The Thermal Conductivity of Elastomers Under Stretch and at Low Temperatures

Abstract

Heat conductivity of natural rubber and GR–S was studied in the range from + 50 °C. to − 170 °C. and from 0 to 100% stretch. The apparatus used was a greatly modified version of one designed by Schallamach. The conductivity of both types of rubber at 0% stretch lies in the range between 3.5 × 10−4 and 4.0 × 10−4 cal./sec. cm. deg. C. Stretching increases the rate of change of conductivity with temperature of both natural rubber and GR–S, and decreases the conductivity of the latter. On lowering the temperature and raising it again natural rubber exhibits a complicated hysteresis phenomenon, while GR–S shows a hysteresis loop caused by a second order transition near the brittle point. The hysteresis phenomena of both types of rubber near the second order transition temperature shows considerable similarity to the changes in specific heat observed by Bekkedahl and coworkers. Above and below the transition region the heat conductivity decreases approximately linearly with temperature as might be expected fro...