Forms of Rubber as Indicated by Temperature-Volume Relationship

Abstract

Abstract This paper describes measurements of the change of volume of rubber with change of temperature, which have been used as a means for determining the forms in which rubber may exist and ascertaining the conditions under which transition from one form to another may occur. This work is part of a study of the basic thermodynamic properties of rubber which is being conducted at the cryogenic laboratory of the National Bureau of Standards. In this study, an attempt was first made to measure the heat capacity of rubber over a wide range of temperature, but under some circumstances anomalies due to change in phase were encountered which took place so slowly that it was impracticable t0 follow them through by calorimetric methods. These anomalies have been studied by the measurement of the changes in volume or coefficient of expansion associated with them, it being possible to follow changes in volume over as long a period of time as desired. At temperatures at which rubber is relatively stiff and rigid, measurements of length have been used as an adjunct to the volume measurements. Measurements of the temperature-volume relations of rubber have been made by several previous investigators who have recognized the existence of rubber in different forms. The contribution of the present investigation lies in the fact that it reports a somewhat more comprehensive and systematic study than has been made previously. The findings are largely in accord with those of the other workers, as will be brought out in a subsequent section of the paper.