Encapsulation of SiO2 and TiO2 Fine Powders with Poly( dl -lactic-co-glycolic acid) by Rapid Expansion of Supercritical CO2 Incorporated with Ethanol Cosolvent

Rapid expansion of supercritical carbon dioxide solution (RESS) for encapsulating core powders with a polymer shell was experimentally examined. Poly( dl -lactic-co-glycolic acid) polymer (PLGA) and 1.4-μm SiO 2 as well as 70-nm TiO 2 powders were employed as model encapsulating agent and core particles, respectively. A solution of PLGA in supercritical carbon dioxide (SC-CO 2 ) was prepared incorporated with ethanol cosolvent. The RESS process was then performed by spraying the supercritical mixture through a capillary nozzle, leading to formation of well-dispersed PLGA nanoparticles. The precipitation of PLGA accompanying with its dispersion on core powder surface could be ascribed to the rigorous shear stress acting on the expanding flow of SC-CO 2 . The cumulative deposition of the precipitating PLGA could result in the uniform encapsulation of the SiO 2 and TiO 2 powders with 10 to 100 nm-thick PLGA layers in the form of both individual and agglomerating particles. The increased weight ratio of core particle to PLGA could lead to the more promoted encapsulation of core particles due to the higher contact among the core and precipitated PLGA particles after expansion. In comparison with large SiO 2 powders, more rigorous agglomeration of encapsulated TiO 2 powders would be attributed to their higher interparticle collections, which could also interfere with the expansion process.