P- V- T measurements of polystyrene materials

Abstract

Pressure, temperature and specific volume measurements of industrial polystyrene materials (a standard amorphous and atactic polystyrene, a modified polystyrene and a rubber polystyrene modified with carbon black) have been studied by barodilatometric analysis, thermobarometric analysis and differential scanning calorimetry. The isothermal compressibility, isobaric expansion and isochoric pressure coefficients of both glassy and visco-elastic phases were deduced from experiments. The isothermal compressibility in the visco-elastic phase is the only coefficient that cannot be considered to be independent of pressure and temperature, because it involves a volume dependence for the heat capacity at constant volume. Simple equations of state are proposed for both phases. The boundary curves between the phases were determined: they are straight lines in the pressure and temperature ranges studied. Their slopes were compared with the data given by Ehrenfest's relation. The influence of the composition on the specific volume, isobaric expansion and isothermal compressibility coefficients is discussed.