Thermal conductivity, heat capacity and diffusivity of rubbers from 60 to 300 K

Abstract

In this paper measurements are reported on the variation of thermal conductivity, heat capacity and thermal diffusivity of poly(butadiene-co-styrene) rubber, poly(butadiene-co-acrylonitrile) rubber, poly (isobutylene-co-isoprene) rubber, polychloroprene rubber and cis-1, 4-polyisoprene rubber with glass transition temperatures between 60 and 300 K. Thermal conductivity increases almost linearly to a peak value up to a temperature which corresponds to the glass transition temperature of the particular elastomer, and then drops to a temperature-independent value at 290 K. The variations in thermal conductivity are empirically correlated with the present experimental data by the equation K( T) = AT m , where A and m have different values before and after the glass transition temperature. Similarly, heat capacity also increases with temperature and then reaches a temperature-independent value at 290 K. This heat capacity anomaly is found to occur at the same temperature at which the peak values of thermal conductivity are observed. Data for heat capacity show that it varies as C( T) = BT n which is in excellent agreement with the present data, except in the transition zone. Thermal diffusivity also changes with temperature, with a drop occurring in the transition zone. These data are also empirically correlated by an equation, in good agreement with the present experimental data: D( T) = GT P + HT P+1 , where G, H and p have different values before and after the glass transition temperature. It is noted that thermal conductivity, its peak value and its rate, plus temperatures at maxima, the rate of change of heat capacity, thermal diffusivity and its temperature-independent values are decreasing with decrease of molecular weight of the side groups, while heat capacity and its temperature-independent values are increasing with decrease of weight of the side groups for a constant length of the repeating units.