TABLE OF CONTENTS The thermophysical properties are heat capacity, thermal diffusivity and heat conductivity.
Heat capacity is the amount of heat which must be consumed for heating a body up by 1 C. Molar heat capacity, if a mole of substance is considered, and specific heat capacity in the case of 1 g of substance, differ. Heat capacity at constant pressure C p equals the rate of enthalpy change with temperature increase, and heat capacity at constant volume C v - the rate of internal energy change with temperature increase.
In a quite wide temperature range, heat capacity increases linearly with temperature, the temperature coefficient of heat capacity increase for solid polymers possessing the average value of 3 10 -3. At phase or physical transition of the polymer, heat capacity changes in a jump-like manner.
For example, transition from the glassy to rubbery state indicates quite a sharp jump-like increase of heat capacity. When the physical transition is passed, heat capacity returns to weak growth with temperature.
The heat capacity of polymers depends on their chemical structure (Table 50).
| Polymer | | | ||
|---|---|---|---|---|
| Calc. | Experimental | Calc. | Experimental | |
| Polyethylene | 11.02 | 10.4; 11.1; 11.8; 10.15 | 14.7 | 15.1 |
| Polypropylene | 16.9 | 15.7; 16.5 | 21.7 | 21.6 |
| Polyisobutylene | 22.8 | 22.4 | 28.8 | 26.4 |
| Poly-4-methylpentene-1 | 34.6 | 33.6 |
|
|
| Polybutadiene | 20.0 | 21.0 | 26.3 | 24.3 |
| Polyisoprene | 25.8 | 25.7 | 33.3 | 31.3 |
| Polystyrene | 32.4 | 30.5; 29.3 | 43.0 | 42.6 |
| Polyoxymethylene | 8.8 | 10.2; 8.9 | 13.2 |
