, that you will find many differences in the conclu- 

 sions, and I make no claim other than an attempt to point out 

 one company's results. 



HISTORY 



The work on accelerated aging extends over a number of 

 years. It is difficult to recognize definitely the contributing 

 factors, much less to distinguish between the ones which had a 

 direct and those which had an indirect influence on working out 

 a test which would have practical significance in the rubber in-- 

 dustry. For this reason, in giving a historical outline of the 

 accelerated test the theoretical work on oxidation of rubber is 

 included without any attempt being made to evaluate any con- 

 tribution to the fund of knowledge on oxidation, or its result, 

 aging. 



The earliest observation on the 'aging of rubber goods was 

 made by Spiller in 1865'. He noticed that "patent waterproof 

 felt" after six years' service did not possess the close structure 

 and waterproof qualities of the original article; upon extraction 



of the rubber goods and evaporation of the residue, a resinous 

 film which differed from the characteristic rubber film was ob- 

 tained. This product was known as "Spiller's resin" and the 

 phenomenon which was held responsible for its formation was 

 recognized as oxidation. 



About the same time W. A. Miller^ published the results of 

 his findings on investigating the effect of light and exposure to 

 air and moisture of raw and manufactured gutta percha and 

 caoutchouc. 



In 1885 Thomson' observed that vulcanized elastic fabric 

 oxidized very rapidly on exposure to the air at a temperature 

 about 100 degrees C. The rubber became harder, and the theory 

 was advanced that vulcanization was being continued. He also 

 noticed that ozonized air had little action on unstretched or un- 

 strained rubber, but that it acted very rapidly on rubber thread 

 in the stretched or strained condition. 



The first practical accelerated aging test was devised by C. O. 

 Weber' and was termed "sun cracking test," the theory being 

 that the detrimental changes in vulcanized rubber goods were 

 caused by oxidation hastened by sunlight. In attempting to 

 duplicate actual conditions in a laboratory test in which the 

 time involved would be appreciably shortened, ozone was at 

 first considered as an oxidizing medium, but was rejected as 

 impractical since it was difficult to secure regularly a gas of 

 uniform concentration. The weighed rubber strips — in this 

 case tire covers — were immersed in a mixture consisting of ace- 

 tone and hydrogen peroxide for at least two days, after which 

 time the strips were dried at 100 degrees C, weighed and com- 

 pared with an imtreated sample. The increase in weight denoted 

 the amount of oxygen absorbed and was considered a fairly re- 

 liable measure of the sun cracking liability of the sample tested. 



Hcrbst' stmlicd the action of atmospheric oxygen on purified 

 Para rubber and the constitution of the resultant products. By 

 passing a current of air through a solution of the rubber dis- 

 solved in benzene and heated under a reflux condenser for 140 

 hours he obtained a light brown liquid and resinous products 

 similar to Spiller's resin. 



In the same y^ar Ditmar' published a laboratory method for 

 testing the durability of rubl'er and rubber goods; this method 

 could well be termed an accelerated aging test. It was based 

 on the assumption that the durability of rubber and of rubber 

 goods varied inversely to the case with which they were oxidized 

 by atmospheric oxygen and thus partially converted into resin- 

 ous products of the nature of Spiller's resin. The sample to be 



1 Paper ro.id at the International Rubber Conference, London, England, 

 Tunc 7-13. 1921. 



' lournal of the Chemical Society, Vol. 18. 44-6, 1865. 

 'Tmirnal of the Chemical Society, Vol. 18, 273-8, 1865. 

 ''Journal of the Society of Chemical Industry. Vol. 4, 710-19, 1885. 

 » Weber, "Chemistry of the Rubber Industry," 229-30, 1902, 

 • Berichte der Deutsche Chemische Ccsellschaft, Vol. 39, 523-5, 1906. 

 ' Gummi-Zeitung, Vol. 20, 628, 1906. 



