| Supercritical fluid (SCF) is such that both temperature and pressure of the fluid are higher than the supercritical temperature and pressure. The supercritical state is neither gas nor liquid. Supercritical fluid has the advantages of both gas state and liquid state. It can diffuse easily like a gas and possesses good solvency like a liquid. Supercritical state has some special characteristics, such as high solubility, variable density; low viscosity, low surface tension and high diffusivity.Supercritical carbon dioxide (scCO2) is usually used in SCF technology. Its supercritical temperature is 31.05°C, and the supercritical pressure is 7.37 MPa. Near the critical point, a tiny variation of the pressure can bring about a huge change of the density. Since the viscosity, specific heat and solvency are related to the density, the physical and chemical properties of SCF could be controlled through the change of the pressure. The supercritical temperature of CO2 is close the room temperature and its supercritical pressure is not very high, so the equipment is easy to be produced and operated. SCF technique is of great promise in industrial applications.For some polymers such as PLA and PLGA, the Tg reduces greatly in scCO2. The polymer used looks like that it dissolves in the scCO2 in the plastization state. When the pressure of the system decreases, the polymer separates from the CO2.The supercritical spray process is a useful technique for producing biodegradable polymer particles and fibers without solvent. Low Mw PLA or... |
PDF Full Text Request