PREPARATION AND CHARACTERIZATION OF POLY(L-LACTIC ACID) FOAMS

A particulate-leaching method was developed to prepare highly porous b iodegradable polymer membranes. It involves the casting of polymer/sal t composite membranes followed by the dissolution of the salt. Poly(L- lactic acid) porous membranes of controlled porosity, surface/volume r atio, and crystallinity were prepared with sodium chloride, sodium tar trate or sodium citrate sieved particles. For salt weight fractions of 50 and 60 wt%, asymmetric membranes were formed, independent of salt particle size. When 70-90 wt% salt was used, the membranes were homoge neous with interconnected pores. The membrane properties were independ ent of the salt type and were only related to the salt weight fraction and particle size. The porosity increased with the salt weight fracti on, and the median pore diameter increased as the salt particle size i ncreased. The polymer/salt composite membranes could be quenched or an nealed to yield amorphous or semicrystalline foams with desired crysta llinity. All foams were 99.9 wt% salt free and had porosities as high as 0.93 and median pore diameters up to 150 mum.