Study On The Solubility Of Supercritical Carbon Dioxide In Polycaprolactone

Polycaprolactone is an artificially synthesized biological polymer material, which is widely used in tissue engineering material and biological medicine. As a staple foaming material, polycaprolactonehas excellent thermalstability. Supercritial Carbon Dioxide is non-toxic and unharmful, which can be used as blowing agent to prepare PCL foaming material. In order to obtain good foaming polymer material, it is a key to study the swelling process and thermodynamic law besides selection of appropriate blowing agent, because of which plays an important role in nucleation step and performance and function of final product. In this paper, the swelling process of PCL in CO2 and the thermodynamic model of CO2/PCL system, preparation of PCL foaming material and Nifedipine/Polycaprolactone slow-released system in SC-CO2 were mainly studied.Solubility of CO2 in PCL was calculated by flooding method and the solubility equilibrium time of two phase system of CO2/PCL. The effects of temperature, pressure on the solubility of CO2 in PCL were investigated through the single factor experiment. The influence of organic solvent on the solubility was analyzed. The results show that the solubility of CO2 declines with increasing temperature while rises with increasing pressure. The addition of organic solvent can further improve the solubility of CO2. At the same temperature and pressure, the maximum solubility of CO2 containing 2 mL CH2Cl2 was 28.06% higher than that of pure CO2.Orthogonal experiments show that pressure is the most critical factor which affects the solubility, followed by temperature and addition of dichloromethane. The optimum experiment conditions for the solubility were determined as follows:the temperature is 313.15 K, the pressure is 30 MPa and additive volume of CH2Cl2 is 4 mL. Under such condition, the solubility is 2.867 g co2/g PCL.The solubility law was fitted and calculated by cubic equation of state as a thermodynamic model. The solubility of CO2 in polycaprolactone can be predicted well by three parameters of the Patel-Teja equation, the comparative results of calculated value and experimental value of which show that the relative error ranges from -12.53% to 12.01% except the last five data of 363.15 K. Hence, the solubility of CO2 in PCL can be well predicted by Patel-Teja equation.The micro morphology of PCL foaming products were analyzed by X-ray diffraction and scanning electron microscope. When the temperature was higher than 313.15 K and the pressure was higher than 10 MPa, SC-CO2 would induce PCL to be crystalized. The effects of temperature, pressure and addition of CH2Cl2 on the crystal form and orientation were little. The crystallization level rises with temperature while declines with pressure and the addition of CH2Cl2 can enlarge the crystallinity of crystal. Macropore was the main structure of PCL foaming product at SC-CO2 condition and using CO2/CH2Cl2 compound blowing agent can improve the microstructure of porous material. The three structure parameters of PCL foaming product varies with temperature were investigated. The results show that, the apparent density declines with temperature while the cell density and diameter rises with temperature.The slow release behavior of Polycaprolactone/Nifedipinesystemprepared by SC-CO2 was studied and slow release curve of it was drawn. The porous microstructure of Polycaprolactone/Nifedipine at 25 MPa is good, the drug-released time of which can reach over 24 hr. The influence of temperature, pressure and drug amount on impregnation amount were also researched.