Specific heat and increases of entropy and enthalpy of the synthetic rubber GR-S from 0 degrees to 330 degrees K

Abstract

Specific heat measurements were made over the range 12° to 330° K on a sample of synthetic rubber GR-S (Buna S) by means of a n adiabat ic vacuum-ty pe calorimeter. A D ebye specific he["t function was used to calculate values below 15 0 K . At about -61 0 C the material undergoes a transition of the second order, the specific heat increasing rapidly by about 40 percent. From -50 0 to +60 0 C, the specific heat values can be calculated to within 0.1 percent by the equation C. = 0,4346 + 7.029 X lO-' t+ 1.156 X 10-a t2 in calories gram-I degree Kelvin -I. At 25 0 C the specific heat is 1.894 internat ional joules gram-1 degree Kelvin-I (0.4528 calorie gram-1 degree K elvin -I). The increase in entropy from 0° to 298.16 0 K is calculated to be 1.824 internations.l joules gram -I degree Kelvin -I (0.4359 caloriE' gram -I degree K elvin -I). Values of specific heat, and increases of entropy, enthalpy , and free energy are tabuls.ted at 5-degree intervals. The experimental data indicate that values below the transition are dependent upon the thermal history of the ~ample . This phenomenon, as well as the temperature drifts observed, ca n be explained on the theory that the transition results from an increasingly slow s.pproach to the equilibrium state at temperatures in the transition region and below.

Specific Heats of Hevea,,GR-S, GR-I Stocks

“…According to the results of Rands, Ferguson, and Prather (12) the average value of the specific heat of GR-S over the same temperature range is 0.461 calorie/gram/°C . Since the equivalence of the two stocks is somewhat questionable, it is not certain whether the average value reported by Roth, Wirths, and Berendt is too high or not.…”

“…TRl, TR2. 750 volts, c. Rands, Ferguson, and Prather (12) find that over the temperature range -50°to +60°C. the specific heat for GR-S is given precisely by: ep = 0.4346 + 7.029 X 1CT41 + 1.156 X 10~s i2…”