The Chemistry of the Integument I—Fresh Catskin and Its Post-Mortem Changes^1,2

Abstract

INDUSTRIAL AND ENGINEERING CHEMISTRY 1475With a pure gum compound the progressive effect of strain is not as pronounced as in a tread compound. It appears rather that a small initial strain affects the whole of the stress-strain curve. RemarksThe data given show the elusive character of the stressstrain curve of rubber. The initial-stretch curve, which is ordinarily used in evaluating a rubber compound, is possibly the most definite but it is interesting to note that it is the curve least permanent in character. It apparently cannot be retraced after the rubber has once been stretched. If the stress-strain curve is to be used in designing rubber compounds for specific purposes, it is obvious that the conventional curve may not give the proper stress-strain relations.A study of the phenomena encountered in the repeated stressing of rubber, taking into consideration different compounding ingredients, different degrees of vulcanization, etc., should throw light on the structure of rubber compounds and on the behavior of different compounding ingredients in them. This work indicates that the lower part of the stress-strain curve, which is seldom accurately determined, may have an important bearing on the real properties of a compound.The apparatus described was constructed primarily for investigational studies, but the speed and ease with which a stress-strain record of a rubber sample is made suggests the use of a machine of this type for certain classes of routine testing. ConclusionsThe stress-strain relations of a sample of rubber are very markedly affected by the previous strain history.Rubber will recover to some extent from the effects of a strain, but not completely.In a rubber compound, such as tread stock, a series of increasing strains has a pronounced progressive action, each increase in strain producing added effects.The conventional stress-strain curve does not represent the permanent characteristics of a rubber compound.