A STUDY OF MICROSTRUCTURAL CHANGES DURING DEHYDRATION OF HYDROLYTICALLY DEGRADED POLY(GLYCOLIC ACID)

The effect of dehydration on the microstructure of hydrolytically degr aded, unoriented semi-crystalline poly(glycolic acid), PGA, was examin ed using environmental scanning electron microscopy (ESEM), thermograv imetric analysis (TGA) and simultaneous small and wide angle x-ray sca ttering (SAXS/WAXS). Samples were degraded in phosphate-buffered salin e solution at 37 degrees C and monitored during dehydration. Few micro structural changes were observed on drying PGA after 1 hour degradatio n. However, on drying the hydrolytically damaged PGA, the lamellar rep eat distance decreased as crystal lamellae collapsed together. The SAX S intensity profile showed voids simultaneously opening. Cracks became visible at the surface and the crystallites became more strained. The changes in surface microstructure on dehydration were found to be dep endent on both the extent of hydrolytic attack and on the rate of remo val of water. Significant differences in microstructure and degree of hydration were observed between degraded PGA analysed wet, after freez e-drying and after vacuum-drying. These findings indicate the importan ce of sample preparation in the study of degradable materials.