Mechanical Properties of Polymers in the Range of Their Softening. Elongation Diagrams of Raw and Vulcanized Rubber

Abstract

Abstract A study of the mechanical properties of polymers through the softening range is interesting for two reasons: on the one hand, it throws light on the process of vitrification, and, on the other, a study of reactions at low temperatures can give at least qualitative indications of the behavior of a material at high temperatures and during rapid dynamic processes, i.e., under conditions where direct investigation involves considerable difficulties in the experimental method. The following substances were studied: unloaded butadiene rubber before and after vulcanization, and vulcanized natural rubber. The temperature range studied was ™100° to 20° C. The elongation diagrams were obtained by means of a mechanism constructed in our laboratory. The specimens were stretched in a temperature-controlled chamber. Variations of temperature below 0° C did not exceed 0.5° C, and above 0° C did not exceed 0.2° C. The deforming force F was measured with a spring ring dynamometer. The opening of the clamps was calibrated with respect to the relative elongation λ. A correction was introduced here for deformation of samples in the clamps. The use of a reducing mechanism made it possible to vary the rate of deformation within the limits v=0.0016 and 0.08 cm. per sec., corresponding to rates of deformation from 0.05 to 2.5 per cent per second.