The Study Of Supercritical Carbon Dioxide Induced Swelling And Retrograde Vitrification Of Amorphous Polymer

In this work, an self-designed in-situ optical determination apparatus has been adopted to monitor supercritical carbon dioxide (scCO2)-induced swelling behavior of amorphous polymers, such as polystyrene (PS) and polymethylmethacrylate(PMMA). The relationship of swelling ratio of these two amorphous polymers is:PMMA>PS.The Sanchez-Lacombe equation of state (S-L EoS) is suitable in describing thermodynamic behaviors of low molecular weight solvent-polymer system. Through combination of pVT data from NIST database, Tait Equation and pure component S-L EoS, the characteristic parameters of CO2(338.75K,422.82MPa,1398.87 kg/m3,r=4.72), PS(861.88K,219.10MPa,1071.26 kg/m3)and PMMA(898.27K,211.51MPa,1206.70 kg/m3) were obtained respectively under certain temperature and pressure conditions.The binary interaction number was obtained by fitting equilibrium swelling ratio into mixture S-L EoS, which results show that modeled values agree well with experimental data.Linear fitting was applied to acquired relationships between binary interaction number and temperature (ΨPS=-3.825*10-4T(K)+1.049 andΨPMMA=-3.809*10-4 T(K)+1.188), which can be used to predict diffusion and swelling behavior of CO2-polymer system under certain temperature and pressure range.According to various PMMA swelling data at high pressure,ΔV/V0 versus T curve was obtained in order to find the inflexion points (Tg) of volume change.In the same time, Chow equation and entropy equation were applied in modeling the depression of glass transition temperature of PMMA, respectively.Such fundamental research work has great importance for the application of scCO2 in the polymer processing.