(618ak) Preparation of Polycaprolactone Foms by Supercritical Carbon Dioxide Foaming

  The study is about the preparation of biocompatible and biodegradable polymer, Polycaprolactone (PCL), foams by supercritical carbon dioxide and finding the optimun foaming conditions.

  PCL, a semi-crystalline polyester is subjected to biodegradation because of the susceptibility of its aliphatic ester linkage to hydrolysis. Matrices with porous surfaces are often desirable in tissue engineering applications. PCL are also used frequently for this purpose. In many studies, in order to enhance the interconnectivity of the pores and the average-size cell of the foamed material, the Supercritical Carbon Dioxide Foaming technique was applied in methods of preparing porous structures.

  There is great potential for utilizing supercritical carbon dioxide as the medium in all these processes, because the material may be thermally labile, therefore should be free from any organic solvent residues and artifacts. Supercritical carbon dioxide is an attractive solvent or antisolvent in these processes, owing to the tunability of its solvent power with small variations in pressure and temperature and to its excellent transport properties(e.g., viscosity and diffusivity); in addition, it is nontoxic, nonflammable and environmentally friendly. The major advantages of these methods include single-step operation, a mild operating temperature, and a very narrow size distribution of matrices with controlled morphology, unlike the conventional techniques. All considered, supercritical carbon dioxide is one of the best choice in many applications.

  The effects of saturation time, foaming temperature, saturation pressure and depressurization rate on the foam structure and volume expansion ratio were investigated, with the intention of finding the most influencial terms.

  In this study, PCL (M_n= 80,000) was used to point out the effect of the operation conditions on the PCL porous structures, such as the temperature, the pressure, the depressure time and the soaking time. According to the experimental results, at the temperature of 40°C and pressure of 2000psi., with the soaking time of 120 minutes, and the depressization time of 2 seconds, we can obtain ideal PCL porous structures (i.e., with the average cell size of the foamed material 76 μm).

  The supercritical carbon dioxide foaming usually accompany with the morphology and crystallization behavior change. DSC was used to examine the morphology and crystallization situation. In the experiment, PCL get more crystallization region after foaming.