Abstract
The T-50 test, which has already been used for the last twenty years in many rubber factories has, up to the present time, been used solely as a means of checking vulcanization conditions, and so far no one has attempted to derive any mathematical relations from the results obtained. In the first part of this work it is shown that the T-50 test can be regarded as a useful and efficient means for studying much more complex and important problems, as, for example, the determination of the vulcanization characteristics of a rubber compound, both with respect to the ingredients and from the thermal point of view. In fact, this test makes it possible to obtain quantative data rapidly, which can be utilized to render any study easier and more conclusive than is possible with other tests commonly used, e.g., dynamometric parameters, aging tests, relaxation at elevated temperatures, etc. In making a study of the T-50 test, the approach was from the point of view of the chemical and physical nature of the phenomena involved in the test. It has been established with a considerable degree of exactitude that results obtained with the test conform to an energy law common to many chemical-physical phenomena, viz., the law of Arrhenius, which expresses the relation between the rate of a reaction and the temperature of a process by means of a parameter which depends on the activation energy of the process itself. In fact, analysis of experimental data shows clearly that, except in the case of mixtures having peculiar vulcanization characteristics, the activation energy of the process is practically independent of the composition of the mixture. One is led to believe, therefore, that such energy depends directly on the nature of the polymer itself and on its vulcanization reactions with sulfur, and that it is independent of the chemical and physical factors which control vulcanization reactions. On account of the nature of our work, we could not undertake a thorough scientific study of the aspect of this fact, considered from the point of view of the molecular structure of cross-linked high polymers. Instead, we have limited ourselves to developing an application of considerable practical utility, based on the fact that the activation energy is practically constant. In fact, a simple correlation diagram can be established which can be used for most types of vulcanizates, and by means of which it is possible to obtain directly the equivalent coefficients for passing from one vulcanization temperature to another with the longest temperature range which it was possible to use, i.e., from 78° to 151 ° C. It has thus been possible to interpret the results of the T-50 test for temperatures other than for the temperature at which the test was made, and thus to obtain a more complete and comprehensive picture directly related to the same chemico-physical phenomena. Passing on to the subject of dynamometric parameters, it is shown that, for these too, the above law applies with sufficient approximation. Again, since the order of magnitude of the activation energy is similar to that found by the T-50 test, the same correlation diagram applies, thus appreciably increasing its practical importance. Finally, the satisfactory accord between the activation energy values obtained by the T-50 test and those obtained by stress relaxation tests reveals an intimate relation between the two phenomena, which otherwise would appear to be completely different. Thus a further contribution is made to the complex study of relaxation.
The effect of Na+ and K+ on the thermal denaturation of Na+ and + K+-dependent ATPase