Thermal behaviors of polystyrene plasticized with compressed carbon dioxide in a sealed system

The thermal behavior of polystyrene (PS) plasticized with compressed carbon dioxide (CO 2 ) was studied using differential scanning calorimetry with a high‐pressure stainless steel pan in a sealed system. The technique proved to be a simple and convenient way to study the thermal behavior of a polymer plasticized with compressed CO 2 at pressures up to 100 atm, which covers both the gas and supercritical states. A sharp fall in the decrease rate of the glass transition temperature ( T g ) under conditions near the critical point of compressed CO 2 was firstly observed, which corresponded with the solubility of CO 2 in PS. Since the system is scaled, which results in a stable pressure at a certain temperature, it is more suitable to study the effect of annealing. An endotherm was detected after the PS was annealed at a temperature below its T g under compressed CO 2 . The enthalpy of this endotherm increased linearly with increasing logarithm of annealing time under a certain pressure. The endotherm was affected by two thermodynamic equilibrations at a temperature below its T g : (i) enthalpy relaxation of the PS; and (ii) the absorption/desorption of CO 2 . POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers